ISA BCMA key terms

A thin layer of dividing cells between the bark and the wood that produces new xylem inward and new phloem outward, letting trunks and branches grow wider each year.

The woody tissue that conducts water and dissolved minerals from roots to leaves and gives the trunk most of its strength. It forms the bulk of a tree's cross-section.

The inner bark tissue that carries sugars and other organic compounds from leaves to roots and growing tissues. It lies just outside the vascular cambium.

The tree's process of walling off decay and injury with boundaries of altered wood, limiting the spread of pathogens and discoloration. Trees do not heal damaged wood; they isolate it.

Special wood formed to correct lean or support heavy limbs. Flowering trees make tension wood on the upper side; conifers make compression wood on the lower side.

The widened transition zone where trunk tissue meets root tissue, normally at or just below the soil surface. It should stay visible and not be buried by mulch or soil.

A plant selected and propagated for specific traits such as form, color or pest resistance, and maintained so those traits stay consistent. Cultivar names appear in single quotes.

A geographic rating based on average annual minimum temperature used to predict whether a tree can survive winter at a site. Local microclimates can differ from the mapped zone.

A branching pattern with a strong central leader and lateral branches that shorten toward the top, producing a conical crown. Many conifers and some shade trees grow this way.

Bark trapped inside a narrow branch union or between codominant stems, leaving little wood connection. Such unions are weak and prone to splitting under wind or load.

The relative amounts of sand, silt and clay particles in soil. Texture affects drainage, aeration, water storage and nutrient retention and is very difficult to change.

The dry weight of soil per unit volume, including pore space. Higher bulk density usually means compaction and less pore space for roots, air and water.

The ability of clay and organic matter to hold positively charged nutrient ions and release them to roots. Higher capacity generally means better nutrient retention.

Compression of soil that squeezes out pore space, raises bulk density and restricts roots, air and water. Traffic, equipment and stockpiling are common causes.

The soil and roots lifted with a transplanted tree. Its size, moisture and handling affect survival, and it should be supported by the ball rather than the trunk.

The position of the root collar relative to final grade. Too deep buries the root flare and can cause decline, girdling roots and root rot.

The time after planting when roots grow into surrounding soil and the tree adapts to its site. It often lasts about one year per inch of trunk diameter.

A root that circles the trunk or another root and presses into vascular tissue, restricting water and sugar movement. It can begin in the nursery or from deep planting.

Injury or poor health caused by nonliving factors such as drought, frost, flooding, nutrient shortage, chemicals or mechanical damage, rather than by an insect or pathogen.

Yellowing of leaves from loss of chlorophyll, often caused by nutrient deficiency, poor drainage, root damage or high soil pH. It reduces photosynthesis and tree vigor.

A localized dead area of bark and cambium, often sunken or discolored, caused by pathogens or abiotic injury. Cankers can expand and girdle stems.

Progressive death of twigs and branches from the tips inward. It is a symptom of stress such as root injury, drought or cankers, not a disease by itself.

A decision process that uses monitoring, action thresholds, cultural methods, biological control and, when needed, pesticides chosen to minimize harm to people and the environment.

The pest population or damage level at which treatment is justified to prevent unacceptable harm. It helps decide whether and when to act.

Managing pests by encouraging or releasing natural enemies such as predators, parasitoids and pathogens. It works best as one part of an integrated program.

The swollen ring of trunk or parent-branch tissue at the base of a branch. Cutting just outside it helps the tree seal the wound.

A pruning cut that removes a larger limb back to a smaller lateral branch capable of becoming dominant. It lowers height or spread while keeping a more natural form.

A pruning cut that removes a branch where it attaches to the parent branch or trunk. It reduces crown density without shortening the remaining branches.

Severe cutting of large limbs between nodes, leaving stubs. It causes vigorous sprouting, decay and weak attachments and is not an accepted pruning practice.

The area around a tree, usually measured as a radius from the trunk, where soil disturbance and root damage are restricted during construction or other work.

The soil area holding the roots a tree needs for health and stability, often estimated as one foot of radius per inch of trunk diameter.

Cutting roots, often to make a clean trench or prepare a tree for transplanting. Severe or close cuts reduce water uptake and can destabilize the tree.

The combination of how likely a tree or tree part is to fail and the consequences of that failure to people, property or other targets.

A person, vehicle, building or other object that could be struck and damaged if a tree or tree part fails. Without a target, a defect poses little risk.

The chance that a tree or tree part will fail within a stated time, based on species, structure, defects, site conditions and weather exposure.

All the trees and woody plants in a city, town or suburb, including street trees, parks, yards, green spaces and natural areas.

A systematic record of trees or plots that includes location, species, size and condition. It supports planning, maintenance, budgeting and risk management.

A planning principle of matching a tree's mature size, site needs and function to the available space and conditions so it grows with minimal conflict.