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Forestry Terms  - T -

T & E SPECIES HABITAT: Those areas currently or potentially occupied or utilized by threatened and endangered species.

  • Critical Habitat: Those areas officially designated by the Secretary of
  • Interior or Commerce as needed for survival and recovery of listed species.
  • Proposed Critical Habitat: Those areas officially proposed for designations as critical habitat by the Secretary of Interior or Commerce.
  • Occupied Habitat: Those areas currently occupied or utilized by threatened and endangered species.
  • Potential Habitat: Areas of historic habitat not currently occupied or designated as critical that could potentially contribute to the recovery of threatened and endangered species.

TEMPERATURE, AMBIENT: The hourly air temperature of the surrounding area.

TEMPERATURE, WATER: A measure of water temperature heterogeneity.

THINNING - A tree removal practice that reduces tree density and competition between trees in a stand. Thinning concentrates growth on fewer, high-quality trees, provides periodic income, and generally enhances tree vigor. Heavy thinning can benefit wildlife through the increased growth of ground vegetation.

THOUSAND BOARD FEET -Unit of measurement equal to 1,000 feet of wood having a thickness of 1 inch.

TIMBER -General term applied to forests and their products.
-Sawed lumber more than 4 by 4 inches in breadth and thickness.

TIMBER APPRAISAL -Economic appraisal of the monetary value of a timber stand.

TIMBER PRODUCTS OUTPUT (TPO) -Timber products cut from roundwood and byproducts of wood-manufacturing plants. Roundwood products include logs, bolts, or other round sections cut from growing stock trees, cull trees, salvable dead trees, trees on nonforest land, noncommercial species, sapling-size trees, and limbwood. Byproducts from primary manufacturing plants include slabs, edging, trimmings, miscuts, sawdust, shavings, veneer cores and clippings, and screenings of pulp mills that are used as pulp chips or other products.


TIMBER TREATMENT OPPORTUNITY CLASS: A class to identify the physical opportunity for increasing timber production.

TIME SINCE DISTURBANCE: The number of years between when the most recent disturbance took place (STAND HISTORY) and the time of plot establishment.

TIMBER STAND IMPROVEMENT (TSI) - Improving the quality of a forest stand by removing or deadening undesirable species to achieve desired stocking and species composition. TSI practices include applying herbicides, burning, girdling, or cutting.

TOLERANT SPECIES - A species of tree that has the ability to grow in the shade of other trees and in competition with them.

TOTAL DISSOLVED SOLIDS: A measure of total filterable residue in water. Expressed as mg/l.


TRAFFIC LANES: Numeric code indicating the number of traffic lanes contained within the traveled way of an existing road management section.

TREE: A woody plant usually having one or more perennial stem at least 3 inches d.b.h. at maturity, a more or less definitely formed crown of foliage, and a height of at least 16 feet at maturity.

TREE AGE: The total age of the above ground stem of the tree in years (not the age of the rootstock or the total age from seed). Total age is usually the annual ring count to the pith of the tree at breast height plus an estimate of the number of years it took the tree to reach breast height. This must be an estimate based on local knowledge.

TREE CLASS: The overall quality of live trees 1.0 inches d.b.h. and larger.

  • Growing Stock: Merchantable tree.
  • Rough Cull Tree: Tree that does not meet regional merchantability standards because of excessive sound cull. May include noncommercial tree species.
  • Rotten Cull Tree: Tree that does not meet regional merchantability standards because of excessive unsound cull. May include noncommercial tree species.

TREE FARM - A privately owned forest or woodland in which timber crop production is a major management goal. Many tree farms are officially recognized by the American Tree Farm System, an organization sponsored by the American Forestry Council.

TREE HISTORY: A classification of the current status (living or dead) of a tally tree.

Live trees:

  • Survivors: At initial measurement: any live tree on a plot. At remeasurement: survivor--tree previously measured and still living.
  • Ingrowth: At remeasurement: ingrowth--newly established seedling or a tree that passed the minimum size for measurement since the previous measurement.
  • Ongrowth: At remeasurement: -- a tree not previously measured or previously measured on a smaller plot or with some different sampling probability which has by the time of remeasurement grown enough to be measured on a larger plot or with a different sampling probability.

Dead trees:

  • Cut Trees: At initial measurement: A tree cut within the last n years. The number of years, n, within which cut trees are counted will be determined by field units. At remeasurement: a tree present and alive at previous measurement but since cut.
  • Nonsalvable mortality: At initial measurement: A tree found dead and judged to have died within the past n years. The number of years, n, will be determined by Regions. At remeasurement: a tree of any size which was alive at the previous measurement, but has since died.
  • Salvable mortality: At initial measurement: A tree found dead, judged to have died within the past n years and which, at the time of inventory met the growing stock standards for merchantability. At remeasurement: a tree alive at previous measurement and has since died; at time of death it would meet the growing-stock standards for merchantability.

TREE LENGTH (Height): The total span of a tree from ground level along bole to tip of tree. -Entire tree, excluding the unmerchantable top and limbs.

TREE-LENGTH LOGGING -Felling and transporting the trimmed bole in one piece, whenever possible, for crosscutting at a landing or mill.
-Unbucked, limbed, and topped trees.

TREE SPACING - The distance between trees, which is most often regulated at the time of planting or during a harvest or thinning operation. Spacing, like stand density, affects understory vegetation, seed production, growth rate, and wildlife habitat.

TREE TOP CONDITION: An indication as to whether or not the top of the tree is intact. Use for volume estimates.

  • Intact live top.
  • Broken top.
  • Intact dead top. Because tops may be either dead or merely defoliated, use this category with caution.

TREE VOLUME: The amount of wood in a tree. This may be expressed in board feet or cubic feet. It may be gross volume or net volume (gross less defects).