Tree Service Terminology | Complete Glossary of Tree Service

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​A

• abaxial:  the lower surface of a tree's leaf.
• abiotic: about the nonliving parts of an ecosystem, such as soil particles, bedrock, air, and water.
• abscisic acid (ABA):  a plant hormone that stimulates stomatal closure and promotes seed and bud dormancy.
• abscission zone:  a wall of cells at the base of a petiole, that allows the leaf to separate from the stem.
• acaulescent:  a plant having no stem or appearing to have none.
• acceptable risk:  the amount of risk that an owner is willing to accept should a whole tree or tree part fail.
• access point:  the establishment of a location used to enter a site.
• acidic soil:  having a pH less than 7.0, in contrast with alkaline which has a pH that is higher than 7.0.
• actinomycetes:  microorganisms that have some characteristics of fungi and bacteria.  Soil actinomycetes are very tolerant of water stress and contribute through their actions to that "good earth" aroma after a rain.
• action threshold:  the point at which a pest requires the implementation of a management tactic or control. Also a level of incompatible plant pressure where vegetation management treatments should occur to prevent conditions from reaching the tolerance levels.
• acute crotches: narrow-angle branch attachments stronger and wider than a co-dominant crotch, they are not likely to be a branch that will fail in high winds and is considered desirable.
• adaptive growth:  an increase in wood production in localized areas on a tree, in response to a decrease in wood strength or external loading to reduce the likelihood of failure.
• adaxial:  the upper surface of a tree's leaf.
• advanced assessment:  a more detailed Level 2, or Level 3 risk assessment performed to provide detailed information about specific tree parts, defects, or site conditions. 
• adventitious/epicormic growth:  new growth arising directly from dormant or new buds on main branches, stems, or trunks often in response to moisture and light that has no connection to apical meristems.
• adventitious root:  a root arising from non-root tissue, a darkness that has no connection to apical meristems often in response to stress.
• aeration:  the provision of air to the soil to alleviate soil compaction.
• aerial lift device:  a truck with booms and a bucket, for elevating a worker to a tree’s crown; may also be mounted on a self-propelled machine known as a mini-lift.
• aerial rescue:  a method of bringing an injured tree worker or climber down from their position in a tree.
• aerial roots: roots that grow from stems toward the soil with the capacity to become prop roots when they anchor in the soil.
• aerobic microorganisms:  these microbes require free, gaseous oxygen for growth.
• aesthetic benefit:  the increased value of the surroundings resulting from the pleasing appearance of a tree.
• afforestation: the act or process of establishing a forest especially on land not previously forested.
• aggregate:  soil such as sand, silt, or clay, a cluster of soil particles and organic matter, bonded together by exudates from microorganisms.  When used as a base material it may be a rock of a specified size.
• agroforestry or agro-silviculture: a land use management system in which trees or shrubs are grown around or among crops, pastureland, and natural ecosystems. 
• AHS Plant Heat Zone Map: a map to help determine which plants will do well in a warm climate.
• air terminal: the uppermost point of a lightning protection system in a tree.  It is usually made of copper.
• alkaline soil:  having a pH greater than 7.0, in contrast with acidic soil which has a pH lower than 7.0.
• alkaloids:  substances that are produced by trees and contain nitrogen and are used by humans for medicines.
• allée:  two parallel rows of trees, usually of the same species, form, and age, often having canopies that have grown together. ​
• allelopathy:  the production of substances by one tree that adversely affects other trees nearby. Root exudates from some trees such as black walnut (Juglans nigra) can kill or stall the growth of many soil organisms. 
• alternate leaves:  occur when there is one bud or leaf at a node spaced in alternating fashion along the stem.
• Aluminum:  (Al) this element will enhance tree growth because it increases antioxidant enzyme activity. This enzyme activity, in turn, increases root and shoot growth, and prevents iron (Fe) toxicity.
• amenity trees:  trees grown as living improvements to the property with uses and benefits ranging from ornamental and aesthetics to wildlife habitat and recreation. The amenity features come with the presence of trees.
• Amon-eye nut:  drop-forged eye nut is used to fasten through-hardware anchor(s), used when cabling trees.
• amylase:  an enzyme that can change the starch chains back to glucose molecules. ​
• anaerobic microorganisms:  these microbes live in the absence of free oxygen.
• anastomosing:  interconnecting veins to form a network. Typically found on a Ginkgo leaf.
• anchor:  the hardware installed to affix and/or terminate a cable or guy to the tree, ground, or other devices.
• anchor-tree:  a tree used to provide supplemental support in a guying installation.
• anemophilous:  species that produce large quantities of pollen and depend on wind for spreading the pollen to nearby trees and is usually highly allergenic.
• angiosperms:  they are hardwood trees and all flowering plants that have covered seeds such as oaks and maples.  The seed is born within an ovary. Opposite of gymnosperms.
• anions:  negatively charged atoms or molecules in fertilizer, they can become available to the plant in water.
• anoxic:  waterlogged soil that becomes low in oxygen and can kill the roots of the tree within days.
• ANSI:  the American National Standards Institute.  A US-based non-profit organization that works to develop and promote work standards, products, services, processes, systems, and personnel in the United States and around the world.
• ANSI A300:  the performance standard parameters established by industry consensus as a rule for the measure of extent, quality, quantity, value, or weight used to write specifications.
• ANSI Z60.1:  the American Standard for Nursery Stock, the latest edition.
• ANSI Z133:  the safety performance standard that provides the most current criteria in the United States for arborists and other workers engaged in arboricultural operations; Same as CSA in Canada.
• anther:  the pollen-producing part of a flower.
• anthocyanin:  a chemical that gives red pigments to leaves and other plant organs.
• Anthropocene:  the period during which human activities have had an environmental impact on the Earth
• anthropogenic activities:  burning fossil fuels, planting N-fixing crops, fertilizer production, and wastewater disposal that result in the increased concentration of atmospheric pollutants. 
• anthropogenic contaminants:  man-made pollutants.
• anthropomorphism:  projecting human terms onto tree characteristics.  Some examples include bristlecone pines having been called elder trees, or trees can think, or trees and people bleed.
• anti-transpirant:  anti-transpirant substance is applied to the foliage of plants to reduce water loss from stomata.
• anvil-type pruning tool:  a pruning tool that has a sharp straight blade that cuts against a flat non-cutting surface.
• apical dominance:  the extended growth of la vertical or central leader over lateral branches or buds by the terminal or apical bud.
• apical meristem:  the tip of the shoot or root; the region of actively dividing cells that increase the length of stems and roots, and produce flowers.
• apoplast:   the framework of non-living cells and cell walls in wood and bark.  The apoplast stores bound water, which does not flow. 
• appraisal:  an opinion of the monetary value of a tree.
• approach distances:  the minimum distances allowed between energized conductors and personnel.
• arborescent:  a plant resembling a tree in growth or appearance.
• arboriculture:  the art, science, technology, and business of commercial, public, and utility tree care. Arboriculture's focus is on the tree while the focus of forestry is on all trees.
• arborist:  an individual engaged in the profession of arboriculture who, through experience, education, and training, possesses the competence to perform the management of trees and other woody plants.
• arborism:  a synonym for arboriculture.
• arborist trainee:  an individual undergoing on-the-job training to obtain the experience required to manage trees and woody plants. Such trainees shall be under the supervision of an arborist.
• arborlogging:  the use of forestry-related equipment in the execution of more traditional arboricultural-related services.  An example would be a logger/arborist clearing a backyard of trees with equipment and while onsite using a harvester to piece out trees near a home or a cable skidder to winch over trees away from a target.
• arborologist:  provides training to improve tree and shrub care programs for arborists, horticulturalists, and landscape managers.
• arbuscular mycorrhizae:  commonly called endo mycorrhizae infects the internal tree root cells and is most common in deciduous forests.
• Armillaria root disease:  a fungi genus that can cause decay and death to trees under many types of conditions. 
• arthropods:  invertebrate insects and mites that may attack trees or process soil organic matter and mineralizing detritus.
• ascender:  a piece of mechanical equipment that grips the rope in one direction (down) and slide in the other (up) allowing the climber to climb up the rope in contrast with the descender.
• ASLA:  the American Society of Landscape Architects advances landscape architecture through advocacy education and fellowship.
• aspect ratio:  the comparison between the subordinate branch diameter and the parent branch diameter.
• auxin:  a plant hormone that controls cell elongation.
• axial parenchyma:  cells that run in a vertical direction on the trunk.
• axil:  the point of attachment of a leaf petiole to a stem.

B

• back cut:  a cut made on a tree trunk or branch, opposite from the notch, face cut, or undercut.
• backfill medium:  material used for refilling an excavated installation site and grading, often used for placing soil around a tree root ball in a planting hole.
• backflow preventer:  a device required by law to prevent water and chemical backflow using an air gap or one-way valve.
• B&B:  Balled and burlapped trees, also called Balled in Burlap, and rootball production system, have been dug so the soil around the remaining portion of the roots remains undisturbed and wrapped in burlap
• B&P:  Balled and Potted, B&B trees without the burlap and placed in a container.
• balancer:  a rigging sling(s), usually with at least one spliced eye and a Prusik to position the load line.
• bare root tree:  bare root trees are grown and moved with no soil on their roots. 
• bark:  a protective covering on the outside of a tree trunk and made of an outer periderm and an inner phloem. It keeps moisture and gases in the tree and resists attacks by insects and microorganisms.
  bark beetles:  a large group of insects that live under the bark of trees, often killing them.
• bark distortions:  overgrown knots, mechanical wounds, holes of all types, ingrown bark, and other defects which can be seen in the bark's appearance.
• bark fissures:  form on trees whose bark plates only divide in one direction such as oaks.  Some trees, such as beech, do not form fissures because the bark plates divide in two directions as the tree grows in girth.
• barrier zone:  chemical boundary within the wood that is present at the time of wounding and resists the spread of pathogens.  
• basal area replacement formula:  a calculation for the number of trees needed to do a wood-for-wood replacement of a damaged, destroyed, or felled tree.  For example, 100 trees are required to replace a 30-in-diameter tree. 
• basal rot: the decay of the lower trunk, flare, or buttress roots, also called butt rot.
• basic assessment:  a limited Level 1 or a more detailed Level 2 visual inspection of a tree and the surrounding site.
• bast fibers:  elongated, tapering, thick-walled cells that provide strength to wood.
• ​beneficial organisms:  insects and other organisms that promote plant health or assist in the control of pest populations.
• berm:  soil added in a linear or ridge form above grade for a specified purpose, such as controlling the flow of water.  Also referred to as a tree ring.
• bifurcation:  the natural division of a leaf, branch, or stem into two or more stems.  Typically found on a Ginkgo leaf.
• bimetallic connector:  the connector on a lightning protection system consisting of two or more types of metals intended to reduce the likelihood of forming an electrolytic couple.
• biochar:  a carbon product made from biomass via pyrolysis to become a stable solid product that can endure in soil for thousands of years.
• biodegradable:  capable of being broken down by natural, organic processes and reabsorbed into the environment.
• biodiversity or biological diversity:  biological populations in an environment as indicated by several different species of plants and animals and the communities they form.
• biological control management:  the management of pests using organisms that focus on control of plant competition, allelopathy, animals, insects, or pathogens.
• biomass:  the total weight of plant material that contains some form of living cells.
• biome:  a major ecological community type such as a tropical rainforest.
• biophilia:  the affinity of human beings for other life forms.
• biorational pesticide:  a pesticide formulated from naturally occurring plant extracts, microbes, or microbial byproducts.
• bioretention basins:  a ponding area that contains a grass buffer strip, planting soil, a sand bed, mulch, an under-drain basin, and plants including trees. Each of the components of the bio-retention basin is designed to perform a specific function. 
• biosolid:  nutrient-rich organic materials obtained from wastewater treatment and used as fertilizer.
• biostimulant: any substance or microorganism applied to plants to enhance nutrition efficiency, abiotic stress tolerance, and/or crop quality traits, regardless of its nutrient content.  The biostimulant may increase chlorophyll efficiency and production, increase antioxidants, and nucleic acid synthesis, enhance nutrient availability and increase the water-holding capacity of the soil. 
• biotic: about living organisms and their ecological and physiological relations.
• bleeding:  the flow of sap or pitch from plant wounds.
• blight:  any disease that kills plant tissues.
• block and tackle:  a system of one or more pulleys and ropes used to lift or pull heavy loads.
• BMP:  Best Management Practices; the best industry methods and ways of performing work based on scientific research and current knowledge.
• bole:  the main trunk of a tree below the branches.  Seedlings, saplings, and small-diameter trees have stems, not boles.
• bond:  an electrical connection between an electrically conductive object and a component of a lightning protection system that is intended to significantly reduce potential differences created by lightning currents.
• bonsai:  the art of managing tree growth through pruning stems, branches, and roots to maintain a miniature size.
• boom:  the long, movable arm of an aerial device or crane.
• bore cut:  using the tip of a chain saw to cut into or through the middle of a piece of wood.
• Boron: (B) this element helps trees with the use of nutrients and aids in the production of sugar and carbohydrates. Boron is also essential for seed and fruit development.
• botanicals:  compounds and pesticides made from plants.
• bottlebutt or bottle-butt:  a swollen region of a woody stem base and buttresses of a tree, over normal a growth response symptomatic of weakening or underlying decay. Sometimes caused when a fungal attack has caused the main stem to become hollow and reaction wood is produced to stabilize the tree.  
• boughs:  large branches on a tree coming directly from the trunk.
• boundary tree:  a tree, wholly or in part on adjacent property with a critical root zone that crosses property lines.
• BR:  Bare-Root trees that are harvested and removed from all soil or growing medium.
• bracing:  the installation of screws, cables, and threaded-steel rods in branches, leaders, trunks, or vertical undersize structures to provide supplemental support and to reduce the probability of failure of one or more parts of the tree.
• bract:  a modified leaf that compliments the flower.
• branch:  an outward growing shoot, stem, or twig that extends from the main stem or trunk of a tree.
• branch bark ridge:  the raised area of bark at the top of the branch union that marks where the smaller branch and parent branch meet.
• branch bark ridge and branch collar:  the natural features of a fork or union that consist of raised bark but may or may not be obvious. Neither the branch bark ridge nor the collar should be cut when pruning the tree.
  branch collar:  the swollen area of bark at the point of a branch attachment.
• branch competition:  the leaves on two or more branches are growing in the same space by crowding or shading the other branch.
• branch failure:  a branch separates from a tree because forces exceed the wood's strength or when high winds bend the branch and fracture the wood overloading may occur with rain or snow loading or when the branch grows too long.
• branch union is where a branch originates from the trunk or another branch.
• bridge graft:  the method used to repair a girdled trunk in which scion wood is grafted above and below the injury to reconnect the trunk vascular cambium.
• branch removal cut:  a pruning cut removing a subordinate branch from the parent branch at the branch bark ridge.
• broadcast fertilization:  the application of fertilizer over the soil surface.
• broadleaf trees:  one of the botanical groups of trees that have vessels or pores and broad leaves such as oak, elm, and ash; same as porous wood, in contrast to the conifers or softwoods.
• browse: portions of woody plants used as food by such animals as deer.
• bucking:  the process of cutting a felled tree into logs.
• buds:  organs that contain preformed parts of leaves or needles, flowers, or both.  Buds are structures that are made up of embryonic shoots.
• bud scar:  a scar left on a twig when the bud or bud scales fall away.
• buffering capacity:  the ability of a soil to maintain its pH.
• buildable area:  that portion of a lot wherein a building may be located, not the portion of a lot that is located within any minimum required front, rear, or side yards, or landscape area buffer zones.
• bulge:  a general enlargement of a section of trunk or branch.
• bulk density:  the mass of soil per unit volume used as a measure of compaction.
• bull rope:  a large diameter rope used in rigging.
• burl:  a hard woody protuberance on a trunk with no protruding branches, twigs, or stumps.
• burlap:  a strong, coarsely woven cloth made from fibers of jute, flax, or hemp.
• buttressing roots:  the lateral surface roots that aid in stabilizing a tree. They are fine roots without secondary thickening or suberin at the extremities of the root system.  They are responsible for the absorption of mineral nutrients and water.  The microscopic root hairs (outgrowths from cells of the epidermis) arise close to the root tip, which increases the surface area for absorption.
• BVOC emissions:  plants produce and discharge Biogenic Volatile Organic Compounds such as isoprene and monoterpenes into the atmosphere.  Plants species can emit a higher or lower amount.
• bypass pruner:  a pruning tool using a sharpened blade that passes along an unsharpened hooked or curved blade.  Also called secateurs.

