Ecology and Evolutionary Biology, University of Kansas, 2101 Constant Avenue Takeru Higuchi Hall, Lawrence, KS, 66047, USA.
Department of Biological Sciences, Louisiana State University, Baton Rouge, USA.
Oecologia. 2020 Jul;193(3):631-643. doi: 10.1007/s00442-020-04699-5. Epub 2020 Jul 22.
Frequent fires maintain nearly 50% of terrestrial ecosystems, and drive ecosystem changes that govern future fires. Since fires are dependent on available plant or fine fuels, ecosystem processes that alter fine fuel loads like microbial decomposition are particularly important and could modify future fires. We hypothesized that variation in short-term fire history would influence fuel dynamics in such ecosystems. We predicted that frequent fires within a short-time period would slow microbial decomposition of new fine fuels. We expected that fire effects would differ based on dominant substrates and that fire history would also alter soil nutrient availability, indirectly slowing decomposition. We measured decomposition of newly deposited fine fuels in a Longleaf pine savanna, comparing plots that burned 0, 1, 2, or 3 times between 2014 and 2016, and which were located in either close proximity to or away from overstory pines (Longleaf pine, Pinus palustris). Microbial decomposition was slower in plots near longleaf pines and, as the numbers of fires increased, decomposition slowed. We then used structural equation modeling to assess pathways for these effects (number of fires, 2016 fuel/fire characteristics, and soil chemistry). Increased fire frequency was directly associated with decreased microbial decomposition. While increased fires decreased nutrient availability, changes in nutrients were not associated with decomposition. Our findings indicate that increasing numbers of fires over short-time intervals can slow microbial decomposition of newly deposited fine fuels. This could favor fine fuel accumulation and drive positive feedbacks on future fires.
频繁的火灾维持着近 50%的陆地生态系统，并推动了控制未来火灾的生态系统变化。由于火灾依赖于可用的植物或细可燃物，因此改变细可燃物负荷的生态系统过程（如微生物分解）尤为重要，并可能改变未来的火灾。我们假设短期火灾历史的变化会影响这些生态系统中的燃料动态。我们预测，在短时间内频繁发生火灾会减缓新细可燃物的微生物分解。我们预计，火灾的影响将根据主要基质而有所不同，并且火灾历史也会改变土壤养分的可利用性，从而间接减缓分解。我们在长叶松稀树草原中测量了新沉积细可燃物的分解，比较了 2014 年至 2016 年期间分别燃烧 0、1、2 或 3 次的样地，并将其分别置于靠近或远离林冠松（长叶松，松属 palustris）的位置。在靠近长叶松的样地中，微生物分解较慢，随着火灾次数的增加，分解速度减慢。然后，我们使用结构方程模型来评估这些效应的途径（火灾次数、2016 年燃料/火灾特征和土壤化学）。火灾频率的增加与微生物分解的减少直接相关。虽然火灾的增加降低了养分的可利用性，但养分的变化与分解无关。我们的研究结果表明，在短时间间隔内增加火灾次数会减缓新沉积的细可燃物的微生物分解。这可能有利于细可燃物的积累，并对未来的火灾产生积极的反馈。
