The Science

Scientists at the University of Notre Dame used a new mechanistic vegetation dynamics model based on the Ecosystem Demography (ED2) model, which has been augmented to account for nitrogen and phosphorus limitations of vegetation productivity, explicit soil microbial and enzyme processes, and plant-microbe competition for nutrients (Medvigy et al. 2019). The model realistically represented vegetation differences across tropical forests sites that have very large gradients in vegetation biomass and nutrient availability. The researchers used the model to explain observed variations in vegetation at spatial scales finer than those represented in current Earth system models, implying needed improvements to those models.

The Impact

Current land models applied for large-scale assessments of nutrient controls on vegetation processes have large uncertainties. This study used a mechanistic dynamic vegetation model to demonstrate that soil property variations can be mechanistically linked to plant biomass and composition. Representing geodiversity at sub-gridcell scales is therefore critical for large-scale dynamic vegetation models, such as the Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM) Land Model (ELM)-Functionally Assembled Terrestrial Ecosystem Simulator (FATES) model being developed for the E3SM.

Summary

Observations in tropical forests reveal large variation in biomass and plant composition. In this study, scientists from the University of Notre Dame evaluated whether such variation can emerge solely from realistic variation in a set of commonly measured soil chemical and physical properties. Controlled simulations were performed using a mechanistic model that includes forest dynamics, microbe-mediated biogeochemistry, and competition for nitrogen and phosphorus. Observations from 18 forest inventory plots in Guanacaste, Costa Rica, were used to determine realistic variation in soil properties. In simulations of secondary succession, the across-plot range in plant biomass reached 30% of the mean and was attributable primarily to nutrient limitation and secondarily to soil texture differences that affected water availability. The contributions of different plant functional types to total biomass varied widely across plots and depended on soil nutrient status. In simulations, large variation in plant biomass and ecosystem composition arose mechanistically from realistic variation in soil properties and climate. In general, model predictions can be improved through better representation of soil nutrient processes, including their spatial variation. These results inform ongoing development in DOE’s dynamic vegetation model integrated in E3SM (ELM-FATES).

Principal Investigator

David Medvigy
University of Notre Dame
lianhong-gu@ornl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

The Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science.

References