Glossary

Below are definitions of terms used in this web module. Some of these definitions have been adapted from the following sources, which are recommended as further reading:


Helms, J.A. (ed). 1998, The Dictionary of Forestry. Society of American Foresters, Bethesda, MD. http://dictionaryofforestry.org/

Hanley, D.P., D.M. Baumgartner, and L. Charbonneau. Revised 2006. Terminology for Forest Landowners. Washington State University Extension Bulletin EB1353. Washington State University, Pullman, WA. http://cru.cahe.wsu.edu/CEPublications/eb1353/eb1353.pdf

  • Acre – A unit of land area measurement used in the United States. An acre is 43,560 square feet, (a square with sides equal to 208.71 feet) which is equivalent to an area 1 chain wide by 10 chains long. There are 640 acres in a square mile.
  • Acreage measuring grid – A grid or series of evenly spaced dots that are often printed on clear plastic and used to measure area on a map.
  • Azimuth – A direction expressed in the degrees of a circle that starts with north at 0° and proceeds clockwise to east (90°), south (180°), west (270°), and back to north (360°). Also refers to a style of compass in which directions are expressed as azimuths (in contrast to a quadrant style compass)
  • Basal area - The cross-sectional area of a tree trunk at breast height. The combined basal area of all the trees in a stand on a per acre basis is a function of both the number and size of trees in the stand. As such, it is a measure of the overall level of competition in the stand and is sometimes used to determine whether a stand should be thinned.
  • Basal area factor (BAF) – A calibration factor for prisms (either glass wedge or keyhole) that relates each “in” tree in a variable plot to a total amount of basal area in the stand (e.g. a BAF of 30 means that each “in” tree represents 30 square feet of basal area in the stand as a whole).
  • Base age – The age on which a site index is based, usually 50 or 100 years. For example, a site index with a base age of 50 would tell you how tall the dominant trees can be expected to be at age 50.
  • Board foot – A unit of wood volume measuring 1 foot x 1 foot x 1 inch. Board foot volume is often expressed in terms of thousands of board feet, which is abbreviated as Mbf.
  • Breast height – 4.5 feet (54 inches) above the ground on the uphill side of the tree. This is the standard location for measuring tree diameter, basal area, and age.
  • Breast height age – The age of a tree measured 4.5 feet above the ground on the uphill side of the tree (breast height). Breast height age is not the total age of the tree, as it does not include the number of years it took for the tree to reach breast height.
  • Chain – A length of 66 feet. There are 80 chains in a mile.
  • Circular plot – A sample plot that is in the shape of a circle (rather than a square or rectangle).
  • Circumference – The length of the outer edge (perimeter) of a circle.
  • Clinometer – An instrument for measuring tree heights by measuring vertical angles between your eye and the top and bottom of the tree.
  • Competition – The fight for resources (light, water, nutrients) among neighboring trees.
  • Conifers – Cone-bearing trees. Examples include pine, fir, hemlock, spruce, cedar, and larch.
  • Cubic foot – A unit of wood volume that is 1 foot x 1 foot x 1 foot. Cubic foot values in LMS include all the wood volume in a tree, including parts that may not merchantable (salable for products).
  • Diameter – The width of a circle or cylinder.
  • Diameter at breast height (DBH) – The width of the trunk of a tree measured 4.5 feet above the ground on the uphill side of the tree (breast height).
  • Diameter tape – A special measuring tape that has been calibrated such that when you wrap it around the circumference of the tree, you are actually reading the measurement in diameter units (i.e. the measurements have been divided by the constant Pi).
  • Dominant tree – A tree whose crown rises above the general level of the forest canopy.
  • Expansion factor - Converts values (number, basal area, volume, etc.) from an individual tree basis to a per acre basis. For example, if you have 1 tree with an expansion factor of 10, that tree represents 1 x 10 = 10 trees per acre.
  • Extrapolate – To use information about something that is known to make inferences about something that is unknown (e.g. to use known values from sample plots to make inferences about unknown values for a forest stand as a whole).
  • Fixed area plot – A sample plot that has a defined size (e.g. 1/10th acre).
  • Furlong – A length of 10 chains, or 660 feet.
  • Geographic north – This is the “true” north (i.e. the North Pole), on which maps are based. It is different than magnetic north, which is located in the Canadian Arctic and shifts over time. Declination is the difference between magnetic and geographic north. Compasses should be adjusted for declination so that they will point to geographic north.
  • Glass wedge prism – A piece of glass that has been specially cut to deflect light and displace the image of a tree when looked at through the prism. It is used to determine whether a tree is “in” a variable radius plot.
  • Growth cycle – The time increment in which LMS “grows” trees (either 5 or 10 years).
  • Growth model – Computer programs that predict the growth of trees over time. Growth models are core components of LMS.
  • Hardwoods – Broadleaf (usually deciduous) trees. Examples include maple, hickory, oak, alder, ash, elm, birch, etc.
  • Increment borer – A tool resembling a drill that is used to extract an increment core from a tree, allowing the user to count annual rings and determine tree age in a non-destructive manner.
  • Increment core – A thin piece of wood extracted from the stem of a tree by an increment borer for counting the annual rings to determine tree age.
  • Keyhole prism – A tool with different-sized openings to look through to determine whether a tree is “in” a variable plot.
  • Landscape Management System (LMS) – LMS is a unique and innovative program that will allow you to work with your inventory data to generate statistics about your forest, create representative images of your forest, predict how your forest will grow and change over time, and even experiment with different management alternatives. For more information and free software downloads, visit http://lms.cfr.washington.edu/.
  • Live crown ratio – The proportion of the height of a tree that has live foliage.
  • Logger’s tape – A retractable tape that typically comes in 50-, 75-, and 100-foot lengths, has distance measurements (usually in feet and 1/10th’s of feet) on one side, and is a diameter tape on the other.
