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The Central Amazon Biomass Sink Under Current and Future Atmospheric CO 2 : Predictions From Big‐Leaf and Demographic Vegetation Models
Author(s) -
Holm Jennifer A.,
Knox Ryan G.,
Zhu Qing,
Fisher Rosie A.,
Koven Charles D.,
Nogueira Lima Adriano J.,
Riley William J.,
Longo Marcos,
NegrónJuárez Robinson I.,
Araujo Alessandro C.,
Kueppers Lara M.,
Moorcroft Paul R.,
Higuchi Niro,
Chambers Jeffrey Q.
Publication year - 2020
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2019jg005500
Subject(s) - environmental science , sink (geography) , carbon sink , atmospheric sciences , carbon cycle , biogeochemical cycle , biomass (ecology) , eddy covariance , ecosystem model , carbon sequestration , amazon rainforest , canopy , vegetation (pathology) , climatology , ecosystem , ecology , geography , biology , carbon dioxide , medicine , cartography , pathology , geology
There is large uncertainty whether Amazon forests will remain a carbon sink as atmospheric CO 2 increases. Hence, we simulated an old‐growth tropical forest using six versions of four terrestrial models differing in scale of vegetation structure and representation of biogeochemical (BGC) cycling, all driven with CO 2 forcing from the preindustrial period to 2100. The models were benchmarked against tree inventory and eddy covariance data from a Brazilian site for present‐day predictions. All models predicted positive vegetation growth that outpaced mortality, leading to continual increases in present‐day biomass accumulation. Notably, the two vegetation demographic models (VDMs) (ED2 and ELM‐FATES) always predicted positive stem diameter growth in all size classes. The field data, however, indicated that a quarter of canopy trees didn't grow over the 15‐year period, and while high interannual variation existed, biomass change was near neutral. With a doubling of CO 2 , three of the four models predicted an appreciable biomass sink (0.77 to 1.24 Mg ha −1 year −1 ). ELMv1‐ECA, the only model used here that includes phosphorus constraints, predicted the lowest biomass sink relative to initial biomass stocks (+21%), lower than the other BGC model, CLM5 (+48%). Models projections differed primarily through variations in nutrient constraints, then carbon allocation, initial biomass, and density‐dependent mortality. The VDM's performance was similar or better than the BGC models run in carbon‐only mode, suggesting that nutrient competition in VDMs will improve predictions. We demonstrate that VDMs are comparable to nondemographic (i.e., “big‐leaf”) models but also include finer scale demography and competition that can be evaluated against field observations.