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

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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.