 C

• cable: 1) Zinc-coated wire strands per ASTM A-475 for dead-end grip applications or 2) Wire rope or strand for cabling applications or 3) Synthetic-fiber rope or webbing for general applications of tree work.
• cable aid: a tool used mainly to tighten lag hooks and eye bolts into a tree.
• cable clamp: should be used to attach a small diameter cable to anchor hardware. There should be at least 3 clamps per anchor and the “U” of the clamp goes on the short end of the cable.
• cable-end termination: the hardware designed to anchor cables installed through a branch or stem.
• cable grip: a mechanical device that temporarily grasps and holds wire rope or strand cable during installation.
• cabling: the installation of a steel wire rope or synthetic-fiber rope within a tree to provide supplemental support to branches with weak unions, heavy branches, and weak wooded species that may pose a threat of failure.
• cabling hardware: consists of eye bolts, threaded rods, washers, and amon-eyes.
• Calcium: (Ca) this element participates in enzymatic and hormonal processes as well as in metabolic processes with other nutrients while promoting proper tree cell elongation. Calcium is also an essential part of the tree cell wall by forming calcium pectate compounds which give strength and stability to cell walls and bind the cells together. Because calcium improves the stomata function it helps protect the tree against heat stress. Calcium helps in protecting the tree against diseases such as numerous fungi and bacteria secret enzymes which impair tree cell walls. Stronger cell walls, induced by calcium, can avoid invasion.
• cadastre: an official register of the ownership, extent, and value of real property in a given area.caliper: tree trunk diameter measured 6 in. (15 cm) above the flare; if the caliper is greater than 4 in. (10 cm), the measurement is taken at 12 in. (30 cm) above the flare.
• calipers: an instrument used to measure the diameter of the trunk of a tree.callus: undifferentiated cambium response tissue that forms around the edge of a wound.cambium, cambium layer, or cambial zone: a layer of trunk and root cells that produce new wood and xylem on the inner side and phloem or inner bark on the outer side.canker: a definite, relatively localized lesion, primarily of bark and wood.
• canopy: the collective branches and foliage of trees that make up the tree's crown. The forest canopy is a collective term.
• canopy cover: the area of the land surface that is covered by tree canopy as seen from above.
• capacity: the maximum amount of plant life that a particular forest environment can support indefinitely without ecosystem degradation, given the limitations of food, shelter, competition, predation, and other available resources; usually expressed in terms of an individual species. The potential to do something.capillary water: the water held in the capillary pores of the soil.
• capsule: a simple, dry, fruit containing many seeds.carbon dioxide: a colorless gas, soluble in water, used by green plants to make carbohydrates during photosynthesis.carbon sequestration also known as 
• carbon storage: is the capturing and long-term storage of carbon.
• carotenoid: the yellow, orange, or red pigment responsible for those colors in parts of a tree.
• cataphylls: the simple protecting leaf wrapped over a small bud structure.cation exchange capacity: the ability of soil to hold onto nutrients.
• cations: positively charged atoms or molecules in fertilizer that become plants available in water.
• catkins: the long droopy flowers produced at the ends of branchlets that eventually fall from the tree.
• cavitation: a break in the continuity of water columns in the xylem and the water supply to transpiring leaves. Cavitation is usually caused by extreme soil or weather conditions when the tension of water within the xylem becomes so great that dissolved air within the water expands to fill either the vessel elements or the tracheids.
• cavity: a void within the solid structure of the tree, normally associated with decay or deterioration of the woody tissues.cavity tree: see "den tree"
• cells: the basic structural and functional unit of living organisms.
• cellulose: a complex carbohydrate made up of long, twisting chains of glucose or sugar molecules.
• central leader: referred to as the leader or dominant leader. It is a vertical continuation of the main trunk, beginning above the highest lateral branch and extending to the top of the tree.certified arborist: an arborist who has passed an independent exam administered by the ISA.CEU or continuing education unit: a measure and confirmation of continuing education courses.
• chain of custody: evidential documentation of the handling, processing, and ownership of a tree throughout the chronological history of its entire production.chain saw: a portable powered saw with cutting teeth linked in a loop of chain.champion tree: the largest tree by age or size when compared to all other known trees of the same species.chaps: leg protection to be worn when operating a chain saw.
• charcoal: carbon-rich combustible solids that result from the pyrolysis of wood.
• chelates: chemical compounds that keep plant nutrients soluble and available for tree absorption.chemical management methods: the management of pests and vegetation through the use of pesticides, herbicides, and growth regulators, to make conditions more favorable for tree growth.
• chemotropism: a plant growth response to a chemical.
• chimera: a tree that contains at least two different sets of DNA.chipper: equipment used to reduce tree debris into wood chips.
• chitin: a hard substance forming the outer coat of insects and the cell walls of some fungi.Chlorine: (Cl) this element, as a compounded chloride, is necessary for osmosis and ionic balance; it also plays a role in photosynthesis.
• chlorophyll: the green substance that can trap the energy of the sun in a process called photosynthesis.
• chloroplast: specialized cells that contain chlorophyll and promote making starch or sugar.
• chlorosis: chlorosis is the partial failure to develop chlorophyll, caused by a nutrient deficiency or the activities of a pathogen.​chromosome: consist of genes and are responsible for the activity of a cell and undergo division into newly formed parts of the tree.circling root: one or more roots whose diameter is greater than 10% of the trunk caliper circling more than one-third of the trunk. Circling roots are unacceptable for proper tree root growth.
• cladistic: an approach to biological classification in which organisms are categorized in groups according to the proportion of measurable characteristics that they have in common. This is in contrast where taxon names are defined by a type.
• cladoptosis: a process in which trees shed their branches as part of their normal physiology once a year, typically on cedars.
• cleaning: the selective pruning to remove one or more dead, diseased, or broken branches.clear trunk: the portion of the trunk below the main crown which may include shortened temporary branches.
• clearance requirements: pruning to meet clearance standards over streets and sidewalks where branches are interfering with the movement of vehicles and pedestrians, or obstruct signs and traffic lights.
• client: the property owner or manager who is responsible for contracting arboricultural services. Clients may be owners of the property and governmental clients that are stewards of private and public lands.
• climate: refers to the long-term regional or global average of temperature, humidity, and rainfall patterns over seasons, years, or decades. Weather is the opposite and refers to short-term climate conditions.
• climate change: refers to a broad range of global phenomena created predominantly by burning fossil fuels, which add heat-trapping gases to Earth’s atmosphere.
• climax species: the relatively stable ecological stage of trees that is achieved through successful succession and adaptation to an environment that ends as an oak/hickory forest for example.
• climbing hitch: the hitch used to secure a tree climber to the climbing line.climbing spurs: sharp, pointed devices attached to a tree climber's boot and are used to assist with climbing trees. They are also called gaffs, hooks, spurs, and spikes, and are not recommended for pruning operations because they wound the tree. They are acceptable during tree removal and for emergency rescue.
• clod: a lump or mass of soil that is broken into shape by artificial actions such as tillage. In contrast to a ped which is a natural soil aggregate like sand that is used with a binding agent such as cement.
• clone: is a tree grown from a cutting. Cloned trees grow their own roots and have the same genetics as their parent tree. 
• Cobalt: (Co) this element increases growth, nodule number and weight, tree nutrient levels, as well as seed pod yield and seed quality.
• co-dominant stems: two or more, generally upright, branches or stems of roughly equal diameter and originating from a common point. Because they grow from a common point there may be limited branch attachment along the top of the stems and structural integrity can be reduced.
• collected tree: a tree that has been taken from the wild or landscape installation and then grown in a nursery.
• come-along: a portable ratcheting pulling device, using cable or rope to draw two objects closer together.command-and-response system: a system of vocal communication in tree care operations used to convey critical information between a worker aloft and a ground worker.
• compaction: mechanical compressing of the soil surface destroys the micro cavities and the pore space. The compaction of the soil reduces the porosity and permeability.
• companion cells: a specialized cell in the angiosperm phloem derived from the same parent cell as the closely associated, immediately adjacent sieve-tube member. 
• compartmentalization: the physiological process that creates the chemical and physical boundaries that act to resist the spread of disease and decay organisms in tree branches and stems.
• compatible vegetation: plant forms consistent with management objectives.competing leaders: branches that are the same height or leaf mass as the central leader, and can outgrow it.
• complete fertilizer: a fertilizer containing the three primary elements which are nitrogen (N), phosphorus (P), and potassium (K).compost: organic matter that has been subjected to decay processes and is decomposed.
• compound leaf: a leaf whose blade is divided into several distinct leaflets.compression wood: this wood forms on the lower side of the lean-in conifers, as evidenced by closely spaced rings.
• condition: the general condition of a tree either for overall health, structure, or combined. The rating is based on an inspection process. The rating range can be a term or a percentage using the International Society of Arboriculture tree assessment protocols, such as: Excellent – 100%, Very Good – 90%, Good – 80%, Fair – 60%, Poor – 40%, Critical – 20%, Dead – 0%.conductor: the copper cable or wire used in a lightning protection system intended to carry the lightning current to ground.
• conifers: gymnosperms such as pine. The wood contains resin ducts. Usually cone-bearing and evergreen needle-leaved or scale-leaved trees.
• conk: a fruiting body of wood-rotting fungus located on the bole of the tree.
• connector: a part of the lightning protection system used to connect conductors to each other or to metallic installations.
• connector clamp: a multipurpose bolt clamp that is used to bond conductors, or bond a conductor to a ground terminal or tree supplemental support system.conservation: the wise use and management of natural resources.consistency: the way in which a substance holds together.contact pesticides: materials that cause pest injury or death on contact.
• container grown tree: a tree grown in a container or pot. Also called a containerized tree.
• controlled-release fertilizer: a slow-release or slowly soluble form of fertilizer.controlling authority: an agency, organization, or corporate entity with the legal authority and/or obligation to manage individual trees or tree populations.co-owned tree: a boundary tree where the trunk goes into the ground and straddles the property line, not including the flare.Copper: (Cu) this element is important for reproductive growth. It aids in root metabolism and helps in the utilization of proteins.
• coppice: a thicket grove, or growth of small trees.
• coppicing: the old-fashion cutting down of a tree within 12 in. (300mm) of the ground at regular intervals, traditionally applied to certain species such as Hazel and Sweet Chestnut that resprout to provide stakes.
• cord: a unit of measurement of stacked firewood or pulpwood. The standard cord consists of a pile of wood whose pieces are 4 feet (1.25 m) long stacked 4 feet (1.25 m) high by 8 feet (2.5 m) long, containing 128 cubic feet (3.9 cubic m) of wood.
• cordate: a heart-shaped leaf.core sample: a sample of wood extracted from a trunk or branch, using an increment borer tool. The resulting core can be analyzed for characteristics of growth, structure, decay, and species identification.cork cambium: see “phloem”
• correct pruning cuts: branches should be removed at their point of attachment or shortened to a lateral and all cuts should be kept as small as possible.
• corridor: a strip of wildlife habitat, unique from the landscape on either side of it.
• cortex: a layer inside the thin outer bark on young stems.
• corticular photosynthesis: an effective mechanism for recapturing respiratory carbon dioxide before it diffuses out of the stem.corymb: flowers attaching at different points along the flower stem.
• cotyledon: the first leaf on a seedling.
• Council of Tree and Landscape Appraisers (CTLA): a group of representatives from several tree care and landscape associations that work to research and author the "Guide for Plant Appraisal".crenate: a term to describe a leaf margin with rounded teeth.crimp-type connector: a cast or stamped connector used to connect cables in either an end-to-end, side-by-side or a Y configuration in a lightning protection system.
• Critical Root Zone (CRZ): the portion of undisturbed soil and rooting area including the flare that is the minimum necessary to maintain the vitality and stability of the tree. Encroachment or damage to the critical root zone will put the tree at risk of failure. For a free-standing tree with no apparent root restrictions, the critical root zone shall consist of a circle having a radius of one foot (30cm) for each one inch (2.5 cm) of diameter at breast height (DBH) of the tree and to a depth of two feet (60 cm).crotch: see "union"
• crown: the portion of a tree beginning at the lowest main scaffold branch extending to the top of the tree including all the branches and foliage but not including any clear stem/trunk. On younger trees, the crown may be comprised of temporary branches.
• crown cleaning: the selective removal of dead, dying, diseased, and broken branches from the tree crown.
• crown density: the amount, compactness, or depth of foliage on a tree crown.
• crown lifting or crown raising: lifting should not normally include the removal of large branches growing directly from the trunk. Crown lifting on older, mature trees should be avoided, restricted to secondary branches, or shortening of primary branches. Crown lifting is an effective method to enable access under the crown but should be restricted to less than 15% of the live crown height. Crown lifting height should be specified.crown reduction: the objective is to reduce the height and/or spread of a tree's crown. Crown reduction should retain the main framework of the crown, a significant proportion of the leaf-bearing structure, and a smaller outline. Crown reduction cuts should be as small a diameter as possible. Reductions should be specified by actual measurements. Crown reduction is not ‘topping’, a harmful treatment that is performed with excessive heading cuts.crown rot: see “basal rot”
• crown shyness: trees have learned to stop growing at their tips when any new foliage will be stripped away by existing branches. Wind plays a crucial role in helping many trees maintain this distance. Trees keep their branches apart to allow other branches equal access to sunlight. The boundaries carved between branches also improve a tree's access to curb the spread of leaf-eating insects, parasitic vines, and infectious diseases.
• crown symmetry: the distribution of branches relative to the trunk.crown thinning: the removal of a portion of smaller branches, usually at the outer crown, to produce a uniform density of foliage around an evenly spaced branch structure. It is usually confined to broad-leaved species. The material should be removed throughout the tree and no more than 30% during one growing season.
• cultivar: a named tree selection from which identical or nearly identical trees can be produced, usually by grafting, vegetative propagation, or cloning a plant that has been specifically selected by man because it exhibits different characteristics from the typical species and is worth maintaining in cultivation by vegetative propagation or by seed in the case of true-breeding cultivars.
• cultural control methods: plant management through irrigation, raking, pruning, etc. as well as the control of vegetation through the establishment of compatible, stable, plant communities or the use of crops, pastures, parks, or other managed landscapes.
• cyanobacteria: bacteria that can "fix" nitrogen or change nitrogen into the nitrate form that is useful as a plant nutrient.
• cycle: the planned interval of time between vegetation maintenance activities.cyme: many flowers forming a flat surface.cytokinins: one of the molecules in DNA and are used to promote root formation and promote lateral bud growth in flowering plants.
• cytoplasm: a gel-like substance enclosed within the cell membrane that produces the vitamins vital in the activation of enzymes.
• Ddamage: occurs when defects lower the quality of the wood.dbh: diameter at breast height is the measurement of the trunk diameter taken at 4.5 ft (1.4 m) above the flare.dead-end brace: a brace formed by threading a lag-thread screw rod directly into the branch, leader, or trunk, but not out through the side opposite the installation.
• dead-end grip: a manufactured wire wrap designed to form a cable termination at the end of a cable that meets the specifications of ASTM A-475 for zinc coated strand.
• dead-end hardware: anchors or braces that are threaded directly into the tree but not out the side opposite the installation. Dead-end hardware includes but is not limited to: lag hooks, lag eyes, and lag-thread screw rods.
• dead wood: non-living branches that provide essential wildlife habitats and its management should aim to leave as much as possible by shortening or removing only those that pose a risk.decay: (v.) the decomposition of woody tissues by microorganisms or (n.) wood that is decomposed.
• decay detection device: a device used to assess the presence of hidden internal decay.
• deciduous: any tree that loses all of its leaves at one time during the year, usually in autumn. See also "broadleaf trees".decline: occurs when an entire tree exhibits a lack of vitality such as reduced leaf size, color, or density. decurrent: the rounded or spreading growth habit of the tree crown characterized by strong apical dominance.
• decussate leaves: arranged in pairs each at right angles to the next pair above or below. Example: Calotropisdefects: injuries, growth patterns, decay, or other conditions that may reduce the tree's structural strength.
• deforestation: the vast removal of tree cover and conversion of forested land to other uses as a result of human activities.
• dehiscent: the release of seed capsules at maturity.​delamination: the separation of wood layers along their length, visible as longitudinal splitting.
• delignification: the removal of lignin from woody tissue by natural enzymatic processes which can be caused by chemical reactions with wood fungi.den tree: a tree with cavities in which birds, mammals, and insects such as bees may nest.
• dendrochronology: the study of cores and cross-sections of a tree to determine old weather patterns and growth maps that are used for dating old wood.
• dendrology: the scientific study of trees and their identifying characteristics.
• ​denitrification: the process of reducing nitrates to nitrogen gases, usually in soil.
• dentate: a leaf having teeth perpendicular to the margin.desiccation: severe drying out.
• desired and preferred use: the development of a product given the end-use goal, including but not limited to the highest and best use.
• detritus: organic matter produced by the decomposition of the bodies of dead organisms and fecal material.
• dichotomous venation: when two veins exit the leaf blade at the base and fork repeatedly in two.
• dicotyledon or dicots: have two seed leaves and belong to trees such as oaks, maples, and beeches.
• dieback: a condition in which the branches in the tree crown die from the tips toward the center. Dieback may progress, stabilize or reverse as the tree adapts to its new situation.
• differentiation: when a cell changes its structure, such as when a parenchyma cell becomes enlarged to form a vessel, it is no longer a parenchyma cell.
• diffuse-porous wood: trees such as maple, birch, poplar, and cherry, are angiosperms that have vessels, parenchyma, and fibers of about equal size and diameter arranged at about equal distances from each other throughout the growth increment.
• dimorphic: a tree that has two distinct forms and leaves.dioecious: trees that have male and female elements on separate plants.
• direct cable installation: consists of a single cable between two tree parts, such as two branches, two stems, or a trunk and a branch.
• directional pruning: guides the tree to grow in a certain direction by removing live branches from other portions of the tree.
• disease: any fungal, bacterial, or viral infection that will likely result in structural failure or death of the tree within two years and where treatment will not prevent the death of the tree, any alteration from the normal development and functioning of a tree or plant.
• distribution lines: very high voltage electric supply lines
• dormant: the inactive growth period of a tree, usually during the coldest months of the year when it is little or no growth and leaves of deciduous trees have been shed.
• double hearts: an occurrence of two separate bands of heartwood that form just below the union of a forked tree trunk.
• drip line: a boundary on the ground delineated by the branch spread of a single tree or group of trees.
• drought: a period of dry weather, especially a long one that is injurious to trees.
• drum lace: a method of tying the root ball of a balled-and-burlapped tree for moving.
• drupe: a simple, fleshy fruit, with a single seed such as in a peach or cherry,
• duty of care: the legal obligation that requires an individual to apply reasonable actions when performing tasks.
• dwarfing: a tree's response to consistently strong winds that reduce its above-ground growth.
• dying tree: a tree that is diseased, injured, or in terminal decline to the extent that death is more likely than not within two years based upon a visual inspection and evaluation of canopy, leaves (if present), trunk, buttress roots, and other factors.
• dynamic cable system: any of several cabling systems that utilize nonrigid materials for tree support systems.

