Anthropogenic climate change has increased the frequency of drought, wildfire, and invasions of non-native species. Although high-severity fires linked to drought can inhibit recovery of native vegetation in forested ecosystems, it remains unclear how drought impacts the recovery of other plant communities following wildfire. We leveraged an existing rainfall manipulation experiment to test the hypothesis that reduced precipitation, fuel load, and fire severity convert plant community composition from native shrubs to invasive grasses in a Southern California coastal sage scrub system. We measured community composition before and after the 2020 Silverado wildfire in plots with three rainfall treatments. Drought reduced fuel load and vegetation cover, which reduced fire severity. Native shrubs had greater prefire cover in added water plots compared to reduced water plots. Native cover was lower and invasive cover was higher in postfire reduced water plots compared to postfire added and ambient water plots. Our results demonstrate the importance of fuel load on fire severity and plant community composition on an ecosystem scale. Management should focus on reducing fire frequency and removing invasive species to maintain the resilience of coastal sage scrub communities facing drought. In these communities, controlled burns are not recommended as they promote invasive plants.

中文翻译：

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长期干旱会降低野火的严重程度，从而促进物种入侵

人为气候变化增加了干旱、野火和非本地物种入侵的频率。尽管与干旱相关的严重火灾会抑制森林生态系统中原生植被的恢复，但目前尚不清楚干旱如何影响野火后其他植物群落的恢复。我们利用现有的降雨操纵实验来检验这样的假设：在南加州沿海鼠尾草灌丛系统中，降水量、燃料负荷和火灾严重程度的减少会将植物群落组成从原生灌木转变为入侵草本。我们测量了 2020 年西尔维拉多野火前后经过三种降雨处理的地块的群落组成。干旱减少了燃料负载和植被覆盖，从而降低了火灾的严重程度。与减少水区相比，增加水区的原生灌木在火前覆盖范围更大。与火后增加的水区和周围水区相比，火后减少的水区的原生覆盖率较低，入侵覆盖率较高。我们的结果证明了燃料负荷对生态系统规模上火灾严重程度和植物群落组成的重要性。管理应侧重于减少火灾频率和清除入侵物种，以保持沿海鼠尾草灌木群落面临干旱的恢复能力。在这些社区中，不建议进行控制性烧伤，因为它们会促进入侵植物的生长。