RAPID: Topographic variation in tornado blowdown severity, and consequences for forest regeneration

生态学家最近开始认识到，自然干扰是森林兴衰的固有组成部分，但对森林对自然干扰的反应的理解充其量是零星的。人们对森林对火灾、虫害爆发和飓风的反应有很好的了解，但对森林对冰暴、洪水和龙卷风的反应却知之甚少。该项目将检查2011年4月27日至28日创纪录的龙卷风爆发中三个长轨道龙卷风造成的森林破坏。一场龙卷风穿过田纳西州南部的大烟山国家公园西部，另外两场龙卷风穿过乔治亚州北部的查塔胡奇国家森林。该项目的核心目标是开发龙卷风路径沿线森林破坏严重程度的详细清单，并使用这些严重程度信息来测试三种生态模型，这些模型假设了森林如何应对不同严重程度的干扰。这项研究需要迅速开始，以便准确地测量干扰的严重程度，并在被回收或分解之前确定被吹倒的树种。一旦沿龙卷风路径确定了森林破坏的严重程度，就会对森林的恢复进行监测，看看哪个模型最准确地预测了森林的恢复。预测最准确的模型将被确认为对森林如何对风干扰作出反应的最佳理解。了解森林如何应对干扰对社会很重要，原因如下：1)指导管理决策，例如是否在干扰后砍伐木材；2)预测扰动后未来可能的物种组成，即50年后龙卷风吹落区是以樱桃和枫为主，还是以桦树和铁杉为主；3)提高再生森林的碳固定预测，这是森林在高二氧化碳大气中提供的一项至关重要的服务；而且，如果未来的气候变化带来极端天气事件的增加，4)可以预测森林在改变的扰动状态下将如何变化。

Ecologists have recently come to recognize that natural disturbances are an inherent part of the ebb and flow of forests, yet understanding of forest response to natural disturbances is patchy at best. There exists a good understanding of forest responses to fire, insect outbreaks, and hurricanes, but a poor grasp of forest response to ice storms, floods, and tornadoes. This project will examine forest damage caused by three long-track tornadoes that were part of the record-setting April 27-28, 2011 tornado outbreak. One tornado passed through the western section of Great Smoky Mountains National Park in southern Tennessee, and the other two through Chattahoochee National Forest in northern Georgia. The core goals of the project are to develop detailed inventories of the forest damage severity along these tornado tracks, and use that severity information to test three ecological models that hypothesize about how forests respond to different severity of disturbance. The study needs to begin promptly in order to accurately measure the severity of the disturbance and to identify the tree species that were blown down before they are salvage-logged or decompose. Once forest damage severity has been characterized along the tornado tracks, the recovery of the forests will be monitored, to see which model most accurately predicted the recovery of the forest. The model whose predictions are most accurate will be confirmed as the best understanding of how forests respond to wind disturbance. Knowledge of how forests respond to disturbance is important to society for a number of reasons: 1) guide management decisions, such as whether or not to log downed timber after disturbance; 2) project the likely future species composition after disturbance, i.e. will the tornado blowdown areas in 50 years be mostly cherry and maple, or mostly birch and hemlock?; 3) improve projections of carbon fixation in regrowing forests, a vitally important service provided by forests in a high-CO2 atmosphere; and, if future climate change brings increases in extreme weather events, 4) allow forecasts of how forests will change under the altered disturbance regime.