van Mantgem Phillip J, Stephenson Nathan L, Byrne John C, Daniels Lori D, Franklin Jerry F, Fulé Peter Z, Harmon Mark E, Larson Andrew J, Smith Jeremy M, Taylor Alan H, Veblen Thomas T
U.S. Geological Survey, Western Ecological Research Center, Three Rivers, CA 93271, USA.
Science. 2009 Jan 23;323(5913):521-4. doi: 10.1126/science.1165000.
Persistent changes in tree mortality rates can alter forest structure, composition, and ecosystem services such as carbon sequestration. Our analyses of longitudinal data from unmanaged old forests in the western United States showed that background (noncatastrophic) mortality rates have increased rapidly in recent decades, with doubling periods ranging from 17 to 29 years among regions. Increases were also pervasive across elevations, tree sizes, dominant genera, and past fire histories. Forest density and basal area declined slightly, which suggests that increasing mortality was not caused by endogenous increases in competition. Because mortality increased in small trees, the overall increase in mortality rates cannot be attributed solely to aging of large trees. Regional warming and consequent increases in water deficits are likely contributors to the increases in tree mortality rates.
树木死亡率的持续变化会改变森林结构、组成以及诸如碳固存等生态系统服务。我们对美国西部未受管理的老龄森林的纵向数据进行分析后发现，近几十年来背景（非灾难性）死亡率迅速上升，各地区的倍增期在17至29年之间。死亡率的上升在不同海拔、树木大小、优势属以及过去的火灾历史中也普遍存在。森林密度和基部面积略有下降，这表明死亡率的上升并非由竞争的内生性增加所致。由于小树的死亡率也在上升，所以死亡率的总体上升不能仅仅归因于大树的老化。区域变暖以及随之而来的水分亏缺增加可能是树木死亡率上升的原因。
