Forest Stewardship: Terminology

Terminology from various disciplines, including ecology, forestry, wildlife, and recreation are defined in this article to aid private landowners in communications with natural resource managers.
Forest Stewardship: Terminology - Articles


As you work with resource professionals in managing your land, you will gain a deeper understanding and appreciation of the forest resource and its complexity.

Advanced regeneration

Seedlings or saplings present in the understory before harvesting mature trees in the overstory.


Forest value, rooted in beauty and visual appreciation, affording inspiration, contributing to the arts, and providing a special quality of life.


The establishment of forest trees by planting or seeding an area not previously forested.


A cultivation system combining agriculture and forestry where trees and crops are interplanted; not common to Pennsylvania.

Allegheny hardwood type

A portion of the northern hardwood forest in Pennsylvania, of which black cherry, white ash, and tulip poplar are major components.

Area sensitive species

Plants or animals with very specific habitat requirements that are susceptible to population decline when their habitat is altered.


The orientation of a slope with respect to the compass; the direction toward which a slope faces; north facing slopes are generally cooler than southern facing slopes.

Basal area

A measurement of the cross-sectional area of a tree trunk in square feet at breast height. Basal area (BA) of a forest stand is the sum of the basal areas of the individual trees, and is reported as BA per acre.

Best management practices (BMPs)

Practices recommended by agencies or organizations to control pollution and erosion off a harvested site.

Biological diversity

The variety of plants and animals, the communities they form, and the ecological functions they perform at the genetic, stand, landscape, and regional levels.

Biological maturity

The point in the life cycle of a tree at which there is no net biomass accumulation; the stage before decline when annual growth is offset by breakage and decay.

Biological simplification

The reduction of biological diversity that results from altering the environment in ways that favor, either directly (e.g., through management) or indirectly (e.g., through pollution), certain species over many others.


The total weight of all organisms in a particular population, sample, or area; biomass production may be used as an expression of site quality. Biomass is also defined as a wood product, usually in the form of wood chips, for energy production.


The largest ecological unit, distinguished by an extensive complex of terrestrial communities, corresponding to a particular climatic zone or region, and associated with an environmental region such as the northern coniferous forest, the Great Plains, the tundra, or as in Pennsylvania, the eastern temperate hardwood biome.

Board foot

A unit of wood 1 inch thick, 12 inches long, and 12 inches wide. One board foot contains 144 cubic inches of wood.


The main trunk of a tree.


Portions of woody plants including twigs, shoots, and leaves used as food by such animals as deer.

Buffer strips

Forestland left relatively undisturbed to lessen visual or environmental impacts of timber harvesting, usually along a road or waterway.


The upper level of a forest, consisting of branches and leaves of taller trees. A canopy is complete (or has 100 percent cover) if the ground is completely hidden when viewed from above the trees.

Carrying capacity

The maximum amount of animal or 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.


A harvesting and regeneration technique that removes all the trees, regardless of size, on an area in one operation. Clearcutting is most often used with species like aspen or black cherry, which require full sunlight to reproduce and grow well, or to create specific habitat for certain wildlife species. Clearcutting produces an even-aged forest stand.

Commercial forestland

See timberland.


A collection of living organisms in a defined area that function together in an organized system through which energy, nutrients, and water cycle.


The wise use and management of natural resources to ensure its existence and function in perpetuity.

Consumptive activities

Forest uses which involve the removal of something from the site (hunting, fishing, timber harvesting). Nonconsumptive activities include hiking, bird watching, and nature study.


A strip of wildlife habitat, unique from the landscape on either side of it, that links one isolated eco- system "island" (e.g., forest fragment) to another. Corridors allow certain species access to isolated habitat areas, which consequently contributes to the genetic health of the populations involved.


A geographic unit of cover for wildlife (usually game); for example, a thicket or underbrush sheltering grouse or deer.

Crop tree

A term traditionally reserved to describe a tree of a commercially desirable species, with the potential to grow straight, tall, and vigorously. However, a crop tree can be one selected for nontimber purposes (varying with landowner objectives), such as mast production or den tree potential.