  • Magnetic north – This is the “north” that a compass needle will point to. Magnetic north is located in the Canadian Arctic and shifts over time. Maps are based on geographic (true) north, which is located at the North Pole. Declination is the difference between magnetic and geographic north. Compasses should be adjusted for declination so that they will point to geographic north.
  • Merchantable cubic feet – Cubic foot volume that only includes the merchantable (salable for products) parts of the tree.
  • Overstory – The trees in a stand that form the upper canopy of the forest.
  • Pacing – Counting your steps to measure distance. Every other step (one complete stride) is counted as one pace (e.g. every time your right foot hits the ground).
  • Percent slope – The change in vertical elevation per 100 feet of horizontal distance.
  • Pi – A constant with the approximate value of 3.14 that represent the ratio between the circumference and the diameter of a circle or cylinder.
  • Planting file – A file that tells LMS how to simulate tree planting; specifically the size, species, and number of trees that are expected to be on the site one growth cycle after planting.
  • Plot boundary – The outer edge or perimeter of a fixed area plot. Trees that fall within the boundary are considered “in” the plot.
  • Plot radius – The distance between the plot center and the outer edge (plot boundary).
  • Plot sampling – A method for measuring a large forested area (e.g. a stand) without having to measure each individual tree. Measurements are taken in small areas, called sample plots, which are distributed throughout the larger area. The measurements from these plots are combined and used to represent the larger area as a whole.
  • Portfolio – An LMS dataset that includes the inventory data for one or more stands.
  • Proportional thin – A thinning in which trees are removed equally from all size classes.
  • Quadrant – A style of compass in which directions are divided into 4 quadrants, each reading from 0º (starting with north or south) to 90º (ending at east or west).
  • Quadratic mean diameter (QMD) – The diameter of a tree with average basal area. With QMD, the average diameter will be weighted toward the larger, overstory trees (which are usually of more interest from a management perspective). If the quadratic mean diameter is significantly different from the average diameter, it is an indication that there are many very small trees mixed with a few larger ones.
  • Reference point – An identifiable location on the ground (such as a clearing, bend or intersection of a road, etc.) used as the starting point for sample plot grid.
  • Sample bias – A situation in which sample plots do not accurately represent the larger area as a whole.
  • Sample plot – A small area that is used to represent a larger area (e.g. a stand). When doing a forest inventory, only the trees in these small areas are measured, rather than every tree in the stand (see also plot sampling).
  • Scale – Corresponds the units on a map or aerial photo to actual distance on the ground. For example, 1 inch = 1,000 feet.
  • Scribner scale – A protocol for measuring how many board feet of lumber could be created from a log. Scribner is one of several different protocols that exist.
  • Silvicultural treatment – A forest management activity such as thinning, harvesting, planting, pruning, etc.
  • Site index – A measure of forestland quality or productivity for a given species based on the average expected height of the dominant trees at a given base age (usually 50 or 100 years). For example, a 50-year Douglas-fir site index of 120 means that at age 50, the dominant Doulas-fir trees would be expected to be 120 feet tall.
  • Snag – A standing, dead tree.
  • Spacing – How far apart trees are in the forest.
  • Species composition – The mixture of tree species (and their relative proportions) present in a stand.
  • Stand – A distinct, recognizable management unit of the forest consisting of a contiguous area that is relatively uniform in species composition, age, structure, etc.
  • Stand density index (SDI) – A measure developed by Reineke (1933) that measures the density of a stand relative to a standard level of competition.
  • Stand Visualization System (SVS) – A computer program that can create computer-generated images of a forest based on inventory. SVS is a component of LMS.
  • Step size – The time increment in which LMS “grows” trees (either 5 or 10 years). This is the same as the growth cycle.
  • Systematic sampling – A sampling procedure in which sample plots are selected based on objective, pre-determined criteria (such as on a grid), rather than a random selection or a selection based on convenience or preferences (e.g. locating plots near the road).
  • Taper – The progression of the diameter (width) of a tree from wide at the base to a narrow point at the top, giving the stem of the tree a cone shape.
  • Thin from above – Thinning in which the largest trees are removed and the smallest trees are retained (also called high thinning).
  • Thin from below – Thinning in which the smallest trees are removed and the largest trees are retained (also called low thinning).
  • Thinning – The removal of some of the trees in a stand, making more resources available for the remaining trees. Thinning is done to increase the growth, vigor, and/or quality of the remaining trees, improve forest health, reduce fire risk, stimulate understory growth, generate wood products, and other reasons.
  • Total age – The complete age of a tree from when it first started growing, not just from the point at which it reached breast height. Total age is usually about 4-5 years longer than breast height age.
  • Trees per acre (TPA) – A basic measure of how dense a stand is, expressed as the average number of trees that would be found on one acre of land.
  • Uniformity – Similarity in a group of trees (e.g. same species, similar size, even spacing, etc.).
  • Variable plot – Sample plots that do not have a specifically defined plot radius or plot boundary. A special angle gauge tool (e.g. glass wedge prism or keyhole prism) is used to determine whether a tree is “in” or “out” rather than the tree’s location within a defined boundary. The larger a tree is or the closer it is to plot center, the greater likelihood of it being “in” the plot.
  • Volume table – A table listing the approximate volume of wood in a tree based on its height and diameter at breast height.
  • Woodland stick – Also called a Biltmore stick or a cruiser stick.  This inexpensive tool resembles a yardstick and is used to measure tree heights and diameters quickly and easily (though not as accurately as with a clinometer or diameter tape).
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