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GUIDELINES for . . .
Spacer graphic Developing Stand Density Management Regimes

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      addition A mixed-stand structural condition where trees of a secondary tree species occupy a separate stand niche or stratum, thereby adding to the timber production of the primary tree species of the stand (e.g., where regeneration of a complementary species becomes established and grows beneath the crown canopy of an existing species).

      age class distribution A histogram of the area occupied by (timber volume represented by) distinct age classes (usually five or 10 year intervals) of growing stock within an area of forest land.

      average diameter The arithmetic mean of all tree diameters measured outside the bark, at breast height (1.3 m).

      biodiversity objective A type of management objective aimed at preserving or enhancing the presence and richness of species of plant, animal and other living organisms in all their forms and levels of organization (genes, species, communities), including the evolutionary and functional processes that link them.

      biogeoclimatic subzone A geographic area having similar patterns of energy flow, vegetation and soils as a result of a broadly homogeneous macroclimate, as categorized by the Biogeoclimatic Ecosystem Classification System of British Columbia.

      brush competition Non-commercially valued vegetation that impedes the survival, growth and production of commercially valuable tree species.

      brushing A general term for a range of silviculture activities designed to eradicate or reduce the growth of non-commercially valued vegetation in order to reduce its interference with the survival, growth and production of commercially valuable tree species.

      chainsaw effect 1) A reduction in the top height of a stand resulting from improper crop tree selection during juvenile spacing or commercial thinning; this effect lowers the vigour and timber production capacity of the residual stand. 2) An increase in average diameter caused by a low thinning (see definition for low thinning). This is an artifact of treatment, not a biological response to thinning.

      close utilization Harvesting the maximum volume of timber from a stand, as measured by the minimum stump height, stump diameter and top diameter of each tree harvested.

      clumping A spatial pattern of tree establishment where small groups, or clumps of trees are distributed throughout a stand, as opposed to random or even distribution of single trees.

      commercial thinning A partial cut in stands where the timber removed is sold; conducted in even-aged stands, provides an interim timber harvest during a stand rotation.

      community watershed A natural drainage area above the most downstream point of water diversion on a stream; water use is for human consumption and is licenced under the Water Act for either a waterworks or a domestic purpose if the licence is held by or is subject to the control of a water users' community incorporated under the Water Act; or an area designated as a community watershed under the Water Act.

      crossover volume response A timber volume response to thinning (pre-commercial or commercial) that eventually exceeds the volume production of a similar, unthinned stand.

      crown class A relative measure of the size and position of a tree's crown within the canopy of a stand; numerical or subjective categories of crown size and position have been defined (e.g., dominant, co-dominant, intermediate, overtopped).

      crown closure The point during the growth of an even-aged stand when the branches of adjacent trees make physical contact; a continuous canopy of tree foliage.

      crown competition The process of branch and foliage growth whereby trees compete for aerial growing space.

      culmination of mean annual increment The mean annual increment (MAI) of a stand increases for many years, then declines. The maximum MAI and age at which it culminates may be used to assess productivity and set rotation lengths that maximize volume production in perpetuity.

      decay inoculum The infectious spores, mycelia or mycorrhizae of decay-causing fungi.

      diameter at breast height (DBH) The bole diameter of a tree measured outside the bark at a height of 1.3 m.

      discount rate The rate of interest used to measure future expected costs and revenues in today's dollars; the rate of interest used for discounting is a function of social time preference, the opportunity cost of capital, and investment risk.

      dominant A qualitative measure of the size and height and of a tree's crown; a tree whose crown is receiving full light from above and partly from the sides, is larger than the average size of crowns in the stand, is well developed, although somewhat crowded on the sides.

      economic efficiency The level of production of economic goods and services with the lowest level of inputs (labour and capital) capable of producing only the amount of outputs demanded in the marketplace, at the highest attainable level of profit; a measure used to determine the optimum combination of inputs required to produce goods and services that meet both cost minimization and profit maximization objectives.

      economic rotation age The point in time (stand age) during the growth of a stand when the rate of increase of the net value of the stand begins to decline; the economic rotation age generally occurs before the physical rotation age (culmination of mean annual increment).

      espacement density The initial number of trees per unit area regenerated by planting, or by natural means after a reasonable seed-in period; often expressed as average inter-tree distance (i.e., distance between trees if square spacing is assumed).

      establishment density A density similar to espacement density (see espacement density above) except it may exclude trees removed in an early spacing operation.

      expected value A value that will be realized with some known level of probability in a future time period.

      feasibility analysis A method used to determine the net benefits from a given set of management activities; the benefits may be measured in either volume and/or value terms and the activities may occur in present and/or future time periods.

      fire-origin stand A stand which regenerates following a fire; usually consisting of tree species that rely on fire to regenerate.

