title: Do dynamic global vegetation models capture the seasonality of carbon fluxes in the Amazon basin? A data-model intercomparison.
abstract: To predict forest response to long-term climate change with high confidence requires that dynamic global vegetation models (DGVMs) be successfully tested against ecosystem response to short-term variations in environmental drivers, including regular seasonal patterns. Here, we used an integrated dataset from four forests in the Brasil flux network, spanning a range of dry-season intensities and lengths, to determine how well four state-of-the-art models (IBIS, ED2, JULES, and CLM3.5) simulated the seasonality of carbon exchanges in Amazonian tropical forests. We found that most DGVMs poorly represented the annual cycle of gross primary productivity (GPP), of photosynthetic capacity (Pc), and of other fluxes and pools. Models simulated consistent dry-season declines in GPP in the equatorial Amazon (Manaus K34, Santarem K67, and Caxiuanã CAX); a contrast to observed GPP increases. Model simulated dry-season GPP reductions were driven by an external environmental factor, 'soil water stress' and consequently by a constant or decreasing photosynthetic infrastructure (Pc), while observed dry-season GPP resulted from a combination of internal biological (leaf-flush and abscission and increased Pc) and environmental (incoming radiation) causes. