Ecosystem and Population Consequences of Alien Grass Invasion of Seasonally Dry Hawaiian Woodlands

引种牧草的入侵是世界范围内的普遍现象，有可能对社区和生态系统产生巨大的影响。这项研究将调查外来草入侵在夏威夷的氮素有限、季节性干燥的林地和委内瑞拉的天然稀树草原上引起的生态系统属性的变化。夏威夷的生态系统是这类测试的理想选择，因为它们的群落相对简单，而且入侵行为很容易被记录下来。两种草本植物入侵这些林地的方式截然不同：丛生裂褶草入侵未受干扰的林地，并促进火灾。火过后，小花梅里尼主要取代裂果属植物和本地林地物种，导致草地物种多样性低，更容易被烧毁。养分的有效性随着火的产生而发生可预测的变化，这是一种清晰的植被变化模式，很可能与土壤养分的可预测变化相吻合。研究人员建议调查驱动植被和土壤养分变化的过程，并检查火灾和火灾后外来草的存在对养分限制的影响。具体地说，他们将检验这样一个假设，即草类入侵导致营养循环发生大规模变化，这些变化反馈影响涉及本地物种和引进物种的种群水平过程。委内瑞拉的研究将允许对任何结论的一般性进行测试。

Invasions by introduced grasses are a common phenomenon worldwide, with the potential for dramatic community and ecosystem-level effects. This study will investigate changes in ecosystem properties induced by alien grass invasion in a nitrogen-limited, seasonally dry woodland in Hawai'i and a natural savanna lands in Venezuela. Hawaiian ecosystems are ideal for such tests because of the relative simplicity of the communities and the ease with which invasions can be documented. Two grass species have a distinct pattern of invasion into theses woodlands: Schizachyrium condensatum invades undisturbed woodland and promotes fire. After fire, Melinis minutiflora largely replaces both Schizachyrium and native woodland species resulting in a low diversity, more readily burned grassland. Nutrient availability changes predictably with fire, yielding, a clear pattern of vegetation change that likely coincides with a predictable change in soil nutrients. The researchers propose to investigate the processes driving vegetation and soil nutrient changes and to examine the influence of fire and the post-fire presence of alien grasses on nutrient limitation. Specifically, they will test the hypothesis that grass invasion induces largescale changes in nutrient cycling and that these changes feedback to influence population-level processes involving both native and introduced species. The Venezuela study will permit tests of the generality of any conclusions.