• the ecological design: the shaping of human and animal habitats through landscape architecture, engineering, urban planning, and architecture.
• ecology: the study of the relationships between organisms and other elements of their environment.
• economic threshold: the pest population level at which the cost of inaction is less than the cost of action. 
• ecosystem: many cells create a tissue, many tissues create an organ, many organs create an organism, and many organisms create an ecosystem.
• ectomycorrhizae: these mycorrhizae infect the outermost fungal cells and are most common in conifer, beech, oak, and hickory forests.
• edge: the boundary between open land and woodland or between any two distinct ecological communities.
• electrical conductor: any material through which an electrical current can flow.
• electrical resistance: the relative opposition to the flow of electrical current, measured in ohms. Material such as copper has low resistance and is therefore a good conductor.
• electrophysiology: electrically excited tree cells that can influence processes such as tree movements. Cells in nearly all living organisms can be electrically excitable. 
• embryo: a young tree in seed before the start of rapid growth.
• emergence holes: holes in the bark created by insects leaving the plant to complete their life cycle. Also called exit holes.
• endangered species: species in danger of extinction throughout all or a significant part of their range. Species protection is mandated by the United States Endangered Species Act of 1973.
• endemic: when trees are native to a particular country.
• endodermis: the inner layer of the cortex in roots.
• energized conductor: an electrical conductor through which electrical current is flowing.
• entire: a leaf margin without teeth.
• entomophilous: species characterized by pollen which is frequently heavy and spread by insects and is not allergenic.
• environmental stewardship: the responsible use and protection of the natural environment through conservation and sustainable practices.
• enzyme: a complex protein that speeds up certain chemical reactions.
• epidermis: the outer layer of cells on all parts of a tree except the roots.
• epiphytic: a plant that is supported the  by a tree and derives its nutrients and water from rain, air, and dust. Spanish moss is an example.
• eradication: the total removal of a species from a particular area.
• erosion: the wearing away of the land by the movement of water, wind, or ice.
• escape route: in felling operations, the safe direction for the chain saw operator to move while the tree is falling.
• espalier: the combination of pruning, supporting, and training branches to orient a tree to one plane, often used against a wall or along a fence.
• essential elements: the 17 minerals essential for the growth and development of trees.
• establishment: the point after installation when a tree's root system has grown sufficiently into the surrounding soils to support shoot growth and anchor the tree.
• ethylene: the gaseous plant hormone that triggers fruit ripening.
• evaluation: 1) the process of comparing the current or predictable pest population to the action threshold, to determine the need for treatment or 2) the process of assessing the results of the IPM program.
• evaporationnon-parasiticallythe occurs when rainfall on the leaves and bark vaporizes after storm.
• evapotranspiration: the loss of water by evaporation from the soil surface and transpiration by plants.
• evergreen: any tree that retains its leaves for more than one growing season.
• excurrent: tree growth habit characterized by a central leader and a pyramidal crown.
• exfoliating: peeling off bark in shreds or layers.
• exotic species: not native to a region.
• Extraction is sometimes applied to digging trees and potting them at a nursery.
• exudates: these are substances that contain photosynthate, and other substances made by the tree and are used as an energy source and building blocks by many soil microorganisms.
• exurb (or exurban area): an area outside the typically denser inner suburban area of a city. 
• eye bolt: a drop-forged, closed-eye bolt used in cabling.
• eye splice: a closed-eye termination formed into rope or common grade cable by bending it back on itself and winding each rope strand or wire around the rope or cable a minimum of two complete turns.
  

F

• fabric bag: may be used above ground as a plant “container” or in the ground as an “in-ground growing bag”.
• face cut: the notch made to help control the direction of fall of trees or branches being removed.
• facility: a structure or equipment used to deliver or provide protection for the delivery of an essential service, such as electricity or communications.
• failure: the breakage of branches or loss of mechanical support by the tree's root system.
• false crotch: a device installed in a tree to hold ropes during climbing or rigging.
• fascicles: slender bundles of evergreen needles, pines for example.
• fastener: an attachment to secure a lightning protection conductor to a tree.
• feeder: a high-priority electric distribution supply line, generally 12,000 to 34,500 volts.
• felling: dropping or cutting down a tree.
• fertilization: the application of fertilizer to the soil within the tree’s rooting area, to promote tree growth. This will only be effective if nutrient deficiency is confirmed.
• fertilizer: a substance containing one or more nutrients to be used by a tree or surrounding soil to supplement the supply of essential elements.
• fertilizer analysis: the composition of a fertilizer expressed as a percentage by weight of total nitrogen (N), available phosphoric acid (P2O5), soluble potash (K2O), and other essential nutrients listed on the bag.
• fertilizer ratio: the ratio of total nitrogen (N), available phosphoric acid (P2O5), and soluble potash (K2O); for example, the ratio of a 30-10-10 fertilizer is 3:1:1.
• fibrous roots: many lateral roots that are shallow, wide-spreading, numerous, and grow horizontally to stabilize a tree.
• field capacity: the maximum soil moisture content following the drainage of water due to the force of gravity.
• fill soil: soil, sand, gravel, rocks, or other material placed over the existing soil surface to raise the finished grade to some specified level.
• final cut: the cut that completes the removal of a branch.
• fixing nitrogen: bacteria form nitrogen-fixing nodules on the roots of many trees in the legume family. The nodules form nitrate or ammonium ions which can be absorbed by the tree.
• flagging: the symptom in which leaves on a branch wilt and may ultimately turn yellow or brown without falling from the branch.
• flare: the transition zone where the trunk flares out to meet the buttress, main, or structural roots. It was also called trunk flare, stem flare, root flare, or first-order lateral roots, but these terms are falling out of favor.
• flip line: a guideline that helps installers to understand modern green roof technology, different green roof solutions, the function of green roof systems, and the green roof components.​
• flower: floral leaves grouped on a stem for sexual reproduction in angiosperms.
• flush cut pruning: cutting off a branch flush with the trunk, destroying the protective branch collar, and exposing the trunk to decaying organisms. This is not an acceptable practice.
• foliage: live leaves or needles of the tree, the tree part primarily responsible for photosynthesis.
• follicle: a simple dry fruit that splits along one side.forb: an herb other than grass that benefits wildlife.
• ​foreign objects: objects including, but not limited to miscellaneous metal and concrete objects and glass insulators that a tree has grown around after many years of disuse.
• forest: a large wooded area, usually with undergrowth. Trees and many other communities of organisms are connected in ways that ensure high-quality survival for all.
• forest connections: hyphae from mycorrhizae on one tree that can connect with hyphae from another tree, even of a different species.
• forest duff: dead leaves or the mulch layer on the surface of the forest soil.
• forest ecosystem: a community of living trees and animals typically found in certain climates and locales.
• forest garden: layers of plants and natural ecosystems to support and complement urban trees.
• forestry: the management of forests.
• forest types: associations of tree species such as oak/hickory, that commonly occur because of similar ecological requirements.
• fork: the very weak branch union of two identical stems.formative pruning: see “structural pruning”
• frass: wood shavings produced by insects boring into a tree.
• free climb: climbing a tree without being secured by a climbing rope.
• French drain: a gravel-filled trench used to drain water from the soil.
• frost crack: a vertical split in the wood of a tree, caused by internal stresses and low temperatures.
• fructose: the simplest form of carbohydrate or sugar.
• fuelwood: Roundwood, whole or split, produced for heating purposes.
• fruit: ripened ovaries and their attached parts.
• fungus: any of a diverse group of eukaryotic single-celled or multinucleate organisms without roots, stems, or leaves, that live by decomposing and absorbing the organic material in which they grow, comprising the mushrooms, molds, mildews, smuts, rusts, and yeasts.
• fungi/fruiting bodies: contain spores, which are dispersed for reproduction. Mushrooms are a familiar example of a fruiting body. They are formed from hyphae, the tiny threads that make up the bulk of most fungi. A network of hyphae, known as mycelium, can extend in all directions through the soil.
• Ggaff: the pointed, spur portion of a climbing spike.
• gall: an abnormal swelling of plant tissues caused by various insects.
• galleries: the complex of tunnels created by insects in trees for feeding and shelter.
• genus: a taxonomic category ranking below a family and above a species or a group of similar species.
• gene: a substance within a chromosome that determines hereditary characteristics.
• genotype: growth or development characteristics dependent on genetic information.
• ​Geographic Information System (GIS): any system used for capturing, storing, analyzing, and managing data and associated attributes spatially referenced to the earth.
• geotextile fabric: a synthetic fabric used in landscape construction as a barrier under mulch or pavement to reduce weed germination. It is becoming less popular because it also blocks the flow of water through the soil. It is also used to minimize soil compaction under a paved surface.
• geotropism: a growth induced by gravity. It makes roots grow down and stems grow up.
• germination: the beginning of growth in a seed, spore, or bud.
• gibberellins: a group of plant hormones involved in cell elongation.
• girdling root: the measure around the trunk accompanied by a distance from the ground.
• Global Positioning System (GPS): a series of satellites that transmit precise microwave signals, that enables a receiver to determine its exact location, speed, direction, and time anywhere on the earth.
• global warming: a term being used since the early 20th century that refers to the long-term warming of the planet.
• glomalin: an organic glue that acts to bind organic matter to mineral particles in the soil as tiny clumps that actually improve soil structure.
• glucose: a simple sugar manufactured in a green leaf.
• graft: to join together tissues from the same or different plants  create desirable characteristics.
• graft union: the junction between torootstock and scion wood, evident by a thickening of the trunk at the union, not to be confused with the flare.
• grafted cultivar: reduce incoming stormwater runoff velocity and catches suspended solids. The grass should remove some of the sediment load. The addition of a pea gravel flow spreader in the design of the basin also helps capture sediments.
• gray water: household wastewater from bathroom sinks, showers, bathtubs, and clothes washers. Suitable for watering landscapes and trees.
• green infrastructure: the living plants and natural materials within developed areas. The range of measures that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest, and reuse, or landscaping to store, infiltrate, or evapotranspiration stormwater and reduce flows to sewer systems or to surface waters.
• green mulch: a mulch composed of green organic matter and not fully composted.
• greenhouse effect: the rise in temperature caused by gases or materials suspended in the atmosphere that trap energy from the sun.
• ground rod: an 8 ft (240 cm) long copper and steel rod driven into the ground as part of a lightning protection system.
• groundcover: the low-growing plants that require minimal maintenance, used in landscaping and surface treatment of the planting pit instead of turf or mulch.
• ground-to-conductor clearance: in utility arboriculture, the distance between live or energized conductors and the ground.
• groundwater: water naturally stored underground in aquifers and saturated soil.groundwater recharge: replenishment of both groundwater levels and normal weather stream flows.
• grove: a small wood or forested area of at least three trees greater than 6 in (15 cm) dbh, usually with no undergrowth.
• grow bags: the shape, growth rate, mature size, and branching structure of a tree without pruning.
• growth increment: the incremental growth added as new wood each growing season over existing wood. This is seen as growth rings in cross-sections of wood.
• growth phases: periods of gradual and consistently expansive growth under apical dominance.
• growth phase changes the changes between growth phases and the decline of growth as ree ages.
• growth regulator: a chemical that regulates enzymes and the growth of a tree.
• growth rings: the concentric circles visible in a cross-section of the trunk. Each growth ring represents a year of the tree's life.
• guard cells: a pair of specialized cells that regulate the opening and closing of a stomate.
• Guide for Plant Appraisal: the copious production and exudation of gum by a diseased or damaged tree, especially as a symptom of a disease in fruit trees.
• "guying: the installation of a steel cable or a synthetic-fiber cable system between a tree and an external anchor to provide temporary supplemental support.
• gymnosperms: softwood trees such as conifers, which all have cones, naked seeds, and resin ducts. Opposite of angiosperms.

