Background

Observations from networks of forest plots show important differences in biomass and turnover of forests across continents, and how these dynamics are changing through time. These patterns are not well captured by the current generation of Earth System Models (ESMs). Vegetation demographic models (VDMs) improve the representation of vegetation within ESMs, for instance by accounting for vertical competition for light, and the effects of canopy disturbance on successional dynamics. However, we lack a standardized set of benchmarks with which to assess the ability of VDMs to capture the spatial and temporal trends in forest dynamics that are observed in forest plot data.

Objectives

We aim to create a standardized set of benchmarks from forest plot data that can be used to assess VDM outputs. We aim to incorporate these benchmarks into the International Land Model Benchmarking Project (ILAMB) and use them for the global calibration of the Energy Exascale Earth System Model - Functionally Assembled Terrestrial Ecosystem Simulator (E3SM-FATES).

Methods

We used forest plot data from several sites to design a set of benchmarks that capture current forest structure and function at a site, and potential changes through time. Since broad spatial and temporal patterns in forest dynamics emerge from the demographic rates of individual plants, we included demographic metrics such as growth and mortality rates, along with aboveground biomass, forest size structure, and aboveground woody carbon turnover. Dynamics at each site were compared to outputs from E3SM-FATES as a starting point for calibration of demographic rates. We aim to extend the initial set of sites, in order to create benchmarks with global coverage.

Implications

Forests exchange vast amounts of energy, water and carbon with the atmosphere, and in doing so play a critical role in regulating the global climate. To predict future forest dynamics, and their impacts on climate, VDMs must be able to capture trends in forest dynamics, driven by changing demographic rates. By leveraging forest plot data to create a standardised set of model benchmarks, we aim to facilitate global calibration of VDMs and enable more accurate predictions of the role of forests in the biosphere.