Crown class

An evaluation of an individual tree's crown in relation to its position in the canopy and the amount of full sunlight it receives. The four recognized categories are: dominant (D), codominant (C), intermediate (I), and overtopped or suppressed (S).

Crown Classes


A tree of such poor quality that it has no merchantable value in terms of the product being cut. However, a timber cull tree may have value for wildlife or aesthetics.


See diameter at breast height.


The unintentional or intentional conversion of land use from forest to nonforest. Associated with nonrenewable timber harvesting practices in ecologically sensitive areas, such as tropical rainforests.

Den tree

A tree with cavities in which birds, mammals, or insects such as bees may nest (also known as cavity tree).

Diameter at breast height (dbh)

The diameter of the tree measured at 4.5 feet above ground level. The abbreviation generally is written without capital letters and without periods.

Diameter-limit cut

A timber harvesting treatment in which all trees over a specified diameter may be cut. Diameter-limit cuts often result in high-grading.


A natural or human-induced environmental change that alters one or more of the floral, faunal, and microbial communities within an ecosystem. Timber harvesting is the most common human disturbance. Windstorms and fire are examples of natural disturbance.


The transfer of rights (usually development) associated with the land to a conservancy or public agency through purchase or donation. Easements are used as a conservation tool to retain the natural resources on land and reduce its likelihood to be used in undesirable ways.


The study of interactions between living organisms and their environment.

Economic maturity

The point in the life cycle of a tree or stand when harvesting can be be most profitable, i.e., when the rate of value increase of an individual tree or stand falls below a desired alternative rate of return.


A natural unit comprised of living organisms and their interactions with their environment, including the circulation, transformation, and accumulation of energy and matter.


A genetic subdivision of a species resulting from the selective action of a particular environment and showing adaptation to that environment. Ecotypes may be geographic, climatic, elevational, or soil related. Red maples and northern red oaks are both adapted to moist soils, but can also be found on drier sites where the genetic difference is their enhanced ability to retain water.


The boundary between open land and woodland or between any two distinct ecological communities. This transition area between environments provides valuable wildlife habitat for some species, but can be problematic for sensitive species, due to increased predation and parasitism.

Emergent wetlands

A class of wet- land dominated by grasses, sedges, rushes, forbs, and other rooted, water-loving (possibly broad-leaved) herbaceous plants that emerge from the water or soil surface; marshes are an example.

Endangered species

Species in danger of extinction throughout all or a significant part of their range. Protection mandated by the United States Endangered Species Act, 1973.

Epicormic branching

Branching that occurs on the tree trunk after other branches have developed higher; usually occurs from drastically modified environmental conditions, such as increased sunlight.

Even-aged stand

A group of trees that do not differ in age by more than 10 to 20 years or by 20 percent of the rotation age.


The eradication of a species from a portion of its natural range.


A biological community dominated by trees and other woody plants.

Forest health

The condition of a forest, taking into consideration its age, structure, vigor, and the presence of insects and diseases.

Forest interior dependent species

Animal species that depend upon extensive areas of continuous, unbroken forest habitat to live and reproduce, and are susceptible to higher rates of predation and population decline when interior forest habitat is fragmented or disturbed.

Forest inventory

The survey of a forest landowner's property. Inventories are conducted by sampling plots to estimate average conditions across forest stands. The summation of stand data represents the inventory. (See stand analysis.)

Forest recovery

The complex natural process by which floral, faunal, and microbial communities respond to disturbance in the forest ecosystem. More resilient ecosystems respond rapidly to disturbance, returning to the pre-disturbance ecological state within a relatively short time period (perhaps decades as opposed to centuries).

Forest stewardship

The wise care and use of forest resources to ensure their health and productivity for years to come.

Forest types

Associations of tree species that commonly occur because of similar ecological requirements. Pennsylvania's three major forest types are oak-hickory, northern hardwoods, and Allegheny hardwoods.