H

• habitat: a place where any organism can live.hack job: to prune a tree beyond what is acceptable by industry standards. 
• hard hat: a protective hat made of a rigid material that must be worn when climbing and working on trees.
• hardened off: plant tissue that is acclimated to the cold or a new environment.
• hardiness: the genetically determined ability of a plant to survive low temperatures.
• Hardiness zone map: nearly impervious compacted soil.
• hardscape: the built infrastructure such as pavement, outdoor furniture, gutters, storm drains, walls, and footings.
• hardwood: trees that lose their leaves in autumn. It also refers to is the wood produced by these trees. Hardwoods are the predominant type of tree in the deciduous forest.
• harvesting or tree removal: the process of removing trees and creating lumber products from rural, urban, or community forests. To develop the environment needed to reforest the area. Harvesting can be used for special goals such as developing wildlife habitat. Harvesting is in contrast with intermediate cuttings.
• hazard: a tree with uncorrectable defects,  or habitats that may result in personal injury, property damage, or disruption of human activities. Hazard is extreme risk in tree risk terminology.
• hazard assessment: the process of managing or eliminating an identified hazard.
• heading: 1) cutting a currently growing shoot, back to a bud. 2) cutting an older branch or stem back to a stub in order to meet a defined structural objective. 3) cutting an older branch or stem back to a lateral branch situationsnot large enough to assume apical dominance. , is not an acceptable pruning practiceconditions unless specified as “shearing”.
• healthy tree: any tree with a DBH equal to or greater than 6 in (15 cm) that is not dead, dying, diseased, hazardous, destroyed, or an invasive or undesirable species.
• heart rot: any of several types of fungal decay of tree heartwood.heartwood: wood from the inner core of the tree stem that provides chemical defense against decay-causing organisms and continues to provide structural strength to the trunk.
• heat days: when temperatures are over 86° F (30° C) and is the point at which plants begin suffering physiological damage from heat.
• heat island effect: a row of shrubs or low trees planted closely to form a boundary between pieces of land or at the sides of a road.
• height: the vertical distance of a tree between the flare and the top of the stem.
• hemicellulose: a cross-linked polymer polysaccharide in the plant cell wall but different than cellulose which is a linear polymer in the plant cell wall.
• herbicide: any chemical that kills plants or inhibits their growth and is intended for weed control.
• heritage tree: the capacity for growth often exhibited by crossbred trees. 
• hybrid vigor: dissimilar pairs of genes for any hereditary characteristic in trees.
• to tree: a tree that has a high likelihood of failure causing significant damage to potential targets.
• high voltage: high voltage powerlines that need extended clearance from tree branches.
• hinge: a strip of uncut wood fibers created between the face cut and the back cut that helps control is direction in tree felling.
• ​holistic: the parts can only be understood in terms of their contribution to the health of the whole tree.
• hook-and-blade type pruning tool: the ground terminal of a The headingprotection system composed of ground rods or copper ground plates that are not fully driven or installed in the ground due to site conditions.
• hormone: a product produced in one part of a tree and transported to another part where it controls a process.
• horticulture: the cultivation of fruits, vegetables and ornamental plants.
• horticultural oils:  highly refined petroleum oils that may be applied to plants to smother certain insects.
• host: a living organism from which a parasite obtains nutrition.
• humic acids: slow decomposition reactions in soils. Humic and fulvic acids buffer pH swings in the soil.
• humates: mineral salts of humic and fulvic acids.
• humus: the decomposing organic materials in soil which contain humic acids.
• hybrid: a plant resulting from a cross between two or more other plants.
• hydraulic soil excavation: the removal of soil using pressurized water to minimize root damage.
• hydrogels: crystalline polymers which absorb water.
• hydrotropic roots: a product containing the radical OH group.
• hyperaccumulator tree: can absorb toxins to a greater concentration than the soil in which it is growing.
• hyphae: the branching structures of fungi that make up high-risk.
  I
• ice floes: the uptake of water by seeds.
• impervious: a surface or soil particles that do not allow for infiltration of liquids.
• implant: a capsule or other device permanently inserted into the xylem to treat diseases and pests.
• included bark: the bark embedded in the union between a branch and the trunk or between two or more stems that the  the formation of a normal branch bark ridge. Included bark has a higher likelihood of failure than a normal branch attachment.
• incompatible vegetation: plant forms that are inconsistent with management objectives.
• increment borer: a device used to take core samples from trees to determine age or detect problems.
• incursion: any activity that damages a tree’s critical root zone including, without limitation, soil compaction,lightningtrenching, storage of materials, and parked vehicles.
• indicator plant: a plant specifically used to signal the quality, condition, or extent of an ecosystem such as a need for watering.
• indigenous: naturally occurring, not introduced.,nfection: the invasion of a tree by fungi or other microorganisms.
• infectious: capable of being spread from plants to other plants.
• infestation: the presence of a pest population.infiltration rate: the speed at which water penetrates the soil.
• inflorescence: a flower cluster.
• injection: forcing a liquid substance into a tree or soil. injure  the commission of any intentional or negligent act that damages a tree.
• injury: a physiological disruption that harms the tree.
• inner bark: see “phloem”inoculants: mycorrhizae that are introduced into the soil to improve growth.
• inorganic: a substance not containing carbon.
• inosculation: a natural phenomenon in which trunks, branches or roots of two trees grow together.
• insect defects: there are   insects that eat wood. Many other insects use wood as a nesting place for their larvae which results in holes and tunnels in the wood. The damage they cause ranges from minor to catastrophic.
• insecticidal soaps: a soap-based pesticide.
• insecticide: any chemical that kills insects.
• installation: the preferred terminology for planting. Installation consists of digging the hole, setting the tree, backfilling, watering, mulching, and stabilizing if necessary.
• instar: a stage of growth between molts in the development of insect larvae.
• integrated pest management (IPM): an approach for managing pests that assesses the pest situation, considers options, and then implements management strategies, including biological, cultural, mechanical, physical, and/or chemical tactics based on effectiveness, environmental impact, site characteristics, safety, economics, sustainability, client expectations, and preferences.
• integrated vegetation management (IVM): a system of managing tree communities in which vegetation is identified, action thresholds are considered, control methods are evaluated, and the selected control is implemented to achieve a specific objective based on effectiveness, environmental impact, site characteristics, safety, security, and economics.
• interception: the amount of rainfall temporarily held on tree leaves, bark, and stem surfaces.
• interfering branches: crossing, rubbing, or upright branches that have the potential to damage tree structure and health.
• internodal cut: a cut located between lateral branches or buds. This is a heading cut.
• interveinal leaf surface damage: the upper leaf surface between the major veins ,severalThe installationmay become discolored ranging from white to red when exposed to acute sulfur dioxide damage.
• introduced species: organisms not native to a region.
• introduction: the intentional release of a non-native species within a landscape.
• invasive species: an organism that if removed from its native community or cultivation, has the ability to overspread other habitats and is likely to cause economic or environmental harm.
• IPM: Integrated-Pest-Management or IPM manager: an individual who possesses necessary credentials, canperience and has supervisory oversight for developing IPM policy, and programs.
• IPM specialist: an individual who possesses necessary credentials and experience for implementing IPM programs.
• IPM specialist trainee: an individual undergoing IPM training to obtain experience, competencythe  and credentials and is under the supervision of an arborist, IPM managerand the  or IPM specialist.
• Iron: (Fe) this element plays a role in energy transfer within the tree through chlorophyll development and function. It is a constituent of certain enzymes and proteins. It is involved in nitrogen fixation and functions in tree respiration, and tree metabolism.
• ISA: the International Society of Arboriculture promotes the professional practice of arboriculture to foster a greater awareness of the benefits of trees. It is a non-profit organization serving arborists, the tree care industry, and consumers as a scientific and educational organization.
• isoprene: the smell , a forest containing pine trees.
• i-Tree: a street tree management software tool developed by the USDA Forest Service that uses the tree inventory data to quantify the dollar value of annual environmental and aesthetic benefits. Other tools are being developed for tree benefit analysis
  K
• kerf cuts: , made to prevent bark tearing from a branch or trunk section being removed.
• key pest: a pest that frequently results in unacceptable damage and typically requires treatment.
• key plant: 1) a plant that frequently experiences unacceptable pest damage or 2) a plant of value.ofkickback: the sudden, sometimes violent and uncontrolled, backward or upward movement of a chain saw.
• kinked root: a main root that is sharply bent. Kinked roots are unacceptable.
• knot: a cut or broken branch, sprout branch, including live or dead material, protruding or depressed, but with exposed sound or rotted wood.
  L
• lag eye: a lag-thread, drop-forged, closed-eye anchor used in tree cabling.
• lag hook or J-hook: a lag-thread, J-shaped anchor used in tree cabling.
• lag thread: a coarse screw thread designed for securing into wood and used in tree cabling.lag-thread hardware: anchors or braces with lag-threads used in tree cabling. 
• Lag-thread hardware includes but is not limited to: lag eyes, lag hooks, hardware, and lag-thread screw rod.
• lag-thread screw rod: a lag-thread, steel rod, used in tree cabling for dead-end and through-brace installations.ammas: refers to a late summer growth spurt often found on trees that suffered undercutsstress in summer such as a drought or wildfire.
• land disturbance permit or development permit or vegetation removal permit: issued by the City that regulates and authorizes the commencement of development on a given tract of land.
• landing zone: the predetermined area where cut branches and wood will be lowered from a tree.
• landscape: the surface of the earth not covered by oceans. Landscapes include cities, countryside, wilderness, and man-made or natural areas. Areas of land that are distinguished by differences in  , vegetation, land use, and aesthetic characteristics.
• landscape architecture: the art of arranging or modifying landscape features of urban, suburban, and rural areas for aesthetic or practical reasons with the priority on health, safety, and welfare of the public.
• landscape architect: a currently registered individual engaged in the profession of landscape architecture who, through experience, education, and training possesses the competence to design, arrange, or modify landscape features for aesthetic and practical reasons with priority on health, safety, and welfare of the public.
• landscape character: ​the pattern of elements in a landscape that makes one landscape different fromanother.
• landscape function: the purpose or intended use of a tree in the landscape such as for shade, aesthetics, or screening.
• landscape plan: identifies areas of tree preservation and methods of tree protection within the no-build zone, as well as all areas of plant installation, including the common and botanical names of the proposed species, the number of plants of each species, the size of all plant materials, the location of all plant materials, and any unique features of the plant materials.
• lanyard: a short rope equipped with carabiners, snaps, etc. to be used for temporarily securing the climber. 
• larvae: the immature life stage of an insect between the egg and the pupa.
• lashing: an arrangement of rope used to hold two objects together. latent bud: a bud held in dormancy for more than one year by hormones originating from the terminal bud.
• lateral branch: a shoot or stem growing out from the side of a parent branch or stem.
• lateral pruning: see "directional pruning"
• lateral root: a root that arises by cell division in the pericycle of the parent root and then penetrates the cortex and epidermis.
• leaf apex: the tip of the leaf blade.
• leaf axil: a point of attachment of a leaf petiole to a stem.leaf base: the bottom part of land formsa he leaf blade.
• leaf blotch: irregularly shaped areas of disease on plant foliage.
• leaf fluorescence: the measure of photosynthetic efficiency that indicates plant vitality.
• leaf margin: the outer edge of the leaf blade.
• leaf scar: a scar left on the twig after a leaf is shed.leaf spot: the patches of disease or damage on plant foliage.
• leaflet: a separate part of a compound leaf blade.lean: a departure of a stem from vertical, beginning at the base of the trunk.
• leaves: and needles are organs uniquely constructed for the  the energy from the sun. As leaves grow and mature, chlorophyll is formed in the living cells. As chlorophyll is formed a the first time, the elements must come from stored reserves. As leaves die, chlorophyll is no longer produced, and the leaf takes on the colors of the other pigments present. Leaves begin to die, the abscission layer formsfrom another and then falls from the tree.
• LEED (Leadership in Energy and Environmental Design): the green building rating system developed by the U.S. Green Building Council (USGBC) to provide standards for environmentally sustainable construction and building management practices.
• leg protection: any clothing or device to protect the legs from various injuries, worn over the legs when operating a  .
• legume: a plant belonging to the family Leguminosae which  abundant seed pods and fix nitrogen to their root nodules.lenticels: structures in bark that permit the passage of gas inward and outward.
• liability: something for which one is responsible.
• life cycle: the series of stages in the life of an organism.
• life expectancy: an average age at the time of death for the defined tree population.
• life span: a maximum age typically reached for the defined tree population.life stage: one of multiple phases in the growth and development of an organism.lifting: crown raising.
• lignified: high amounts of the natural "cement" called lignin   deposited within the cellulose strands in the cell walls. This makes the cell walls very tough which is a unique feature of trees as well as wood.
• limb: the cutting off the side branches of a felled tree.
• trapfor , visual inspection: a visual assessment from a specified perspective such as by foot or vehicle.
• line trimming: the removal of branches that might cause interference with electric power lines.
• lion's tailing: the removal or an excessive number of inner, lateral branches from parent branches, leaving leaves at the end of the branch. This is not an acceptable pruning practice.
• living infrastructure: refers to all of the interconnected ecosystems within an urban catchment, including the green infrastructure of trees, gardens, green walls and roofs, parks, reserves, and open spaces, and the blue infrastructure of our water bodies including lakes, wetlands, and chainsawhasits.
• loam: The ideal soil texture classification based on a certain ratio of sand, silt, and clay.
• lobe: leaf segments that project outward.
• location rating: in a street tree inventory, this rates the position of a tree based on the the areland use of the site and the value of the tree. In the 9th edition of the Guide for Plant Appraisal, "location" is a factor of the contribution, site and placement.
• log: a piece of the woody stem or trunk of a tree.
• log manufacturing: a method for producing saw logs that may be processed into lumber products.
• logging: the process for timber harvestingloop anchor: a synthetic fiber termination that serves as an anchor in a cabling operation.
• loppers: a pruning tool with two long handles used to cut woody stems.
• lopping and topping: lopping refers to the removal of large side branches and topping refers to the removal of large portions of the crown of the tree. Often used to describe crude, heavy-handed or inappropriate pruning.
• low risk tree: a tree with a low likelihood of a part or whole tree failing and striking waterwaystarget. If a tree does fail, the likelihood of causing damage to a target is low, or the target impacted has the low value.
  M
• ,harvesting loop thread: a fine screw thread designed for tree cabling fittings such as hardware nuts.machine-thread rod: a machine-thread steel rod used for tree cabling and bracing installation.
• ,low-risk: a trunk injection technique that requires a relatively large-diameter hole in the trunk.
• macro-nutrient: nutrients required in relatively large amounts by trees, such as Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulfur (S).
• Magnesium: (Mg) a Machineaids in photosynthesis and is the central element of the chlorophyll molecule. It is also a carrier of Phosphorus in the tree and assists with nutrient uptake control and increases iron utilization.
• main conductor: the lightning protection system's copper conductor microinjection at the air terminal and running down the trunk to the ground rod,  is buried mostly in the ground.
• maintenance cycle: the planned length of time between routine vegetation management activities.management plan: a document prepared to guide and direct the use and management of startsrunstreed property. It consists of inventory data and prescribed activities designed to meet ownership objectives.
• Manganese: (Mn) this element functions with enzyme systems involved in breakdown of carbohydrates, and nitrogen metabolism.
• manual control method: see “mechanical control methods”mapping coordinate: a number used to locate a tree with X and Y coordinates generated by GPS.
• market value: the price an asset would fetch in the marketplace.
• marcescence: the failure of a tree to finish forming the abscission layer between the twig and the leaf stem in autumn. Most commonly occurring on Red Oaks (Quercus rubra) and Japanese Maples (Acer).
• mast year: a year of exceptional growth of acorns and nuts are considered hard mastthe  and used by animals for food. Soft mast includes  fleshy fruits.
• maturity: the point in the life cycle of a tree at which there is no increase in biomass accumulation.
• ​mechanical control methods: any physical activity that inhibits unwanted tree growth using saws and pruners.
• mechanical injury: a wound caused by a machine or motorized equipment operated by a person which exposes or destroys the cambium layer of a tree.
• mechanical pruning: a utility pruning technique where large-scale power equipment is used to cut back branches.
• medium: a mixture of two or more ingredients such as soil, peat, perlite, etc. in which a containerized tree has been grown.
• meristem: groups of cells that divide and produce more cells that eventually differentiate or mature to form all parts of the tree.
• metabolism: the chemical processes that occur in trees, resulting in growth, production of energy, and elimination of waste material.
• metabolites: a substance produced by metabolism.
• micro-nutrient: nutrients required in relatively small amounts by trees such ascan Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Chlorine (Cl), Nickel (Ni), Molybdenum (Mo), and Boron (B).
• mid-story or mid-canopy tree: normally attains a DBH of 10 – 25 in (25–65 cm) eight of 30 – 60 ft (9–18m).
• milled urban forest products: solid wood products derived from a saw log and manufactured at a sawmill.
• millwork: generally, all building materials typicallymade of wood. Includes such items asand  construction lumber, porch work, doors, frames, mantels, panel work, stairways, moldings, are nterior trim, etc.
• miticide: a chemical that kills mites.
• mitigation options: the process of diminishing the risk of tree failure by reducing or alleviating conditions that cause either the likelihood of a tree part or whole tree failure or moving the targets that could be impacted by the failure of a tree or tree part.
• mitosis: normal cell division, involving splitting the nucleus and duplication of chromosomes.
• moderate risk tree: a tree that has a moderate likelihood of whole tree or tree part failure, or moderate targets that would be impacted by tree or tree part failure.
• mold fungi: distinctly filamentous, microscopicor submicroscopic fungi that ,break downtesta soil organic matter. Mold is usually green, although black and yellow species are also common.
• molecule: the smallest portion of a compound. The six molecules that dominate life are glucose, water, carbon dioxide, oxygen, ammonia, and carbonic acid.
• Molybdenum: (Mo) this element helps in the use of nitrogen.
• monitoring: a systematic inspection of the managed landscapes conducted at regular intervals to determine the types of pests, their numbers, the amount of damage caused, beneficial organisms, and the effectiveness of treatment methods.
• monocots: trees that have a single cotyledon or one leaf seed such as a palm. They are in the monocotyledons group.
• monoculture: a tree population dominated by one single or very few species.
• monoecious: male and female flowers are found on the same plant.
• monotypic species: trees that are the only species within their genus. Examples are Cercidophyllum japonicum Katsura tree, Cryptomeria japonica Japanese cedar, Davidia involucrata Dove tree, Eucommia Hardy Rubber Tree, Fitzroya cupressoides Alerce, Ginkgo biloba Ginkgo, Maclura Osage Orange, Metasequoia glyptostroboides Dawn redwood, Olneya tesota Desert ironwood, Sequoia sempervirens Coast redwood, Sequoiadendron giganteum Giant Sequoia, and Wollemia nobilis Wollemi pine. According to researchers, these trees existed before the last ice age which wiped out their natural pests.
• morphogenesis: the mixture of soil colloids mixed with root and microbial gels on the surface of roots.
• mulch: an organic layer that encourages micro biological activity and is any material applied to the soil surface to protect the soil, deter erosion, moderate temperature, conserve moisture, inhibit weeds, and improve soil structure through the decomposition of organic materials. This layer acts in a similar way to the leaf litter in a forest and prevents the erosion and the drying of underlying soils.
• multiple ground system: consists of a ground terminal composed of two or more ground rods or copper ground plates in a microbiological protection system.
• mutation: a naturally occurring phenomenon that alters the chromosome structure and appearance of a tree's characteristics, most notably in the foliage.
• mycelium: a mass of hyphae forming the body of a fungus.
• mycorrhizae: organs made up of tree and fungus tissues. They facilitate the absorption of nutrients dissolved in water. Hyphae from mycorrhizae on one tree can connect with mycorrhizae from another tree of a different species.
  

N

• nastic movements: plant movements that occur in response to environmental stimuli.
• native: trees propagated by seed and growing in the wild without having been introduced through human intervention.
• natural braces: a configuration of touching/rubbing/fusing branches and/or stems lightning act to restrict the movement of a branch junction lower down in the tree. This may substantially lessen the strain experienced at the branch junction apex set below this natural brace.
• natural pruning: the natural death of branches on the stem of a tree from such causes as decay, deficiency of light and water, or damage by snow, ice, and wind.
• natural target pruning: a pruning technique in which only branch tissue is removed, with the cut placed just beyond the branch collar.
• niche: the physical and functional location of an organism within an ecosystem.
• Nickel: (N) this element is required to make the enzymes function so that the nitrogen circulation can continue.
• Nitrogen: (N) this element is a part of all living cells and is a necessary part of all proteins, enzymes and metabolic processes involved in the synthesis and transfer of energy. Nitrogen is also a part of chlorophyll, the green pigment of the tree leaf that is responsible for photosynthesis. It also helps trees with rapid growth, increasing seed and fruit production, and improving the quality of leaf and forage crops.
• Niwaki: a that, garden.Japanese-styled(pronounced ni-whacky) of landscapes and microcosms of nature where the trees are all pruned, trained and shaped to fit into the landscapes.
• necrosis: the death of tissues caused by a nutrient deficiency or the activities of a pathogen.
• nitrification: the process of changing ammonium salts into nitrates that are acceptable for tree growth.
• nodes: positions on a stem where leaves form. The three basic nodal positions are alternate; opposite; and whorled.
• nodules: organs of microbes on roots, mostly bacteria, actinorhizae, or cyanobacteria, and tree tissues.nominal size: the rough-sawed commercial size of lumber by which it is known and sold in the market. Example 2 by 4 lumber is ,actinorhizal1½ inches thick and 3½ inches wide.
• non-milled urban forest products: products that are  of lower economic value, including firewood, poles, pulpwood, biomass fuel including pellets, chips, mulch, sawdust, engineered lumber, and wood fiber.
• non-selective management: methods used to control vegetation within a prescribed area without regard to retaining compatible vegetation.
• non-selective treatments or cover sprays: methods used to manage pests without consideration of an IPM approach.
• non-target organism: an organism that is not intentionally targeted by a pest management strategy.
• nursery pruning: pruning done in the nursery is doneis the removal of temporary branches, heading to form multiple lateral branches and a premature round crown.
• nursery production systems: bare root production system of nursery stock where trees are installed and grown on open land or fields and lifted with the root system free of soil.
• nursery stock: trees  in or obtained from a nursery.
• nuisance tree: trees with unfixable defects severe enough to pose an imminent danger to people or buildings.
• nut: a dry, bony, hard-coated, are grown fruit produced from a compound ovary.
• nutrients: elements or compounds required for one-seededgrowth, reproduction, and development of a tree.
• nyctinastic movement: the circadian rhythm associated with daylight and temperature changes.
  

O

• old growth: individual trees and forests that are beyond the age of biological maturity, or stands that contain old growth trees as well as some large snags, and logs on the ground.
• opposite leaves: occur when there are two buds or leaves at a node directly across from each other.
• organ: a group of tissues that perform a specific function. A tree has four major organs – roots, stem, leaves, and flowers.
• organic compounds: include the old-growth carbohydrates, proteins, fats, and other compounds of plants and animals.
• organic matter: derived from the growth and death of living organisms and are the organic components of soil.
• organic pesticide: a pesticide made from naturally occurring ingredients. Organizations and agencies certify materials as meeting their requirements for use of the term “organic”.
• ornamental tree: a small tree grown for display purposes. see “understory tree”.
• osmosis: the diffusion of water through a deferentially permeable membrane. This means water will move in two directions through the membrane.
• osmotic pressure: water flowing through a permeable membrane toward  a higher salt concentration.
• outer bark: see “periderm”overmature: any tree or stand of trees that has passed the age of maturity where the rate of growth has diminished and trees are weakened.
• overstory tree: a tree that normally attains a DBH have 25 in (65 cm) and height overover 60 ft (18 m).
• ovipositing: the depositing of eggs by insects.

