Collaborative: How the Timing of Summer Precipitation Affects the Responses of Boreal Forest to Climate Change

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。越来越多的证据表明，高纬度地区的生态过程对事件发生的时间和程度同样敏感。在北方森林中，夏季的水分供应既影响树木的生长，也影响火灾的发生。夏季是短暂的，季节转换很快，所以即使是降水模式的微小变化也会产生很大的影响。阿拉斯加北部针叶林最引人注目的季节性现象之一是夏末频繁的锋面风暴。这一活动通常在7月中旬举行，但有些年份会推迟到8月甚至9月。夏季，当降雨被推迟时，当160万公顷被烧毁的时候，更有可能成为特大火灾季节。该项目将检验这样一种假设，即暖季降水的季节性变化可能是北方森林对未来气候变化反应的关键驱动因素--S。夏末降水对阿拉斯加树木生长和火灾的影响将通过两种方式进行量化：第一，通过分析气候、火灾和树木生长之间的相互作用(特别是年轮宽度、年轮密度和木材同位素组成)；第二，通过使用新的统计方法分析火灾-气候关系。总而言之，这些结果将改进露天森林模型的参数化，然后将被用于测试关于未来气候、树木生长、火灾及其对全球气候系统的集体反馈之间的相互联系的额外假设。暖季期间可用水的季节性变化可能是决定全球北方森林如何应对未来气候变化的关键。这里提出的多学科研究代表了回答一个新问题的新方法。以前还没有人研究过暖季降水的时间和幅度的季节性变化对北部针叶林的植被分布、树木生长和火灾状况的影响。这将是北方森林落叶树种的年轮首次被用来通过测量年轮宽度、晚材密度和木材同位素来描述过去夏季降雨量的变化。我们建议使用的广义助推技术以前还没有被应用于气候-火灾记录。这些树木年轮和统计分析的结果将改进露天森林模型的参数化，并使我们能够更现实地探索北极系统这一部分组成部分之间的相互作用。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).There is increasing evidence that ecological processes at high latitude are just as sensitive to the timing of events as to their magnitudes. In the boreal forest, moisture availability in summer affects both tree growth and the fire regime. Summers are brief and seasonal transitions rapid, so even slight shifts in the timing of precipitation patterns can have large impacts. One of the most striking, seasonal phenomena in the Alaskan boreal forest is the onset of frequent frontal storms in late summer. This event usually comes in mid-July but is delayed into August or even September in some years. Summers when the rains are delayed have a greater chance of being mega-fires seasons when 1.6 million ha burn. This project will test the hypothesis that shifts in the seasonality of warm-season precipitation could be a key driver of the boreal forest?s responses to future climate changes. The effect of late-summer precipitation on tree growth and fire in Alaska will be quantified in two ways: First, by analyzing interactions between climate, fire, and tree growth (specifically ring-width, ring density, and wood-isotope composition); second, by analyzing fire-climate relationships using a new statistical approach. Together, these results will improve parameterization of the forest model ALFRESCO, which will then be used to test additional hypotheses about the interconnections among future climates, tree growth, fire, and their collective feedbacks to the global climate system. The shifting seasonality of water availability during the warm season may be of key importance in determining how the global boreal forest responds to future climate changes. The multidisciplinary research proposed here represents a new approach to answering a novel question. No one has examined the impacts of seasonal shifts in the timing and magnitude of warm-season precipitation on vegetation distribution, tree growth, and fire regime in the boreal forest before. This will be the first time that tree rings from deciduous species in the boreal forest are used to describe past variations in summer rainfall through measurements of ring-width, late-wood density, and wood isotopes. The generalized boosting technique we propose using has not been previously applied to climate-fire records. The results of these tree-ring and statistical analyses will improve parameterization of the ALFRESCO forest model and allow us to explore the interactions among components of this part of the Arctic system with greater realism.