Characteristics Of Leaf Area Index Of Artificial Robinia Pseudoacacia Forest In Loess Hilly Region

Gully region of loess hilly region is important implementation area of national policy of returning farmland to forest,Ansai county,located in the center of loess hilly region,is the earliest national experimental demonstration county of returning farmland to forest.This study took Robinia Pseudoaozcia forest in zhifanggou forest area of ansai county as the research object,and analyzed the regression relationship between the branch capacity of Robinia pseudoacacia and the number of branch axes,the number of leaves,leaf area and total area from branches to individual plants were recorded,and the leaf area indexes of different DBH,microtopography influencing factors and forest age were compared.The results measured from single leaf level were converted to single plant and the whole stand scale.A regression model of the relationship between leaf area and DBH was established to predict the change of productivity of Robinia pseudoacacia forest.The purpose is to promote the sustainable development of regional ecology and consolidate the results of returning farmland to forest,and to provide theoretical guidance for the sustainable development of Regional ecosystem environment.The main results are as follows:the branches and leaves model of Robinia pseudoacacia species is established with the number of branches as the independent variable,and the mathematical model fitting the number of branches and the law of branches is the most effective,which is an effective parameter to measure the leaf area.There was a significant anisotropy relationship between the number of leaves and the number of branches,with R2 as high as 0.957-0.986.After the selection of the optimal model,the allometric growth equation has the highest fitting degree,R2=0.958,so the allometric growth equation can well indicate the correlation between leaf area and DBH.With the DBH as the only variable,the optimal model was established to model the area of a single leaf of Robinia pseudoacacia speeies.Through analyzing and comparing the differences of Robinia pseudoacacia forest leaf area index under different impact factors with OrginPro software,it can not only directly determine the leaf area index of Robinia pseudoacacia forest under different forest ages,but also predict the change of leaf area.Therefore,the method of site survey combined with the dba-leaf area model can be an effective method to estimate the stand leaf area index and its dynamic change.Leaf area index of Robinia pseudoacacia was positively correlated with forest age.At the same time,there was a significant difference between the leaf area index on the negative slope and the leaf area index(LAI)on the positive slope.The growth of Robinia pseudoacacia at different slope position had the best performance.The growth condition of Robinia pseudoacacia on overcast slope was better than that on half-overcast slope,half-sunny slope and sunny slope.Can be seen from the average leaf area index of acacia,the same forest age of acacia when slope degree is less than or equal to 9 ° slope to be significantly higher than the average leaf area index of the average leaf area index;When the slope degree is more than 9 ° but less than 35°,acacia,on average,leaf area index declined with the rise of the slope;When the slope is greater than 35°,acacia average leaf area index increase.