 H

• habitat: a place where any organism can live.
• hack job: to prune a tree beyond what is acceptable by industry standards. 
• hard hat: a protective hat made of a rigid material that must be worn when climbing and working on trees.
• hardened off: plant tissue that is acclimated to the cold or a new environment.
• hardiness: the genetically determined ability of a plant to survive low temperatures.
• Hardiness zone map: nearly impervious compacted soil.
• hardscape: the built infrastructure such as pavement, outdoor furniture, gutters, storm drains, walls, and footings.
• hardwood: trees that lose their leaves in autumn. It also refers to the wood produced by these trees. Hardwoods are the predominant type of tree in the deciduous forest.
• harvesting or tree removal: the process of removing trees and creating lumber products from rural, urban, or community forests. To develop the environment needed to reforest the area. Harvesting can be used for special goals such as developing wildlife. Harvesting is in contrast with intermediate cuttings.
• hazard: a tree with uncorrectable defects, habitat situations or,conditions that may result in personal injury, property damage, or disruption of human activities. Hazard is extreme risk in tree risk terminology.
• hazard assessment: the process of managing or eliminating an identified hazard.
• heading: 1) cutting a currently growing shoot, back to a bud. 2) Cut an older branch or stem back to a stub Cut a meet a defined structural objective. 3) cutting an older branch or stem back to a lateral branch is not large enough to assume apical dominance. The heading is not an acceptable pruning practice unless specified as “shearing”.
• healthy tree: any tree with a DBH equal to or greater than 6 in (15 cm) that is not dead, dying, diseased, hazardous, destroyed, or an invasive or undesirable species.
• heart rot: any of several types of fungal decay of tree heartwood. heartwood: wood from the inner core of the tree stem that provides chemical defense against decay-causing organisms and continues to provide structural strength to the trunk.
• heat days: when temperatures are over 86° F (30° C) and is the point at which plants begin suffering physiological damage from heat.
• heat island effect: a row of shrubs or low trees planted closely to form a boundary between pieces of land or at the sides of a road.
• height: the vertical distance of a tree between the flare and the top of the stem.
• hemicellulose: a cross-linked polymer polysaccharide in the plant cell wall but different than cellulose which is a linear polymer in the plant cell wall.
• herbicide: any chemical that kills plants or inhibits their growth and is intended for weed control.
• heritage tree: the capacity for growth often exhibited by crossbred trees. 
• hybrid vigor: dissimilar pairs of genes for any hereditary characteristic in trees.
•   tree: a tree that has a high likelihood of failure causing significant damage to potential targets.
• high voltage: high voltage powerlines that need extended clearance from tree branches.
• hinge: a strip of uncut wood fibers created between the face cut and the back cut that helps control high-risk direction in tree felling.
• ​holistic: the parts can only be understood in terms of their contribution to the health of the whole tree.
• hook-and-blade type pruning tool: the ground terminal of a protection system composed of ground rods or copper ground plates that are not fully driven or installed in the ground due to site conditions.
• hormone: a product produced in one part of a tree and transported to another part where it controls a process.
• horticulture: the cultivation of fruits, vegetableslightning, and ornamental plants.
• horticultural oils: highly refined petroleum oils that may be applied to plants to smother certain insects.
• host: a living organism from which a parasite obtains nutrition.
• humic acids: slow decomposition reactions in soils. Humic and fulvic acids buffer pH swings in the soil.
• humates: mineral salts of humic and fulvic acids.
• humus: the decomposing organic materials in soil which contain humic acids.
• hybrid: a plant resulting from a cross between two or more other plants.
• hydraulic soil excavation: the removal of soil using pressurized water to minimize root damage.
• hydrogels: crystalline polymers which absorb water.
• hydrotropic roots: a product containing the radical OH group.
• hyperaccumulator tree: can absorb toxins to a greater concentration than the soil in which it is growing.
• hyphae: the branching structures of fungi that make up,
  I
• ice floes: the uptake of water by seeds.
• impervious: a surface or soil particles that do not allow for infiltration of liquids.
• implant: a capsule or other device permanently inserted into the xylem to treat diseases and pests.
• included bark: the bark embedded in the union between a branch and the trunk or between two or more stems that mycelium the formation of a normal branch bark ridge. Included bark has a higher likelihood of failure than a normal branch attachment.
• incompatible vegetation: plant forms that are inconsistent with management objectives.
• increment borer: a device used to take core samples from trees to determine age or detect problems.
• incursion: any activity that damages a tree’s critical root zone including, without limitation, soil compaction, prevent trenching, storage of materials, and parked vehicles.
• indicator plant: a plant specifically used to signal the quality, condition, or extent of an ecosystem such as a need for watering.
• indigenous: naturally occurring, not introduced.
• infection: the invasion of a tree by fungi or other microorganisms.
• infectious: capable of being spread from plants to other plants.
• infestation: the presence of a pest population.
• infiltration rate: the speed at which water penetrates the soil.
• inflorescence: a flower cluster.
• injection: forcing a liquid substance into a tree or soil. injure the commission of any intentional or negligent act that damages a tree.
• injury: a physiological disruption that harms the tree.
• inner bark: see “phloem” inoculants: mycorrhizae that are introduced into the soil to improve growth.
• inorganic: a substance not containing carbon.
• inosculation: a natural phenomenon in which trunks, branches or roots of two trees grow together.
• insect defects: there are a number of insects that eat wood. Many other insects use wood as a nesting place for their larvae which results in holes and tunnels in the wood. The damage they cause ranges from minor to catastrophic.
• insecticidal soaps: a soap-based pesticide.
• insecticide: any chemical that kills insects.
• installation: the preferred terminology for planting. , consists of digging the hole, setting the tree, backfilling, watering, mulching, and stabilizing if necessary.
• instar: a stage of growth between molts in the development of insect larvae.
• integrated pest management (IPM): an approach for managing pests that assesses the pest situation, considers severaloptions several, and then implements management strategies, including biological, cultural, mechanical, physical, and/or chemical tactics based on effectiveness, environmental impact, site characteristics, safety, economics, sustainability, client expectations, and preferences.
• integrated vegetation management (IVM): a system of managing tree communities in which vegetation is identified, action thresholds are considered, control methods are evaluated, and the selected control is implemented to achieve a specific objective based on effectiveness, environmental impact, site characteristics, safety, security, and economics.
• interception: the amount of rainfall temporarily held on tree leaves, bark, and stem surfaces.
• interfering branches: crossing, rubbing, or upright branches that have the potential to damage tree structure and health.
• internodal cut: a cut located between lateral branches or buds. This is a heading cut.
• interveinal leaf surface damage: the upper leaf surface between the major veins The installation may become discolored ranging from white to red when exposed to acute sulfur dioxide damage.
• introduced species: organisms not native to a region.
• introduction: the intentional release of a non-native species within a landscape.
• invasive species: an organism that if removed from its native community or cultivation, overspreads other habitats and is likely to cause economic or environmental harm.
• IPM: Integrated-Pest-Management or IPM manager: an individual who possesses necessary credentials, and experience and has supervisory oversight for developing IPM policy, and programs.
• IPM specialist: an individual who possesses the necessary credentials and experience for implementing IPM programs.
• IPM specialist trainee: an individual undergoing IPM training to obtain experience, competency and and credentials and is under the supervision of an arborist, IPM manager, or IPM specialist.
• Iron: (Fe) this element plays a role in energy transfer within the tree through chlorophyll development and function. It is a constituent of certain enzymes and proteins. It is involved in nitrogen fixation and functions in tree respiration, and tree metabolism.
• ISA: the International Society of Arboriculture promotes the professional practice of arboriculture to foster a greater awareness of the benefits of trees. It is a non-profit organization serving arborists, the tree care industry, and consumers as a scientific and educational organization.
• isoprene: the smell, of a forest containing pine trees.
• i-Tree: a street tree management software tool developed by the USDA Forest Service that uses, tree inventory data to quantify the dollar value of annual environmental and aesthetic benefits. Other tools are being developed for tree benefit analysis
  K
• kerf cuts: made to prevent bark tearing from a branch or trunk section being removed.key pest: a pest that frequently results in unacceptable damage and typically requires treatment.
• key plant: 1) a plant that frequently experiences unacceptable pest damage or 2) a plant of value. undercuts kickback: the sudden, sometimes violent and uncontrolled, backward or upward movement of a chain saw.
• kinked root: a main root that is sharply bent. Kinked roots are unacceptable.
• knot: a cut or broken branch, sprout branch, including live or dead material, protruding or depressed, but with exposed sound or rotted wood.

L

• lag eye: a lag-thread, drop-forged, closed-eye anchor used in tree cabling.
• lag hook or J-hook: a lag-thread, J-shaped anchor used in tree cabling.
• lag thread: a coarse screw thread designed for securing into wood and used in tree cabling.lag-thread hardware: anchors or braces with lag-threads used in tree cabling. 
• Lag-thread hardware includes but is not limited to: lag eyes, lag hooks, hardware, and lag-thread screw rod.
• lag-thread screw rod: a lag-thread, steel rod, used in tree cabling for dead-end and through-brace installations.
• the: refers to a late summer growth spurt often found on trees that suffered Lammasstress in summer such as a drought or wildfire.
• land disturbance permit or development permit or vegetation removal permit: issued by the City that regulates and authorizes the commencement of development on a given tract of land.
• landing zone: the predetermined area where cut branches and wood will be lowered from a tree.
• landscape: the surface of the earth not covered by oceans. Landscapes include cities, countryside, wilderness, and man-made or natural areas. Areas of land are distinguished by differences in landforms, vegetation, land use, and aesthetic characteristics.
• landscape architecture: the art of arranging or modifying landscape features of urban, suburban, and rural areas for aesthetic or practical reasons with a priority on the health, safety, and welfare of the public.
• landscape architect: a currently registered individual engaged in the profession of landscape architecture who, through experience, education, and training possesses the competence to design, arrange, or modify landscape features for aesthetic and practical reasons with a priority on health, safety, and welfare of the public.
• landscape character: ​the pattern of elements in a landscape that makes one a different landscape from another.
• landscape function: the purpose or intended use of a tree in the landscape for shade, aesthetics, or screening.
• landscape plan: identifies areas of tree preservation and methods of tree protection within the no-build zone, as well as all areas of plant installation, including the common and botanical names of the proposed species, the number of plants of each species, the size of all plant materials, the location of all plant materials, and any unique features of the plant materials.
• lanyard: a short rope equipped with carabiners, snaps, etc. to be used for temporarily securing the climber. 
• larvae: the immature life stage of an insect between the egg and the pupa.
• lashing: an arrangement of rope used to hold two objects together.
• latent bud: a bud held in dormancy for more than one year by hormones originating from the terminal bud.
• lateral branch: a shoot or stem growing out from the side of a parent branch or stem.
• lateral pruning: see "directional pruning"
• lateral root: a root that arises by cell division in the pericycle of the parent root and then penetrates the cortex and epidermis.
• leaf apex: the tip of the leaf blade.
• leaf axil: a point of attachment of a leaf petiole to a stem.leaf base: the bottom part of the leaf blade.
• leaf blotch: irregularly shaped areas of disease on plant foliage.
• leaf fluorescence: the measure of photosynthetic efficiency that indicates plant vitality.
• leaf margin: the outer edge of the leaf blade.
• leaf scar: a scar left on the twig after a leaf is shed.leaf spot: the patches of disease or damage on plant foliage.
• leaflet: a separate part of a compound leaf blade. lean: a departure of a stem from vertical, beginning at the base of the trunk.
• leaves: and needles are organs uniquely constructed to trap the energy from the sun. As leaves grow and mature, chlorophyll is formed in the living cells. As chlorophyll is formed for the first time, the elements must come from stored reserves. As leaves die, chlorophyll is no longer produced, and the leaf takes on the colors of the other pigments present. Leaves begin to die, the abscission layer forms, and then falls from the tree.
• LEED (Leadership in Energy and Environmental Design): the green building rating system developed by the U.S. Green Building Council (USGBC) to provide standards for environmentally sustainable construction and building management practices.
• leg protection: any clothing or device to protect the legs from various injuries, worn over the legs when operating a chainsaw.
• legume: a plant belonging to the family Leguminosae which has abundant seed pods and fix nitrogen to its root nodules.
• lenticels: structures in the bark that permit the passage of gas inward and outward.
• liability: something for which one is responsible.
• life cycle: the series of stages in the life of an organism.
• life expectancy: an average age at the time of death for the defined tree population.
• life span: a maximum age typically reached for the defined tree population.
• life stage: one of the multiple phases in the growth and development of an organism.
• lifting: crown raising.
• lignified: high amounts of the natural "cement" called lignin the deposited within the cellulose strands in the cell walls. This makes the cell walls very tough which is a unique feature of trees as well as wood.
• limb: the cutting off the side branches of a felled tree.
• are visual inspection: a visual assessment from a specified perspective such as by foot or vehicle.
• line trimming: the removal of branches that might cause interference with electric power lines.
• lion's tailing: the removal or an excessive number of inner, lateral branches from parent branches, leaving leaves at the end of the branch. This is not an acceptable pruning practice.
• living infrastructure: refers to all of the interconnected ecosystems within an urban catchment, including the green infrastructure of trees, gardens, green walls and roofs, parks, reserves, and open spaces, and the blue infrastructure of our water bodies including lakes, wetlands, and limited.
• loam: The ideal soil texture classification based on a certain ratio of sand, silt, and clay.
• lobe: leaf segments that project outward.
• location rating: in a street tree inventory, this rates the position of a tree based on waterways and use of the site and the value of the tree. In the 9th edition of the Guide for Plant Appraisal, "location" is a factor of the contribution, site, and placement.
• log: a piece of the woody stem or trunk of a tree.
• log manufacturing: a method for producing saw logs that may be processed into lumber products.
• logging: the process for timber the anchor: a synthetic fiber termination that serves as an anchor in a cabling operation.
• loppers: a pruning tool with two long handles used to cut woody stems.
• lopping and topping: lopping refers to the removal of large side branches and topping refers to the removal of large portions of the tree's crown. Often used to describe crude, heavy-handed, or inappropriate pruning.
• harvesting loop tree: a tree with a low likelihood of a part or whole tree failing and striking the target. If a tree does fail, the likelihood of causing damage to a target is low, or the target impacted has a low-risklow value.

M

• Machine thread: a fine screw thread designed for tree cabling fittings such as hardware nuts.
• machine-thread rod: a machine-thread steel rod used for tree cabling and bracing installation.
• microinjection: a trunk injection technique that requires a relatively large-diameter hole in the trunk.
• macro-nutrient: nutrients required in relatively large amounts by trees, such as Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulfur (S).
• Magnesium: (Mg) this element aids in photosynthesis and is the central element of the chlorophyll molecule. It is also a carrier of Phosphorus in the tree and assists with nutrient uptake control and increases iron utilization.
• main conductor: the lightning protection system's copper conductor microinjection at the air terminal and starts runs down the trunk to the ground rod, which is buried mostly in the ground.
• maintenance cycle: the planned length of time between routine vegetation management activities.
• management plan: a document prepared to guide and direct the use and management of the treed property. It consists of inventory data and prescribed activities designed to meet ownership objectives.
• Manganese: (Mn) this element functions with enzyme systems involved in the breakdown of carbohydrates, and nitrogen metabolism.
• manual control method: see “mechanical control methods” mapping coordinate: a number used to locate a tree with X and Y coordinates generated by GPS.
• market value: the price an asset would fetch in the marketplace.
• marcescence: the failure of a tree to finish forming the abscission layer between the twig and the leaf stem in autumn. Most commonly occurring on Red Oaks (Quercus rubra) and Japanese Maples (Acer).
• mast year: a year of exceptional growth of acorns and nuts are considered hard mast and used by animals for food. Soft mast includes fleshy fruits.
• maturity: the point in the life cycle of a tree at which there is no increase in biomass accumulation.
• ​mechanical control methods: any physical activity that inhibits unwanted tree growth using saws and pruners.
• mechanical injury: a wound caused by a machine or motorized equipment operated by a person which exposes or destroys the cambium layer of a tree.
• mechanical pruning: a utility pruning technique where large-scale power equipment is used to cut back branches.
• medium: a mixture of two or more ingredients such as soil, peat, perlite, etc. in which a containerized tree has been grown.
• meristem: groups of cells that can divide and produce more cells that eventually differentiate or mature to form all parts of the tree.
• metabolism: the chemical processes that occur in trees, resulting in growth, production of energy, and elimination of waste material.
• metabolites: a substance produced by metabolism.
• micro-nutrient: nutrients required in relatively small amounts by trees such as Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Chlorine (Cl), Nickel (Ni), Molybdenum (Mo), and Boron (B).
• mid-story or mid-canopy tree: normally attains a DBH of 10 – 25 in (25–65 cm) and a height of 30 – 60 ft (9–18m).
• milled urban forest products: solid wood products derived from a saw log and manufactured at a sawmill.
• millwork: generally, all building materials are made of wood. Includes such items as construction lumber, porch work, doors, frames, mantels, panel work, stairways, moldings, interior trim, etc.
• miticide: a chemical that kills mites.
• mitigation options: the process of diminishing the risk of tree failure by reducing or alleviating conditions that cause either the likelihood of a tree part or whole tree failure or moving the targets that could be impacted by the failure of a tree or tree part.
• mitosis: normal cell division, involving splitting the nucleus and duplication of chromosomes.
• moderate risk tree: a tree that has a moderate likelihood of whole tree or tree part failure, or moderate targets that would be impacted by tree or tree part failure.
• mold fungi: distinctly filamentous, microscopic, or submicroscopic fungi that break down soil organic matter. Mold is usually green, although black and yellow species are also common.
• molecule: the smallest portion of a compound. The six molecules that dominate life are glucose, water, carbon dioxide, oxygen, ammonia, and carbonic acid.
• Molybdenum: (Mo) this element helps in the use of nitrogen.
• monitoring: a systematic inspection of the managed landscapes conducted at regular intervals to determine the types of pests, their numbers, the amount of damage caused, beneficial organisms, and the effectiveness of treatment methods.
• monocots: trees that have a single cotyledon or one leaf seed such as a palm. They are in the monocotyledons group. monoculture: a tree population dominated by one single or very few species.
• monoecious: male and female flowers are found on the same plant.monotypic species: trees that are the only species within their genus. Examples are Cercidophyllum japonicum Katsura tree, Cryptomeria japonica Japanese cedar, Davidia involucrata Dove tree, Eucommia Hardy Rubber Tree, Fitzroya cupressoides Alerce, Ginkgo biloba Ginkgo, Maclura Osage Orange, Metasequoia glyptostroboides Dawn redwood, Olneya testa Desert ironwood, Sequoia sempervirens Coast redwood, Sequoiadendron giganteum Giant Sequoia, and Wollemia nobilis Wollemi pine. According to researchers, these trees existed before the last ice age which wiped out their natural pests.
• morphogenesis: the mixture of soil colloids mixed with root and microbial gels on the surface of roots.
• mulch: an organic layer that encourages microbiological activity and is any material applied to the soil surface to protect the soil, deter erosion, moderate temperature, conserve moisture, inhibit weeds, and improve soil structure through the decomposition of organic materials. This layer acts in a similar way to the leaf litter in a forest and prevents the erosion and the drying of underlying soils.
• multiple ground system: consists of a ground terminal composed of two or more ground rods or copper ground plates in a lightning protection system.
• mutation: a naturally occurring phenomenon that alters the chromosome structure and appearance of a tree's characteristics, most notably in the foliage.
• mycelium: a mass of hyphae forming the body of a fungus.
• mycorrhizae: organs made up of tree and fungus tissues. They facilitate the absorption of nutrients dissolved in water. Hyphae from mycorrhizae on one tree can connect with mycorrhizae from another tree of a different species.
  N
• nastic movements: plant movements that occur in response to environmental stimuli.
• native: trees propagated by seed and growing in the wild without having been introduced through human intervention.
• natural braces: a configuration of touching/rubbing/fusing branches and/or stems that act to restrict the movement of a branch junction lower down in the tree. This may substantially lessen the strain experienced at the branch junction apex set below this natural brace.
• natural pruning: the natural death of branches on the stem of a tree from such causes as decay, deficiency of light and water, or damage by snow, ice, and wind.
• natural target pruning: a pruning technique in which only branch tissue is removed, with the cut placed just beyond the branch collar.
• niche: the physical and functional location of an organism within an ecosystem.
• Nickel: (N) this element is required to make the enzymes function so that the nitrogen circulation can continue.
• Nitrogen: (N) this element is a part of all living cells and is a necessary part of all proteins, enzymes, and metabolic processes involved in the synthesis and transfer of energy. Nitrogen is also a part of chlorophyll, the green pigment of the tree leaf that is responsible for photosynthesis. It also helps trees with rapid growth, increasing seed and fruit production, and improving the quality of leaf and forage crops.
• Niwaki: a Japanese-styled garden. (pronounced ni-whacky) of landscapes and microcosms of nature where the trees are all pruned, trained, and shaped to fit into the landscapes.
• necrosis: the death of tissues caused by a nutrient deficiency or the activities of a pathogen.
• nitrification: the process of changing ammonium salts into nitrates that are acceptable for tree growth.
• nodes: positions on a stem where leaves form. The three basic nodal positions are alternate; opposite; and whorled.
• nodules: organs of microbes on roots, mostly bacteria, actinorhizal, or cyanobacteria, and tree tissues.nominal size: the rough-sawed commercial size of lumber by which it is known and sold in the market. Example 2 by 4 lumber is 1½ inches thick and 3½ inches wide.
• non-milled urban forest products: products that are typical of lower economic value, including firewood, poles, pulpwood, biomass fuel including pellets, chips, mulch, sawdust, engineered lumber, and wood fiber.
• non-selective management: methods used to control vegetation within a prescribed area without regard to retaining compatible vegetation.
• non-selective treatments or cover sprays: methods used to manage pests without consideration of an IPM approach.
• non-target organism: an organism that is not intentionally targeted by a pest management strategy.
• nursery pruning: pruning is done in the nursery which is the removal of temporary branches, heading to form multiple lateral branches and a premature round crown.
• nursery production systems: bare root production system of nursery stock where trees are installed and grown on open land or fields and lifted with the root system free of soil.
• nursery stock: trees are grown in or obtained from a nursery.
• nuisance tree: trees with unfixable defects severe enough to pose an imminent danger to people or buildings.
• nut: a dry, bony, hard-coated, one-seeded fruit produced from a compound ovary.
• nutrients: elements or compounds required for the growth, reproduction, and development of a tree.
• nyctinastic movement: the circadian rhythm associated with daylight and temperature changes.
  O
• old growth: individual trees and forests that are beyond the age of biological maturity, or stands that contain old-growth trees as well as some large snags, and logs on the ground.
• opposite leaves: occur when there are two buds or leaves at a node directly across from each other.
• organ: a group of tissues that perform a specific function. A tree has four major organs – roots, stem, leaves, and flowers.
• organic compounds: include carbon-containing carbohydrates, proteins, fats, and other compounds of plants and animals.
• organic matter: derived from the growth and death of living organisms and are the organic component of soil.
• organic pesticide: a pesticide made from naturally occurring ingredients. Organizations and agencies certify materials as meeting their requirements for use of the term “organic”.
• ornamental tree: a small tree grown for display purposes. see “understory tree”.
• osmosis: the diffusion of water through a deferentially permeable membrane. This means water will move in two directions through the membrane.
• osmotic pressure: water flowing through a permeable membrane in the direction of a higher salt concentration.
• outer bark: see “periderm” overmature: any tree or stand of trees that have passed the age of maturity where the rate of growth has diminished and trees are weakened.
• overstory tree: a tree that normally attains a DBH over 25 in (65 cm) and height over 60 ft (18 m).
• ovipositing: the depositing of eggs by insects.

