Short-term post-fire field studies have shown that native shrub cover in chaparral ecosystems negatively affects introduced cover, which is influenced by burn severity, elevation, aspect, and climate. Using the southern California 2003 Old and Simi fires and the 2008 Sesnon Fire, we investigated the role of native shrubs in post-fire ecosystem responses across gradients of elevation, aspect, climate, burn severities, fire histories, and time. We collected field estimates of species cover in 2004 and 2015 at nested sampling sites. We used structural equation models with introduced and shrub cover as dependent variables. Shrub cover in 2004 was most influenced by the number of reburns, while shrub cover in 2015 was most influenced by the time between the two most recent fires. In 2004, introduced cover was most influenced by burn severity in 2003; similarly, in 2015, introduced cover was most influenced by burn severity in 2008. In both one and twelve years post fire, average precipitation increased the length of time between fires and decreased the number of times a site burned. This direct reduction in the number of times a site had burned due to average precipitation resulted in lower shrub cover one and twelve years post fire. Additionally, mean annual precipitation increased burn severity one year post fire, which resulted in lower introduced cover. However, this indirect relationship between precipitation and introduced cover through burn severity was no longer present twelve years post fire. Shrub cover increased with a longer average time between fires twelve years after fire. Shrub cover did not mediate any indirect relationships between burn severity or fire history metrics and introduced cover in either year, suggesting competitive exclusion of introduced species by shrubs. Our research found that significant fire effects on shrub and introduced species are often mediated by precipitation. Precipitation trends are likely to change fire regimes and thus alter plant community dynamics.

中文翻译：

---

有灌木吗？火灾后，降水介导了长期灌木并引入了丛林群落中的草地动态

短期的火后野外研究表明，丛林生态系统中的天然灌木覆盖对引入的覆盖产生了负面影响，其受到烧伤严重程度，海拔，纵横比和气候的影响。我们使用了加利福尼亚南部的2003年老火和西米火以及2008年塞斯农火，研究了海拔高度，纵横比，气候，烧伤严重程度，火灾历史和时间梯度上原生灌木在火灾后生态系统响应中的作用。我们在嵌套采样点收集了2004年和2015年物种覆盖的现场估计。我们使用结构方程模型，将引入的和灌木覆盖率作为因变量。2004年的灌木覆盖受再燃次数影响最大，而2015年的灌木覆盖受最近两次大火之间的时间影响最大​​。2004年，2003年烧伤严重程度对引入的覆盖层影响最大。同样，在2015年，引入的覆盖物在2008年受到烧伤严重性的影响最大。在火灾后的十二年和十二年中，平均降水量增加了两次火灾之间的时间长度，并减少了现场燃烧的次数。由于平均降水量，现场燃烧次数的直接减少导致火灾后一和十二年灌木覆盖率降低。此外，年平均降水量增加了火灾后一年的烧伤严重性，从而导致较低的引入覆盖率。但是，火灾后十二年不再存在降水与通过烧伤严重性引起的覆盖之间的间接关系。火灾后十二年，两次火灾之间的灌木平均覆盖时间增加。灌木覆盖没有调解烧伤严重程度或火灾历史指标与任何一年引入的覆盖之间的任何间接关系，这表明灌木对引入种的竞争性排斥。我们的研究发现，对灌木和引入物种的重大火灾影响通常是由降水介导的。降水趋势可能会改变火势，从而改变植物群落的动态。