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

引种草的入侵是世界范围内的一种普遍现象，具有巨大的群落和生态系统效应的潜力。本研究将研究外来草入侵对夏威夷氮有限的季节性干旱林地和委内瑞拉天然稀树草原土地生态系统特性的影响。夏威夷的生态系统是进行此类测试的理想选择，因为群落相对简单，入侵也容易被记录下来。两种禾草入侵这些林地的方式截然不同：荆裂草（Schizachyrium condensatum）入侵未受干扰的林地并促进火灾。火灾后，小花蕊草（Melinis minutiflora）在很大程度上取代了裂果属植物和原生林地物种，导致多样性低，更容易被烧毁的草地。养分可用性随着火灾、产量和植被变化的清晰模式而变化，这可能与土壤养分的可预测变化相吻合。研究人员建议研究驱动植被和土壤养分变化的过程，并研究火灾和火灾后外来草的存在对养分限制的影响。具体来说，他们将测试这样一个假设，即草的入侵会引起营养循环的大规模变化，这些变化会反馈影响涉及本地和引进物种的种群水平过程。委内瑞拉的研究将允许检验任何结论的普遍性。

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.