Dynamics of Size-structured Populations and Community Organization

本文提出了一个扩展的森林树径结构动态模型，用以模拟森林地带性随全球环境变化而沿沿着的变化。为了预测森林对全球变化的响应，有必要构建林木种群的功能模型。与基于个体的模型相比，基于大小结构的模型所需的内存和计算步骤要少得多，并且很容易将地理位置的维度纳入模型以描述森林类型分布的大尺度动态。增加大小增长率的影响，预计从增加大气中的二氧化碳，减少了在林分断面积密度，因为由片面的竞争调节。模型模拟了长达一个世纪的全球变暖，温度约为3摄氏度，预测：（1）生物量在常驻森林中发生变化，而同时对变暖做出反应;（2）在不同森林类型的边界处，特别是在常驻森林类型最终将被取代的情况下，生物量的移动有相当长的时间滞后。在经历了长达一个世纪的变暖期之后，森林类型需要几千年的时间才能在转移后达到新的稳态分布。因此，全球变暖造成生物量分布沿着纬度梯度呈锯齿形，即，增加在较冷的一侧边界的森林类型和减少在较热的一侧边界。分析相同的模型在群落组织方面建议，填充的物种沿着垂直森林剖面增加潜在的增长率和减少死亡率。本文的研究结果否定了森林更新周转率越高，物种多样性越高的解释。

A geographically extended model of the dynamics of tree size structure of forests is proposed to simulate the change of forest zonation along latitude in response to global environmental change. To predict the response of forests to global change, it is necessary to construct functional models of forest tree populations. The size-structure-based model requires far less memory and steps of calculation compared with individual-based models, and it is easy to incorporate the dimension of geographic locations into the model to describe large-scale dynamics of forest-type distributions. The effect of increasing size growth rate, expected from increasing atmospheric carbon dioxide, was diminished at the stand-level basal area density, because of regulation by one-sided competition. Model simulations of a century-long global warming at around 3^oC predicted that (1) biomass changed in resident forests rather simultaneously in response to warming, and that (2) there was a considerable time lag in movement at the boundaries of different forest types, particularly under the existence of resident forest types that would be finally replaced. It required several thousand years after a century-long warming spell for forest types to attain new steady-state distributions after shifting. As a consequence, global warming created a zigzag pattern of biomass distribution along a latitudinal gradient, i.e., an increase in the cooler-side boundary of forest types and a decrease in the warmer-side boundary.Analyzes of the same model in terms of community organization suggested that the packing of species along a vertical forest profile is enhanced by increasing potential growth rate and by decreasing mortality. Such explanation that higher turn-over rate of forest regeneration promotes higher species diversity was rejected from the present results.