Geography Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2773
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Item Advanced Modeling Using Land-use History and Remote Sensing to Improve Projections of Terrestrial Carbon Dynamics(2021) Ma, Lei; Hurtt, George; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Quantifying, attributing, and projecting terrestrial carbon dynamics can provide valuable information in support of climate mitigation policy to limit global warming to 1.5 °C. Current modeling efforts still involve considerable uncertainties, due in part to knowledge gaps regarding efficient and accurate scaling of individual-scale ecological processes to large-scale dynamics and contemporary ecosystem conditions (e.g., successional states and carbon storage), which present strong spatial heterogeneity. To address these gaps, this research aims to leverage decadal advances in land-use modeling, remote sensing, and ecosystem modeling to improve the projection of terrestrial carbon dynamics at various temporal and spatial scales. Specifically, this research examines the role of land-use modeling and lidar observations in determining contemporary ecosystem conditions, especially in forest, using the latest land-use change dataset, developed as the standard forcing for CMIP6, and observations from both airborne lidar and two state-of-the-art NASA spaceborne lidarmissions, GEDI and ICESat-2. Both land-use change dataset and lidar observations are used to initialize a newly developed global version of the ecosystem demography (ED) model, an individual-based forest model with unique capabilities to characterize fine-scale processes and efficiently scale them to larger dynamics. Evaluations against multiple benchmarking datasets suggest that the incorporation of land-use modeling into the ED model can reproduce the observed spatial pattern of vegetation distribution, carbon dynamics, and forest structure as well as the temporal dynamics in carbon fluxes in response to climate change, increased CO2, and land-use change. Further, the incorporation of lidar observations into ED, largely enhances the model’s ability to characterize carbon dynamics at fine spatial resolutions (e.g., 90 m and 1 km). Combining global ED model, land-use modeling and lidar observation together can has great potential to improve projections of future terrestrial carbon dynamics in response to climate change and land-use change.Item Spatial and Temporal Dynamics of Disturbance Within and Between Forest Regions of the U.S.(2015) Dolan, Katelyn Anne; Hurtt, George C; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forest disturbances play a critical role in shaping forest structure and influencing the ecosystem services that forests provide. However, the rates, patterns and consequences of disturbance remain largely uncertain. How do disturbance rates vary within and between regions and how vulnerable are forests to changes in disturbance? This research takes a tiered approach to quantifying the spatial and temporal patterns and impacts of disturbance within and between diverse forested landscapes of the contiguous U.S. First an intraregional characterization of the patterns and process of disturbance, as captured by over a quarter century of Landsat imagery was performed over the highly forested northeastern state, New Hampshire U.S. Next an inter- regional comparison of disturbance rates, trends and size distributions were conducted across three regions representing diverse forested landscapes in the U.S. with different dominant disturbance regimes. Finally, a framework was developed to assess the vulnerability of forested ecosystems to disturbance and how vulnerability may change in the future. Results showed that disturbance is not homogenous but varies both spatially and temporally within and between regions. Further ecosystem vulnerability to disturbance varies strongly across the U.S., with western forests generally exhibiting greater sensitivity and vulnerability to disturbance under current climates. Under a potential climate scenario, the majority of U.S. forest area was estimated to increase in resiliency to disturbance, which may buffer some of the impact of intensified forest disturbance. The challenge and opportunities going forward is to continue to quantify and integrate the complex rates, patterns and processes of disturbance into ecosystem models and field study designs that link impact assessment of changes to ecosystem function and services.