Diameter Distributions Of Individual Species Components Of Natural Mixed Forest Of Larix Gmelini-Betula Platyphylla In Daxing’an Mountains

The purpose of this study is to disaggregate diameter distribution of mixed forest, namely when the information of the whole stand diameter distribution is known, the diameter distribution of each individual specie component can be obtained. The paper select109sample plots as the study object to disaggregate diameter distribution of mixed forest. In this paper, three methods are used:a finite mixture model (FMM); a simultaneous equations model; the system of moments for diameter distribution parameter recovery.(1) A finite mixture model (FMM) is used to disaggregate diameter distribution of mixed forest, comparing with traditional methods including a single Weibull function to fit the whole plot only and a single Weibull function to fit each species component separately and the summation of the individual species produced the whole plot.a) FMM fits the species component distributions simultaneously with the constraint that the individual components add up to the whole plot, without requiring the observed frequencies for each species across the diameter classes, as well as provide the distribution estimation for each species component and the mixing proportions. But the distribution estimation for each species component and the mixing proportions are not ideal.b) Traditional methods are only suitable to regular and unimodal diameter distributions such as balanced reversed-J shape. Although Traditional methods may be able to fit each species component well if its frequency distribution is known and available in the data, they ignore the inter-species relationships within a given plot. Thus, the summation of the species components may not produce a good fit for the whole plot.c) The FMM models are more flexible to describe highly skewed and irregular diameter distributions for the whole plot.(2) A simultaneous equations model is used to disaggregate diameter distribution of mixed forest, the method applies mainly simple statistics of diameter-the arithmetic mean diameter of stand (DBH), the mean diameter of stand(Dg), the standard deviations of diameter(SD), the coefficient of variation of diameter(CV), skewness, kurtosis, the minimum diameter(Dmin), the maximum diameter(Dmax) to disaggregate diameter distribution of each species component.a) The simultaneous equations model can obtain scale parameter b and shape parameter c for diameter Weibull distribution of each species component in natural mixed forest of Larix gmelini and Betula platyphylla in Hei longjiang. The results show the simultaneous equations model for diameter Weibull distribution of each species component in natural mixed forest of Larix gmelini and Betula platyphylla in Hei longjiang yielded promising results, whether if each species component or the whole stand.b) Comparing with traditional methods, a simultaneous equations model takes on better effects. Because the method can characterizes either unimodal diameter distributions or highly skewed and irregular diameter distributions.3A system of moments for diameter distribution parameter recovery is used to disaggregate diameter distribution of mixed forest. The method used the stand factors, including the arithmetic mean diameter of plot (DBH), the mean diameter of plot (Dg), the minimum diameter (Dmin), the stand age(t) and the stand mean height (H), to develop the system of moments for diameter distribution parameter recovery. The system include two steps, the first is to use these factors to model the arithmetic mean diameter of Larix and white birch (LD and BD) and the mean diameter of Larix and white birch (LDg and BDg), the second is to used LD, BD, LDg and BDg to recovery parameters of diameter distribution of Larix and white birch. The results show:a) The method can characterizes diameter distribution of each species of mixed forest. This system can also be used to study on estimating each species yields by size class.b) Comparing FMM, traditional methods and simultaneous equations model, this system characterizes the whole stand better than traditional methods; for characterizing each species, underperforming simultaneous equations model and better than FMM, traditional methods.The study to disaggregate diameter distribution of mixed forest can provide foundation for more refined and effective forest management and planning.