Study On Determination Of Optimum Stand Density Of Planted Pinus Tabulaeformis Forest Based On Crown Growth

In view of the common characteristics of Pinus tabulaeformis forest in Beijing suburb,the density of the forest is not reasonable,low possibility of entering and the overall quality is not high.This study was carried out from three aspects:the crown growth,individual competition model establishment and selection,growth process and growth model establishment,to establish the theoretical density table of Pinus tabulaeformis forest at different competitive levels,different site conditions and different ages.To provide a reference for the scientific management of the forest,making them play a greater role in the protection of the ecological environment of the capital.The main conclusions are as follows:(1)The total radius and the change of the crown radius of the dominant wood were higher than that of the average wood.Competition will have a certain impact on the growth of branches,weak competitive intensity is beneficial to the horizontal extension of branches.In lower density,the peak value of average growth of the branches appeared later,the growth rate is relatively high.Through density control,the growth of reserved trees can be effectively promoted.(2)The crown competition index was sensitive to heterogeneous environment.For Pinus tabulaeformis forest distance independent competition index based on crown surface area(RCS)is best for fitting the crown growth(R2=0.6506),better than distance related competition index.The stronger the competitive intensity,the smaller the value of the RCS competition index.(3)Based on the Richard equation as the basic equation,the crown radius growth dynamics of Pinus tabulaeformis forest was simulated by the method of growth increment.There are 3 parameters in the diameter growth model,including site index(SI),stand density index(SDI)and age.Tree height growth model includes site index and age parameters.The crown radius growth model includes 6 parameters:diameter,tree height,age,site index,stand density index and RCS competition index.The determination coefficient(R2)of three models were 0.911,0.9058,0.8436,and the accuracy of model independence test is above 85%.(4)The stand density table was established by the crown area control method to control the management of different sites,different ages and different competition intensity.The pure forest of Pinus tabulaeformis,which is used to provide semi enclosed forest landscape,may choose the radius growth or theoretical density when the competition index is 0.8-0.9 to calculate.To construct the middle and low density Pinus tabulaeformis pure forest with open forest leisure space,the competition index may choose 1.0-1.2.In practical application,the density control table should be formulated according to the local density and management requirements.