Forested wetland

An area characterized by woody vegetation over 20 feet tall where soil is at least periodically saturated with or covered by water.


The segmentation of a large tract or contiguous tracts of forest to smaller patches, often isolated from each other by nonforest habitat. Results from the collective impact of residential and commercial development, highway and utility construction, and other piecemeal land use changes.


Growth or development characteristics dependent on genetic information. The genetic constitution of an organism or a species in contrast to its observable characteristics.


A method of killing unwanted trees by cutting through the living tissues around the bole. Can be used instead of cutting to prevent felling damage to nearby trees. Girdled trees can provide cavities and dead wood for wildlife and insects.


Species similar in their habitat needs as well as their response to habitat changes (e.g., ovenbird and woodthrush). One species in a guild is often used to represent the others when developing a stewardship management plan.


The geographically defined area where environmental conditions (e.g., climate, topography) meet the life needs (e.g., food, shelter) of an organism, population, or community.


The process of cutting, removing, and processing trees from the forest.


A type of timber harvesting in which larger trees of commercially valuable species are removed with little regard for the quality, quantity, or distribution of trees and regeneration left on the site; often results when a diameter-limit harvest is imposed.

Horizontal structure

The spatial arrangement of plant communities; a complex horizontal structure is characterized by diverse plant communities within a given geographic unit.

Improvement cut

Any cutting treatment used to alter species composition and tree spacing to realize ownership objectives. Thinning is a type of improvement cut.

Indicator species

Species with such specialized ecological needs that they can be used for assessing the quality, condition, or extent of an ecosystem on the basis of their presence and density, or the accumulation and effect of materials in their tissues.

Interfering plants

Competing plants that interfere with the germination and growth of desirable seedlings by casting dense shade across the forest floor.

Land ethic

The principles and values guiding our use and treatment of the land. Forest stewardship is a land ethic. (See forest stewardship.)


The professional hired to harvest trees from the forest.

Management plan

A document prepared by natural resource professionals to guide and direct the use and management of a forest property. It consists of inventory data and prescribed activities designed to meet ownership objectives.


All fruits of trees and shrubs used as food for wildlife. Hard mast includes nutlike fruits such as acorns, beechnuts, and chestnuts. Soft mast includes the fleshy fruits of black cherry, dogwood, and serviceberry.


See economic maturity and biological maturity.


The environment at a small, localized area; includes biotic, climatic, topographic, and soil conditions at the specific site.

Multiple use and value

A conceptual basis for managing a forest area to yield more than one use or value simultaneously. Common uses and values include aesthetics, water, wildlife, recreation, and timber.

Natural resources professionals

Specially trained and educated natural resources managers who work with landowners and the land to achieve sustainable goals from wildlife to harvesting and regeneration.

Neotropical birds

Birds that breed in the northern hemisphere during summer months, and winter in tropical regions (e.g., woodthrush or barn swallows). One-third of Pennsylvania's breeding birds are neo-tropical migrants.


The physical and functional location of an organism within an ecosystem; where a living thing is found and what it does there.

Nonindustrial private forestland (NIPF)

See private forestland.

Nonrenewable resource

A naturally occurring resource whose quantity is diminished by use.


Forests that approximate the structure, composition, and functions of native forests prior to European settlement. They vary by forest type, but generally include more large trees, canopy layers, standing snags, native species, and dead organic matter than do young or intensively managed forests.


A small area of a particular ecological community surrounded by distinctly different ecological communities, such as a forest stand surrounded by agricultural lands or a small opening surrounded by forestland.

Patch dynamics

The process of recolonization by plant and wildlife species following the creation of a patch. Small patches and ones close to a source of plant and animal species will be recolonized faster than larger, more isolated patches.


Outward appearance or physical attributes of an organism resulting from both the effects of the environment and genetic makeup.

Pole stand

A stand of trees with dbh ranging from 5 to 9 inches.


A group of individuals of one plant or animal taxon (species, subspecies, or variety).

