Abstract
Abstract. The Ecosystem Demography model version 2.2 (ED-2.2) is a terrestrial biosphere model that simulates the biophysical, ecological, and biogeochemical dynamics of vertically and horizontally heterogeneous terrestrial ecosystems. In a companion paper (Longo et al., 2019a), we described how the model solves the energy, water, and carbon cycles, and verified the high degree of conservation of these properties in long-term simulations that include long-term (multi-decadal) vegetation dynamics. Here, we present a detailed assessment of the model's ability to represent multiple processes associated with the biophysical and biogeochemical cycles in Amazon forests. We use multiple measurements from eddy covariance towers, forest inventory plots, and regional remote-sensing products to assess the model's ability to represent biophysical, physiological, and ecological processes at multiple timescales, ranging from subdaily to century long. The ED-2.2 model accurately describes the vertical distribution of light, water fluxes, and the storage of water, energy, and carbon in the canopy air space, the regional distribution of biomass in tropical South America, and the variability of biomass as a function of environmental drivers. In addition, ED-2.2 qualitatively captures several emergent properties of the ecosystem found in observations, specifically observed relationships between aboveground biomass, mortality rates, and wood density; however, the slopes of these relationships were not accurately captured. We also identified several limitations, including the model's tendency to overestimate the magnitude and seasonality of heterotrophic respiration and to overestimate growth rates in a nutrient-poor tropical site. The evaluation presented here highlights the potential of incorporating structural and functional heterogeneity within biomes in Earth system models (ESMs) and to realistically represent their impacts on energy, water, and carbon cycles. We also identify several priorities for further model development.
Highlights
Terrestrial ecosystems are fundamental components of the Earth system
Land use change, and increase in atmospheric CO2 are likely to alter the ability of terrestrial ecosystems to accumulate carbon, yet the magnitude and even the persistence of terrestrial biosphere sink, as predicted by dynamic global vegetation models (DGVMs), remains highly uncertain (Friedlingstein et al, 2006, 2014; Krause et al, 2018)
We found that ED-2.2 predicted a similar extent of leaf area index (LAI) over the Amazon region when compared to MODIS estimates (Fig. S5)
Summary
Terrestrial ecosystems are fundamental components of the Earth system. Current estimates suggest that net terrestrial biosphere carbon uptake is near 3.2 GtC year−1 (equivalent to 30 % of fossil fuel carbon emissions), albeit this sink is partially offset by land use change (1.5 GtC year−1) or 16 % of fossil fuel carbon emissions (Le Quéré et al, 2018). Land use change, and increase in atmospheric CO2 are likely to alter the ability of terrestrial ecosystems to accumulate carbon, yet the magnitude and even the persistence of terrestrial biosphere sink, as predicted by dynamic global vegetation models (DGVMs), remains highly uncertain (Friedlingstein et al, 2006, 2014; Krause et al, 2018). The emergent nature of the large-scale properties of terrestrial ecosystems has important consequences for how terrestrial ecosystems respond to climate change and other forms of environmental perturbation (Moorcroft, 2003, 2006; Evans, 2012; Fisher et al, 2018)
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