Study On The Spatial Structure And The Growth Model Of The Sassafras Tsumu Mixed Forest

Taking the Sassafras tsumu mixed forest in the national osmanthus forest farm in Hubei province as the research object, we study on its spatial structure and growth. Four indices (mingling intensity, neighborhood comparison of the diameter and the tree height, uniform angle index) are used to describe and compare the spatial structure of the Sassafras tsumu mixed forest. Using the empirical equation and theoretical equation to fit the analytic trees and test plots. Using the neighborhood comparison of the diameter to classify each plant trees, this classification method is better than the classification method just based on the tree species. This article's content is a part of the public welfare industry of the state forestry administration research projects:"Southern collective secondary forest tending and thinning and efficient use of technology research (The Item Number:201004032)." In this paper the study contents include:the study on the law of the spatial structure and the growth, modeling its growth changes of the Sassafras tsumu mixed forest.(1) The part of the study on the law of the spatial structure was as followed:four indices (mingling intensity, neighborhood comparison of the diameter and the tree height, uniform angle index) are used to describe and compare the spatial structure of the mixed forest of Sassafras tsumu-Cunninghamia lanceolata, Sassafras tsumu-Choerospondias axillaris, Sassafras tsumu-Pinus massoniana, Sassafras tsumu-Liriodendron chinense.The results showed that the mingling intensity of Sassafras tsumu in Sassafras tsumu-Cunninghamia lanceolata mixed forest was maximum, so the space isolation degree was largest. When using neighborhood comparison method to characterize the size differentiation of trees, Sassafras tsumu had an advantage in Sassafras tsumu-Cunninghamia lanceolata mixed forest but had an disadvantage in Sassafras tsumu-Pinus massoniana mixed forest. Considering tree distribution pattern using uniform angle index, the stands in Sassafras tsumu-Cunninghamia lanceolata mixed forest was found to be a clumped distribution, but random distribution in other mixed forest. In conclusion, here the best mixed tree of Sassafras tsumu is Cunninghamia lanceolata. (2) The part of the study on the law of its growth and modeling was as followed: using Logistic model,Weibull function,Compertz model,Negative exponential function,Gauss model,Johnson Schumacher model,Richards model and Bertalanffy model to fit the relationship between the diameter and the age gradation, the relationship between the volume and the age gradation to get the age and the stock of the current stand. Then use the classification model to forecast the growth changes in the next15years. From the forecasting results we can see that when the age of the Sassafras tsumu-Cunninghamia lanceolata mixed forest is21,the stand can get the maximum stock increment, at the same time mingling intensity is bigger, the stand have a better growth; in the next15years, the stock increment of the Sassafras tsumu-Pinus massoniana mixed forest is rising trend year by year; the age of the maximum stock increment of the Sassafras tsumu-Choerospondias axillaris mixed forest is31,after that year the stock increment will become to decrease, at the same time its stock increment is much smaller than the Sassafras tsumu-Cunninghamia lanceolata mixed forest, and the age of the maximum stock increment is8,9years later than the Sassafras tsumu-Cunninghamia lanceolata mixed forest. So, here the best mixed tree of Sassafras tsumu is Cunninghamia lanceolata.Comprehensively consider the law of the spatial structure and the stand stock growth changes of each plot, we put forward the management practice based on the intermediate cutting. In plot1,4and5, we need to intermediately cut the quantitatively mature Cunninghamia lanceolata to keep the maximum stand growth; in plot2, we need to intermediately cut the Sassafras tsumu whose uniform angle index is bigger than0.517; in plot3, in the next15years we just need to tend the forest; in plot6, we need to intermediately cut the quantitatively mature Sassafras tsumu and Choerospondias axillaris.