Demographic Modeling and Landsat Sensitivity to Forest Recovery Following Tropical Clear-Cuts and Boreal Heat-Driven Forest Mortality Events

Wednesday, December 12, 2018 - 08:45
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The inclusion of dynamic vegetation demography in Earth System Models (ESMs) has been identified as a critical step in moving ESMs toward more realistic representation of plant ecology and the processes governing climatically important fluxes of carbon, energy, and water. To help this advancement of ESMs, we integrated demographic processes using the Functionally-Assembled Terrestrial Ecosystem Simulator (FATES) in the newly developed E3SM Land Model (ELM). We tested model performance of forest recovery processes against observations in a tropical evergreen forest in Brazil and an Alaskan mixed needleleaf and deciduous boreal forest, in order to test variances in trajectories of forest recovery, which are dependent on the disturbance and ecosystem type. However, temporal measurements of recovery trajectories, especially in the tropics, are scarce. Therefore, we used the Landsat (LEDAPS) and found that the near infrared (NIR) band captured the dynamics of recovery pathways from clear-cuts in the Central Amazon. In general, following disturbance NIR increased with an increase in the vegetation cover, reaching its maximum after the close of canopy by pioneers, and then decreasing slowly with the dynamics of succession. Clear-cut simulations using ELM-FATES, showed that both modeled albedo and NIR bands had very fast recovery, returning to pre-clearcut values after only a few years, while biomass accumulation was slower than observed. These latter biases potentially affect larger scale carbon-cycling and energy projections in E3SM. In another critical ecosystem type, high-latitude boreal forests, rising temperature is leading to more wildfires and heat-driven mortality events. These climate related disturbances are predicted to shift boreal forests to higher dominance of deciduous vegetation. However, the relative influence of climate change or disturbance-recovery dynamics towards the greening vs. browning of boreal forests remains uncertain. Therefore, we used ELM-FATES to analyze impacts of vegetation cover shifts on carbon fluxes, water use efficiency (WUE), evaporative fluxes, and soil water storage, and compared these predictions to Landsat-based maps of boreal forest cover change and MODIS-derived estimates of surface energy and carbon budgets.

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