基于结构方程模型的城郊森林公园林分空间结构评价

Evaluation on Stand Spatial Structure of Suburban Forest Park Based on Structural Equation Model

为探索优化林分空间结构的有效措施,以太原森林公园为研究对象,以水平空间结构、垂直空间结构和竞争空间结构为一阶因子,以林分空间结构为二阶因子,依据传导机制建立结构方程模型,对指标赋权,并基于样地实测数据,对太原森林公园林分空间结构进行综合评价。结果表明,林分空间结构评价结构方程模型的平均适配度指数(χ^(2)/df)为1.285,近似误差均方根(RMSEA)为0.046,增值适配度指数CFI、TLI和NFI分别为0.986、0.973和0.941,各拟合指数均符合适配度参考值,可满足研究需要。林分空间结构评价体系中,3个准则层因子,即水平、垂直和竞争空间结构的权重分别为0.352、0.347和0.301,水平和垂直空间结构为影响林分空间结构的关键因素。研究区各样地林分空间结构综合得分为0.31~0.78,集中在Ⅱ、Ⅲ和Ⅳ等级;处于不同等级的样地数量表现为Ⅳ等级(7块)>Ⅲ等级(6块)>Ⅱ等级(1块)。林分空间结构主要受水平和垂直空间结构影响;为改善整体林分空间结构,应采取单株采伐抚育、抚育间伐和多树种补植等措施。

In order to explore effective measures to optimize stand spatial structure,taking Taiyuan Forest Park as study object,structural equation model was established based on conduction mechanism by taking horizontal spatial structure,vertical spatial structure and competitive spatial structure as first-order factors,stand spatial structure as second-order factor,and indexes were assigned with weights.Based on measured data of sample plots,stand spatial structure of Taiyuan Forest Park was evaluated comprehensively.Results showed that average fitness index(χ^(2)/df)of structural equation model for stand spatial structure evaluation was 1.285,root mean square error of approximation(RMSEA)was 0.046,and value-added fitness indexes including CFI,TLI and NFI were 0.986,0.973 and 0.941 respectively,which were in line with reference values of fitness and could satisfy research needs.Weights of three factors in criterion layer in stand spatial structure evaluation system,which were horizontal,vertical and competitive spatial structures,were 0.352,0.347 and 0.301 respectively,with horizontal and vertical spatial structures being key factors affecting stand spatial structure.Comprehensive scores of stand spatial structures in sample plots of study area ranged from 0.31 to 0.78,concentrating on gradesⅡ,ⅢandⅣ.Number of sample plots in different grades followed order of gradeⅣ(7 plots)>gradeⅢ(6 plots)>gradeⅡ(1 plot).Stand spatial structure was mainly affected by horizontal and vertical spatial structures.In order to improve overall stand spatial structure,measures such as single-tree harvesting,thinning and multispecies replanting should be taken.