DISSERTATION RESEARCH: Linking Tree Demography and Nonstructural Carbon in Eastern US Forests

森林覆盖了约30%的陆地表面，为人类健康和经济利益提供了许多好处，对生物多样性至关重要。尽管森林对社会很重要，但森林对气候变化的反应仍然非常不确定。这种不确定性在很大程度上是由模型如何代表森林对环境压力的反应所驱动的。该项目将通过探索树木能量储存对树木生长和死亡率的重要性来解决这种不确定性。虽然大多数动物以脂肪的形式储存能量，但树木以非结构性碳水化合物（NSC;淀粉和糖）的形式储存能量。据推测，树木在环境压力时期依赖于这些能量储备;然而，很少有数据支持这一假设。利用从美国东部3,000多棵不同种类的树木中收集的木材样本，该项目将回答三个重要问题：1）树木分配多少碳用于储存和新生长？2)什么样的树木碳分配模型能最好地解释观测到的NSC模式？3)神经干细胞可以用来预测美国东部森林中的树木死亡吗？这些信息将用于改善对森林如何应对未来全球变化的预测，从而为如何使用和保护世界上最重要的资源之一的决策提供信息。该项目中使用的样本代表了在美国东部10个地点收集的数十种树种。在这项研究中采样的树木的环境和分类学的广度将首先被用来评估树木NSC存储和增长之间的权衡。接下来，研究人员将使用这些数据来校准陆地生物圈模型，即生态系统人口统计学（ED 2）模型，并测试有关影响树木NSC大小和周转率的约束的多个假设。最后，ED 2模型将与美国林务局森林资源清查和分析（FIA）中的树木死亡数据相结合，以更好地了解NSC与死亡率之间的关系。

Forests cover about 30% of the land surface, provide numerous human health and economic benefits, and are critically important to biodiversity. Despite the importance of forests to society, the responses of forests to climate change remain highly uncertain. Much of this uncertainty is driven by how models represent forest responses to environmental stress. This project will address this uncertainty by exploring the importance of tree energy storage to tree growth and mortality rates. While most animals store energy as fat, trees store energy as non-structural carbohydrates (NSCs; starch and sugar). It is hypothesized that trees rely on these energy reserves during times of environmental stress; however, few data are available to support this hypothesis. Using wood samples collected from over 3,000 trees of many different species in the eastern US, this project will answer three important questions: 1) How much carbon are trees allocating to storage versus new growth? 2) What model of tree carbon allocation best explains observed NSC patterns? 3) Can NSCs be used to predict tree death in eastern US forests? This information will be used to improve predictions of how forests will respond to future global change in an effort to inform decisions about how to use and preserve one of the world's most important resources.The samples used in this project represent dozens of tree species collected at 10 sites across the eastern US. The environmental and taxonomic breadth of the trees sampled in this study will first be used to assess trade-offs between tree NSC storage and growth. Next, the researchers will use the data to calibrate a terrestrial biosphere model, the Ecosystem Demography (ED2) model, and test multiple hypotheses regarding the constraints that affect the size and turnover rate of tree NSC. Finally, the ED2 model will be combined with data on tree death in the US Forest Service Forest Inventory and Analysis (FIA) to better understand the relationship between NSCs and mortality.