Abstract
Earth system models (ESMs) have been widely used for projecting global vegetation carbon dynamics, yet how well ESMs performed for simulating vegetation carbon density remains untested. We compiled observational data of vegetation carbon density from literature and existing data sets to evaluate nine ESMs at site, biome, latitude, and global scales. Three variables—root (including fine and coarse roots), total vegetation carbon density, and the root:total vegetation carbon ratios (R/T ratios), were chosen for ESM evaluation. ESM models performed well in simulating the spatial distribution of carbon densities in root (r = 0.71) and total vegetation (r = 0.62). However, ESM models had significant biases in simulating absolute carbon densities in root and total vegetation biomass across the majority of land ecosystems, especially in tropical and arctic ecosystems. Particularly, ESMs significantly overestimated carbon density in root (183%) and total vegetation biomass (167%) in climate zones of 10°S–10°N. Substantial discrepancies between modeled and observed R/T ratios were found: the R/T ratios from ESMs were relatively constant, approximately 0.2 across all ecosystems, along latitudinal gradients, and in tropic, temperate, and arctic climatic zones, which was significantly different from the observed large variations in the R/T ratios (0.1–0.8). There were substantial inconsistencies between ESM-derived carbon density in root and total vegetation biomass and the R/T ratio at multiple scales, indicating urgent needs for model improvements on carbon allocation algorithms and more intensive field campaigns targeting carbon density in all key vegetation components.
| Original language | English |
|---|---|
| Pages (from-to) | 2282-2297 |
| Number of pages | 16 |
| Journal | Journal of Geophysical Research: Biogeosciences |
| Volume | 122 |
| Issue number | 9 |
| DOIs | |
| State | Published - Sep 2017 |
Funding
The authors thank Yiqi Luo and Xiaochun Zhang for their comments on early version of this manuscript. We appreciated Aaron Ruesch and Holly K. Gibbs for sharing their global living biomass data for this study. Three anonymous reviewers had constructive comments that have significantly improved this manuscript. This study was supported through the Biogeochemistry Feedbacks Scientific Focus Area (BGC Feedbacks SFA), which is sponsored by the Regional and Global Climate Modeling (RGCM) Program in the Climate and Environmental Sciences Division (CESD) of the Biological and Environmental Research (BER) Program in the U.S. Department of Energy Office of Science. Support for X.S. and X.X. was proved by San Diego State University and the University of Texas at El Paso. Financial assistance was partially provided by the SPRUCE and NGEE Arctic projects, which are supported by the Office of Biological and Environmental Research in the U.S. Department of Energy Office of Science. Contributions by F.H., C.M.I., and J.K. were supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the US Department of Energy under contract DE-AC05-00OR22725. Early work of this study was carried out at an internal cluster at the Climate Change Science Institute at Oak Ridge National Laboratory. This work partially used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant ACI-1053575. Authors state that there is no conflict of interest.
Keywords
- Earth system models
- carbon density
- root
- root/vegetation ratio
- vegetation