Vegetation Demographics in Earth System Models: A Review of Progress and Priorities

An assessment of current approaches to including individual plant dynamics in ESMs and the need for new types of observations to benchmark these models.

The Science

A team from the National Center for Atmospheric Research (NCAR) and Next-Generation Ecosystem Experiments (NGEE)–Tropics reviewed the state of the science for models that have attempted to include the dynamics of individual plants, including their growth and death, within coupled Earth system models (ESMs). The researchers reviewed approaches to resolve environmental heterogeneity along key gradients of light, water, and nutrients; how differences in plant states determine the dynamics of competition for resources; and issues of scaling from groups to individuals.

The Impact

The researchers argue for the need for specific observations, including forest inventory data, rates of individual-level resource acquisition and use, and the observations that link individual-level growth and mortality rates to environmental conditions as key benchmarks to improve and test the next generation of ESMs.

Summary

Solving the problem of including processes such as growth and mortality of individual trees is needed to have a robust estimate of ecosystem responses and contributions to global change. ESMs have traditionally not included individual-level dynamics, instead using bulk ecosystem level properties. However, the limitations of this approach have become clearer and so multiple ESM groups are including plant demographic processes within them. They review multiple approaches across a wide range of ESMs, to discuss commonalities and differences between these approaches. In particular, they describe differing attempts to represent size- and trait-structured competition for within the canopy, water, and nutrients underground, and the role of disturbance and mortality processes in governing ecosystem heterogeneity. The research team describes a set of requirements for testing and benchmarking the models, with a focus on the need to test the competition among individuals for resources, and the need for observations that test scaling between individual-level vital rates and environmental conditions.

Principal Investigator

Rosie Fisher
National Center For Atmospheric Research
rfisher@ucar.edu

Program Manager

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

Funding

CDK, BC, RK, JH, TP, JS, CX , and SPS were supported by the Next-Generation Ecosystem Experiments (NGEE)–Tropics project, which is supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science.

Related Links

References

Fisher, R. A., C. D. Koven, W. R. L. Anderegg, and B. O. Cristoffersen, et al. "Vegetation demographics in Earth System Models: a review of progress and priorities". Global Change Biology 24 (1), 35–54  (2018). https://doi.org/10.1111/gcb.13910.