Individual Tree Growth Models Of Natural Mixed Forest In Northern China

The data used to develop individual models for natural mixed forests were collected from remeasured permanent sample plots Daxing'an Mountain and Jilin province(Baihe Forest Bureau and Wangqing Forest Bureau ), northeast China. Based on analyzing relationship between diameter increment of individual trees with tree size, competitive status, and site condition and finding out the major independent variables, the growth models for individual trees in the natural mixed forests, that have simple form, good predicting precision, and easily applicable, were developed using stepwise regression method. At the same time ,the Logistic model is selected to build individual tree mortality model . The last part of this paper is to design a easily applicable computer model system whose program language is VBA.The research results for individual trees growth model of each species show that main variable to influence on diameter increment of individual trees for natural mixed forests were tree size (D) and then competition index and last site condition. In the last form of individual trees growth model shows that the natural logarithm of DBH (lnD) which demonstrate the bigger the diameter, the faster growth of the trees appeared the most times in all the variables and then the square of diameter (D~2) whose function is to limit the growth of the trees. From the competitive part in growth model can know that as the relative diameter (RD and DDM) increase, tree's competitive capacity and diameter increment increase and as canopy closure (P), stand basal area (G) and Stand Density Index (SDI) increase, tree increment decreases. The site conditions, such as Site Class Index (SCI), slope and aspect, are performance less of factors in increment predictions and were deleted from model. In addition, mortality model for each species was developed based on logistic equation. Tree's diameter was significantly related to mortality. As diameter decrease, the mortality probability increases. At last , VBA which is a object-oriented program language is selected to design the computer model system which can easily calculate the stand factors , such as the mean diameter basal area per hectare Stand Density Index (SDI) and Site Class Index (SCI) etc. and predict the definite periodic individual tree diameter growth , definite periodic individual tree mortality probability, stand volume growth and stand volume mortality etc..The individual growth model developed in this study can actually reflect the tree increment and be generally well suited for simulating tree and stand growth for natural mixed forests in theDaxing'an mountain and Jilin province. Furthermore, it will provide detail information of tree increment to intensive forest management and decision-making for natural mixed forest. Therefore, this research has the theoretic foundation and practical value.