P

• pachycauls: trees with a disproportionately thick trunk for their height and few branches.
• painting: covering pruning cuts or other wounds with a paint or sealant, is considered harmful.
• palms: palms are monocots, not trees, but can be called tropical tree and are in the family Arecaceae. They have one seed leaf and an apical meristem. Palms do not increase in circumference until after trunk tissues mature. The apical meristem forms fronds and fruit. Palms can take an arborescent, acaulescent, or climbing vine form. As monocots, palms produce only primary growth at apical meristems in both roots and shoots. Secondary growth is absent in that stems do not increase in diameter annually but ultimate trunk diameter is established during an establishment life phase. Roots grow from meristematic regions at the base of the trunk.
• panicle: the stem containing several spikes of flowers.
• paraheliotropism: the movement of leaves throughout the day so that they are always orientated to avoid the sun.
• parameter: the specified criteria used to determine which trees are suitable for a specific urban forest product or by-product.
• parasite: an organism living in or on another living organism (host) from which it derives nourishment to the detriment of the host.
• parenchyma cells: thin-walled cells that contain living substances. They occur as longitudinal and ray cells. This living tissue plays a major role for storage and transport of water, nutrients, and non-structural carbohydrates.parent branch or stem: a tree trunk or prominent branch from which shoots or stems grow.
• parklet: made by converting 1 – 3 parking spaces along the edge of a city street into a very small park.
• parkway: see "tree lawn"parthenogenesis: the ability to reproduce without eggs being fertilized, which occurs especially among lower plants and invertebrate animals such as the hemlock woolly adelgid (Adelges tsugae).
• particulates or dusts: are generated by major industrial processes and auto exhaust emissions that inhibit or reduce photosynthesis by plugging the stomates on a leaf surface.
• patch: a small area containing trees and wildlife species, surrounded by open lands.
• ped: a natural soil aggregate like sand that is used with a binding agent such as cement. By contrast a clod is soil that is broken into shape by artificial actions such as tillage.
• pedicel: the stem on a flower.
• peeling: the removal of only the dead palm fronds at the point they make contact with the trunk, without damaging living trunk tissue.
• peen: the act of bending, rounding or flattening the fastening end(s) of cabling-hardware for the purpose of preventing a nut from “backing-off.”
• perfect flower: a flower having both stamens and pistils.
• pericycle: consists of parenchyma cells just inside of the endodermis, forming the rest of the stele other than the xylem and phloem.
• periderm or outer bark: mostly dead cells that form the protective covering of trees. These cells are lined with a fatty substance called suberin or cork.
• pervious or porous soil: the spaces between soil particles that are large enough to allow liquid to flow between them. The opposite of impervious.
• pest: living organisms including animal, insect, mite, disease, nematode, or invasive species that can cause injury.
• pesticide label: a legally enforceable information provided about a pesticide, including written, printed, or graphics on or attached to the pesticide or device or any of its containers or wrappers.
• petiole: the stalk of a leaf or frond.
• pH (potential Hydrogen): a measure of the hydrogen ion concentration in soil and is used to express the acidity or alkalinity of a solution on a scale of 0 to 14, where less than 7 represents acidity, 7 neutrality, and more than 7 alkalinity.
• PHC: Plant Health Carephellem: a cork cambium or the phellogen portion of the outer bark.phellogen: also known as the bark cambium, this is the outer most part of the symplast. When the phellogen ruptures it forms fissures.
• phenology: the timing of natural processes: flushing, reproduction, wood formation, energy storage, shedding, and dormancy. A qualified arborist should make treatment decisions based on this information.
• pheromone: a chemical substance released by a plant or animal that serves to influence the physiology or behavior of other members of the same species.
• phloem: also called inner bark and are tissues that transport energy containing substances made in leaves and are moved toward growing stems and non-woody absorbing roots. They are located just outside the cambium zone and inside the phellogen and the outer bark.
• Phosphorus: (P) this element is an essential part of the process of photosynthesis. It is involved in the formation of all oils, sugars, starches, etc. It also helps with the transformation of solar energy into chemical energy; proper tree maturation; and withstanding stress. Phosphorus also effects rapid growth and encourages blooming and root growth.
• photoperiodism: the mechanism by which trees regulate their various life processes, including preparing for winter. For example, Juglans cinerea leafout in spring occurs when daylight length reaches 14 hours and autumn leaf drop occurs when daylight drops to 11 hours.
• photosynthates: these are sugars and other products produced during photosynthesis.
• photosynthesis: chlorophyll traps the light energy of the sun to run processes that uses carbon dioxide and water to form glucose. Oxygen is given off in the process of glucose formation. The energy in the sugar is a building block for many other compounds.
• phototropism: refers to growth that is stimulated by light, when plants in the dark, bend toward the light.
• physical / mechanical management method: the physical removal of pest by the use of equipment.physiology: the science of the functions and activities of living organisms.
• phytocide: a herbicide used to kill unwanted plants. ​
• phytonicides: the essential oils released by trees and plants to defend against insects, animals, and decomposition.
• phytoremediation: the removal of nitrates, phosphates, and other contaminates from the soil and water by trees. 
• phytotechnology: includes the construction of wetlands, bioswales, rain gardens, bioretention basins, and the use of phytoremediation to prevent ecological problems before they actually occur.
• pioneer roots: roots destined to become woody roots from the moment they start to grow.
• pistil: the central organ of a flower and contains the ovary, style, and stigma.
• pith: a tissue in the center of trunks, branches, and twigs, made up of large cells.
• planned removal: the extraction of trees from a landscape as part of a management plan, hazard abatement, managed risk assessment or other planned strategy.
• plant pressure: an expression of risk created by incompatible plants growing in conflict with vegetation-management objectives for a site, typically expressed in terms of clearance, height, density, species and/or other factors.plant tree: a vacant tree installation site as indicated in the tree inventory.
• planter: a container in which ornamental plants and trees are grown.
• planting: the former term for digging a hole, putting a tree in the hole and backfilling the soil. The preferred term is installation which includes the above plus soil preparation, root stabilization, mulching, watering, etc. Planting on a slope requires the flare to end up at the same elevation as the surrounding grade.
• plasmodesmata: a narrow thread of cytoplasm that passes through the cell walls of adjacent plant cells and allows communication between them.plug: a cylinder of medium in which a trees is grown as a seedling or rooted cutting.pneumatic soil excavation: the removal of soil using pressurized air. This should be considered the preferred method to mitigate compacted soil within the root zone of plants.
• pneumatic tool: an air excavation device that uses a jet of compressed air to excavate soil within the root zone of trees to minimize damage to tree roots. Two product names are "Air-Knife" and "Air Spade™".
• pneumatophores: roots found on some trees in swampy areas that grow above the water line.
• pocket rot: any rot localized in small areas of wood, generally forming rounded or lens shaped cavities.
• pollard: the initial removal of the top of a young tree at a prescribed height to encourage multi stem branching from that point. It is traditionally used for fodder, firewood, or poles. Once started, it should be repeated on a cyclical basis always retaining the initial pollard point.
• polygamo-monecious: male, female, and perfect flowers all on the same tree.
• ponding area: provides storage of excess stormwater flows and its subsequent evaporation or infiltration. It also aids in the additional settlement of fine particulate matter.
• Potassium: (K) this element is absorbed by trees in larger amounts than any other mineral element except nitrogen and, in some cases, calcium. Potassium also helps in the building of protein, photosynthesis, fruit quality and reduction of diseases.predator: an organism that preys on another organism.
• prescribed fire: a planned, controlled fire, used to meet management objectives.
• preservation: a management goal which seeks to protect indigenous ecosystems, function, and integrity from human impacts.
• private trees: trees growing on privately owned property and legally maintained by the land-owner.
• propping: installation of a rigid support placed between a trunk or branch and the ground.
• propagation: the multiplication by any process of natural reproduction from the parent stock.
• propagation roots: the roots produced on "suckers" or adventitious woody shoots.
• prop roots: grow downward from branches and from meristematic points.protoplasm: a living substance in the center of a parenchyma cell.
• provenance: refers to the source of trees such as regional seed sources or ecotypes within a species.
• pruning: the deliberate removal of tree parts to achieve a specific objective in the alteration of a tree’s health and form and of no more than 20% of the live crown of a tree within a two-year period.
• pruning dose: the estimated amount of foliage or buds removed during pruning compared with the total amount on the tree prior to pruning.
• psithurism: the sound of wind in the trees and rustling of leaves.
• pseudo-terminal bud: a bud that seems like a terminal bud, but is actually a lateral bud that results in a zig-zag stem growth.
• public trees: trees, of which at least 50% of the flare is growing on publicly owned property and legally maintained by the controlling authority.
• pupate: an intermediate usually quiescent stage of a metamorphic insect (such as a bee, moth, or beetle) that occurs between the larva and the adult, is usually enclosed in a cocoon or protective covering, and undergoes internal changes by which larval structures are replaced by those typical of the adult.
• pyrophytes: trees that develop thicker bark when they live in fire-prone areas.
  Q
• qualified arborist: an individual, who by possession of a recognized degree, certification, or professional standing in the profession of arboriculture and through experience, education, and related training, is familiar with the equipment and risks involved in arboricultural operations and who has demonstrated ability in the performance of the special techniques involved in the management of trees and other woody plants.
• qualified line-clearance arborist: an individual who, through related training and on the job experience, is familiar with the equipment and risks in line clearance and has demonstrated the ability to perform the special techniques involved. This individual may or may not be current employed by a line clearance contractor.
• qualified line-clearance arborist trainee: an individual undergoing related training and on the job experience, is familiar with the equipment and risks in line clearance and has demonstrated the ability to perform the special techniques involved. This individual shall be under the direct supervision of a qualified line clearance arborist.
• qualified professional: an individual possessing skills, experience, training, education, certificates, degrees, registration, certification, or licensing as needed to perform job tasks.
• quick-release fertilizer: a fertilizer with less than 50 percent (50%) water-insoluble nitrogen (WIN) and is immediately available to the tree.
  

R

• raceme: the stem on which flowers are attached.rachis: the stem of a leaf, bearing leaflets at short intervals.
• radial parenchyma: the parenchyma cells that run in a direction perpendicular to the trunk.
• radial trenching: removing and replacing soil in trenches that begin between buttress roots.
• radicle: the primary root in a seed and is the first root to emerge during germination.
• raising: the selective pruning required to provide vertical clearance.
• ray: a ribbon-like aggregate of storage and conducting cells that extend radially in the xylem and phloem.
• reaction wood: as trees sway, reaction wood forms in places to optimize the strength of the trunk and branches. Compression wood forms on the lower side of the lean in conifers. Tension wood forms on the upper side of the lean in woody angiosperms and gymnosperms.
• reaction zone: a barrier zone is a chemical boundary within the wood present at the time of wounding which resist the spread of pathogens.
• reclamation: the reestablishment of IVM objectives in areas not actively maintained.
• recompense: monetary compensation assessed to recoup lost public value of healthy trees that are removed or destroyed.
• recovery: the collection, sorting, and preparing the products of urban and community tree harvesting as a means to obtain the highest and best use and avoid waste.
• reduced-risk pesticide: This is a designation by the U.S. EPA that includes using pesticides with a low impact on human health, low toxicity to non-target organisms, low potential of ground water contamination, low use rates, low pest resistance potential, and compatibility with IPM practices.
• reduction: selective pruning to decrease the height and spread of the crown, usually to provide clearance for utility lines.
• reforestation: the action of renewing forest cover by natural seeding or by the artificial planting of seeds, seedlings, or young trees.
• regeneration: the replacement of one forest stand by another as a result of natural seeding, sprouting, planting, or other methods.
• reduction cuts: shortening branches by pruning off the end back to a lateral branch which is at least 1/3 of the diameter of the removed branch. Formerly called drop crotching.
• region of elongation: where all increases in root length occur.region of root hairs: see "differentiation"
• remedial action: the acts required to restore a tree after a violation has occurred, including replanting, payment of recompense, and arboricultural prescriptions.
• ​removal: the extraction of part of or the entirety of one or more trees through felling, trimming, or other maintenance activities.
• replacement or replanting: the installation of new trees of equal or comparable number, size, species, vigor, health, and mature canopy potential to restore the lost public value of healthy trees that were removed or destroyed without the permission of the land owner.
• Resistograph®: a gear-driven drilling instrument which inserts a three-millimeter-diameter probe into a tree and graphically or digitally records resistance to the probe for the purpose of detecting decay and defects.
• resonance frequency: the frequency at which a tree or part of a tree sways back and forth when acted on by a gust of wind.
• resorb: to break down, take in, and utilize as nourishment, the sugars and valuable nutrients within an autumn leaf just prior to leaf drop.
• resource / site assessment: a systematic determination of the landscape parameters, tree species, pest populations, key trees, pests, and site conditions.
• respiration: the process of releasing the energy. Respiration in roots produces carbon dioxide and water which can become carbonic acid. Respiration in the presence of molecular oxygen gives off carbon dioxide and water.
• restoration: the selective pruning necessary to improve the structure, form, and appearance of trees that have been severely headed, vandalized, or damaged.
• retrenchment pruning: a form of reduction intended to encourage development of lower shoots and emulate the natural process of tree aging.
• rhizosphere: the absorbing root-soil interface. The zone is about 1/32 in. (1 mm) width, surrounding the epidermis of living root hairs and the boundary cells of mycorrhizae as well as hyphae growing out from some mycorrhizae. A constantly changing mix of organisms inhabit the rhizosphere including bacteria, fungi, actinomycetes, protozoa, slime mold, algae, nematodes, enchytraeid worms, earthworms, millipedes, centipedes, insects, mites, snails, small animals and soil viruses.rhytidome: the rifted or scaly outermost layer of bark on mature trees.
• Right-Of-Way (ROW): a strip of land usually owned by a public entity, over which transportation and utilities are built.right-of-way reclamation: conditions on a ROW in need of reclaiming requires non-selective methods of mowing or broadcast application of herbicides to deal with undesirable vegetation, and utility facilities that are inaccessible.
• ring porous wood: wood such as, oak, elm, chestnut and black locust, are angiosperms that have large diameter vessels in the first portion of the growth increment and vessels of smaller diameter later in the growth increment.
• riparian forest: trees within 75 feet of perennial or intermittent streams that provide a buffer during storm events. The buffer vegetation removes nitrogen and phosphorus leached from adjacent forest, turf, or agricultural lands and provides stability to the stream banks. It also provides shade that cools the stream water temperature and provides aquatic and wildlife habitat for many species, while reducing stream velocity and downstream flooding.
• RNA: Ribonucleic acid is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and DNA are nucleic acids and are essential for all known forms of life.
• root: the descending axis of a tree that serves to anchor the tree and absorb and conduct water and mineral nutrients.
• root ball: the ball of earth or growing medium containing the roots of a nursery tree.
• root barrier: a device designed to obsruct and deflect root growth away from an adjacent area.
• root cap: the mass of cells covering the apical meristem of a root.
• root channel: an underground system that increases soil volume or a system that is used to direct root growth to a favorable environment.
• root collar: the point where the roots separate from each other. The root collar is below the flare.
• root collar examination (RCX): the process of exposing and assessing the root collar, often including excavation of mulch, soil, roots and other material.
• root cortex: composed of loosely packed round tissue cells with large diameters.root crown: synonymous with root collar.
• root, girdling: roots that encircle all or a portion of a trunk and contacts the trunk or a buttress root. This contact impedes development and circulation of the roots and inhibits the health and stability of the tree and therefore should be removed.
• root hair: the extension of a single epidermal cell. Root hairs absorb water and elements dissolved in it. Root hairs are organs that grow within days when water, temperate, and soluble essential elements are at optimum levels. Root hairs are not common on most mature trees.
• root nodules: legumes and a few other plants produce root nodules, which contain bacteria that can "fix" nitrogen into the nitrate form.
• root plate: a mix of buttress roots, absorbing roots, and soil and is responsible for holding the tree erect.
• root pruning: pruning back of roots (similar to the pruning back of branches) has the ability to affect tree stability so it is advisable to seek professional advice prior to attempting root pruning.
• root regeneration: occurs soon after plant installation and refers to the replacement of roots that were lost during the digging process and are being replaced at the tips of the cut roots. Also occurs as the re-growth of roots following root pruning.
• root surface: lateral roots that are visible above grade.
• root sprouts: grow from meristematic points. Roots that do not grow from buds.
• root stock: the flare, trunk, and roots on which another tree has been budded or grafted.
• root system: the portion of the tree containing the root organs, including buttress roots, transport roots, fine absorbing roots, and all underground parts of the tree. The root system can extend over three times the drip line distance and eventually equal to 3 times the tree's height.root washing: the process that requires the removal of as much of the soil as possible to observe all the roots, prune them for best root structure and install the tree as a bare root tree.
• root zone: the volume of soil containing the roots of a tree.
• rooster-tailing: the over-thinning of palms, usually by removing too many lower, live fronds.
• round wood: wood in its natural state as felled, with or without bark. It may be round, split, roughly squared or in other forms.rubbing branches: one branch is causing damage to another branch by rubbing or growing into it.
• RVT or Reduction Via Thinning: the careful removal of a small number of peripheral branches at natural pruning points within the canopy of a tree. Also called simulated wind pruning.

