Tree girth measurement

Tree girth measurement is one of the most ancient, quickest, and simplest, of foresters' measures of size and records of growth of living and standing trees. The methods and equipment have been standardized differently in different countries. A popular use of this measurement is to compare outstanding individual trees from different locations or of different species.

Girth is a measurement of the distance around the trunk of a tree measured perpendicular to the axis of the trunk. In the United States it is measured at breast height, or at 4.5 feet (1.4 m) above ground level. Elsewhere in the world it is measured at a height of 1.3 meters (4.3 ft), 1.35 meters (4.4 ft)1.4 meters (4.6 ft), or 1.5 meters (4.9 ft). The base of the tree is measured for both height and girth as being the elevation at which the pith of the tree intersects the ground surface beneath, or where the acorn sprouted. On a slope this is considered as halfway between the ground level at the upper and lower sides of the tree. This "breast height" value is a measurement grandfathered from decades of forestry applications. It was developed because of the simplicity and ease of measurement. There is no one ideal height at which to measure girth. Tree trunks flare outward at their base. In some trees this flare or buttressing extends only a short distance up the trunk, while in others it may extend thirty feet (9.1 m) or more up the tree, but the measurement is still taken at this default height for consistency. If the flare at the base of the tree extends above this default girth height, then ideally a second girth measurement should be collected where possible above the basal flare and this height noted.

Tree girth is one of the parameters commonly measured as part of various champion tree programs and documentation efforts. Other commonly used parameters, outlined in Tree measurement include height, crown spread, and volume. Additional details on the methodology of Tree height measurement, Tree crown measurement, and Tree volume measurement are presented in the links herein. American Forests, for example, uses a formula to calculate Big Tree Points as part of their Big Tree Program that awards a tree 1 point for each foot of height, 1 point for each inch of girth, and ¼ point for each foot of average crown spread. The tree whose point total is the highest for that species is crowned as the champion in their registry. The other parameter commonly measured, in addition to the species and location information, is wood volume. A general outline of tree measurements is provided in the article Tree Measurement Overview with more detailed instructions in taking these basic measurements is provided in "The Tree Measuring Guidelines of the Eastern Native Tree Society" by Will Blozan.

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