Budyko scatter reveals interactions between wildfire, land cover change, and climate

The Southeastern United States (SEUS) experiences millions of acres of burned area from both prescribed burns and wildfires on an annual basis. Forests in the SEUS also serve as important carbon sinks for the global carbon budget. However, this carbon sink is threatened by extreme weather events. Climate predictions indicate that the risk of large wildfire events is likely to increase in the coming decades with expected prolonged periods of drought, which would affect vegetation growth and carbon uptake dynamics. How fire-induced changes to the land surface affect carbon and water fluxes over seasonal to decadal time scales is a current knowledge gap. The present manuscript addresses this gap by evaluating differences in land surface fluxes for a forested region in the SEUS under “fire” and “no-fire” conditions. As an unmanaged nature preserve prone to wildfires during dry periods, the Okefenokee Swamp located in the SEUS provides an ideal case study of fire-vegetation interactions. While small fires occur annually throughout the Okefenokee region, large wildfires occur every three to five years, keeping with the natural fire frequency of the Coastal Plains of the SEUS. In order to investigate how wildfire events affect carbon, water, and energy budgets, we use a land-surface hydrology model to simulate land-atmosphere interactions for the Okefenokee Swamp. Model simulations with forced phenology data from the Moderate Resolution Imaging Spectroradiometer (MODIS) are used to evaluate vegetation responses to fire, while simulations coupled with a predictive phenology model allow us to investigate vegetation dynamics as if no fire occurred. Results suggest fire-induced land cover change can reduce annual carbon uptake by up to 50% following large fires. The Budyko framework is used to analyze how post-fire vegetation recovery dynamics and structural changes alter water and energy balances in the coupled water-carbon-energy system. Transiency in Budyko phase space reveals that fire events over the past 20 years shifted the Okefenokee region from a wetter forest towards a drier savanna. These results are significant as the Okefenokee Swamp is representative of fire-affected ecosystems throughout the SEUS. Results from this study improve our understanding of how fire-vegetation dynamics impact the contributions of the SEUS to the global carbon budget.

Duke Scholars

Author Ana P. Barros Civil and Environmental Engineering