Terrestrial ecosystems provide a substantial carbon sink that helps mitigate climate change, sequestering roughly 30% of anthropogenic carbon emissions annually. However, the long-term future of this sink is not well understood. In this dissertation, I use satellite remote sensing, in-situ measurements, and models to improve understanding of the nature and magnitude of spatial and temporal variation in the primary productivity of Eastern Deciduous Forests of the United States. In my first research chapter, I use remote sensing to model to the phenology of two key variables that control forest productivity: leaf area index (LAI) and the fraction of absorbed photosynthetically active radiation (fAPAR). Results show that the relationship between remotely sensed vegetation indices and both LAI and fAPAR is strongly influenced by systematic variation in near infrared reflectance arising from seasonal changes in canopy shadow fraction that are independent of physical changes in forest canopy properties. In my second research chapter, I use estimates of gross primary production (GPP) derived from eddy covariance measurements at four temperate deciduous sites to model the phenology and controls on light use efficiency (LUE) within and across sites. Results show that multiple modes of variation in incoming radiation dominate daily and seasonal variation in LUE, and provide a refined basis for understanding how variability in environmental controls affect LUE and how the strength of these drivers change throughout the growing season. In my third research chapter, I use the long-term record of Landsat imagery, in-situ phenological observations, and estimates of GPP derived from eddy covariance measurements at two temperate deciduous forest sites to investigate how phenology controls interannual variability in GPP at these sites. Results demonstrate that phenology metrics derived from remote sensing are consistent with in-situ measurements, and that interaction between the timing of growing season anomalies and incoming radiation explains a significant proportion of interannual variation in GPP. Taken together, results from this dissertation demonstrate how variation in phenology and LUE control variation in deciduous forest productivity, which is essential for reducing uncertainty in how future climate changes will impact the carbon budget of deciduous forest ecosystems.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/49208 |
| Date | 06 September 2024 |
| Creators | Lee, Leticia X. |
| Contributors | Friedl, Mark A. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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