Historical contingency in ecology and restoration: climate change, year effects, and priority effects in California grasslands

关于自然群落在受到干扰后如何发展，有两种截然相反的模型。有一种理论预测，群落的组成将倾向于回到干扰前的状态，而不管早期建立的变化莫测。另一种说法是，构成群落的物种在很大程度上是由殖民者到达的顺序决定的。未解决的问题是：从长远来看，不同的物种到达时间是否会产生不同的稳定群落，还是相似地点的植物群落最终会有相似的组成？本研究试图回答这个问题，同时评估年际时间变化是否会影响这些过程的长期结果。不同年份的环境变化（例如，降雨量和降雨模式的变化）可以影响多年跟踪的实验结果，在不同年份产生不同的结果。同样，罕见的气候事件往往会推动长期的群落结构。尽管如此，大多数生态学研究只跟踪一年，绝大多数生态学实验都是在一年内开始的。这个多年的研究项目将研究加州草原的植物群落生态学，在降雨量逐年变化的背景下控制植物的定植顺序。该研究对生态系统恢复具有实际意义。这些措施包括开发技术以增加恢复项目的物种多样性，通过将种植工作集中在最有可能成功的年份来提高项目的成功率，通过减少重新种植来降低恢复成本。这项研究还将测试罕见的气候事件是否比平均气候的逐渐变化对植物群落更重要，这将对我们如何应对气候变化产生影响。此外，该项目将加强我们实验室与学生和土地所有者教育和流域管理（SLEWS）项目之间的长期关系，该项目将高中青年（通常来自弱势群体）带到农村环境中，协助当地农场的恢复项目。这个项目不仅使学生和农民受益，也使研究生导师受益。

There are two opposing models of how natural communities develop after disturbance. One theory predicts that community composition will tend to return to the pre-disturbance state, regardless of the vagaries of early establishment. Alternatively, it has been suggested that the species that make up communities are largely determined by the order of arrival of colonizers. The unresolved question is: Do different arrival times of species produce different stable communities in the long term, or do plant communities on similar sites eventually end up with similar compositions? This study seeks to answer this question while at the same time assessing whether interannual temporal variation affects the long-term outcome of these processes. Environmental variation across years (for example, variation in the amount and pattern of rainfall) can affect the results of experiments followed for multiple years, producing different results in different years. Similarly, rare climatic events may often drive long-term community structure. Despite this, most ecological studies are followed for only a single year, and the vast majority of ecological experiments are initiated in a single year. This multi-year research program will examine the plant community ecology of California grasslands, controlling for colonization order of plants in the context of year-to-year variation in rainfall.The research has practical implications for ecosystem restoration. These include developing techniques to increase species diversity on restoration projects, and improving the success of projects by focusing planting efforts on years with highest likelihood of success, decreasing the cost of restoration by decreasing replanting. This research will also test whether rare climatic events are more important for plant communities than gradual changes in average climate, with implications for how we respond to climate change. In addition, this project will enhance the long-term relationship between our lab and the Student and Landowner Education and Watershed Stewardship (SLEWS) program, which brings high school youth (often from disadvantaged groups) into rural settings to assist in restoration projects on local farms. This program benefits not only the students and the farmers, but also the graduate student mentors.