The role of fire in the carbon dynamics of the boreal forest III. - North America model simulations of historical fire disturbance and carbon dynamics (1900-2100).

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）储存着巨量碳储量，野火（wildfire）在该区域内频发。为深化对野火如何影响该区域碳动态（carbon dynamics）的认知，研究人员开发了将火灾的时空效应纳入陆地生态系统模型（Terrestrial ecosystem Model, TEM）的方法。研究在生态系统对大气二氧化碳（CO₂）与气候变化的响应框架下，评估了历史火灾对北方针叶林区域碳动态的作用。结果显示，历史火灾对北方针叶林碳动态的整体作用形成了净碳汇（net carbon sink）；但野火在源汇关系（source/sink relationships）的年际与年代际尺度（interannual and decadal scale）波动中扮演了核心角色。为预估未来野火对北方针叶林碳动态的影响，研究量化了气候与野火之间的时空显式经验关联（spatially and temporally explicit empirical relationships）。燃料湿度（fuel moisture）、月度火灾严重性评级（monthly severity rating）与气温，能够解释观测到的年过火面积（annual area burned）变异中的显著部分。利用上述经验关联，可预估气候变化未来情景（future scenarios of climate change）下的年过火面积，并将其与TEM耦合，以评估21世纪内未来野火对北美北方针叶林区域（North American boreal region）碳动态的作用。基于TEM的模拟结果表明，受二氧化碳施肥效应（CO₂ fertilization）、气候波动与野火的共同影响，北美北方针叶林整体表现为碳汇；但野火活动增强会削弱该区域的碳汇强度（sink strength）。尽管本研究凸显了野火对北方针叶林碳动态的重要性，但TEM模拟中野火的影响仍存在诸多不确定性。这些不确定性与欧亚大陆北部（northern Eurasia）火灾数据稀缺、碳消耗量（carbon consumption）估算存在误差，以及难以验证历史火灾记录（historical fire record）起始前火灾表征相关假设的合理性有关。未来研究应纳入动态植被的作用，以更精准地刻画火后演替过程（post-fire successional processes）；引入随时空变化的火灾严重性参数；并整合其他干扰因子的作用，以及它们与未来火灾格局（fire regimes）的相互影响。