      forest estate A collection of stands, of varying types, ages, etc., administered as an integrated unit and managed for some continuity or flow of harvest volume. For the purpose of this document, the forest estate is synonymous with the sustained-yield unit which includes timber supply areas, tree farm licences and woodlot licences.

      forest estate model A representation of the growth and natural dynamics of a pre-defined area of forest; used to simulate the effects of harvesting and silviculture on the long-term availability of timber supply from defined forest areas.

      forest-level objectives All definable timber and non-timber goods and services, values and activities for a specific bounded area of forest land over a specified period of time.

      free growing stand A stand of healthy trees of a commercially valuable species, the growth of which is not impeded by competition from plants, shrubs and other trees.

      gross production The total yield of timber biomass contained in the stems of all trees (living and dead) as measured by volume per unit area at a given age.

      growth and yield model One or more mathematical relationships which employ tree, stand and treatment (e.g., thinning) variables to project the growth and yield of stands.

      harvest constraints Limits imposed on a condition or activity within a forest estate; defined as part of an overall forest estate model; are usually defined by forest-level objectives.

      harvest scheduling flexibility The relative variability permitted in the order and timing of stand harvest activities in a forest estate model; defined by the interaction between forest-level objectives, harvest constraints, and the current and future conditions of the forest estate.

      height-diameter ratio The diameter (DBH) of a tree relative to its total height at a given age; a measure of tree slenderness and susceptibility to wind and snow pressures.

      height growth repression A condition that occurs in stands established at high density (usually greater than 10 000 trees/ha); results in a reduction in the rate of height growth of the stand compared to similar stands that are less dense; observed and documented in the species lodgepole pine.

      hemlock square A characteristic lumber dimension sawn for the Japanese export market; variable in dimension from 3.5 x 3.5 inches to 15 x 15 inches; a common end product from coastal BC sawmill operations.

      higher level plan Higher level plans establish the broader, strategic context for operational plans, providing objectives that determine the mix of forest resources to be managed in a given area.

      income distribution The allocation and disposition of wealth among individuals, households and businesses in an economy; policies and laws governing taxation and the collection of resource rents are designed to address issues related to income distribution in an economy.

      inflationary expectations The expected decline in the value of money over some future time period; determine the difference between the real rate of interest and the nominal (or money) rate of interest.

      inter-generational equity The distribution of resources and wealth between current generations and future generations of individuals; use and consumption of resources and creation of wealth affects the ability of future generations to consume resources and create wealth.

      intermediate A qualitative measure of the size and height of a tree's crown; a tree whose crown is shorter than trees in the stand classed as dominant or codominant, but extending into the crown cover formed by codominant and dominant trees; receiving a little direct light from above but none from the sides; usually with small crowns, and considerably crowded on the sides.

      inventory projection A method for tracking the stock and state (timber volume and distribution of stand age classes) of an area of forest over time; forms the basis for virtually all forest estate models.

      juvenile spacing (pre-commercial thinning) The removal of excess and undesirable trees from a stand before the thinnings have any commercial value.

      juvenile wood In some species, wood formed in the vicinity of the crown has different characteristics than that formed in the stem below. In most species, this juvenile wood has properties (e.g., low density, short fibres, low strength) that limit its utility. Juvenile wood occupies the central core of stand grown trees because, as the crown lifts and hormone concentrations drop, the increment added below the crown changes to mature wood. Juvenile wood is also called crown-formed wood or core wood. (See definition of mature wood).

      kerf The width of a saw blade used for cutting logs or cants into boards; displaces a certain amount of solid wood and thus affects the amount of solid wood produced in boards from a log or cant.

      landscape unit objective A landscape unit is defined by the district manager. It is generally an area of land up to 100 000 hectares in size delineated according to topographic or geographic features such as a watershed or series of adjacent watersheds. The district manager must establish objectives for a landscape unit, and may vary or cancel an objective.

      linear programming model A method for determining an optimal level of output from an activity - the optimal level of output is determined by the availability of conditions and inputs required to perform activities defined in the model; often used to define the timing and quantity of harvest levels that can be obtained from a forest estate while maintaining the forest in a condition that provides for all other defined forest values.

      low thinning A thinning regime in which the smaller trees are favoured for removal. Also known as "thinning from below."

      lumber recovery The ratio of the volume of sawn wood recovered from a log to the total volume of wood in the log.

      machine stress rated lumber (MSR lumber) Lumber that is graded according to stiffness as measured by a machine that correlates lumber stiffness to measured modulus of elasticity.

      management unit plans A forest management plan approved under a tree farm licence or a woodlot licence, usually in effect for a period of five years and specifies proposed management activities to establish, tend, protect and harvest timber resources, and to conserve other resource values.

