Department of Biology, University of Florida, Gainesville, Florida, USA.
Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Tartu, Estonia.
Nature. 2018 Apr 5;556(7699):99-102. doi: 10.1038/nature26152. Epub 2018 Mar 21.
Forests have a key role in global ecosystems, hosting much of the world's terrestrial biodiversity and acting as a net sink for atmospheric carbon. These and other ecosystem services that are provided by forests may be sensitive to climate change as well as climate variability on shorter time scales (for example, annual to decadal). Previous studies have documented responses of forest ecosystems to climate change and climate variability, including drought-induced increases in tree mortality rates. However, relationships between forest biomass, tree species composition and climate variability have not been quantified across a large region using systematically sampled data. Here we use systematic forest inventories from the 1980s and 2000s across the eastern USA to show that forest biomass responds to decadal-scale changes in water deficit, and that this biomass response is amplified by concurrent changes in community-mean drought tolerance, a functionally important aspect of tree species composition. The amplification of the direct effects of water stress on biomass occurs because water stress tends to induce a shift in tree species composition towards species that are more tolerant to drought but are slower growing. These results demonstrate concurrent changes in forest species composition and biomass carbon storage across a large, systematically sampled region, and highlight the potential for climate-induced changes in forest ecosystems across the world, resulting from both direct effects of climate on forest biomass and indirect effects mediated by shifts in species composition.
森林在全球生态系统中扮演着关键角色，承载着世界上大部分的陆地生物多样性，并作为大气碳的净汇。这些以及其他由森林提供的生态系统服务可能对气候变化以及更短时间尺度上的气候变化（例如，年际到十年际）敏感。以前的研究记录了森林生态系统对气候变化和气候变化的响应，包括干旱引起的树木死亡率增加。然而，在很大的区域范围内，使用系统采样的数据来量化森林生物量、树种组成和气候变化之间的关系尚未得到证实。在这里，我们使用 20 世纪 80 年代和 2000 年代美国东部的系统森林清查数据，表明森林生物量对十年尺度的水分亏缺变化有响应，并且这种生物量响应因同时发生的群落平均干旱耐受能力变化而放大，这是树种组成的一个重要功能方面。水分胁迫对生物量的直接影响的放大是因为水分胁迫往往会导致树种组成向更能耐受干旱但生长更缓慢的物种转移。这些结果表明，在一个大的、系统采样的区域内，森林物种组成和生物量碳储存同时发生变化，并强调了由于气候对森林生物量的直接影响以及通过物种组成变化介导的间接影响，世界范围内森林生态系统可能发生气候变化。
