Abstract
Abstract A bivariate generalized beta distribution (GBD-2) is fit to the joint frequency distribution of tree diameters and heights of 43 Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) plots in Idaho. The model fitting and performance are compared with the Johnson's SBB distribution using goodness-of-fit χ2 tests for the marginal distributions of diameters and heights, a bivariate goodness-of-fit test for the joint distribution of the two variables, and model predictions of tree heights and volumes. We found that the GBD-2 is more flexible and successful than the Johnson's SBB in describing both marginal and joint distributions of tree diameters and heights. On average, the relative bias (%) from the GBD-2 is three times smaller than that from the Johnson's SBB across the 43 plots when the models are used in tree volume prediction. FOR. SCI. 48(1):47–58.
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