基于结构方程模型分析林分空间结构对草本物种多样性的影响

林分空间结构的改变直接影响林下草本物种的多样性。以针叶纯林、针阔混交林和常绿阔叶林为研究对象，采用结构方程模型研究了林分空间结构对林下草本物种多样性的影响，并探讨了林分水平空间结构，垂直空间结构以及林木竞争态势对林下草本物种多样性的影响的相对重要性。结果表明，林分水平空间结构对林下草本的物种多样性指数和物种均匀性指数均存在极显著的影响（P < 0.001），影响系数高达0.96和0.89，对林下草本物种丰富度存在显著影响（P < 0.01），影响系数为0.22；林分垂直空间结对林下草本丰富度和物种均匀性指数均存在极显著的影响（P < 0.001），影响系数分别为0.86和0.43，对林下草本物种多样性指数存在显著影响（P < 0.01），影响系数为0.16；林木竞争指数与林下草本丰富度和物种多样性指数也均存在极显著的影响（P < 0.001），但影响系数较小，分别为-0.47和-0.30，而对林下草本物种均匀性指数未达到显著影响作用（P > 0.05），影响系数仅为-0.04。整体上看，林分水平空间结构、垂直空间结构和林木竞争态势均对林下草本物种多样性有较强的影响作用，但从影响系数看，林分水平空间结构的影响作用最大，垂直空间结构次之，林木竞争态势的影响作用最小。因此，欲维持或改善林下草本物种多样性，应采取调整林分水平空间结构为主，垂直空间结构调整为辅，并适当降低林木竞争程度的综合经营措施。

Effects of stand spatial structure on herbaceous species diversity in forests based on structural equation modeling

Changes in stand spatial structure affect herbaceous species diversity in forests. Our goal was to explore the relationship between stand spatial structure and herbaceous species diversity in the understory of forests and provide optimum conditions for maintaining and improving herbaceous species diversity in the forest understory. In this study, the effects of stand spatial structure on herbaceous species diversity were investigated in pure coniferous forests, mixed broadleaved and coniferous forests, and evergreen broadleaved forests. The contributions of stand spatial horizontal structure, vertical structure, and individual trees competition to the herbaceous species diversity were estimated. Results showed that the stand horizontal structure had a significant effect on the species diversity and species evenness of herbaceous species (P < 0.001), with influence coefficients of 0.96 and 0.89, respectively. The stand horizontal structure significantly affected herbaceous species richness (P < 0.01) with an influence coefficient of 0.22. The stand vertical structure had a significant effect on species diversity and species evenness (P < 0.001) and species richness (P < 0.01), with influence coefficients of 0.86, 0.43, and 0.16, respectively. Individual tree competition had a significant effect on species richness and species diversity (P < 0.001) with influence coefficients of -0.47 and -0.30, respectively. However, the competition of individual trees had no significant influence on species evenness (P > 0.05), and the corresponding influence coefficient was -0.04. Our results indicated that the herbaceous species diversity within the studied forests was primarily affected by the horizontal spatial structure of the stand, followed by the vertical spatial structure of the stand, and finally, individual tree competition in the studied forests, although these three stand structure variables had strong correlations with herbaceous species diversity. The study suggested that to maintain or improve the herbaceous species diversity in forests, comprehensive forest management should be adopted to mainly adjust the stand horizontal spatial structure. Additionally, regulated stand vertical spatial structure and appropriate reductions in the degree of individual tree competition in the forests should be included.