Precommercial thinning

The removal of trees (sapling to pole stage) to concentrate growth on desired trees; usually does not generate financial return.


A management philosophy or goal which seeks to protect indigenous ecosystem structure, function, and integrity from human impacts. Management activities are generally excluded from "preserved" forests.

Private forestland (PFL)

Forestland owned by a private individual, group, or corporation not involved in wood processing.

Rare species

Species which exist only in one or a few restricted geographic areas or habitats or occur in low numbers over a relatively broad area.


The reestablishment of forest cover by natural or artificial means on areas recently supporting forest cover.


The replacement of one forest stand by another as a result of natural seeding, sprouting, planting, or other methods; also young trees which will develop into the future forest.

Regeneration cut

A timber harvest designed to promote and enhance natural establishment of trees. Even-aged stands are perpetuated by three types of regeneration cuts: seed tree, shelter-wood, and clearcutting. Uneven-aged stands are perpetuated by selecting individual or small groups of trees for removal (e.g., the selection system).


Removal of overtopping trees to allow understory or overtopped trees to grow in response to increased light.

Renewable resource

A naturally occurring resource that is not reduced in quantity and ability for future use as a result of current use.


Growth of a new forest plant community.

Residual stand

Trees remaining following any cutting operation.

Riparian zone

An area adjoining a body of water, normally having soils and vegetation characteristic of flood-plains or areas transitional to upland zones. These areas help protect the water by removing or buffering the effects of excessive nutrients, sediments, organic matter, pesticides, or pollutants.


The planned time interval between regeneration cuts in a forest.

Salvage cut

The removal of dead, damaged, or diseased trees with the intent of recovering value prior to deterioration.


A small tree, usually defined as being between 2 and 4 inches dbh.


A log large enough to yield lumber. Usually the small end of a sawlog must be at least 6 to 8 inches in diameter for softwoods and 10 to 12 inches for hardwoods.

Second growth

The forests reestablished following the removal of virgin (i.e., previously unharvested) or old-growth stands. Most of Pennsylvania's forests are either second or third growth.

Seed tree cut

A regeneration cut where mature trees are left standing in a harvested area to provide seed for regeneration of the cut-over site.


A young tree originating from seed that is less than 4 feet tall and smaller than 2 inches in diameter at ground level.

Selection cut

A regeneration cut designed to create and perpetuate an uneven-aged forest. Trees may be removed singly or in small groups. A well-designed selection cut removes trees of lesser quality and trees in all diameter classes along with merchantable and mature high-quality sawlog trees. Should be differentiated from "select" or "selective" cuts, which often equate to high-grading.

Selective cut

A timber harvesting treatment in which the largest, most valuable trees are removed. Selective cuts often result in high-grading.


A regeneration cut designed to stimulate reproduction by removing all overstory trees. This is achieved by a series of cuts over several years. Gradual reduction of stand density protects understory trees and provides a seed source for stand regeneration.


The art, science, and practice of establishing, tending, and reproducing forest stands.


The combination of biotic, climatic, topographic, and soil conditions of an area; the environment at a location.

Site quality

The inherent productive capacity of a specific location (site) in the forest affected by available growth factors (light, heat, water, nutrients, anchorage); often expressed as tree height at a given age.

Skid road

Roads incorporating water control and erosion structures designed for frequent use by skidding equipment. Skid trail--trails used infrequently to drag logs to skid roads.


Branches, tops, and cull trees left on the ground following a harvest. Although some of this material can be used for firewood, slash may be arranged in brush piles to provide wildlife cover. Left scattered, slash can protect seedlings and sprouts from deer browsing and reduce soil erosion.


A standing dead tree with few branches, or the standing portion of a broken-off tree. Snags may provide feeding and/or nesting sites for wild- life.


A subordinate classification to a genus; reproductively isolated organisms that have common characteristics, such as eastern white pine or white-tailed deer.

Species richness

The number of species present in a community or a defined area.

