ISA AM key terms

The branch of arboriculture focused on managing publicly owned trees and forests in streets, parks, and other civic spaces for safety, ecosystem services, and community benefit.

The total assemblage of trees and woody vegetation across a city, including street trees, park plantings, yards, greenways, and remnant natural areas, considered as one managed resource.

A strip of publicly controlled land, typically between the curb and private property line, where street trees and utilities are commonly located and where planting permits may be required.

A tree planted or retained within the public right-of-way or other municipally controlled ground along a roadway, managed for clearance, sightlines, and public safety.

The planted strip between the curb and sidewalk where street trees are often sited; also called a planting strip or verge, its width strongly affects rooting space and tree survival.

A municipal official, in some jurisdictions statutory, responsible for the care and removal of public shade trees and for holding required public hearings before certain removals.

A local law that sets rules for planting, pruning, and removing trees on public or private land, often including permits, replacement requirements, and penalties.

A regulatory designation that restricts removal, pruning, or construction damage to specified trees, sometimes applied to individual heritage trees or to whole stands.

A tree formally recognized for exceptional age, size, historical association, or cultural significance, often given extra legal protection and monitoring.

A tree recorded as the largest known of its species in a defined area, usually ranked by a formula combining trunk circumference, height, and crown spread.

A systematic record of individual trees or canopy areas, capturing location, species, size, condition, and maintenance needs to support planning and budgeting.

The proportion of a defined area covered by tree crowns when viewed from above, a common metric for urban forest goals and equity analysis.

A long-range document setting goals, policies, budgets, and operational priorities for a municipality's tree resource, usually with measurable targets and review cycles.

A freely available suite of models and tools from the USDA Forest Service for estimating urban forest structure and the ecosystem services and monetary value trees provide.

The measurable benefits people derive from trees, such as stormwater interception, air pollutant removal, carbon storage, cooling, and habitat provision.

The study of how trees grow, function, and respond to their environment, including water transport, photosynthesis, hormone signaling, and defense.

The thin lateral meristem between bark and wood whose divisions produce new xylem inward and new phloem outward, driving diameter growth.

The woody water-conducting tissue that moves water and dissolved minerals from roots to leaves and also provides most of a tree's structural strength.

The inner bark tissue that transports sugars and other organic compounds from leaves to roots and other living tissues.

The loss of water vapor from leaves through stomata, which pulls water up the xylem and cools the canopy.

Small pores in the leaf epidermis, controlled by guard cells, that regulate gas exchange and water loss and close under drought stress.

A tree's active defense that forms chemical and physical boundaries around wounds and infections, walling off decayed or colonized tissue from healthy wood.

Compartmentalization of decay in trees: a model describing four walls a tree forms to limit the spread of pathogens and decay after wounding.

Abnormally dense wood formed in response to leaning or mechanical stress, called tension wood in angiosperms and compression wood in conifers.

Physiological strain from prolonged water shortage, showing as reduced growth, wilting, early leaf drop, dieback, and greater susceptibility to pests.

A progressive, often irreversible loss of vigor and dieback caused by interacting stresses such as drought, soil compaction, pests, and age.

Compression of soil that reduces pore space for air and water, restricting root growth and gas exchange and a leading cause of urban tree decline.

The soil area around a trunk, often defined by a radius related to trunk diameter, where roots essential to tree health and stability are protected from disturbance.

Pruning that develops a strong central leader and well-spaced scaffold branches in young trees to reduce future failure risk.

Two or more stems of similar size arising from one point, often with included bark, creating a weak attachment prone to splitting.

Bark trapped between two closely joined stems or branches, preventing a strong wood connection and forming a common failure point.

The swollen tissue at the base of a branch where it joins the trunk, containing the tree's natural defense zone; proper cuts leave it intact.

New tissue that grows over a pruning cut or wound from the edges inward, distinct from callus and a sign of active tree response.

A structured process of identifying a tree's potential to fail, the likelihood of that failure, and the consequences to targets, producing a risk rating.

A person, structure, vehicle, or other thing of value that could be injured or damaged if a tree or tree part fails.

A categorized or scored judgment of risk, often combining likelihood of failure, likelihood of impact, and consequences, to prioritize mitigation.

Actions taken to reduce tree risk, such as pruning, cabling, bracing, root zone protection, target relocation, or removal.

The ongoing municipal program that sets risk tolerance, schedules inspections, trains staff, documents decisions, and allocates resources for tree safety.

A deviation of the trunk from vertical, which may be normal growth or a sign of root failure; recent or increasing lean warrants closer inspection.

The shallow mass of roots and soil that anchors a tree and can tilt or lift when roots fail, often revealing a failure before the trunk does.

The breakdown of wood by fungi, reducing strength and often detectable as cavities, soft wood, or fungal fruiting bodies.

A written record authorizing and tracking a specific tree maintenance task, including location, scope, crew, and completion status.