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Quantifying forest stand diversity using stand structure Staudhammer, Christina Lynn

Abstract

Stand structure is an important component of the overall description of biological diversity in a stand. The diversity of tree sizes within a stand affects tree growth and yield, and is highly correlated with the biodiversity of a stand. Four measures of stand diversity based on the stand distribution of basal area by height, diameter, and species were proposed, assuming a baseline of maximum diversity corresponding to a uniform distribution. First, the Extended Shannon Index (ESI), a measure based on Shannon's Index, was derived. Second, a measure based on fitting the univariate and bivariate distributions of diameter and height was investigated. The third measure, STRI, was derived as a modified R-squared, based on the fit of the distribution to that of a uniform distribution. The fourth measure, STVI, was derived based on comparing the variance of a distribution to that of a uniform distribution. The four measures were evaluated with simulated data and inventory data from the Malcolm Knapp Research Forest (MKRF). The ESI and STVI resulted in logical orderings of both the simulated data and the MKRF data. The advantages of the ESI include its known sampling distribution and accepted use in forestry; however, the ESI depends on allocating data to arbitrary classes. The STVI does not require classifying data; however, its sampling distribution is unknown. Since the measures derived require only normally collected inventory plot data, they are relatively inexpensive to use. However, a thorough investigation of the properties of each should be undertaken. Since evaluating structural diversity is becoming an increasingly important part of forest assessment, a quantitative measure is needed to measure diversity. These measures provide a starting point toward finding an inexpensive, practical measure of structural diversity which gives reasonable results.

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