Scheiter Simon, Higgins Steven I
Lehrstuhl fur Vegetationsokologie, Technische Universitat Munchen, 85350 Freising-Weihenstephan, Germany.
Am Nat. 2007 Oct;170(4):587-601. doi: 10.1086/521317. Epub 2007 Aug 7.
A classic problem in coexistence theory is how grasses and trees coexist in savannas. A popular deterministic model of savannas, the rooting niche separation model, is based on an assumption that is not empirically supported in many savannas. Alternative models that do not rely on the rooting niche assumption invoke intricate stochastic mechanisms that limit their attractiveness as general models of savannas. In this article we develop an alternative deterministic model of grass-tree interactions and use it to analyze the conditions under which grass-tree coexistence is possible. The novel feature of this model is that it partitions aboveground and belowground competition and simulates the fact that fire and herbivory remove only aboveground biomass. The model predicts that stable coexistence of grasses and trees is possible, even when grasses and trees do not have separate rooting niches. We show that when aboveground competition is intense, grasses can be excluded by trees; under such conditions, fire can prevent grasses from exclusion and induce a stable savanna state. The model provides a general framework for exploring the interactive effects of competition, herbivory, and fire on savanna systems.
共存理论中的一个经典问题是草本植物和树木如何在稀树草原中共存。一个流行的稀树草原确定性模型——根系生态位分离模型，是基于一个在许多稀树草原中未得到实证支持的假设。不依赖根系生态位假设的替代模型引入了复杂的随机机制，这限制了它们作为稀树草原通用模型的吸引力。在本文中，我们开发了一个草本植物与树木相互作用的替代确定性模型，并用它来分析草本植物与树木共存可能的条件。该模型的新颖之处在于它划分了地上和地下竞争，并模拟了火灾和食草作用仅去除地上生物量这一事实。该模型预测，即使草本植物和树木没有单独的根系生态位，它们也有可能稳定共存。我们表明，当地上竞争激烈时，草本植物可能会被树木排除；在这种情况下，火灾可以防止草本植物被排除，并诱导出稳定的稀树草原状态。该模型为探索竞争、食草作用和火灾对稀树草原系统的交互作用提供了一个通用框架。
