Estimating the Volume of Top-Killed Trees With the Behre Hyperpoloid

1980

S. 179-186

11 Lit. Ang.

Unselbständiges Werk

200032108

A straighforward procedure is proposed for estimating the volume of top- killed trees. The procedure was developed to increase the accuracy of volume estimates from timber cruises and stand simulations that included trees that had been top-killed by defoliators such as Douglas-fir tussock moth and western spruce budworm. Although the method can be used with any volume equation, its greatest utility is in the absence of a compatible volume- taper equation. The procedure is based on the following information: 1) an estimate of total height, total volume and cylindrical form factor in the absence of top-kill; and 2) the percentage of the merchantable volume below the top-kill (termed the percentage correction factor), assuming that the tree is a Behre hyperboloid of revolution. The product of the percentage correction factor and the estimated total volume (in the absence of top-kill) yields the estimated volume of the top-killed tree. A species-specific local height-diameter curve based on undamaged trees can provide the estimated total height; diameter and the estimated total height are used with the local or regional total volume equation to estimate both volume and cylindrical form factor in the absence of top-kill. Cylindrical form factor is then used to estimate the one parameter in the Behre hyperbola, which is integrated as a solid of revolution to produce the terms that comprise the percentage correction factor. In effect, the procedure estimates a taper curve for each top-killed tree, utilizing only minimal information that describes the shape of the tree: height of top-kill, diameter, and total height and volume in the absence of top-kill. The procedure is demonstrated for inland Douglas-fir growing in northern Idaho and northwestern Montana. Using over 4000 truncated stem sections, the procedure estimated the true truncated volume with a standard deviation of 2.3 percent.