Dissertation Research: The influence of rainfall pulses and disturbance on the invasion of coastal sage scrub

气候变化模型预测，在中纬度地区，降雨事件规模将增加，风暴频率将减少。这些变化可能会强烈影响外来物种是否会入侵本地栖息地，特别是在同时受到干扰影响的系统中。在半干旱的沿海鼠尾草灌丛中，外来的一年生草本植物威胁着高度多样化的原生群落。此外，火灾干扰的频率也在增加。这项拟议的研究将检验这样一种预测，即更大、更少频率的降雨事件增加了当地灌木在火灾后的相对竞争能力，减缓了CS向一年生外来草地的转变。这些更大、更不频繁的事件应该有利于像灌木这样的物种，这些灌木的根更深，对干旱时期的耐受性更强。为了验证这些预测，将在燃烧和未燃烧的CS中操纵降雨分布(增加事件规模和减少频率)。种植了CS、草或竞争混合物的小区将被用来评估物种在降雨操纵下的相对表现。温室测量物种的土壤水分需求将补充田间实验，为生态学理论提供强有力的检验，并为预测群落对多种全球变化因素的反应奠定基础。这些结果将被用于在入侵压力增加、干扰机制改变和降水模式改变的情况下，为CS和其他系统的保护和恢复决策提供信息。除了影响自然区域管理，该项目还将通过独立研究培训本科生，并通过会议、演讲和出版物提高社区意识。

Climate change models predict that, in mid-latitude regions, rainfall event size will increase and storm frequency will decrease. These changes may strongly influence whether exotic species can invade native habitats, particularly in systems that are simultaneously impacted by disturbance. In semi-arid coastal sage scrub (CSS), exotic annual grasses threaten the highly diverse native community. In addition, fire disturbance is increasing in frequency. The proposed research will test the prediction that larger, less frequent, rainfall events increase the relative competitive ability of the native shrubs after fire, slowing the conversion of CSS to annual exotic grassland. These larger, less frequent events should favor species like the shrubs with deeper roots and greater tolerance to dry periods. To test these predictions, rainfall distribution will be manipulated (increasing event size and decreasing frequency) in burned and unburned CSS. Subplots planted with CSS, grasses, or a competitive mixture will be used to evaluate species' relative performance under the rainfall manipulations. Greenhouse measurements of species' soil moisture requirements will supplement field experiments to provide a strong test of ecological theory and a base for predictions of community response to multiple global change factors. The results will be used to inform conservation and restoration decisions in CSS and other systems subjected to increased invasion pressure, altered disturbance regimes, and changed precipitation patterns. In addition to influencing natural area management, the project will train undergraduate students though independent research and promote community awareness through meetings, presentations, and publications.