The role of fire in the carbon dynamics of the boreal forest I. - Response of area burned to changing climate in western boreal North America using a Multivariate Adaptive Regression Splines (MARS) approach (2003-2100).

The boreal forest contains large reserves of carbon, and across this region wildfire is a common occurrence. To improve the understanding of how wildfire influences the carbon dynamics of this region, methods were developed to incorporate the spatial and temporal effects of fire into the Terrestrial ecosystem Model (TEM). The historical role of fire on carbon dynamics of the boreal region was evaluated within the context of ecosystem responses to changing atmospheric CO2 and climate. These results show that the role of historical fire on boreal carbon dynamics resulted in a net carbon sink; however, fire plays a major role in the interannual and decadal scale variation of source/sink relationships. To estimate the effects of future fire on boreal carbondynamics, spatially and temporally explicit empirical relationships between climate andfire were quantified. Fuel moisture, monthly severity rating, and air temperature explained a significant proportion of observed variability in annual area burned. These relationships were used to estimate annual area burned for future scenarios of climate change and were coupled to TEM to evaluate the role of future fire on the carbon dynamics of the North American boreal region for the 21st Century. Simulations with TEM indicate that boreal North America is a carbon sink in response to CO2 fertilization, climate variability, and fire, but an increase in fire leads to a decrease in the sink strength. While this study highlights the importance of fire on carbon dynamics in the boreal region, there are uncertainties in the effects of fire in TEM simulations. These uncertainties are associated with sparse fire data for northern Eurasia, uncertainty in estimating carbon consumption, and difficulty in verifying assumptions about the representation of fires that occurred prior to the start of the historical fire record. Future studies should incorporate the role of dynamic vegetation to more accurately represent post-fire successional processes, incorporate fire severity parameters that change in time and space, and integrate the role of other disturbances and their interactions with future fire regimes.北方针叶林（boreal forest）储存着巨量的碳储量，该区域内野火频发。为深化对野火如何影响该区域碳动态的认知，研究人员开发了将野火的时空效应纳入陆地生态系统模型（Terrestrial ecosystem Model, TEM）的方法。本研究在生态系统对大气CO₂浓度与气候变化的响应这一框架下，评估了历史野火对北方针叶林区域碳动态的作用。研究结果表明，历史野火对北方针叶林碳动态的作用整体形成了净碳汇；但野火在源汇关系的年际与年代际尺度波动中扮演着核心角色。为预估未来野火对北方针叶林碳动态的影响，研究人员量化得到了气候与野火之间具有时空显式特征的经验关联。可燃物含水率、月度火险等级以及气温，能够解释观测到的年度过火面积变异中的绝大部分。利用这些经验关联，研究人员预估了气候变化未来情景下的年度过火面积，并将其与陆地生态系统模型（TEM）耦合，以评估21世纪未来野火对北美北方针叶林区域碳动态的作用。基于TEM的模拟结果显示，在CO₂肥效、气候波动与野火的共同作用下，北美北方针叶林整体表现为碳汇；但野火频次的增加会导致该区域的碳汇强度下降。尽管本研究凸显了野火对北方针叶林碳动态的重要性，但陆地生态系统模型（TEM）中野火效应的模拟仍存在诸多不确定性。这些不确定性主要源于欧亚大陆北部的野火观测数据匮乏、碳消耗量估算存在误差，以及难以验证历史野火记录起始前野火表征相关假设的合理性。未来研究应纳入动态植被的作用，以更精准地还原火后演替过程；引入随时空变化的火烈度参数；并整合其他干扰因子的作用，以及它们与未来火灾格局的相互影响。