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.

频繁的大火维持了近50％的陆地生态系统，并推动了控制未来大火的生态系统变化。由于火灾取决于可用的植物或精细燃料，因此改变精细燃料负荷（如微生物分解）的生态系统过程尤为重要，并且可能会改变未来的火灾。我们假设短期火灾历史的变化会影响此类生态系统中的燃料动态。我们预测，短时间内的频繁起火会减缓新细燃料的微生物分解。我们预计，火灾的影响将因主要基质而异，火灾的历史还将改变土壤养分的利用率，间接减慢分解速度。我们测量了Longleaf松大草原中新沉积的细燃料的分解情况，比较了2014年至2016年燃烧0、1、2或3次的地块，松（Pinus palustris）。在长叶松树附近的地块，微生物的分解较慢，并且随着火势的增加，分解也变慢。然后，我们使用结构方程模型评估这些影响的途径（火灾次数，2016年燃料/火灾特征和土壤化学性质）。着火频率的增加与微生物分解的减少直接相关。虽然大火减少了养分的可利用性，但养分的变化与分解无关。我们的发现表明，短时间间隔内越来越多的火灾会减缓新沉积的细燃料的微生物分解。这可能有利于良好的燃料积累，并在未来的火灾中产生积极的反馈。