      mathematical programming model A model based on mathematical algorithms or sets of equations designed to solve a problem based on a pre-defined set of assumptions and starting conditions; a linear programming model is a type of mathematical programming model.

      mature wood In some species, wood formed below the crown has superior cell structure than "juvenile wood" laid down in the vicinity of the crown. As the tree grows and the crown lifts, an outer sheath of mature wood of somewhat higher strength is formed. It extends from ground level to a point near the base of the crown. See definition of juvenile wood.

      maximum density A Forest Practices Code requirement that silviculture prescriptions define the maximum density or upper limit of density for stands to be declared as free growing. Areas exceeding this density must be spaced as part of basic silviculture obligations.

      mean annual increment (MAI) The arithmetic average annual change in the volume of a stand from establishment to a given point in time (MAI = volume/age).

      merchantability standard The minimum top diameter, minimum diameter at breast height, and maximum stump height that defines a merchantable tree.

      microsite The aerial, surface and underground environment in immediate proximity to a seedling or tree; includes the immediate climatic, sunlight, soil nutrition, soil moisture and surrounding vegetation conditions within a few metres of a tree.

      monoculture A stand consisting predominantly of a single-tree species.

      natural disturbance type An area whose soil and vegetation is influenced by a natural disturbance regime.

      net present value (NPV) The sum of all discounted costs and revenues expected over the life of an investment; in forestry, the investment period is usually the rotation length.

      non-timber values Dollar values and/or quantities of natural resources that are not priced or traded in markets, including wildlife, wilderness, scenic views and the utility derived from a wide variety of outdoor activities.

      nutrient cycling The chemical, biological and climatic factors that cause various elements and chemical compounds to be transported through the atmosphere, soil, water, groundwater, dead and decaying matter, plants and animals.

      oligopolistic A market behaviour characterized by a few large firms acting as sellers of goods or services; characterized by demand conditions being affected by each firm's output decisions, resulting in a conscious interaction among firms, leading to a variety of forms of strategic behaviour in production and output decisions.

      opportunity cost of capital The amount a firm must pay to the owners of capital in order to attract the capital (or other factor of production) necessary to engage in the firm's business. The firm must pay the owners of the capital an amount sufficient to induce them to sacrifice the next best alternative use of the capital, which is generally the going market price of the capital, or other factor of production.

      overtopped A qualitative measure of the size and height of a tree's crown; a tree whose crown is entirely below the general level of the canopy, receiving no direct light either from above or from the sides; also called "suppressed."

      parallel volume response A thinned stand whose rate of volume increment continues to accrue at the same rate as a similar unthinned stand, but whose volume yield is reduced by the volume removed in the thinning.

      pre-commercial thinning (juvenile spacing) The removal of excess and undesirable trees from a stand before the thinnings have any commercial value.

      present value The value of some future expenditure, revenue or future series of expenditures and/or revenues discounted at some rate to the value of them in the present period.

      prime trees The 250 trees of largest diameter in a stand at a particular age; the actual membership of trees classed as prime trees may change over time.

      product values The market values of end products produced or expected to be produced after a stand is harvested.

      production economics The theory of the behaviour and decisions of firms that produce goods and services demanded by consumers.

      provenance The geographic source or race from which seed or other tree propagules were obtained.

      real price change The per cent change in market price of goods or services over some time period over and above any change in its price due to inflation; is a reflection of the change in the scarcity of goods or services over time.

      repressed stand A stand in which the height growth of all trees is impaired by high establishment density, and thereby fails to exploit the actual productivity potential of the site; has been documented in BC in dense stands of lodgepole pine greater than 10 000-15 000 trees/ha.

      resource management objectives A statement of intent to ensure the maintenance or production of some level of timber and/or non-timber resources from the area of forest to which the resource management objective applies. The resource management objective may also be defined by a resource management zone, and the chief forester may designate a resource management objective and/or zone as a higher level plan.

      riparian area Also known as a riparian management area; an area of a width determined in accordance with Part 10 of the Operational Planning Regulation of the Forest Practices Code of British Columbia Act, that is adjacent to a stream or wetland or a lake with a riparian class of L2, L3 or L4, and consists of a riparian management zone, and depending on the riparian class of the stream, wetland or lake, a riparian reserve zone.

      rotation age The actual or expected age of a stand when it is harvested.

      sensitivity analysis A method used to determine the relationships between measures and assumptions used in an analysis, and to determine the effects of changing the value of measures and assumptions on the results of an analysis; is usually conducted by recalculating an analysis a number of times each with a change in one measure or assumption at a time.

      shade intolerance A characteristic of plants that describes their propensity to establish and grow in direct or full sunlight conditions.

      shade tolerance A characteristic of plants that describes their propensity to establish and grow under indirect or reduced light conditions most often in the shade of other plants growing around or above them.

      silviculture prescription (SP) A site-specific plan that describes the forest management objectives for an area; must be consistent with any higher level plan that encompasses the area to which the prescription applies; identifies the method for harvesting the existing forest stands and a series of silviculture treatments that will be carried out to establish a free growing crop of trees in a manner that accommodates other resource values as identified; subsequent documents, including cutting authorities and logging plans, must follow the intent and meet the standards specified in the silviculture prescription.

      silviculture regime A series of carefully sequenced and implemented activities at specific time periods and intensities to achieve desired objectives.

      simulation model An integrated set of equations and numerical techniques that mimic the relationships and development of actual systems (e.g., trees, stands, forests).

      site occupancy The degree to which available growing space is utilized by trees.

      site preparation An activity or set of activities which enables the regeneration of a new stand or enhances the survival and growth of regeneration.

      site value (or soil expectation value) The sum of the discounted values of all costs and revenues over an infinite series of investment periods (rotations) of equal length.

      slash The tree tops, branches and other coarse woody debris remaining on the ground after a logging or thinning activity.

      social welfare objectives Government objectives that address the distribution of income or wealth in society; for silviculture in British Columbia, this has meant using silviculture activity as an economic development tool to provide employment in the forest; government can distribute income to silviculture contractors by providing funds for stand density management activities; in this context, it is important to distinguish between wealth generation and redistribution of wealth.

      stand A contiguous group of trees sufficiently uniform in species composition, arrangement of age classes, and condition to be a homogeneous and distinguishable unit.

      stand density management Silviculture activities that alter the quantity and distribution of trees in a stand including espacement, pre-commercial thinning (juvenile spacing) and commercial thinning.

      stand density management diagram A graphical depiction of the relationships between stand density, top height, quadratic mean diameter and mean tree volume.

      stand management prescription (SMP) A site-specific plan describing the nature and extent of silviculture activities planned for a free growing stand of trees to facilitate the achievement of specified or identified social, economic or environmental objectives.

      stand table A tabular display of the number of trees in a stand by diameter class.

      stock table The tabular counterpart to a stand table that displays stand volume by diameter class.

      stocking guide Output from growth and yield projections in the form of a look-up table; displays average values of parameters such as tree volume, average diameter and average height.

      stocking standard The recommended number of seedlings that should be planted per unit area; may also recommend the type of seedling or planting stock, when or how the planting should be conducted, and the types of sites suited to different stocking standards.

      stump height The height above ground of the remaining portion of the stem of a tree after it has been harvested; stump heights are regulated as part of the utilization standard.

      substitution A mixed-species stand resulting from a one-to-one substitution of trees of a monoculture with trees of another species so the total stand density remains constant.

      sunk cost A cost that does not affect the decision to make a further or additional expenditure; an example of a sunk cost in forestry is the cost of planting in relation to a thinning investment; the planting cost does not affect the decision of whether or not to incur a thinning cost since the thinning cost is compared to a regime where no thinning takes place (in order to be comparable, both regimes must either assume a planting cost or no planting cost).

      taper The rate at which the diameter of a tree changes relative to its height over the length of the stem. Taper is affected by the density of the stand; the less dense the stand, the greater the amount of taper.

      tree vigour The general health of a tree; affected by genetic potential and natural growing conditions such as climate and soil, as well as by biotic factors such as competition for resources from other plants, and pathogens such as insects and diseases.

      variable growth intercept method A technique for determining site index for a young stand from measurements of height growth above breast height; ideally suited to stands that are 2-3 m tall until they are about 30 years old; growth intercept models have been developed for western hemlock, interior spruce, lodgepole pine, Sitka spruce and Douglas-fir.

      visual buffer An area of usually mature, undisturbed forest or a topographic feature such as a hill that masks harvesting disturbances such as recent clearcut areas.

      visual quality objective (VQO) Defines a level of acceptable landscape alterations resulting from timber harvesting and other activities; visual quality classes have been defined in BC on the basis of the maximum amount of alteration permitted in a given area over a given period of time.

      wildlife tree A tree or group of trees that are identified in an operational plan designated to provide present or future wildlife habitat.

      wood quality A general term encompassing a wide range of physical wood properties and parameters that affect the end use and value of wood products; wood quality characteristics can be inherent to particular species, but are also influenced by tree growing conditions, and are also defined by end-use requirements; wood quality parameters include basic density, fibre length, juvenile wood content, fibril angle, compression wood, knot size, frequency and distribution, grain, ring width, and quantity and type of extractives.

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Copyright 1999 Province of British Columbia
Forest Practices Branch
BC Ministry of Forests
This page was last updated January 1999

Comments to: Tim Ebata <>