密度制约对西藏色季拉山森林生物多样性影响的研究

Identifying the mechanisms of plant community assembly and species coexistence is a major research topic in ecology. Density dependence has been documented to be one of the most prominent mechanisms and a important exploration for the maintenance of diversity in some forest communities especially in tropical forests. However, is density-dependance a universal regulating mechanism in communities of different regions？ and its characteristics,strength and influence in forest communities of different latitude, geographical conditions are still unconfirmed. In this study, based on periodic investigating data of 5ha permanent plot in the virgin forests on Sergymler Mountain in southest Tibet Platau, we test the following four hypotheses 1) mortalities of seedlings and sapling will increase with conspecific tree density; 2) seedling's probability of survival will be significantly influenced by the distance from patent tees; 3) strength of negtive density-dependent will increase with population abundance(community compensatory trends); and 4) effects of negative feedback from conspecific (or relative species) neighbor trees will be more strength than from other species neighbor trees. The objectives are to test the characteristics of density dependent and its effects on promoting species coexistence, provide usefull basic bata for exploring mechanisms of species coexistence, biodiversity conservation and for promoting the development of biodiversity theory.

物种多样性的共存与维持机制是生态学的核心问题之一，负密度制约假说（简称密度制约）用以解释物种共存在很多森林群落特别是热带地区得到了较多验证，然而是否是跨越不同区域群落的普遍调节机制？以及同纬度带、不同地理环境的森林群落里的发生特点、强度和影响都有待进一步研究。本项目拟以藏东南色季拉山独特的森林群落为研究对象，通过设计5ha面积永久样地长期调查，重点研究：1）种群密度的大小与死亡率的关系；2）幼苗的更新率、成活率等与母株距离的关联性；3）种群大小与负密度制约效发生的强度的关系(群落补偿效应)；4）同种邻体和群落谱系多样性对幼苗成活率的影响。旨在检验负密度制约效应在藏东南森林群落中的作用强度和对物种多样性维持的影响，为探索藏东南森林物种多样性共存机制和生物多样性理论发展提供基础资料。

密度值约效应是森林生物多样性的重要维持机制之一，在热带地区等森林群落得到了验证，然而是否是跨越不同区域群落的普遍调节机制？以及不同地理环境和气候条件下的森林群落里的发生特点、强度和影响都有待进一步研究。本项目在藏东南原始森林区建成了西藏第一个大型森林生物多样性永久监测样地（4 ha）并对群落内所有胸径≥1 cm的木本植物进行调查和分析，我们发现：（1）森林建群种急尖长苞冷杉种群活立木年龄结构良好，从小径极到大径级过程中的自疏作用和密度制约机制在群落各优势度等级的种群中普遍存在。(2)大树对幼树的存活具有显著的空间距离制约效应。（3）群落内物种优势度与幼苗死亡率呈显著的正的线性关系，说明负密度制约显著促进了稀有物种在群落尺度上的存活并促进群落水平的物种共存。（4）植物群落谱系结构特征说明从小径极到大径级的过程中近缘种之间竞争淘汰作用普遍存在。总之，密度制约是影响藏东南暗针叶林群落生物多样性的重要因素，对区域生物多样性维持具有重要作用。