Tree radial growth and carbohydrate storage in eastern U.S. temperate forests
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Covering 30% of the land surface and storing 45% of terrestrial carbon, forest ecosystems play a major role in global biogeochemical cycles and climate. Despite the importance of forests, responses and feedbacks of forests to global change agents remain among the least understood processes in predicting future global change scenarios. We use the temperate forests biome of the eastern US as a case study to ask several general questions about tree physiology and ecology to inform key knowledge gaps relevant to predicting how forests will respond to future global change. Trees invest significant amounts of carbon into support tissues, defense, and storage. To begin, we examine the process of tree carbon storage, as measured by nonstructural carbohydrates (NSCs) by evaluating the extent that NSCs vary as a function of tree life history strategy, physical traits, and phylogeny. We find that NSCs vary largely at broad taxonomic scales, and across study sites. This suggests that a broad-based approach to studying NSCs is needed if they are to effectively inform ecosystem models. Next, we use annual tree ring increments to determine the spatial scales controlling variation in tree growth. We find that individual variability is the largest control on growth, explaining 27% of variability – and primarily explained by tree size, canopy position, and species. Regional-scale variability is the next most dominant, explaining 13% of variability – half of which is explained by changes in species composition across the region. Growth and mortality are important demographic processes responsible for large, and potentially rapid, changes to the terrestrial carbon cycle. In the last chapter, we explore the extent that NSCs explain growth and mortality. We find that stressed trees have significantly lower NSC concentrations than living trees and dead trees have the lowest concentrations. We also find that the strength and direction of the NSC – growth relationship varies greatly by species This dissertation contributes to our understanding of the processes driving tree growth and NSC storage dynamics, as well as the extent to which NSCs drive tree demographic processes across eastern US forests.