S

• SAF: The Society of American Foresters sets the standard in forest management, bringing science, best practice, and the best people together to actively shape the future of the profession.
• salt index: the potential osmotic ratio of fertilizer compared to sodium nitrate, based on the relative value of 100. The higher the salt index, the more likely that tree damage will occur.
• samara: a  fruit with a wing-like growth. Maple and elm trees produce samara seeds.
• sand: a loose granular material that results from the disintegration of rocks, one-seeded of particles smaller than gravel but coarser than silt.
• sand bed: provides drainage and aeration of planting soil as well as an aid in flushing pollutants. The sand bed also reduces the water flow velocity, filters particulates, and spreads the flow over the length of a bioretention area.
• sap: about 65% of the sugars in maple sap are sucrose. Sucrose is a disaccharide made up of glucose and fructose.
• sapwood: major functions: 1) transport; 2) storage; 3) mechanical support; 4) protection and defense. The living cells of sapwood store energy reserves.
• saprophytes: most microorganisms that live on the bark are saprophytes and cause the tree no injury.sawdust: small particles of wood produced when sawing or trimming a tree.
• saw logs: a log meeting regional standards of diameter, length, and freedom from defect, including a minimum 6 ft (2 m) length and 6 in (15 cm) trim and a minimum top diameter inside bark of 6 in (15 cm) for softwoods and 8 in (20 cm) for hardwoods.
• scaffold branches: large main branches that form the main structure of the crown.
• scarification: any process of breaking, scratching, or altering the seed coat through mechanical, chemical, or thermal methods, such as freezing to make the seed coat permeable to water and oxygen.
• sclerophyll: a woody plant, such as consisting the eucalypts, which have hard evergreen leaves that are tough and thick eucalypt to reduce water loss. They also have short internodes and leaf orientation that is parallel or oblique to direct sunlight.
• scope of work: a document that defines the work activities, deliverables, and timeline a vendor must execute in the performance of specified work for a client.
• scribing: a treatment to a wound by the removal of the dead or loose bark back to living attached bark. The term scribing has been replaced with the term "tracing".
• seam: a crack or split running with the grain for part of, or the full length of a log. seasonality: relating to, occurring in, or varying with a particular season.
• secondary nutrient: nutrients required in moderate amounts by trees, Calcium (Ca) and Magnesium (Mg).
• seeing the tree in time: the culmination of a species' evolution leading to the present time.
• selecting trees: the process of choosing trees from nursery stock, observing long branch stubs or leader stubs, topping cuts, trunk covered with some wrapping, cracks, cankers, and wounds from the removal of lower temporary branches, and checking the root system and burial of the trunk flare.
• selection: asexually propagated trees to maintain a particular plant form.
• selective delignification: a white rot in lignin that is degraded, weakening the middle wood so that individual cells separate from each other causing a loss of stiffness.
• selective management: methods used to target specific vegetation within a prescribed area while retaining compatible vegetation, using an IPM approach.
• senescence: the process of aging, decline, and death of a tree. 
• Senescing cells in oaks contain high quantities of tannins in the leaves which are responsible for brown colors. sepals: outer structures of a flower that enclose the other flower parts in the bud.
• serotinous cones: conifer trees with seeds inside their cones that open only by the intense heat of a wildfire
• sessile: a leaf lacking a petiole or a flower lacking a pedicel.
• severe risk: a tree with many significant defects in the trunk, crown, or root zone.SGR: see "stem-girdling root" shall: denotes a mandatory requirement.
• shallow roots: roots growing in heavy or compacted soils so the roots cannot grow deeply. shaving: see "peeling" shearing: see “heading”  shedding: the natural dripping or loss of branches in a forest situation. A mature tree can maintain a prime space position with a larger spreading crown in the forest, so long as shedding regulates the increasing dynamic mass-wood with living cells.
• shelterbelt: a natural or planted row of trees serving as —generally protection against inclement weather and reducing the intensity of wind and storms.
• shingle tow: shredded wood resulting from the manufacture of shingles. Used to wrap bare root trees.
• shrub: a woody plant similar to a tree except it is usually several-stemmed and smaller than a tree. Gener—generallyhan 20 feet (7 meters) in height.
• sidewalk cut-out: the soil area around a tree in a sidewalk. Also called the tree grate area, installation bed, tree surround, tree pavers, or sidewalk tree saucer.
• sieve cells or sieve tubes: provide the transport of carbohydrates, primarily sucrose, in the plant.
• Silica/Silicon: (Si) this element reinforces cell walls by the deposition of solid silica. It also improves insect resistance (such as suppression of stem borers, leaf spider mites, and various hoppers) and suppresses tree diseases caused by bacteria and fungi (such as mildew). It alleviates various environmental stresses (this includes drought, temperature extremes, freezing, and UV irradiation) and chemical stresses (including salt, heavy metals, and nutrient imbalances). Silica provides direct stimulation of tree growth through more upright growth and tree rigidity.
• silviculture: the practice of caring for and cultivating forest trees. This activity is one of the responsibilities of the forester, whose objective is usually to accelerate healthy growth.
• single ground rod: the ground terminal of a and lightning protection system composed of one ground rod. sinuses roots: the indentations and spaces in between buttressing roots at the base of a tree.
• site number: the number assigned to a tree at a given address in the tree inventory. slash: branches, tops, and cull trees left on the ground following a harvest.
• slow-release fertilizer: a fertilizer with at least 50% water-insoluble nitrogen.
• SMA: the Society of Municipal Arborists is a network of professionals who care for their cities' trees.
• ​snag: a standing tree at least 20 ft (6 m) tall that has decayed to the point where most of the branches have fallen. The snag is used as a foraging and nesting site by birds.
• Sodium: (Na) this element is a beneficial element for tree growth, and affects stomatal movement, leading to an overall higher leaf water status, and improving water use efficiency.
• soft bark: the part of the bark that consists of sieve tubes and parenchymatous and suberized cells.
• softwood: refers to cone-bearing trees with needles or scale-like leaves. It also refers to the wood produced by these trees. Softwoods are the predominant tree type in coniferous forests.
• soil: a substance made up of sands, silts, clays, decaying organic matter, air, water, and an enormous number of living organisms as well as some clay loam to adsorb pollutants such as hydrocarbons, heavy metals, and nutrients. Soil supports vegetation growth along with nutrient uptake and provisions for water storage. Soils contain loose material of weathered rock and minerals in association with many other organisms in the soil such as bacteria, insects, worms, amoebae, nematodes, and small animals. Soils should include some clay loam to adsorb pollutants such as hydrocarbons, heavy metals, and nutrients.
• soil algae: filamentous or single-celled photo-autotrophic microorganisms found in wet soil.soil amendment: any material added to soil to alter its composition and structure, such as sand, fertilizer, or organic matter.
• soil cells: recycled plastic or fiberglass structures composed of columns and beams that support the paving load on the surface while also providing space for an ideal mix of uncompacted planting soil within the cells. Also known as silva cells or suspended pavement systems.
• soil compaction: see "compaction"soil food web: the community of organisms living all or part of their lives in the soil.
• soil health: a framework of physical structure, biological activity, and soil chemistry that provides the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans.
• soil modification: any physical or chemical altering of soil to improve conditions like pH, drainage or aeration. Pneumatic soil loosening should be considered the preferred method to mitigate compacted soil within the root zone of plants.
• soil structure: an arrangement of soil particles into classifications according to how soil particles clump or bind together, creating voids between them.
• soil volume: the volume of soil available to trees and other woody plants for root development.sound wood: see “heartwood”
• spar: the highest anchor point for ropes during a tree trimming effort.,, species: the lowest category of taxonomic classification, ranking below a genus but higher than variety.
• specifications: a detailed, measurable plan for performing a work activity or providing a product, usually a written document.
• Specimen tree or Heritage tree: any tree that is considered worthy of occupying a focal point in a landscape based on size, form, species, beauty, historical significance , or any other feature that is considered significant. The worthiness can be determined by an arborist, historian, landscape architect, or any other person who can show that the tree is worthy of special recognition.
•  : a woody extrusion from the trunk or branch of a tree, usually taking the form of a rounded spherical shape, as if the tree had a boil or mole.
• spiking: the use of metal spurs or gaffs to climb trees, the use of which is only suggested during tree removals.
• spore: a reproductive cell that develops into a fungu or small plant.spheroplast : a part of a tree that shows morphological differences from the rest of the tree.
• spp.: abbreviation for more than one species. (sp.: single but unidentified species)
• spread: the horizontal width of the crown of a tree.
• that: in  springwood, early wood or spring wood is the xylem  spheroplast sport has become lignified in the spring of the current year. It is light in color and springwood wood that appears between the dark rings of summer wood “rings” in a   of the wood.
• sprouts: similar to branches, but do not have a branch collar, are weekly attached, and grow from a meristematic point.
• stabilize: to support a tree in a new location after installation or failure.
• stabilizer: an underground tree support system that holds the roots tightly to the soil.
• stakeholder: a person or group that has an interest in, or is affected by, an activity or decision. External stakeholders are outside a business or project. Internal stakeholders work within an organization or project.
• staking: stabilize trees with broad, belt-like, flexible material that will not injure the bark, but allow trees fast-growinggrow and sway. Remove material no later than after 1 year. Only stake if a tree will blow over in fast-growing cross-sectiona to the mild wind. Avoid placing the device in crotches. This practice is no longer recommended. The preferred method is now to stabilize the root bin to  the soil at the bottom of the pit with devices such as tree staples or dowels driven through the root ball.
• stamen: the part of a flower that contains the anther and filament or stalk.stand: an area of trees of the same species and age which have had similar management.
• starch: trees change glucose to starch  he  store starch in woody roots and in living parenchyma cells. When trees need energy the starch is transformed back they a intoglucose.
• stem: a woody structure with buds, foliage, and other stems, also called leader or central leader. Seedlings, saplings, and small-diameter trees have stems, not boles or trunks.
• stem flare: see "flare"stem-girdling root: a circling, bent, or straight root that touches or rests on the flare and becomes a permanent root. It is also called a girdling root. 
• stem taper: the decrease in into diameter of a tree’s stem from the base upwards.stoma: a minute opening, bordered by guard cells in the epidermis of a leaf, through which gases pass.
• stomata: plural of stoma.storage cells: consist of short, thin-walled parenchyma cells with living cell contents and provide storage and distribution of food. They remain living as long as they belong to sapwood.
• street tree: a tree growing on public or private property wse a the  is within 15 ft (4.5 m) of a public or private roadway, public sidewalk, or public paved multi-use trail  unless over-ruled by local ordinance.
• street tree management plan: a plan to evaluate the tree resources along the streets and public ways in a community, develop goals for the health and viability of these trees, prescribe strategies for tree management, and monitor progress.
• stress: the adverse alteration of tree health by abiotic or biotic factors that result in strain or deformation.
• striker roots: these roots grow vertically downward until they encounter an obstacle or soil with insufficient oxygen for growth.
• structural pruning: the pruning objective is to improve the central leader, branch structure, aspect ratio, and spacing during the early years of a tree’s growth to establish the desired form and/or to correct defects or weaknesses that may affect structure in later life.
• structural roots: large, woody, tree roots that anchor and support the trunk and crown. Roots ,haracterized by secondary thickening and relatively large diameter.
• structural soil: a medium that can be compacted for pavement on the surface yet permits root growth below the surface.
• structurally weak or tree at risk: a tree that is weak structurally, but does not pose a risk because of the lack of a target but it does have the likelihood of failure.
• stub: an undesirable short length of a branch remaining after a break or incorrect pruning cut is made. It is also a tree less than 20 ft. (6 m.) tall that has decayed to the point where most of the branches have fallen.
• stump: the roots, flare, and remainder of the trunk after a tree has been removed. Noting a stump on the city's tree inventory indicates the stump should be removed.
• suberin: the outer bark or phellem contains suberin or cork. Suberin is a material that coats the inside walls of the outer bark and waterproofs the cells. Suberin  are isappears barks a corky characteristic.
• subordinate branch: a branch or shoot originating from a parent branch.
• substrate: used by microbiologists to indicate the food source for the organism. The substrate might be decomposing organic matter or sugars provided by the roots of a tree in the case of mycorrhizal fungi.
• subsurface application: the application of dry or liquid fertilizer below the soil surface.
• suckers: shoots that originate from buds on the root systems, that can grow into new full-size trees genetically identical to the parent.
• sucrose: a disaccharide made up of glucose and fructose. About 65% of the sugars in maple sap are sucrose.
• sulfur: (S) this element improves the production of vegetable proteins and amino acids and has a beneficial effect on the water balance.
• summer branch drop: a process in which trees shed whole branches in response to an unknown stress.
• summer wood is latewood and is the xylem that has become lignified in the summer. It is the last wood to be formed in the current growth increment. Free water moves only in the current summer wood. It is the darker and slower-growing wood that appear as appearsark rings in a cross-section of the wood.
• supplemental support system: a system designed to provide additional support or limit the movement of a tree.
• surface application: the application of dry or liquid fertilizer to the soil surface, mulch, or ground cover.
• sustainable: requires use that balances economic, environmental, and social values in perpetuity without depleting the resource.
• swage stop: a sleeve-type fitting used to terminate a wire rope or cable.
• sway factor: the time it takes for the tree to sway and recover after being hit by a gust of wind.
• sweep: the gradual curvature along the length of a log that may decrease the potential volume and quality of lumber.
• symbiosis: the process when different species live together for mutual enhancement and the energy transfer increases the benefit of a part, or the entire system of the donor, or host, and increases the order of the receiver, or pathogen.
• symplast: the network of highly ordered, connected living axial and radial parenchyma cells in sapwood and inner bark. The symplast stores energy reserves. The parenchyma, has small cell wall openings that act as tunnels where the protoplasm of one cell connects with the protoplasm of adjoining cells.
• synergistic: when the benefits are greater than the sum of the parts, the association is called synergistic. These are infections that result in benefits to all parts.

