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Comparing Parameter Estimation Techniques for Diameter Distributions

Diameter distributions play an important role in stand modeling. Frequency by size class can be estimated from a distribution function with estimated parameters. A number of different distribution functions have been utilized to model diameter distributions, including the Beta, Lognormal, Johnson’s Sb, and Weibull. The Weibull function has been widely used due to its flexibility in modeling reverse-J, skewed, and unimodal shapes and because integration is not required to estimate frequencies. For these reasons the Weibull function was chosen for this study. Two of the main methods which have been used to estimate the parameters of the Weibull function are parameter prediction, in which each parameter is directly predicted from stand-level variables with a regression equation, and parameter recovery, where selected percentiles of the distribution are predicted and used to equate parameters to moments of the distribution. The purpose of this study was to determine the parameter estimation technique most appropriate for young plantation-grown loblolly pine, and to present parameter estimation equations incorporating necessary genotype and environmental information.

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Author(s): Ben C. Smith, Bronson P. Bullock, Steven E. McKeand

Publication: Tree Improvement and Genetics - Southern Forest Tree Improvement Conference - 2005