High-severity wildfire leads to multi-decadal impacts on soil biogeochemistry in mixed-conifer forests

During the past century, systematic wildfire suppression has decreased fire frequency and increased fire severity in the western United States of America. While this has resulted in large ecological changes aboveground such as altered tree species composition and increased forest density, little is known about the long-term, belowground implications of altered, ecologically novel fire regimes, especially on soil biological processes. To better understand the long-term implications of ecologically novel, high-severity fire, we used a 44-y high-severity fire chronosequence in the Sierra Nevada where forests were historically adapted to frequent, low-severity fire, but were fire suppressed for at least 70 years. High-severity fire in the Sierra Nevada resulted in a long-term (44+ y) decrease (>50%, p < 0.05) in soil extracellular enzyme activities, basal microbial respiration (56-72%, p < 0.05), and organic carbon (>50%, p < 0.05) in the upper 5 cm compared to sites that had...

过去一个世纪以来，系统性野火抑制（wildfire suppression）措施降低了美国西部的火灾发生频率，同时提升了火灾烈度（fire severity）。尽管该举措已引发地上生态系统的显著变化，例如树种组成改变与森林密度升高，但针对生态型新型火灾制度（fire regimes）带来的长期地下影响，尤其是对土壤生物过程的相关认知仍较为匮乏。为深入解析生态型新型高烈度火灾的长期效应，我们依托内华达山脉（Sierra Nevada）一处为期44年的高烈度火灾年代序列（chronosequence）开展研究——该区域历史上本适应高频低烈度火灾，但因野火抑制措施已有至少70年未发生自然野火。研究结果表明，相较于sites that had...，内华达山脉的高烈度火灾可使表层5 cm土壤的胞外酶活性（soil extracellular enzyme activities）、基础微生物呼吸速率（basal microbial respiration，降幅56%-72%，p<0.05）与有机碳（organic carbon，降幅>50%，p<0.05）出现长达44年及以上的显著降低（均满足p<0.05的显著性水平）。