Study On Spatial Structure Optimization Of Chinese Fir-Phoebe Bournei Mixed Forest On Multifunctional Management

The multi-function of forests means that we need to give full play to the social,economic and ecological values of forests,meet the needs of human production and life,and then enhance the overall benefits of forests.Therefore,more and more scholars began to explore how to transform the forest with fragile ecological stability into a forest with multiple benefits.The spatial structure and non-spatial knot of forest greatly affect the multi-function of forest,and the most intuitive form of presentation and the most basic regulatory factor is the spatial structure index of forest.These structural indicators affect the competition situation and spatial niche among trees,and also determine the selection of spatially felled trees.Rational structure determines the function of forests.The spatial structure of forests is optimized from the aspects of total mixing degree,size ratio,open ratio,forest layer index and angle scale,so as to improve the multi-functional benefits of forests.Based on the multi-functional forest management theory,this study took the Chinese fir-Phoebe bournei mixed forest in Jindong forest farm as the research object,analyzed its spatial structure and plant diversity function,soil and water conservation function,productivity function and productivity function,and established the relationship model between spatial structure factor and multi-functional index.Then solving the Ideal Spatial Structural Model Based on the Whole Function by Using the Method of Multi-objective Optimization.Taking No.5 sample plot as an example,the trees with lower spatial structure index were selected for simulation and optimization.The spatial structure model of the simulated sample plot after cutting was close to the optimal structure based on multi-function under ideal condition.The 3D simulation of the spatial structure of the sample was carried out by Sketchup software.Finally,the corresponding multi-functional management measures are put forward.The main research conclusions are as follows:(1)Spatial structure and multifunctional index analysis of Chinesefir-Phoebe bournei mixed forest.The spatial structure unit was determined based on the four-tree method,and the spatial structure was analyzed by selecting five indexes,including full mixing degree,size ratio,open ratio,forest layer index and Angle scale.The average values of the five structural indicators of the 12 plots were 0.33,0.50,0.76,0.20 and 0.64,respectively.The corresponding plots were in the state of medium mixing,the state of mean,the state of high openness,the state of low differentiation and the state of cluster distribution.Selecting soil water conservation function,species diversity function,carbon fixation function and productivity function as multi-function analysis indexes,CRITIC method was used to calculate the weight between soil water capacity,soil porosity and soil bulk density,and the comprehensive index S1 of soil water conservation was 0.50,which was at a medium level;The weight of richness index,Shannon-wiener index and Pielou evenness index was calculated,and the comprehensive index S2 of species diversity was determined to be 0.49,which was at a medium level;The average carbon reserve of the sample stand mixed forest was 140.25 t/hm2;The average biomass of stands was 41.59 t/hm2.(2)Using the idea of multi-objective optimization,the spatial structure model based on global function optimization is calculated.The models of four multi-functional indexes and spatial structure parameters are constructed by multiple quadratic regression.Then,four ideal spatial structure modes and spatial structure composite index based on single dominant function are calculated by MATLAB software,and then the maximum value of single dominant function is determined.Finally,based on the thought of multi-objective optimization,minimizing the weighted deviation variable of the objective function,to determine the optimal function of the overall spatial structure mode to {0.34,0.59,0.78,0.08,0.574},space structure comprehensive index was 21.89.(3)Simulation of selective cutting of stand spatial structure.After the simulation and optimization of No.5 plot,the total mixing degree of stands reached 0.21,which was 10.5%higher than that before.After the optimization,the index of stand stands remained unchanged,while the vertical stratification of stands changed little.The stand size ratio reached 0.51,which was 3.8%lower than that before selective felling.The open ratio increased by 6.8%,indicating that the light transmittance of stand was improved to some extent.The spatial structure composite index of stands increased by 24.9%to 19.12,close to 21.89 based on the overall function.The parameters of spatial structure before and after optimization are brought into four spatial structure models based on single dominant function.The changes of each multi-functional index after optimization are simulated as follows:The predicted values of soil water conservation function,species diversity function,productivity function and carbon sequestration function increased by 12.08%,9.48%,11.40%and 8.26%,respectively.It shows that the spatial structure of forests has begun to transform to ideal conditions,but because the growth of forests is a dynamic process,it is impossible to maximize the multi-functional benefits of forests at one time,so there is still a gap between the multi-functional indicators and ideal values achieved by selective cutting measures at the current stage.