SGER: Rapid Ecotonal Shifts in the Southwest

[909109]惠瑟姆传统理论认为，在数千年的时间里，过渡带在海拔或纬度上逐渐发生变化。然而，最近的证据表明，由于干旱带来的气候变化，西南地区可能正在发生快速的变化。在低海拔地区，由于1996年的干旱，生长在南坡贫瘠土壤上的小松的死亡率高达40-100%。这项SGER研究有两个主要目标。首先，由于许多这些树木现在都是在打捞作业中采伐的，因此在证据被删除之前记录死亡率的地理模式非常重要。其次，通过研究个别地点的死亡率模式，可以了解到很多决定谁生谁死的因素，提高我们对这种死亡率在社区一级造成的后果的理解。本研究将记录一个在大空间尺度上影响植被格局的事件。这在干旱的西南地区尤其重要，全球气候变化的预测影响被认为是巨大的。此外，由于小松是北美第三大植被类型的优势树种，任何影响这棵树的事情都可能对其他依赖的群落产生连锁反应。分析将为边界种群的动态特性提供证据，记录长寿物种的短期反应，并量化一个优势物种被另一个优势物种迅速取代的林分。证明这些事件对了解社区和生态系统对创纪录干旱和气候变化的反应具有重要意义。该项目的结果将纳入该领域正在进行的LTREB研究方案。

9909109WhithamConventional theory argues that ecotones gradually shift in elevation or latitude over thousands of years. Recent evidence, however, suggests that rapid shifts may be occurring in the Southwest due to climate changes brought about by drought. At low elevations, pinyon pines growing in poor soils on exposed southern slopes have suffered 40-100% mortality as a result of the 1996 drought. This SGER research has two major goals. First, because many of these trees are now being harvested in salvage operations, it is important to document the geographical patterns of mortality before the evidence is removed. Second, by studying the patters of mortality within individual sites, much can be learned about the factors that determine who lives and dies, improving our understanding of the community-level consequences of this mortality. This study will record an event that impacts vegetation patterns at large spatial scales. This is especially important in the arid Southwest where the predicted impacts of global climate changes are thought to be great. Furthermore, because pinyon pine is a dominant tree of the third largest vegetation type in North America, anything that affects this tree is likely to have ripple effects on the rest of the dependent community. Analyses will provide evidence of the dynamic nature of boundary populations, document short-term responses of long-lived species, and quantify rapid stand replacement of one dominant by another. Demonstrating such events has important implications for understanding of community and ecosystem responses to record droughts and climate change. The results of this project will be incorporated into an on-going LTREB research program in this area.