Dynamics of Size-structured Populations and Community Organization

为了模拟全球环境变化对森林地带性变化的响应，提出了一种林木大小结构动态的地理扩展模型。为了预测森林对全球变化的响应，有必要建立森林树木种群的功能模型。与基于个体的模型相比，基于大小结构的模型需要的内存和计算步骤要少得多，而且很容易将地理位置的维度融入到模型中来描述森林类型分布的大尺度动态。由于单方面竞争的调节，在林分水平的断面积密度上，由于大气二氧化碳的增加而预期的尺寸增长速度增加的影响减弱。在3oC左右对长达一个世纪的全球变暖进行的模型模拟预测：(1)居留林的生物量变化与变暖几乎同步，(2)不同森林类型的边界上的移动存在相当大的时间滞后，特别是在最终将被取代的居留林类型存在的情况下。在森林类型经历了长达一个世纪的变暖之后，需要数千年才能在转移后达到新的稳定分布。因此，全球变暖造成了生物量沿纬度梯度的Z字形分布格局，即森林类型的冷侧边界增加，暖侧边界减少。从群落组织的角度对同一模型的分析表明，通过增加潜在增长率和降低死亡率，物种沿垂直森林剖面的堆积得到加强。这种认为较高的森林更新周转率促进较高的物种多样性的解释不被目前的结果所接受。

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.