Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, 47907, USA.
Department of Agronomy, Purdue University, West Lafayette, IN, 47907, USA.
Sci Rep. 2021 Apr 8;11(1):7723. doi: 10.1038/s41598-021-87343-3.
Wildfires are a major disturbance to forest carbon (C) balance through both immediate combustion emissions and post-fire ecosystem dynamics. Here we used a process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM), to simulate C budget in Alaska and Canada during 1986-2016, as impacted by fire disturbances. We extracted the data of difference Normalized Burn Ratio (dNBR) for fires from Landsat TM/ETM imagery and estimated the proportion of vegetation and soil C combustion. We observed that the region was a C source of 2.74 Pg C during the 31-year period. The observed C loss, 57.1 Tg C year, was attributed to fire emissions, overwhelming the net ecosystem production (1.9 Tg C year) in the region. Our simulated direct emissions for Alaska and Canada are within the range of field measurements and other model estimates. As burn severity increased, combustion emission tended to switch from vegetation origin towards soil origin. When dNBR is below 300, fires increase soil temperature and decrease soil moisture and thus, enhance soil respiration. However, the post-fire soil respiration decreases for moderate or high burn severity. The proportion of post-fire soil emission in total emissions increased with burn severity. Net nitrogen mineralization gradually recovered after fire, enhancing net primary production. Net ecosystem production recovered fast under higher burn severities. The impact of fire disturbance on the C balance of northern ecosystems and the associated uncertainties can be better characterized with long-term, prior-, during- and post-disturbance data across the geospatial spectrum. Our findings suggest that the regional source of carbon to the atmosphere will persist if the observed forest wildfire occurrence and severity continues into the future.
野火通过直接燃烧排放和火灾后生态系统动态对森林碳（C）平衡产生重大影响。本研究利用基于过程的生物地球化学模型——陆地生态系统模型（TEM），模拟了 1986 年至 2016 年期间，火干扰对阿拉斯加和加拿大碳预算的影响。我们从 Landsat TM/ETM 图像中提取了火灾的归一化燃烧比（dNBR）数据，并估算了植被和土壤 C 的燃烧比例。研究发现，在 31 年间，该区域是一个 2.74 Pg C 的碳源。观测到的 57.1Tg C 年的碳损失归因于火灾排放，这远远超过了该区域的净生态系统生产力（1.9Tg C 年）。我们模拟的阿拉斯加和加拿大的直接排放处于实地测量和其他模型估计的范围之内。随着燃烧严重程度的增加，燃烧排放有从植被源向土壤源转变的趋势。当 dNBR 低于 300 时，火灾会升高土壤温度并降低土壤湿度，从而增强土壤呼吸。然而，中等到高燃烧严重程度会降低火灾后的土壤呼吸。火灾后土壤排放在总排放中的比例随着燃烧严重程度的增加而增加。火灾后，净氮矿化逐渐恢复，从而增强了净初级生产力。在较高的燃烧严重程度下，净生态系统生产力的恢复速度较快。通过跨地理空间范围获取长期、预先、期间和干扰后数据，可以更好地描述火干扰对北方生态系统碳平衡的影响及其相关不确定性。研究结果表明，如果未来观察到的森林野火发生频率和严重程度持续下去，该区域向大气输送碳的源汇将持续存在。