Spring seep

A class of wetland created by groundwater emerging on lower slopes in small pools surrounded by vegetation. These create snow-free zones critical for wildlife feeding during winter.


A grouping of vegetation sufficiently uniform in species composition, age, and condition to be distinguished from surrounding vegetation types and managed as a single unit.

Stand analysis

The inventory of stands by species composition, average diameter, basal area, crown closure, regeneration, interfering plants, and tree quality to establish a baseline for silvicultural prescriptions. Stand analysis should occur before harvesting takes place.

Stewardship plan

A guide prepared by an approved natural resources professional that tells landowners what their resources are, what conditions they are in, and what can be done to help them achieve their goals.

Stream management zones

Areas adjacent to waterbodies where unique management strategies are applied to protect water quality and maintain stream temperature through shading. Zone width is normally 50 feet, but varies according to site.


The commercial value of standing trees.


The natural series of replacements of one plant community (and the associated fauna) by another over time and in the absence of disturbance.


Caring for the water and wildlife that rely on forests and working to ensure continuant and improved health of forest resources so that future generations receive the same or increased benefits.

Sustained yield

Historically, a timber management concept in which the volume of wood removed is equal to growth within the total forest. The concept is applicable to nontimber forest values as well.


The process of caring for the forest in such a way to ensure its sustainability while advancing the owner's objectives.


Removal of trees to encourage growth of other selected individual trees. May be commercial or precommercial.

Threatened species

A species likely to become endangered in the foreseeable future, throughout all or a significant portion of its range, unless protected.

Timber cruise

The process of estimating the quality, quantity, and characteristics of trees in a forest.


Forestland producing or capable of producing crops of industrial wood (more than 20 cubic feet per acre per year), and not withdrawn from timber utilization. Formerly known as commercial forestland.

Timber stand improvement (TSI)

A combination of intermediate treatments designed to improve growth and composition of the forest; often spoken of as TSI.


A characteristic of trees that describes the relative ability to thrive with respect to the growth factors (light, heat, water, nutrients, anchor- age). For instance, a "shade-tolerant" species may thrive at low light levels.


The smaller vegetation (shrubs, seedlings, saplings, small trees) within a forest stand, occupying the vertical zone between the over-story and the herbaceous plants of the forest floor.

Uneven-aged stand

A group of trees of various ages and sizes growing together on a site.

Urban forestry

The professional management of natural resources in and around urban areas, including trees and associated vegetation, wildlife, and open space.

Vernal or autumnal ponds

A class of wetland characterized by small, shallow, temporary pools of fresh water present in spring and fall, which typically do not support fish but are very important breeding grounds for many species of amphibians. Some species completely depend on such ponds; examples are spring peepers and mole salamanders.

Vertical structure

The arrangement of plants in a given community from the ground (herbaceous and woody shrubs) into the main forest canopy; a complex vertical structure is characterized by lush undergrowth and successive layers of woody vegetation extending into the crowns of dominant and codominant trees. (See crown class.)

Vertical Structure

Virgin forest

A forest that has never been harvested or altered by humans.


A region or area defined by patterns of stream drainage. A watershed includes all the land from which a particular stream or river is supplied.


Areas which are either transitional between land and water (where the water table is at or near the land surface) or areas of land which are covered by shallow water (such as marshes, swamps, bogs, and fens). Although only 2 percent of Pennsylvania remains as wetlands today, these areas fulfill an essential role in our landscapes by maintaining water quality, stabilizing shores and stream banks, controlling floods and erosion, and providing critical habitat to many plant and animal species.

Wolf tree

A large, excessively branchy tree which occupies more space in the forest than surrounding trees. Wolf trees have high wildlife and aesthetic value, but little if any timber value.


See forest.

Prepared by Lynnette S. Wimer, graduate assistant; James C. Finley, assistant professor of forest resources; Steven B. Jones, associate professor of forest resources; and Ellen M. O'Donnell, stewarship associate. Revised by Allyson Muth, stewardship associate.