Divergent shrub-cover responses driven by climate, wildfire, and permafrost interactions in Arctic tundra ecosystems
Divergent shrub-cover responses driven by climate, wildfire, and permafrost interactions in Arctic tundra ecosystems
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DOI：
10.1111/gcb.15451
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发表时间：
2020-12-01
影响因子：
11.6
通讯作者：
Lara, Mark J.
中科院分区：
文献类型：
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作者：
Chen, Yaping;Hu, Feng S.;Lara, Mark J.
灌木在北极苔原上的扩张可能从根本上改变陆地-大气的相互作用。然而，目前尚不清楚灌木扩张模式与气候变化和火灾干扰等关键环境驱动因素之间的关系。在这里，我们使用了40多年的高分辨率（类似于1.0米）航空和卫星图像来估计阿拉斯加北部四个被烧毁和未被烧毁的高地（冰少）和低地（冰多）苔原生态系统的114个研究地点的灌木覆盖变化。通过另外四个高地和低地冻原火灾的数据验证，我们的研究结果表明，夏季降水是最重要的气候驱动因素（r = 0.67, p < 0.001），在1971年至2016年期间，高原冻原灌木扩张占30.8%。林火对高原灌木扩张有显著促进作用（p < 0.001），与林火严重程度呈显著正相关（r = 0.83, p < 0.001）。火灾干扰后30年，高原灌木覆盖面积增加了1077.2 +/- 83.6 m(2) ha(-1)，是相邻未燃烧高原苔原(155.1 +/- 55.4 m（2) ha(-1)）的7倍。与之相反，低海拔冻土带的灌木覆盖在火灾干扰后明显减少，引起热岩溶相关的蓄水，导致30年间灌木覆盖减少52.4%。低洼地灌木盖度与火灾严重程度无相关性（r = 0.01）。1951—2007年夏季平均气温是驱动低地灌木覆盖动态变化的主要因子。温暖的MSAT促进了未燃烧低地灌木的扩张（r = 0.78, p < 0.001），但加速了燃烧低地灌木覆盖的损失（r = -0.82, p < 0.001）。这些结果强调了灌木覆盖对火灾干扰和气候变化的不同响应路径，这取决于近地表永久冻土和排水条件。随着气候变暖和高纬度地区燃烧加剧，我们的研究为陆地-大气相互作用提供了新的见解。
The expansion of shrubs across the Arctic tundra may fundamentally modify land-atmosphere interactions. However, it remains unclear how shrub expansion pattern is linked with key environmental drivers, such as climate change and fire disturbance. Here we used 40+ years of high-resolution (similar to 1.0 m) aerial and satellite imagery to estimate shrub-cover change in 114 study sites across four burned and unburned upland (ice-poor) and lowland (ice-rich) tundra ecosystems in northern Alaska. Validated with data from four additional upland and lowland tundra fires, our results reveal that summer precipitation was the most important climatic driver (r = 0.67, p < 0.001), responsible for 30.8% of shrub expansion in the upland tundra between 1971 and 2016. Shrub expansion in the uplands was largely enhanced by wildfire (p < 0.001) and it exhibited positive correlation with fire severity (r = 0.83, p < 0.001). Three decades after fire disturbance, the upland shrub cover increased by 1077.2 +/- 83.6 m(2) ha(-1), similar to 7 times the amount identified in adjacent unburned upland tundra (155.1 +/- 55.4 m(2) ha(-1)). In contrast, shrub cover markedly decreased in lowland tundra after fire disturbance, which triggered thermokarst-associated water impounding and resulted in 52.4% loss of shrub cover over three decades. No correlation was found between lowland shrub cover with fire severity (r = 0.01). Mean summer air temperature (MSAT) was the principal factor driving lowland shrub-cover dynamics between 1951 and 2007. Warmer MSAT facilitated shrub expansion in unburned lowlands (r = 0.78, p < 0.001), but accelerated shrub-cover losses in burned lowlands (r = -0.82, p < 0.001). These results highlight divergent pathways of shrub-cover responses to fire disturbance and climate change, depending on near-surface permafrost and drainage conditions. Our study offers new insights into the land-atmosphere interactions as climate warming and burning intensify in high latitudes.