Age Class (Cohort)

A distinct aggregation of trees originating from a single natural event or regeneration activity, or a grouping of trees, e.g. 10-year age class, as used in inventory or management.

Artificial Regeneration (Reproduction)

An age class created by direct seeding or by planting seedlings or cuttings.

Basal Area

The area of the cross section of a tree stem, including the bark, generally at breast height (4.5 feet above the ground).

Canopy

the foliar cover in a forest stand consisting of one or several layers

Canopy Closure

see Crown Cover

Cleaning

A release treatment made in an age class not past the sapling stage in order to free the favored trees from less desirable individuals of the same age class which overtop them or are likely to do so (see Improvement Cutting, Liberating, Weeding).

Crop Tree

Any tree that is selected to become a component of a future commercial harvest.

Crown

The part of a tree or woody plant bearing live branches and foliage.

Crown Class

A class of tree based on crown position relative to the crowns of adjacent trees.

Emergent

Trees with crowns completely above the general level of the main canopy receiving full light from above and from all sides.

Dominant

Trees with crowns extending above the general level of the main canopy of even-aged stands or, in uneven-aged stands, above the crowns of the tree's immediate neighbors, and receiving full light from above and partly from the sides.

Codominant

Trees with crowns forming the general level of the main canopy in even-aged stands or, in uneven-aged stands, the main canopy of the tree's immediate neighbors, receiving full light from above and comparatively little from the sides.

Intermediate

Trees with crowns extending into the lower portion of the main canopy of even-aged stands or, in uneven-aged stands, into the lower portion of the canopy formed by the tree's immediate neighbors, but shorter in height than the codominants.  They receive little direct light from above and none from the sides.

Crown Density

The amount and compactness of foliage of the crowns of trees and/or shrubs.

Cutting Cycle

The planned interval between partial harvests in an uneven-aged stand (see Thinning Interval).

Even-Aged Stand

A stand of trees containing a single age class in which the range of tree ages in usually less than 20 percent of rotation.

Even-Aged System

A planned sequence of treatments designed to maintain and regenerate a stand with one age class.  The range of tree ages is usually less than 20 percent of the rotation.  (see Clearcutting, Seed Tree, Shelterwood, Coppice.)

Harvesting Method

A cutting method by which a stand is logged.  Emphasis is on meeting logging requirements while concurrently attaining silvicultural objectives (see Regeneration Methods).

Improvement cutting

A cutting made in a stand pole-sized or larger primarily to improve composition and quality by removing less desirable trees of any species (see Cleaning, Liberating, and Weeding).

Intermediate Treatments (Tending)

a collective term for any treatment designed to enhance growth, quality, vigor, and composition of the stand after establishment or regeneration and prior to final harvest (see Tending, Stand Improvement).

Liberating

A release treatment made in a stand not past the sapling stage in order to free the favored trees from competition of older, overtopping trees.

Nurse Tree (Nurse Crop)

A tree, group or crop of trees, shrubs or other plants, either naturally occurring or introduced, used to nurture, improve survival or improve the form of a more desirable tree or crop when young by protecting it from frost, insolation, or wind.

Overstory Removal

The cutting of trees comprising an upper canopy layer in order to release trees or other vegetation in an understory (see Clearcutting).

Pole

A tree between the size of a sapling and a mature tree.

Precommercial Thinning (PCT)

A thinning that does not yield trees of commercial value, usually designed to reduce stocking in order to concentrate growth on the more desirable trees.

Reforestation

The natural or artificial restocking of an area with trees (syn. Regeneration).

Regeneration

Seedling or saplings existing in a stand; or the act of establishing young trees naturally or artificially (syn. Reforestation).

Regeneration (Reproduction) Method

A cutting method by which a new age class is created.  The major methods are Clearcutting, Seed Tree, Shelterwood, Selection, and Coppice (see Harvesting Method).

