Potter Christopher
NASA Ames Research Center, Moffett Field, Mountain View, CA, USA.
Carbon Balance Manag. 2018 Jan 8;13(1):2. doi: 10.1186/s13021-017-0090-0.
In the summer of 2015, hundreds of wildfires burned across the state of Alaska, and consumed more than 1.6 million ha of boreal forest and wetlands in the Yukon-Koyukuk region. Mapping of 113 large wildfires using Landsat satellite images from before and after 2015 indicated that nearly 60% of this area was burned at moderate-to-high severity levels. Field measurements near the town of Tanana on the Yukon River were carried out in July of 2017 in both unburned and 2015 burned forested areas (nearly adjacent to one-another) to visually verify locations of different Landsat burn severity classes (low, moderate, or high; LBS, MBS, HBS).
Field measurements indicated that the loss of surface organic layers in boreal ecosystem fires is a major factor determining post-fire soil temperature changes, depth of thawing, and carbon losses from the mineral topsoil layer. Measurements in forest sites showed that soil temperature profiles to 30 cm depth at burned forest sites were higher by an average of 8-10 °C compared to unburned forest sites. Sampling and laboratory analysis indicated a 65% reduction in soil carbon content and a 58% reduction in soil nitrogen content in severely burned sample sites compared to soil mineral samples from nearby unburned spruce forests.
Combined with nearly unprecedented forest areas severely burned in the Interior region of Alaska in 2015, total ecosystem fire-related losses of carbon to the atmosphere exceeded most previous estimates for the state, owing mainly to inclusion of potential "mass wasting" and decomposition in the mineral soil carbon layer in the 2 years following these forest fires.
2015年夏季，阿拉斯加州发生了数百起野火，烧毁了育空-科尤库克地区超过160万公顷的北方森林和湿地。利用2015年前后的陆地卫星图像对113起大型野火进行的测绘表明，该地区近60%的面积被中度至高度严重程度烧毁。2017年7月，在育空河上塔纳纳镇附近未燃烧和2015年燃烧过的（几乎相邻的）森林地区进行了实地测量，以目视验证不同陆地卫星燃烧严重程度等级（低、中或高；LBS、MBS、HBS）的位置。
实地测量表明，北方生态系统火灾中地表有机层的损失是决定火灾后土壤温度变化、解冻深度和矿质表层土壤碳损失的主要因素。森林地区的测量显示，与未燃烧的森林地区相比，燃烧过的森林地区30厘米深度的土壤温度剖面平均高出8-10°C。采样和实验室分析表明，与附近未燃烧的云杉林的土壤矿物样本相比，严重燃烧的样本地点的土壤碳含量减少了65%，土壤氮含量减少了58%。
结合2015年阿拉斯加内陆地区几乎史无前例的大面积森林被严重烧毁的情况，生态系统与火灾相关的碳向大气中的总损失超过了该州此前的大多数估计，这主要是因为在这些森林火灾后的两年里，矿质土壤碳层中包含了潜在的“物质流失”和分解。
