Climate change causes critical transitions and irreversible alterations of mountain forests
Climate change causes critical transitions and irreversible alterations of mountain forests
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DOI：
10.1111/gcb.15118
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发表时间：
2020-05-08
影响因子：
11.6
通讯作者：
Seidl, Rupert
中科院分区：
文献类型：
--
作者：
Albrich, Katharina;Rammer, Werner;Seidl, Rupert
由于其温度限制和高度受变暖影响，山区森林特别容易受到气候变化的影响。与此同时，其复杂的地形可能有助于缓冲气候变化的影响，并创造气候避难所。气候变化是否会导致山区森林生态系统的重大转变，以及这种转变是否是可逆的，仍然没有完全弄清楚。我们调查了森林组成和大小结构对气候变化的适应能力，重点是在阿尔卑斯山东部的山地森林景观。使用基于个人的森林景观模型iLand，我们模拟了生态系统对各种气候变化的响应（年平均气温上升6摄氏度，年平均降水量减少30%），测试了不同地形情景下植被大小结构和组成的临界点。我们发现，在升温水平超过+2摄氏度时，一个阈值被越过，系统进入另一种状态。该系统从以大型树木为特征的针叶树为主的景观转变为以较小的阔叶树为主的景观。地形的复杂性缓和了气候变化的影响，平滑和延迟了不同植被状态之间的过渡。我们随后逆转了模拟的气候强迫，以评估景观从气候变化影响中恢复的能力。森林景观表现出滞后性，特别是在降水量较低的情况下。在相同的年平均温度，平衡植被的大小结构和物种组成之间的变暖和冷却的轨迹不同。在这里，我们表明，即使是温和的变暖对应于当前的政策目标可能会导致森林生态系统的关键过渡，并强调地形复杂性作为缓冲剂的重要性。此外，我们的研究结果表明，超过雄心勃勃的气候减缓目标可能是危险的，因为一旦越过临界点，生态影响在千年时间尺度上可能是不可逆转的。
Mountain forests are at particular risk of climate change impacts due to their temperature limitation and high exposure to warming. At the same time, their complex topography may help to buffer the effects of climate change and create climate refugia. Whether climate change can lead to critical transitions of mountain forest ecosystems and whether such transitions are reversible remain incompletely understood. We investigated the resilience of forest composition and size structure to climate change, focusing on a mountain forest landscape in the Eastern Alps. Using the individual-based forest landscape model iLand, we simulated ecosystem responses to a wide range of climatic changes (up to a 6 degrees C increase in mean annual temperature and a 30% reduction in mean annual precipitation), testing for tipping points in vegetation size structure and composition under different topography scenarios. We found that at warming levels above +2 degrees C a threshold was crossed, with the system tipping into an alternative state. The system shifted from a conifer-dominated landscape characterized by large trees to a landscape dominated by smaller, predominantly broadleaved trees. Topographic complexity moderated climate change impacts, smoothing and delaying the transitions between alternative vegetation states. We subsequently reversed the simulated climate forcing to assess the ability of the landscape to recover from climate change impacts. The forest landscape showed hysteresis, particularly in scenarios with lower precipitation. At the same mean annual temperature, equilibrium vegetation size structure and species composition differed between warming and cooling trajectories. Here we show that even moderate warming corresponding to current policy targets could result in critical transitions of forest ecosystems and highlight the importance of topographic complexity as a buffering agent. Furthermore, our results show that overshooting ambitious climate mitigation targets could be dangerous, as ecological impacts can be irreversible at millennial time scales once a tipping point has been crossed.