Study On The Main Forest Types Diameter Distribution Of Natural Secondary Forest In Northeast

In this paper, the object of study is the natural secondary forest in Heilongjiang Province, we studied and analyzed the stand diameter distribution, the diameter distribution of the main forest types, and the dynamic prediction of stand diameter distribution, by using the data of fixed sample plots surveyed in2000and2005. Based on five probability density functions: Weibull distribution, exponential distribution, SB distribution, Beta distribution and normal distribution, we studied the diameter distribution regularities. The result shows that the fitting effect of Weibull distribution diameter is better than the other four. Based on this, we setted up prediction function of Weibull distribution, and forecast the diameter distribution in theory. Due to the fitting effect of the parameter c is relatively poor, while the parameter c is one of the most important parameter of the Weibull distribution, thus making the diameter distribution dynamic prediction is relatively poor.The results of the diameter distribution of the species in stands show that, the diameter distribution of most species in the stands which are in line with Weibull distribution, are in line with Weibull distribution, and there is a clear linear relationship between the parameters of species and stands respectively. There is a more closely linear relationship between the parameters of the dominant tree species and the stands.The results of the diameter distribution of the main forest types show that the fitting effect of Weibull distribution is the best in fitting the diameter distribution of the four main forest types—soft broad-leaved forest, hardwood forests, oak woods and birch forests. The best forest is birch forests, the followed are soft broad-leaved forest, hardwood forests and oak woods. The fitting effects of exponential distribution, Beta distribution and the SB distribution are followed by Weibull distribution, the fitting effects are little difference, while the fitting effect of normal distribution is the worst. This fully shows that the three-parameter Weibull distribution is of greater flexibility, and better able to fit the diameter distribution of natural secondary forest.