Coppice Methods

Methods of regenerating a stand in which the majority of regeneration is from stump sprouts or root suckers.

Coppice

A method of regenerating a stand in which all trees in the previous stand are cut and the majority of regeneration is from sprouts or root suckers.

Coppice with Reserves

A coppice method in which reserve trees are retained to attain goals other than regeneration.  The method normally creates a two-aged stand.

Even-Aged Methods

Methods to regenerate a stand with a single age class.

Clearcutting

A method of regenerating an even-aged stand in which a new age class develops in a fully-exposed microclimate after removal, in a single cutting, of all trees in the previous stand.  Regeneration is from natural seeding, direct seeding, planted seedlings, and/or advance reproduction.  Cutting may be done in groups or patches (Group or Patch Clearcutting), or in strips (Strip Clearcutting).  In the Clearcutting system, the management unit or stand in which regeneration, growth, and yield are regulated consists of the individual clearcut stand (see Group Selection).  When the primary source of regeneration is advance reproduction, the preferred term is Overstory Removal.

Clearcutting with Reserves

Seed Tree

An even-aged regeneration method in which a new age class develops from seeds that germinate in fully-exposed micro-environments after removal of all the previous stand except a small number of trees left to provide seed.  Seed trees are removed after regeneration is established.

Shelterwood

A method of regenerating an even-aged stand in which a new age class develops beneath the moderated micro-environment provided by the residual trees.  The sequence of treatments can include three distinct types of cuttings:  1) an optional preparatory cut to enhance conditions for seed production; 2) an establishment cut to prepare the seed bed and to create a new age class; and 3) a removal cut to release established regeneration from competition with the overwood.  Cutting may be done uniformly throughout the stand (Uniform Shelterwood), in groups or patches (Group Shelterwood), or in strips (Strip Shelterwood).

Shelterwood with Reserves

Two-Aged Methods

Methods designed to maintain and regenerate a stand with two age classes.  In each case the resulting stand may be two-aged or tend towards an uneven-aged condition as a consequence of both an extended period of regeneration establishment and the retention of reserve trees that may represent one or more age classes.

Clearcutting with Reserves

A clearcutting method in which varying numbers of reserve trees are not harvested to attain goals other than regeneration.

Seed Tree with Reserves

A seed tree method in which some or all of the seed trees are retained after regeneration has become established to attain goals other than regeneration.

Shelterwood with Reserves

A variant of the Shelterwood Method in which some or all of the shelter trees are retained, well beyond the normal period of retention, to attain goals other than regeneration.

Uneven-Aged (Selection) Methods

Methods of regenerating a forest stand, and maintaining an uneven-aged structure, by removing some trees in all size classes either singly, in small groups, or in strips.

Group Selection

A method of regenerating uneven-aged stands in which trees are removed, and new age classes are established, in small groups.  The maximum width of groups is approximately twice the height of the mature trees, with small openings providing micro-environments suitable for tolerant regeneration and the larger openings providing conditions suitable for more intolerant regeneration.  In the Group Selection System, the management unit or stand in which regeneration, growth, and yield are regulated consists of a landscape containing an aggregation of groups (see Clearcutting).

Group Selection with Reserves

A variant of the Group Selection Method in which some trees within the group are not cut to attain goals other than regeneration within the group.

Single Tree Selection

A method of creating new age classes in uneven-aged stands in which individual trees of all size classes are removed more-or less uniformly throughout the stand to achieve desired stand structural characteristics.

Regeneration (Reproduction) Period

The time between the initial regeneration cutting and the successful re-establishment of a new age class by natural means, planting, or direct seeding.

Regular Uneven-Aged (Balanced)Stand

A stand in which three or more distinct age classes occupy approximately equal areas and provide a balanced distribution of diameter classes.

Release (Release Operation)

A treatment designed to free young trees from undesirable, usually overtopping, competing vegetation.  Treatments include cleaning, liberating, and weeding (see Stand Improvement).