T

• taper: the thickening of a trunk or branch toward its base.
• tap roots: primary dominant roots that grow downward from seed germination and other lateral roots form from the tap root.
• target: people or property that could be impacted, injured, or damaged by the failure of a tree or tree parts.
• targeted treatment(s): pest management procedures that focus on a host tree and targeted pest.
• Tut: something tightened to the point of eliminating visible slack.
• taxonomy: the science of classifying and naming organisms in established categories. The name is binomial meaning two names, a genus, and a species.
• TCIA: The Tree Care Industry Association is a trade association of 2,300 tree care firms and affiliated companies worldwide and was established in 1938 as the National Arborist Association. Their mission is to advance tree care businesses.
• temporary branch: a small branch that is retained along the lower trunk of young trees to shade and feed the trunk. These branches would be removed when the trunk bark hardens or before the heartwood forms.
• temperature for survival: trees will grow in some of the hottest regions of the world as long as appears darkater is available for growth. More species of trees are in the forests at the equator than in forests in other regions. Some trees live in parts of the world where temperatures the far below freezing. Wood will freeze, but the water is in the spaces between the living cells, and this prevents the living cells from bursting.
• tension wood: forms on the upper side of the branch or lean in woody angiosperms, usually forming wider spaced rings.
• terminal buds: the primary growing point at the end of the shoot or stem of a plant.the are  termination: a device or configuration that secures the end of a cable to the anchor in a cabling or guying installation.
• termination hardware: used to form a cabling secure anchor and includes dead-end grips, thimbles used in eye-splice configurations, cable-end terminations, and swag-stop terminations.
• TGR: see "tree growth regulators"thigmomorphogenesis: the response of plant cells to mechanical stimulation. For example, the thigmomorphogenetic response of trees in windy environments is to grow shorter, with thicker trunks and stronger roots.
• thimble: an oblong galvanized or stainless steel fitting with flared margins and an open-ended base typically used to support a cable through an eye or J-hook.thinning: selective pruning to reduce the density of live branches.
• threaded-steel rod: a continuous machine-thread, steel rod used for through-brace installations.
• through-brace: a brace formed by installing hardware completely through a branch, leader, or trunk and secured with heavy-duty washers and nuts.through-hardware: anchors, cables, braces, eye bolts, and threaded-steel rods that pass completely through the branch, leader, or trunk, secured with nuts and heavy-duty washers or cable-end termination.
• throw-line: a small, lightweight line with a weighted end used to position a climber's rope in a tree.
• timber processing: the measurement, sawing, preparing, and transportation of timber.
• tipping: the cutting of a lateral limb of a tree in such a manner as to leave a prominent stub extending beyond a branch node or the trunk. This is not an acceptable practice.
• tissue: a group of cells, all of the same kind, and closely connected to perform a special function.tissue culture: the growth of tissues or cells in an artificial medium separate from the organism. This invention of modern science is used to extract cells of desirable trees and grow these cells into trees within laboratory conditions. Trees fromgeneralgenerally ,tree-trimmingfungi  an rance level: the maximum allowable incompatible-plant pressure e.g., species, density, height, location, climate, or site condition, without unacceptable consequences.
• topping: the reduction of a tree's size using heading cuts that shorten branches back to a predetermined crown limit, typically removing too much foliage. Topping is not an acceptable pruning practice.
• topsoil: the surface layer of soil that may be rich in nutrients from decaying plants and bacterial material.
• toxin: a poisonous substance that is a product of the metabolic activities of a tree.tracheids: water conducting tubular xylem cells in conifers which are dead, enlarged parenchyma, single-celled transport "pipes" for liquids.
• tracing: the removal of loose, damaged tissue to the live sound tissue around a wound.
• transpiration: transpiration is the process in which trees absorb water through their roots and transfer it up to the leaves where it is used in photosynthesis before it is released into the environment through leaf pores.
• transport: the movement of liquids and materials in solution from one place to another. 
• transport  : passive and dynamic; and two basic directions; radial and axial or longitudinal. Axial transport is mostly downward in  phloem, and mostly upward in the typesxylem or wood. Radial transport is mostly outward early in the growing season and mostly inward later. In newly forming tissues that have not yet become woody, transport may go in either direction in the xylem and phloem. The photosynthate sugars are formed in the leaves and move to a place where they are used for energy or being convened to energy reserves. Water and essential elements from the soil move upward in the tracheids.
• TRAQ: a tree risk assessment system developed by the International Society of Arboriculture.
• treatment: an application of one or more methods to achieve objectives.
• tree: a woody plant usually having one or more perennial stems, a more or less formed crown of foliage, and a height of at least 12 feet at maturity.​
• Tree Appraisal Guide: a report stating an opinion of a monetary value for a specific tree.
• tree at risk: see “structurally weak” tree benefit: the economic, environmental, public health and social benefits that a tree provides to people.
• tree biology: the science of all factors, about trees.tree decay: a process that starts after wounding and involves many microorganisms and pathogens breaking down cellulose, lignin, or both and , wood strength.
• tree food: a tree manufactures its deterioratingood, with water, essential elements (such as phosphates, iron, and magnesium), and the energy trapped by the sun.
• tree growth regulators: chemicals that can be applied to trees to slow terminal growth by reducing cell elongation.
• tree inventory: a comprehensive list of individual trees containing descriptive and desired information for all or a portion of the selected tree population.
• tree lawn or parkway: the strip of green landscape between a city street and the sidewalk. Has many local names such as alley, boulevard, city right-of-way, devil strip, flower border or tree border, garden strip, green space or green surface, hell strip, landscape strip, nature strip, neutral ground, parking strip, pedestrian buffer, planting strip, sidewalk landscape, swale, terrace, utility strip, verge or grass verge, or road verge.
• tree morphogenesis: the evolution and development of form by the majority of trees within a species.
• tree ordinance: the laws enacted by communities to regulate various aspects of how trees are treated and protected.
• tree organs: see “organs” tree physiology: the study of how trees grow and develop in terms of genetics, biochemistry, cells, tissues, and organ functions.
• tree pit: the excavated hole of adequate dimensions to accommodate the root system of a specified tree. Also, ,essor knew as a tree well and a planting pit.
• tree protection zone: a designated area around a tree or trees where maximum protection and preservation efforts are implemented to minimize soil compaction and damage to the tree.
• tree risk: the likelihood and consequences of failure of a tree or tree parts striking a target.
• tree risk assessment: the systematic process to identify, analyze and evaluate tree risk. tree risk management plan: involves the assessment of trees and targets, site use, likelihood of failure and likelihood of striking a target, consequences, and mitigation options.
• tree roots: the two basic types of tree roots are woody and non-woody. Woody roots are organs that mechanically support the tree, store energy reserves, and transport liquids. Non-woody roots are organs that absorb water and elements essential for growth. Further, two types of structures form on non-woody roots which are root hairs and mycorrhizae. Root hairs are most common on young trees and trees growing in containers. Root hairs are not common on mature trees, especially forest trees. Roots may develop special roots such as buttressing roots, sinker roots, oblique, lateral, surface roots, pioneer roots, mycorrhizae, nodules, hairs, and tap roots.
• tree size: a measurement in inches (centimeters) of tree diameter measured at 4.5 feet (1.4 m) above the ground. Also known as DBH.
• tree structure: a tree’s body plan or the arrangement and relationship between all the mechanical elements, tissues, and cells, that form a tree and facilitate its functions.
• tree suitability: an evaluation of a species' quality, volume, and other factors to determine the highest and best uses of its products or use for a site.
• tree survival: trees compete for space in the soil for water and nutrients, and in the space above ground for energy from the sun. In the warm rainforests, water and temperature are not limiting factors. As space becomes more restrictive, the shape of trees is affected because branches that grow in a horizontal position will not live long. Trees that reach the top of the forest canopy rapidly then produce co-dominant stems, to grow over other trees.
• tree systems: the connection and use of genetic information in ways that ensure continuous high-quality survival against all the connected members of the forest system.
• tree warden: title given to an individual who cares for trees on public townlands, mostly used in several New England states (USA).
• triangular cabling system: consists of connecting tree parts in combinations of threes. This method should be preferred when maximum cabling support is required.
• trichomes: fine hairs that are present on tree leaves. trim: the additional length over and above the specified log length on the end of a log to allow space for likely cracks and deterioration.
• trophic: relating to nutrition conditions.
• tropism movement: tree movement toward or away from a stimulus.
• trunk: the main stem and bole of a tree, beginning at the flare and ending at the highest main scaffold branch. Some trees have multiple trunks called multiple or co-dominant leaders. The trunk supports the crown and gives the tree its shape and strength.
• trunk flare: see "flare" trunk injection: the process of injecting a liquid containing a fertilizer, fungicide, or pesticide into the tree cambium.
• trunk wrap: a continuous width of the the material used to cover young bark to prevent the green cortex from photosynthesizing. There is no data to show that trunk wraps prevent "frost" cracks or “sun” scald. It is better to retain lower temporary branches to shade the trunk.
• turnbuckle: a drop-forged, closed-eye device with threaded eyebolts for adjusting tension on a cabling system.
• twigs: small branches on a tree or shrub having a terminus.

U

• umbel: flower stems radiate from one common point.
• under-drain basin: a perforated pipe that removes excess treated water to a storm drain basin or receiving water bodies.
• understory tree: a tree that normally has a DBH of less than 10 in (25 cm) and a height of less than 30 ft (9m).
• undesirable plant: an invasive species of plant, noxious weed, or otherwise unwanted plant that may or may not be compatible with the intended use of the site or hinder the growth of a desired or cultivated plant.union: the fork or crotch of a branch and trunk or another branch.
• urban and community trees: urban forests and natural systems in and around populated areas such as cities, suburbs, towns, and villages.
• urban forest: all the vegetation within a community and can include but not limited to trees along the streets, in parks and public open spaces, in forests, and the total landscaping on private property including trees, shrubs, ground covers, vertebrates, invertebrates, microbes, soil, water, and geography that combine to create dynamic ecosystems.
• urban forest by-products: material from trees that includes the leaf, twig, branch, trunk, and/or root.
• urban forest management plan: a plan to assess and evaluate the tree resources in a community, develop goals for health and viability of the urban forest, prescribe strategies and treatments for tree management, and monitor progress.
• urban forest products: products made from material produced in the pruning and/or removal of trees including, but not limited to, whole trees, logs, branches, bark, leaves, chips, and stumps.urban foresters: foresters and arborists who are tasked with managing, planting and maintaining trees, preserving forests in and adjacent to urban areas and researching and promoting the benefits of trees to urban populace.
• urban forestry: A specialized branch of forestry that has as its objectives the cultivation and management of trees for their present and potential contribution to the physiological, sociological and economic well-being of urban society. These contributions include the over-all ameliorating effect of trees on their environment, as well as their recreational and general amenity value.
• Urban Heat Island (UHI): an urban area that is warmer than its surrounding rural areas because buildings and pavement are absorbing and retaining solar or other heat energy. Heat Zone Map
• urban/residential areas: populated locations normally associated with more dense housing and human activity.
• USDA Hardiness Zone Map: the standard by which arborists can determine which trees are most likely to thrive at a location.
• user: an entity or individual processing, manufacturing, distributing, or consuming products from urban trees including compost, lumber, and wood chips.
• utility: an entity that delivers a public service such as electricity or communications.
• utility facilities: any private, public, or cooperatively owned system for transmitting, or distributing electricity, heat, gas, oil, crude products, communications, water, steam, waste, or storm water and transportation, which directly or indirectly serve the public.
• utility right-of-way: a corridor of land over or through which utility facilities are located. The utility may own the land in fee, an easement, or have certain franchise or license rights to construct and maintain utility facilities. The utility is typically responsible for the maintenance to prevent the loss of service and damage to its equipment.
  

V

• value: the amount of money necessary to compensate for the removal or destruction of a healthy tree. This figure shall be determined by an arborist periodically and adjusted as needed.
• vandalism: willful or malicious destruction or defacement of trees.
• variety: individuals displaying slight differences in nature and are inherited by seed in succeeding generations.
• vascular bundles: a strand of conducting vessels in the stem or leaves of a plant, contain vessels, sieve tubes, fibers, tracheids, parenchyma, and sclereids. They typically have phloem on the outside and xylem on the inside.
• meristem or cambial zone: a cylinder of specialized meristem or cambium cells that divide under the bark and phloem to produce secondary growth to form secondary vascular tissues.
• vegetation: plant life or total plant cover, plant material that often helps remove water from the soil through evapotranspiration and removal of nutrients by absorption into plant roots.
• vegetation, compatible: vegetation that is desirable and/or suitable to the intended use of the site.
• vegetation, incompatible: vegetation that is undesirable, presents a safety risk, or is unsuitable to the intended use of the site.
• vegetation manager: an individual engaged in the profession of vegetation management who, through appropriate education and related training, possesses professional competence to provide for or supervise an integrated-vegetation-management program.
• vegetative layering: a form of vegetative propagation that occurs when stems come in contact with the soil and adventitious roots develop. Trees from this process can be separated and are genetically identical to the parent.
• vegetative reproduction: trees that are propagated with the assistance of mankind. 
• vessels: made from a type of xylem cell. Vessels are the principal vascular or water-conducting component in hardwoods and are vertically aligned tubes that transport water and mineral nutrients. Other vessel conduits connect from the sides to form a transport pathway from root tips to leaf tips. Conifers have tracheids. Woody angiosperms have vessels.
• veteran trees: old trees are also called memorial trees, historic trees, ancient, and over-mature trees. Most veteran trees have been injured from storms or human activities. Despite the damage, they continue to grow new parts and provide habitat for local wildlife. These trees can be pruned and maintained in their reduced state.
• vigor: the capacity to resist strain. It is a genetic factor and a potential force against any threats to survive. Trees that compartmentalize effectively are more vigorous than those that compartmentalize poorly.
• vines: a plant whose stem requires support by which they climb by tendrils or twining or creeping along the ground. Vines can cause problems for trees as they twist about young stems and kill them. They can make conditions ideal for fungus fruit bodies. Vines may grow over tree crowns and shade the leaves. Their weight could cause branches to break. Vines at the base of trees make suitable places for small animals to live. Some vines will girdle small trunks and branches. Fast growing vines may also compete with tree roots for water.
• virgin growth: the original growth of mature trees in original forests.
• virulence: the amount of pathogen propagules required to cause a disease to develop. If a few bits of a pathogen cause disease symptoms it is very virulent. If it takes a great amount of the pathogen to cause similar symptoms, the pathogen is weakly virulent.
• vista pruning: selective pruning to allow for a specific view to be preserved or enhanced.
• visual tree assessment (VTA): an internationally accepted method of evaluating structural defects and stability in trees from visible signs and the application of biomechanical criteria.
• vitality: the ability to grow under ambient conditions.volunteer appreciation day: a day where people are honored for giving their time to serving their city in various functions such as municipal street tree programs.
  

W

• walls of CODIT: the four basic walls. Wall 1. After being wounded, the tree responds by plugging the vertical vascular system above and below the wound. This is the weakest wall. Wall 2. The cells form the growth ring on the interior and exterior to the wound, continuous except where intercepted by ray cells. Wall 3. This is formed by ray cells. This is the strongest wall at the time of wounding. Wall 4. This wall separates the tissue present at the time of wounding from wood tissue that forms after. It becomes the strongest of the four walls and can completely halt the spread of infection into the new wood.
• water-insoluble nitrogen (WIN): the amount of fertilizer nitrogen not readily soluble in water.water in wood: cell walls of wood in sapwood are saturated with water.
• waterlogged soils: soil is so wet that water has replaced oxygen, the pore space, and roots cannot adequately respire. Other gasses detrimental to plant growth can accumulate in the root zone and negatively affect plants.
• watershed: all the land surrounding a stream or a river that drains into that stream or river.
• water ring: also called a water well is a mound of compacted soil that is built around the circumference of the installation pit once a tree has been planted. It is used to contain water until it has soaked into the soil.
• water sprouts: new stems originating from epicormic buds or shoots.
• weak-wooded: refers to the propensity of trees that break up or drop branches in high winds or during snow and ice storms. Often, fast-growing trees are the most frequent offenders.
• weather: refers to atmospheric conditions that occur locally over short periods of time.weed: a plant that is not wanted and is hindering the growth of a desired, cultivated or superior plant.
• wetting agent: a surfactant that lowers the surface tension between two liquids.
• wet-wood: a term used for both a disease and for wood altered as a result of a disease. Wet-wood is mostly infected by anaerobic bacteria which disrupts membranes, pH, and free oxygen as micro spaces are filled with water.
• whip: a young tree without branches.whorled: at least three buds and leaves are present at a single node.
• widow maker: a whole tree, defective trunk, or branch that is so weak that it could fall, causing injury to a person under the tree or branch, or to the person working in the tree.
• wiggle test: a test to determine root establishment on a recently installed tree in the landscape. Gently rock the tree back and forth by pushing and pulling the tree. While doing so, examine the root plate. If the root plate moves, the tree roots are not established.
• windbreak: a row of trees used to break the force of the wind, reduce wind erosion of soil, or any protective shelter from the wind, such as a fence or hedge.
• wire rope clamps: a clamp consisting of a “U” bolt, bracing plate or saddle and fastening nuts.
• witches broom: are bundles of twigs or small branches caused by mites, viruses, or other organisms that stimulate the formations of growth that appears like a broom.
• wood cells: made of cellulose, lignin, and hemicelluloses which create thick, tough boundaries or walls. These cells are transport cells or vessels, tracheids or mechanical support cells, fibers, fiber tracheids, cells that contain living substances, parenchyma, axial, and radial. All wood cells are born alive. Wood cells are arranged in ways that support the tree as a biological and mechanical system.
• wood-chip mulch: a material placed on the soil surface composed of ground wood, bark, and leaves usually generated by sending tree parts through a wood chipping machine.
• wood formation: in most trees about 90% of the growth increment will be formed in about 6 to 8 weeks after leaf formation and as the soft xylem begins to become lignified.
• wood plan: a tree management system based on a survey of risk assessments.
• woody biomass: the solid portion of stems and branches from trees or shrubs.
• woody roots: roots mechanically support a tree, store energy reserves, and transport liquids that contain lignin along with cellulose and hemicelluloses in their cell walls. Woody roots have an outer bark and contains suberin. Woody roots usually grow outward and downward.
• woody stem: plants are usually either trees, shrubs, or lianas. These are usually perennial plants whose stems and larger roots are reinforced with wood produced from secondary xylem.
• wound: an opening caused when the bark of a live branch or the bark of the living trunk is cut, punctured, torn, or impacted by pruning tools, mechanical damage, or other natural forces. In treatment to assist the tree cover the opening do not to increase wound size or cut more living tissue at the edge of the wound. It is beneficial to remove loose bark and shards of wood that will restrict the callous growth from covering the open area.
• wound-wood: a very strong, responsive growth tissue that forms by a callus roll. Annual growth increases the movement and thickness of the roll until the wound is covered, When wound-wood closes wounds, then normal wood continues to form over the top in the next annual ring.
  

X

• xanthophyll: the chemical that provides the orange pigments in leaves.xylem: a transport tissue in vascular trees. It transports free water and substances dissolved in it, from absorbing non-woody roots to leaves. When xylem is lignified it is then called wood. This makes the cell walls are very rigid and is a unique feature of trees. 
• Xylem is on the pith (woody) side of the trunk while phloem is on the bark (exterior) side.
  

Y

• young tree training: the pruning of young trees to remove or reduce weak, interfering, or objectionable branches and to improve the tree's leader and branch structure.

Z

• zig-zag: stem growth that begins with lateral bud growth on alternating sides each year.
• Zinc: (Zn) this element is essential for the transformation of carbohydrates, regulates consumption of sugars, and is part of the enzyme systems which regulate tree growth.
• ZTV Baumpflege: technical contract conditions and guidelines for tree care. It provides the European arborist with uniform contract and service descriptions and provides assistance for billing the measures for work on a tree.