Modeling in Forestry Using Mixture Models Fitted to Grouped and Ungrouped Data
نویسندگان
چکیده
The creation and maintenance of complex forest structures has become an important forestry objective. Complex structures, often expressed in multimodal shapes tree size/diameter (DBH) distributions, are challenging to model. Mixture probability density functions two- or three-component gamma, log-normal, Weibull mixture models offer a solution can additionally provide insights into dynamics. Model parameters be efficiently estimated with the maximum likelihood (ML) approach using iterative methods such as Newton-Raphson (NR) algorithm. However, NR algorithm is sensitive choice initial values does not always converge. As alternative, we explored use expectation-maximization (EM) for estimating aforementioned because it converges ML estimators. Since data frequently occur both grouped (classified) ungrouped (raw) forms, EM was applied explore goodness-of-fit distributions three sample plots that exhibited irregular, multimodal, highly skewed, heavy-tailed DBH where some size classes were empty. EM-based further compared against nonparametric kernel-based estimation (NK) model recently popularized gamma-shaped (GSM) data. In this example application, provided well-fitting all families. number components best-fitting differed among (but families) log-normal gamma families better fit than distribution For data, outperformed GSM and, exception diameter distribution, also NK appears promising tool modeling structures.
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ژورنال
عنوان ژورنال: Forests
سال: 2021
ISSN: ['1999-4907']
DOI: https://doi.org/10.3390/f12091196