Breshears David D, Cobb Neil S, Rich Paul M, Price Kevin P, Allen Craig D, Balice Randy G, Romme William H, Kastens Jude H, Floyd M Lisa, Belnap Jayne, Anderson Jesse J, Myers Orrin B, Meyer Clifton W
School of Natural Resources, Institute for the Study of Planet Earth, and Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721-0043, USA.
Proc Natl Acad Sci U S A. 2005 Oct 18;102(42):15144-8. doi: 10.1073/pnas.0505734102. Epub 2005 Oct 10.
Future drought is projected to occur under warmer temperature conditions as climate change progresses, referred to here as global-change-type drought, yet quantitative assessments of the triggers and potential extent of drought-induced vegetation die-off remain pivotal uncertainties in assessing climate-change impacts. Of particular concern is regional-scale mortality of overstory trees, which rapidly alters ecosystem type, associated ecosystem properties, and land surface conditions for decades. Here, we quantify regional-scale vegetation die-off across southwestern North American woodlands in 2002-2003 in response to drought and associated bark beetle infestations. At an intensively studied site within the region, we quantified that after 15 months of depleted soil water content, >90% of the dominant, overstory tree species (Pinus edulis, a piñon) died. The die-off was reflected in changes in a remotely sensed index of vegetation greenness (Normalized Difference Vegetation Index), not only at the intensively studied site but also across the region, extending over 12,000 km2 or more; aerial and field surveys confirmed the general extent of the die-off. Notably, the recent drought was warmer than the previous subcontinental drought of the 1950s. The limited, available observations suggest that die-off from the recent drought was more extensive than that from the previous drought, extending into wetter sites within the tree species' distribution. Our results quantify a trigger leading to rapid, drought-induced die-off of overstory woody plants at subcontinental scale and highlight the potential for such die-off to be more severe and extensive for future global-change-type drought under warmer conditions.
随着气候变化的推进，预计未来干旱将在温度升高的条件下发生，这里称之为全球变化型干旱，然而，对于干旱引发植被死亡的触发因素和潜在范围的定量评估，仍然是评估气候变化影响的关键不确定因素。特别令人担忧的是上层树木的区域尺度死亡率，这会在数十年内迅速改变生态系统类型、相关的生态系统属性和陆地表面状况。在这里，我们量化了2002 - 2003年北美西南部林地因干旱和相关树皮甲虫侵扰导致的区域尺度植被死亡情况。在该区域一个经过深入研究的地点，我们量化得出，在土壤含水量耗尽15个月后，超过90%的优势上层树种（矮松，一种松属植物）死亡。这种死亡不仅在深入研究的地点，而且在整个区域，通过植被绿度遥感指数（归一化植被指数）的变化得到反映，影响范围超过12000平方公里甚至更广；航空和实地调查证实了死亡的总体范围。值得注意的是，最近的干旱比20世纪50年代以前的次大陆干旱温度更高。有限的现有观测表明，最近这次干旱导致的死亡比前一次干旱更广泛，延伸到了该树种分布范围内更湿润的地区。我们的结果量化了一个导致次大陆尺度上层木本植物因干旱迅速死亡的触发因素，并强调了在更温暖条件下，这种死亡对于未来全球变化型干旱可能会更加严重和广泛的可能性。
