Long term impacts of grass invasions and fire on community change and plant soil feedbacks

在过去的二十年里，科学家、土地管理者和公众已经开始认识到物种入侵的戏剧性后果。尽管有这种认识，但很少有研究证明，当入侵得不到遏制时，入侵会产生长期的生态系统后果。这项拟议的研究评估了夏威夷季节性干燥林地中促火草的长期影响。这些草最初是作为牧草引入的，后来逃到了荒野中，在那里它们促进了火的传播。这些地点的本地物种对火不适应，导致本地物种的急剧丧失，并严重改变了营养循环，包括植物生长的关键资源--氮的损失。这项拟议的研究使用观察和实验来评估入侵者引起的生态系统氮循环的变化，这些变化在20世纪90年代得到了很好的记录，自入侵以来，这些变化随着时间的推移而发生了变化，以及目前的生长条件对本地物种的影响是什么。实验将评估氮素随时间的损失率、土壤碳库的变化以及这些变化对本地和非本地物种的影响。在干旱和半干旱生态系统中，促进火的非原生牧草是一个重要的管理问题。这项研究的结果将使人们更好地了解不对这些入侵进行管理的长期后果，无论是在燃料负荷和土壤养分条件方面，还是在当地物种最终是否会在火灾扑灭下被烧毁的入侵地点恢复方面。最后，结果将提供特定地点的信息，关于哪些本地物种和恢复处理可以用于因火和草入侵而退化的地点。

Over the past twenty years, scientists, land managers and the public have come to recognize the dramatic consequences of species invasions. Despite this recognition, few studies have documented long-term ecosystem consequences of invasions when those invasions go unchecked. The proposed research evaluates long-term impacts of fire-promoting grasses in seasonally dry woodlands in Hawai'i. These grasses, originally introduced as pasture forage, escaped into wildlands where they promote the spread of fire. Native species in these sites are not fire-adapted resulting in a dramatic loss of native species and strongly altered nutrient cycling including losses of nitrogen, a critical resource for plant growth. The proposed research uses observations and experimentation to evaluate how invader-induced changes in ecosystem nitrogen cycling that were well documented in the 1990s, have changed over time since invasion and what the consequences of current growth conditions are for native species. Experiments will evaluate nitrogen loss rates over time, changes in soil carbon pools and the consequences of these changes for native and non-native species. Fire-promoting non-native grasses are a significant management concern in arid and semi-arid ecosystems. The results of this research will provide greater understanding of the long-term consequences of not managing these invasions both in terms of fuel loads and soil nutrient conditions and in terms of whether native species will eventually recover in burned invaded sites under fire suppression. Lastly, results will provide site specific information regarding which native species and restoration treatments can be used in sites degraded by fire and grass invasion.