A point in history that is considered to be representative of the natural conditions of an ecosystem. This point, which may be in the past or present, is chosen such that it is within the historic or natural range of variability for a particular area.

A pattern of regular or semi-regular occurrences or processes that characterizes and governs a natural system, as in precipitation regime, fire regime, disturbance regime, etc.

The planting of trees under silvicultural prescriptions in areas where trees were once located but no longer exist due to disturbance (harvest, fire, wind, insects, etc.).

The outcome of an experiment conducted using the scientific method. This observed result is compared to the expected result according to the research hypothesis, and a conclusion is made about whether the results support or contradict the hypothesis.

The number of years required to grow trees to an ideal size or age; usually trees are grown to either economic maturity or natural maturity.

Generally, temperature decreases as elevation increases. For every 1,000 foot increase in elevation, temperature decreases three (3) degrees Fahrenheit, and vice versa. As latitude becomes more northward in the Northern Hemisphere and more southerly in the Southern Hemisphere, temperature decreases. The general rule is that temperature changes three (3) degrees Fahrenheit for every 300 mile change in latitude at an elevation of sea level. These temperature changes influence greatly the diversity and abundance of plant and animal species from place to place. However, other factors such as soil, topography, aspect, and precipitation are also extremely important in determining the types of plant and animal life that occur in any given area.

A measure of merchantable timber in live trees of merchantable species. Generally, sawlogs should be a minimum of eight inches (8") diameter at breast height (dbh) and eight feet (8') in length.

Live trees of merchantable species that are suitable for harvesting and sawing into lumber according to specific criteria. Generally, sawtimber should be greater than eight inches (8") diameter at breast height (dbh), and should contain at least one (1) sawlog. Merchantable sawlogs are usually a minimum of eight feet (8') in length.

1. The series of rational steps that leads to the proof (or disproof) of a scientific or research hypothesis. The steps are observation, which leads to the formulation of a hypothesis through abductive reasoning, followed by tests or experiments to determine the validity of the hypothesis (deductive reasoning). The observed result of the experiment is compared to the expected result, and a conclusion is made supporting or contradicting the hypothesis. 2. The scientific method is the process by which scientific facts are discovered, proven, or learned.

The practice of manipulating and controlling forest establishment, growth, composition, structure, and to a certain extent, function. Silviculture can be thought of as agriculture for the forest, with trees as crops.

The characteristics of a site that influence growth of vegetation, including soil chemical and physical properties, climate, aspect, elevation, topography, and disturbance regime.

A contiguous group of trees that are similar enough in species composition, age class distribution, and site productivity or characteristics that it can be considered a single unit, regardless of size.

The stocking level of a stand of trees; the relative number of trees within a stand, usually expressed as trees per acre (TPA) or in terms of basal area (BA).

A ratio comparing current stand density to an ideal or reference stand density (usually derived from yield tables), resulting in a stocking percentage (e.g., 75% stocked). Stands of trees may therefore be understocked, overstocked, or fully stocked according to these criteria. Also known as stocking level.

Generally, temperature decreases as elevation increases. For every 1,000 foot increase in elevation, temperature decreases three (3) degrees Fahrenheit, and vice versa. As latitude becomes more northward in the Northern Hemisphere and more southerly in the Southern Hemisphere, temperature decreases. The general rule is that temperature changes three (3) degrees Fahrenheit for every 300 mile change in latitude at an elevation of sea level. These temperature changes influence greatly the diversity and abundance of plant and animal species from place to place. However, other factors such as soil, topography, aspect, and precipitation are also extremely important in determining the types of plant and animal life that occur in any given area.

1. Live trees of merchantable species and sufficient size that they can be profitably harvested and sold. Timber is then milled and made into lumber and other wood products. 2. Forest land covered by trees of suitable size, kind, and quality to be of commercial value.

The total amount of timber available for harvesting at a given or specified time.

Refers to the number of trees on a per acre basis in a specified stand or forest; a useful measure of forest or stand densities and stocking levels.

Popular name for the branch of the U.S. Department of Agriculture responsible for managing the national forests of the United States. See also USDA Forest Service.

A branch of the U.S. Department of Agriculture responsible for managing the national forests of the United States. See also U.S. Forest Service.

1. The return on an investment or the amount of profit, stated as a percentage of the amount invested.
2. The total amount of timber available for harvesting at a given or specified time.

An index used to predict timber yields or volumes based primarily on tree age and site quality.