Problems of scaling plantation plot diameter distributions to stand level

Abstract

Diameter distribution models are used extensively in forest growth and yield modeling. They are usually fitted with fixed area sample plot data but applied at the stand level, the unit of forest production planning. In this process, the distribution obtained at the plot level is assumed to be representative of that at the stand level. In other words, the distribution from each plot of the same stand is assumed (roughly) to be the same, and therefore we can reasonably scale the plot distribution to the stand level. However, because of site-induced within-stand (between-plot) variability and spatial correlation introduced by tree competition and/or microsite effects or other factors, plot distributions may differ markedly from the stand distribution. We use data from 11 slash pine (Pinus elliottii) plantations, each consisting of 10 plots, to address differences in diameter distributions between plot level and stand level. The data indicate that (single) plot distributions are generally significantly different from their stand counterparts, because of spatial heterogeneity among plots within a given stand. For relatively homogeneous stands, diameter distributions obtained by averaging two to three plots may well represent the stand distribution within a certain precision, whereas for stands with more obvious spatial heterogeneity, a relatively large number of plots seem to be necessary for characterizing the stand distribution. Copyright © 2008 by the Society of American Foresters.