Department of Biology, Stanford University, Stanford, CA 94305, USA.
Conserv Biol. 2012 Dec;26(6):1082-90. doi: 10.1111/j.1523-1739.2012.01913.x. Epub 2012 Aug 14.
Forest die-off around the world is expected to increase in coming decades as temperature increases due to climate change. Forest die-off will likely affect understory plant communities, which have substantial influence on regional biological diversity, ecosystem function, and land-atmosphere interactions, but how die-off alters these plant communities is largely unknown. We examined changes in understory plant communities following a widespread, drought-induced die-off of trembling aspen (Populus tremuloides) in the western United States. We assessed shrub and herbaceous cover and volume in quadrats in 55 plots located across a wide range of levels of aspen mortality. We measured species richness and composition of herbaceous plant communities by recording species presence and absence in 12 sets of paired (1 healthy, 1 dying) aspen plots. Although understory composition in healthy and dying stands was heterogeneous across the landscape, shrub abundance, cover, and volume were higher and abundance of herbaceous species, cover, and volume were lower in dying aspen stands. Shrub cover and volume increased from 2009 to 2011 in dying stands, which suggests that shrub growth and expansion is ongoing. Species richness of herbs declined by 23% in dying stands. Composition of herbs differed significantly between dying and healthy stands. Richness of non-native species did not differ between stand types. The understory community in dying aspen stands was not similar to other shrub-dominated plant communities in the region and may constitute a novel community. Our results suggest that changes in understory plant communities as forests die off could be a significant indirect effect of climate change on biological diversity and forest communities.
随着气候变化导致气温升高，预计未来几十年全球范围内的森林死亡数量将会增加。森林死亡可能会影响林下植物群落，这些植物群落对区域生物多样性、生态系统功能和陆地-大气相互作用有很大的影响，但森林死亡如何改变这些植物群落还在很大程度上是未知的。我们在美国西部的一场广泛的、由干旱引起的颤杨（Populus tremuloides）死亡事件后，研究了林下植物群落的变化。我们在 55 个斑块的 12 个对（1 个健康，1 个垂死）的颤杨斑块中评估了灌木和草本植物的覆盖度和体积。我们通过记录 12 组配对的（1 个健康，1 个垂死）颤杨斑块中的物种存在和不存在来测量草本植物群落的物种丰富度和组成。尽管健康和垂死的林下群落在景观上是不均匀的，但灌木的丰度、覆盖度和体积在垂死的颤杨群落中较高，而草本物种的丰度、覆盖度和体积则较低。垂死的颤杨群落中的灌木覆盖度和体积从 2009 年到 2011 年增加，这表明灌木的生长和扩张仍在继续。垂死的颤杨群落中草本植物的物种丰富度下降了 23%。草本植物的组成在垂死的和健康的群落之间有显著差异。非本地物种的丰富度在不同的群落类型之间没有差异。垂死的颤杨群落中的林下群落与该地区其他以灌木为主的植物群落不同，可能构成了一个新的群落。我们的研究结果表明，随着森林的死亡，林下植物群落的变化可能是气候变化对生物多样性和森林群落的一个重要的间接影响。