Reserve Trees (Green Tree Retention)

Trees, pole-sized or larger, retained in either a dispersed or aggregated manner after the regeneration period under the Clearcutting, Seed Tree, Shelterwood, or Coppice Methods (syn. Standards).

Sapling

A tree, usually young, that is larger than a seedling but smaller than a pole.  Size varies by region.

Silviculture

The art and science of controlling the establishment, growth, composition, health, and quality of forests and woodlands to meet the diverse needs and values of landowners and society on a sustainable basis.

Silvicultural System

A planned processes whereby a stand is tended, harvested, and re-established.  The system name is based on the number of age classes (see Even-Aged, Two-Aged, Uneven-Aged), and/or the regeneration method used (see Clearcutting, Seed Tree, Shelterwood, Selection, Coppice, Coppice with Reserves).

Site Index

A measure of actual or potential forest productivity expressed in terms of the average height of a certain number of dominants and co-dominants in the stand at an index age.

Site Quality (Productivity)

The productive capacity of a site, usually expressed as volume production of a given species.

Size Class

Tree size recognized by distinct ranges, usually of diameter or height.

Snag

A standing dead tree from which the leaves and most of the branches have fallen.

Stand

A contiguous group of trees sufficiently uniform in age class distribution, composition, and structure, and growing on a site of sufficiently uniform quality, to be distinguishable unit (see Mixed, Pure, Even-Aged, and Uneven-Aged Stands).

Mixed Stand

A stand in which there is a mixture of species.

Pure Stand

A stand composed of essentially a single species.

Stratified Mixture

A stand in which different species occupy different strata of the total crown canopy.

Stand Density

A quantitative, absolute measure of tree occupancy per unit of land area in such terms as numbers of trees, basal area, or volume.

Stand Improvement

A term comprising all intermediate cuttings made to improve the composition, structure, condition, health, and growth of even- or uneven-aged stands.

Stocking

An indication of growing-space occupancy relative to a pre-established standard.  Common indices of stocking are based on percent occupancy, basal area, relative density, and crown competition factor.

Stratum (Canopy Layer)

A distinct layer of vegetation within a forest community.

Structure

The horizontal and vertical distribution of components of a forest stand including the height, diameter, crown layers and stems of trees, shrubs, herbaceous understory, snags, and down woody debris.

Succession

A series of dynamic changes by which organisms succeed one another through a series of plant community (seral) stages leading to potential natural community or climax.

Thinning

A cultural treatment made to reduce stand density of trees primarily to improve growth, enhance forest health, or to recover potential mortality.

Crown Thinning (Thinning from Above, High Thinning)

The removal of trees from the dominant and codominant crown classes in order to favor the best trees of those same crown classes.

Free Thinning

The removal of trees to control stand spacing and favor desired trees using a combination of thinning criteria without regard to crown position.

Low Thinning (Thinning from Below)

The removal of trees from the lower crown classes to favor those in the upper crown classes.

Mechanical Thinning (Geometric Thinning)

The thinning of trees in either even- or uneven-aged stands involving removal of trees in rows, strips, or by using fixed spacing intervals.

Selection Thinning (Dominant Thinning)

The removal of trees in the dominant crown class in order to favor the lower crown classes.

Thinning Interval

The period of time between successive thinning entries, usually used in connection with even-aged stands (see Cutting Cycle).

Tolerance Shade

The relative capacity of a plant to become established and grow beneath overtopping vegetation.

Two-Aged Stand

A stand composed of two distinct age classes that are separated in age by more than 20 percent of rotation.

Two-Aged System

A planned sequence of treatments designed to maintain and regenerate a stand with two age classes.

Uneven-Aged Stand

A stand of trees of three or more distinct age classes, either intimately mixed or in small groups.

Uneven-Aged System

A planned sequence of treatments designed to maintain and regenerate a stand with three or more age classes (see Single Tree Selection, Group Selection).

Weeding