Forest measurement

(forestry) The branch of forestry concerned with the measurement of standing trees, cut roundwood, and lumber products.

The science and practice of measuring the volume, growth, and development of trees individually and collectively and estimating the products obtainable from them. Foresters use quantitative sciences such as mathematics and statistics for these measurements.

Regardless of the land management objectives—timber, wildlife, recreation, watershed, or a combination of these resources—the tree overstory (the forest canopy) must be quantified for informed decision making. Forest cover is an important part of wildlife habitat, and the understory component is related to the overstory characteristics. The recreation potential of wildland is a function of many variables, including the size and number of trees present. Water yields are related to the composition and density of the tree canopy. The measurement principles discussed here are applicable to all forest resource management situations that require quantitative information about the tree component of the land base.

Standing trees are commonly measured for diameter, height, and age. The diameter and height measurements are used to estimate the volume (or weight) and value of individual trees; ages are used in assessing site quality and predicting growth. See also Dendrology; Wood anatomy.

In addition to inventories aimed at determining current conditions, land managers need trend data. Monitoring consists of collecting information over time, generally on a sample basis by measuring change in key indicator variables, in order to determine the effects of management treatments in the long term. These data, along with research results, can be used to modify management on a continuing basis to ensure that objectives are being met. The sampling design for monitoring generally involves repeated measurements on the same sample plots or individuals.

Forest inventory information is commonly stored, updated, and retrieved through geographic information systems (GISs). A GIS is a computerized database for storing, manipulating, and displaying map (spatial) data and tabular (attribute) information. In a GIS, forest inventory information can be stored in a computer and directly linked to associated forest maps, making it easier and faster to analyze and graphically display the results of forest inventories. GISs can make forest inventory information more powerful by allowing forest resource managers to integrate it with other data commonly needed to make management decisions.

Foresters estimate site quality to assess present and future forest productivity and to provide a frame of reference for land management. Many parameters that affect productivity are difficult or impossible to measure directly, and as a consequence site quality is determined indirectly. Most commonly, site quality is evaluated from tree height in relation to age. Theoretically, height growth is sensitive to differences in site quality, is little affected by varying stand-density levels, is relatively stable under varying thinning intensities, and is strongly correlated with volume. Thus height has been found to be a practical, consistent, and useful indication of site quality.

Quantitative measures of stand density are used when deriving silvicultural prescriptions and predicting growth and yield. The two most commonly used measures of stand density are tree basal area per unit area and number of trees per unit area. Stand basal area is the cross-sectional area at diameter at breast height of all stems, or some specified portion of the stand, expressed on a per-acre (or per-hectare) basis. Similarly, trees per acre may be determined for all stems or for some specified portion of the stand. See also Silviculture.

Growth is the increase (increment) over a given period of time. Yield is the total amount available for harvest at a given time, that is, the summation of the annual increments. The factors most closely related to growth and yield of forest stands of a given species composition are the point in time in stand development, the site quality, and the degree to which the site is occupied. See also Forest and forestry; Forest management.