Fitting irregular diameter distributions of forest stands by Weibull, modified Weibull, and mixture Weibull models |
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Authors: | Lianjun Zhang Chuangmin Liu |
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Institution: | (1) Faculty of Forest and Natural Resources Management, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210, USA;(2) Forintek Canada Corporation, 319 rue Franquet, Sainte-Foy, QC, Canada |
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Abstract: | Irregular diameter frequency distributions of forest stands include multimodal structure of mixed-species stands, highly skewed
and highly irregular shapes of uneven-aged stands, and rotated sigmoid form of old-growth stands. In this study, a traditional
two-parameter Weibull model, a modified two-parameter Weibull model, and a finite mixture of two-parameter Weibull models
were used to fit four artificial example plots. The model fitting and comparison results indicate that the mixture Weibull
model is more flexible to fit various irregular diameter distributions, while the traditional Weibull model fails in every
case to adequately describe these frequency distributions. The modified Weibull model is a good choice for fitting the “rotated-sigmoid”
diameter distribution of an uneven-aged old-growth stand. However, it may not be sufficient when a diameter frequency distribution
is multimodal or highly irregular in shape. |
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Keywords: | Diameter frequency distribution Weibull function Finite mixture model Model fitting and comparison |
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