Tall shrub and tree expansion in Siberian tundra ecotones since the 1960s
Tall shrub and tree expansion in Siberian tundra ecotones since the 1960s
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DOI：
10.1111/gcb.12406
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发表时间：
2014-04-01
影响因子：
11.6
通讯作者：
Epstein, Howard E.
中科院分区：
文献类型：
--
作者：
Frost, Gerald V.;Epstein, Howard E.
人们普遍认为，由于最近的气候变暖，高大的灌木和树木向北极苔原的绕极扩张正在发生，但在北方西伯利亚，几乎没有量化的证据，那里包括世界上最大的森林苔原生态带。我们量化的变化，高大的灌木和乔木树冠覆盖在11个，广泛分布的西伯利亚生态交错景观比较非常高分辨率的照片从冷战时期的Gambit和电晕卫星监视系统（1965年至1969年）与现代图像。我们还分析了植被变化的景观内格局，以评估不同的景观组成部分的敏感性高灌木和树木的增加。11个生态交错带中有9个的高灌木和乔木的总覆盖率增加。在西伯利亚西北部，桤木（桤木）灌木林覆盖增加5.3-25.9%，在5个交错带。在泰梅尔和雅库特，落叶松（落叶松）覆盖率增加了3.0-6.7%，在三个生态交错带，但下降了16.8%，在第四个生态交错带，由于融化的冰丰富的永久冻土。在楚科奇，总覆盖桤木和矮松（松）增加6.1%，在第二个生态交错带内变化不大。在大多数景观中，灌木和树木的增加与特定的地貌环境，特别是那些活跃的干扰制度，如冻土图案地面，洪泛平原，崩积山坡。自20世纪60年代中期以来，夏季平均气温在大多数生态交错区增加，但灌木和乔木冠层覆盖扩张率与温度趋势没有很强的相关性，与年平均降水量有较好的相关性。我们的结论是，灌木和树木覆盖率增加的苔原交错区在北方西伯利亚的大部分地区，但增长率差异很大，在景观尺度。我们的研究结果表明，广泛的变化可以发生在几十年内潮湿，灌木为主的生态交错区，在西伯利亚西北部，而变化可能会发生得更慢，在高度大陆，落叶松为主的生态交错区的中部和东部西伯利亚。
Circumpolar expansion of tall shrubs and trees into Arctic tundra is widely thought to be occurring as a result of recent climate warming, but little quantitative evidence exists for northern Siberia, which encompasses the world's largest forest-tundra ecotonal belt. We quantified changes in tall shrub and tree canopy cover in 11, widely distributed Siberian ecotonal landscapes by comparing very high-resolution photography from the Cold War-era Gambit' and Corona' satellite surveillance systems (1965-1969) with modern imagery. We also analyzed within-landscape patterns of vegetation change to evaluate the susceptibility of different landscape components to tall shrub and tree increase. The total cover of tall shrubs and trees increased in nine of 11 ecotones. In northwest Siberia, alder (Alnus) shrubland cover increased 5.3-25.9% in five ecotones. In Taymyr and Yakutia, larch (Larix) cover increased 3.0-6.7% within three ecotones, but declined 16.8% at a fourth ecotone due to thaw of ice-rich permafrost. In Chukotka, the total cover of alder and dwarf pine (Pinus) increased 6.1% within one ecotone and was little changed at a second ecotone. Within most landscapes, shrub and tree increase was linked to specific geomorphic settings, especially those with active disturbance regimes such as permafrost patterned-ground, floodplains, and colluvial hillslopes. Mean summer temperatures increased at most ecotones since the mid-1960s, but rates of shrub and tree canopy cover expansion were not strongly correlated with temperature trends and were better correlated with mean annual precipitation. We conclude that shrub and tree cover is increasing in tundra ecotones across most of northern Siberia, but rates of increase vary widely regionally and at the landscape scale. Our results indicate that extensive changes can occur within decades in moist, shrub-dominated ecotones, as in northwest Siberia, while changes are likely to occur much more slowly in the highly continental, larch-dominated ecotones of central and eastern Siberia.