Thresholds for boreal biome transitions
Thresholds for boreal biome transitions
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DOI：
10.1073/pnas.1219844110
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发表时间：
2012-12-26
影响因子：
11.1
通讯作者：
Chapin, F. Stuart, III
中科院分区：
文献类型：
--
作者：
Scheffer, Marten;Hirota, Marina;Chapin, F. Stuart, III
尽管北方地区的变暖速度是全球平均速度的两倍，但人们对广袤的北方森林和苔原的反应方式知之甚少。利用卫星数据，我们揭示了北方树木覆盖频率分布中明显的替代模式。在北端和干旱的大陆南端，分别是没有树木的苔原和草原，是唯一可能的状态。然而，在广泛的中等温度范围内，这些无树状态与北方森林（类似75%的树木覆盖率）和两种更开放的林地状态（类似20%和45%的树木覆盖率）共存。这些不同状态之间的中间树覆盖率（例如，类似于10%，类似于30%，类似于60%的树覆盖率）相对较少，这表明它们可能代表系统只是短暂存在的不稳定状态。这种不稳定性的机制仍有待揭示，但我们的研究结果对这些生态系统对气候变化的预期反应具有重要意义。数据显示，北方森林的树木覆盖没有逐渐减少到极限。相反，我们的分析表明，从某种意义上说，它变得不那么有弹性，它可能更容易转变为稀疏的林地或无树状态。同样，中间地带树木覆盖率的相对稀缺性（约为10%）表明，冻土带可能会相对突然地转变为树木覆盖率更丰富的地区。如果我们的推断是正确的，气候变化可能会引起北方生物群落的大规模非线性变化。
Although the boreal region is warming twice as fast as the global average, the way in which the vast boreal forests and tundras may respond is poorly understood. Using satellite data, we reveal marked alternative modes in the frequency distributions of boreal tree cover. At the northern end and at the dry continental southern extremes, treeless tundra and steppe, respectively, are the only possible states. However, over a broad intermediate temperature range, these treeless states coexist with boreal forest (similar to 75% tree cover) and with two more open woodland states (similar to 20% and similar to 45% tree cover). Intermediate tree covers (e.g., similar to 10%, similar to 30%, and similar to 60% tree cover) between these distinct states are relatively rare, suggesting that they may represent unstable states where the system dwells only transiently. Mechanisms for such instabilities remain to be unraveled, but our results have important implications for the anticipated response of these ecosystems to climatic change. The data reveal that boreal forest shows no gradual decline in tree cover toward its limits. Instead, our analysis suggests that it becomes less resilient in the sense that it may more easily shift into a sparse woodland or treeless state. Similarly, the relative scarcity of the intermediate similar to 10% tree cover suggests that tundra may shift relatively abruptly to a more abundant tree cover. If our inferences are correct, climate change may invoke massive nonlinear shifts in boreal biomes.