Simulating CO2 Responses of Secondary-Succession Forests at Duke and Oak Ridge FACE Experiments with ELM-FATES-CNP
Authors
Bharat Sharma1* (sharmabd@ornl.gov), Ryan Knox2, Charlie Koven2, Daniel Ricciuto1, Xinyuan Wei1, Xiaojuan Yang1, Richard J. Norby1, Ram Oren3, Anthony Walker1
Institutions
1Oak Ridge National Laboratory, Oak Ridge, TN; 2Lawrence Berkeley National Laboratory, Berkeley, CA; 3Duke University, Durham, NC
URLs
Abstract
Rising atmospheric carbon dioxide (CO2) can increase vegetation biomass production, which at the global scale can slow atmospheric CO2 growth rates. Elevated atmospheric CO2 (eCO2) experiments have demonstrated significant gains in net primary productivity (NPP) and biomass. Many terrestrial biosphere models have also indicated that eCO2 has caused a large fraction of land carbon sequestration during recent decades and predict that this sequestration will continue to increase into the future. Another significant component of global change has been the conversion of primary forests to secondary forests and several ecosystem-scale Free Air Carbon Dioxide Enrichment (FACE) experiment were sited in plantations. Analysis of these FACE experiments indicated that the variability in the eCO2 response is related to the stage of stand development and progressive nitrogen limitation. Researchers use the E3SM Functionally Assembled Terrestrial Ecosystem Simulator (ELM-FATES-CNP), a size and time-since-disturbance structured vegetation demography model that integrates carbon and nutrient cycling to investigate nutrient constraints on eCO2 responses in even-aged forests. The primary objective of this study is to evaluate the performance of the ELM-FATES-CNP model against the observations from Duke and ORNL FACE experiments to ascertain how best to apply ELMFATES-CNP to investigate stand structure and nutrient controls on ecosystem carbon responses to eCO2. Understanding the interactions of nitrogen availability for plant uptake and growth is necessary to improve predictive capabilities of models to simulate ecosystem carbon storage in response to eCO2. The team compared the net primary productivity (NPP) responses under simulated post-disturbance and counter-factual “equilibrium” forests at Duke and Oak Ridge. Researchers also use a carbon-only version of the model alongside two soil nutrient cycling hypotheses to evaluate the strength of nutrient limitation in FATES-CNP.