<正>通过在江苏省里下河地区连续８年的试验，发现林农复合系统生产力的提高主要来自资源共享增益和林木生产增益。前者通过资源开发途径，后者通过物种间的互利作用。在３年生林分中，资源共享增益占复合经营总生物量的７７．１％～８１．４％，但随林龄增加而降低。而间作引起的林木生长量增加的比值低于３．３％，但随林龄增加有所提高。根据资源共享增益和林木生长增益，确定了随林冠投影面积变化应进行的林分结构的最佳控制数值。

Coexistence gain of populations has been studied for eight years， data from the field experiments of agroforestry system in Lixiahe, Jiangsu Province. Facilitation and resource sharing were identified as main contribution to the overyield of agroforestry. Resource sharing contributed 77.1％～81.4％ of biomass production to the total biomass of agroforestry in the threeyearold stands, decreasing with increasing treestandage. The contribution of facilitation to the total yield of agroforestry was lower than 3.3%, increasing with treestandage. The replacement of high lightrequired crops with low lightrequired ryegrass increased the gain of resource sharing and relative gain of resource sharing in agroforestry systems. The paper presented the tree thinning models for the maximum total biomass production of agroforestry and discussed the optimum control for the composition of tree stands in agroforestry systems.