岩溶区林分生长与影响因子的关系

  目的  通过研究南水北调源头渠首岩溶区不同林分生长及其影响的主导因子,为科学指导岩溶区植被恢复、林地管理与林分改造提供依据。  方法  以南水北调水源地中线渠首所在地淅川县岩溶区为研究对象,基于结构方程模型构建乔木层生物量与基岩裸露度、土壤厚度、树种多样性以及林分密度的模型,进行关系耦合。  结果  基岩裸露度与林分密度为正相关关系(P＜0.01),与树种多样性为极显著正相关关系(P＜0.01),与建群种生物量为极显著负相关关系(P＜0.01)。基岩裸露度对林分密度的直接影响系数为0.198,对树种多样性的直接影响系数为0.519,对建群种生物量的总影响系数、直接影响系数及间接影响系数分别为?0.659、?0.722和0.063,对林分生物量的间接影响系数为?0.604。土壤厚度与建群种生物量呈显著正相关关系(P＜0.05),与树种多样性、林分密度与建群种生物量为正相关关系。土壤厚度对建群种生物量的直接影响系数为0.258,对林分总生物量的间接影响系数为0.262;树种多样性对建群种的直接影响系数为0.084,对林分总生物量的总影响系数、直接影响系数及间接影响系数分别为0.211、0.126和0.085;林分密度对建群种的直接影响系数为0.096,对林分总生物量的间接影响系数为0.098。建群种生物量与林分总生物量为显著正相关关系(P＜0.01),建群种生物量对林分总生物量的总影响系数为1.014。  结论  基岩裸露度、土壤厚度、树种多样性及林分密度与建群种生物量、林分总生物量之间存在着复杂的关系,在岩溶区降低基岩裸露度、增加土壤厚度(即提升立地条件)能够改善林分结构增加建群种和全林分的生物量。生物量与立地条件、树种多样性和林分密度呈正相关,提升立地条件、抚育改变林分结构能够促进个体生长,增加生物量的积累,改善岩溶区的生态环境。图1表3参34

Relationship between stand growth and impact factors in karst area

  Objective  This study aims to explore the dominant factors affecting the growth of different stands in the karst area at the headwaters of South-to-North Water Diversion Project, so as to provide scientific evidence for vegetation restoration, forest management and forest rehabilitation in such area.  Method  The karst area of Xichuan County, where the head of the middle channel of South-to-North Water Diversion Project is located, was taken as the research object. The models of tree layer biomass, bedrock exposure, soil thickness, tree species diversity and stand density were built, based on the structural equation model to carry out relational coupling.  Result  There existed a positive correlation between bedrock exposure and stand density (P＜0.01), a very significant positive correlation with tree species diversity (P＜0.01), and a very significant negative correlation with the biomass of constructive species (P＜0.01). The direct impact coefficient of bedrock exposure on stand density was 0.198, the direct impact coefficient on tree species diversity was 0.519, the total, direct and indirect impact coefficients on biomass of constructive species were ?0.659, ?0.722 and 0.063, respectively, and the indirect impact coefficient on stand biomass was ?0.604. There existed a significant positive correlation between soil thickness and constructive species biomass (P＜0.05), and a positive correlation between tree species diversity, stand density and constructive species biomass. The direct and indirect impact coefficients of soil thickness on the biomass of constructive species were 0.258 and 0.262 respectively. The direct impact coefficient of tree species diversity on constructive species was 0.084, and the total, direct and indirect impact coefficients on total biomass of stand were 0.211, 0.126 and 0.085 respectively. The direct impact coefficient of stand density on constructive species was 0.096, and the indirect impact coefficient on total biomass was 0.098. There was a significant positive correlation between the biomass of constructive species and the total biomass of stands(P＜0.01), and the total impact coefficient of constructive species biomass on the total biomass of stands was 1.014.  Conclusion  There are complex relationships between bedrock exposure degree, soil thickness, tree species diversity, stand density, and constructive species biomass and total stand biomass. Reducing bedrock exposure in karst area and increasing soil thickness (i.e. improving site conditions) can improve the stand structure, as well as the constructive species biomass and stand biomass. Biomass is positively correlated with site conditions, stand density, and tree species diversity. Improving site conditions, tending and changing stand structure can promote individual growth, increase the biomass accumulation, and improve the ecological environment in karst area. [Ch, 1 fig. 3 tab. 34 ref.]