Long-term Ecology Laboratory, Biodiversity Institute, Oxford Martin School, Department of Zoology, University of Oxford, Oxford OX1 3PS, United Kingdom.
Proc Natl Acad Sci U S A. 2013 May 14;110(20):8117-22. doi: 10.1073/pnas.1221278110. Epub 2013 Apr 8.
Forests are expected to expand into alpine areas because of climate warming, causing land-cover change and fragmentation of alpine habitats. However, this expansion will only occur if the present upper treeline is limited by low-growing season temperatures that reduce plant growth. This temperature limitation has not been quantified at a landscape scale. Here, we show that temperature alone cannot realistically explain high-elevation tree cover over a >100-km(2) area in the Canadian Rockies and that geologic/geomorphic processes are fundamental to understanding the heterogeneous landscape distribution of trees. Furthermore, upslope tree advance in a warmer scenario will be severely limited by availability of sites with adequate geomorphic/topographic characteristics. Our results imply that landscape-to-regional scale projections of warming-induced, high-elevation forest advance into alpine areas should not be based solely on temperature-sensitive, site-specific upper-treeline studies but also on geomorphic processes that control tree occurrence at long (centuries/millennia) timescales.
由于气候变暖，森林预计将扩展到高山地区，从而导致土地覆盖变化和高山生境的破碎化。然而，只有当目前的树线上限受到低温生长季节的限制，从而减少植物生长时，这种扩张才会发生。这种温度限制在景观尺度上尚未得到量化。在这里，我们表明，仅温度并不能合理地解释在加拿大落基山脉超过 100 平方公里的大面积高海拔地区的树木覆盖，而且地质/地貌过程对于理解树木在异质景观中的分布是至关重要的。此外，在更温暖的情景下，树木向上坡扩展将受到具有足够地貌/地形特征的可用地点的严重限制。我们的研究结果表明，不应该仅仅基于对温度敏感的、特定地点的树线上限研究，而应该基于控制树木在长（数百年/千年）时间尺度上出现的地貌过程，来对变暖引起的高海拔森林向高山地区扩展进行景观到区域尺度的预测。
