Data from: Fire-regime variability impacts forest carbon dynamics for centuries to millennia

Wildfire is a dominant disturbance agent in forest ecosystems, shaping important biogeochemical processes including net carbon (C) balance. Long-term monitoring and chronosequence studies highlight a resilience of biogeochemical properties to large, stand-replacing, high-severity fire events. In contrast, the consequences of repeated fires or temporal variability in a fire regime (e.g., the characteristic timing or severity of fire) are largely unknown, yet theory suggests that such variability could strongly influence forest C trajectories (i.e., future states or directions) for millennia. Here we combine a 4500-year paleoecological record of fire activity with ecosystem modeling to investigate how fire-regime variability impacts soil C and net ecosystem carbon balance. We found that C trajectories in a paleo-informed scenario differed significantly from an equilibrium scenario (with a constant fire return interval), largely due to variability in the timing and severity of past fires. Paleo-informed scenarios contained multi-century periods of positive and negative net ecosystem C balance, with magnitudes significantly larger than observed under the equilibrium scenario. Further, this variability created legacies in soil C trajectories that lasted for millennia. Our results imply that fire-regime variability is a major driver of C trajectories in stand-replacing fire regimes. Predicting carbon balance in these systems, therefore, will depend strongly on the ability of ecosystem models to represent a realistic range of fire-regime variability over the past several centuries to millennia.野火是森林生态系统中占主导地位的干扰因子，塑造着包括净碳平衡（net carbon balance）在内的关键生物地球化学过程。长期监测与年代序列（chronosequence）研究表明，生物地球化学性质（biogeochemical properties）对大规模、林分更替型高烈度火灾事件（stand-replacing, high-severity fire events）具有恢复能力。与之相反，重复火灾或火制度（fire regime）的时间变异性（例如火灾的特征发生时间或烈度）所带来的生态后果，在很大程度上仍未明确；但理论研究显示，此类变异性可在数千年尺度上强烈影响森林碳轨迹（forest C trajectories，即未来的状态与发展方向）。本研究将一份长达4500年的火灾活动古生态学记录（paleoecological record）与生态系统建模（ecosystem modeling）相结合，旨在探究火制度变异性对土壤碳（soil C）与生态系统净碳平衡（net ecosystem carbon balance）的影响。研究发现，古生态约束情景（paleo-informed scenario）下的碳轨迹，与恒定火灾间隔期（fire return interval）的平衡情景（equilibrium scenario）存在显著差异，这一差异主要源于过往火灾发生时序与烈度的变异性。古生态约束情景下存在持续数个世纪的生态系统净碳平衡正负波动期，其波动幅度显著高于平衡情景下的观测结果。此外，此类变异性对土壤碳轨迹产生了持续数千年的遗留效应。本研究结果表明，在林分更替型火制度中，火制度变异性是森林碳轨迹的核心驱动因子。因此，要精准预测此类生态系统的碳平衡，很大程度上取决于生态系统模型能否在数百年至数千年的尺度上，表征出符合实际的火制度变异性范围。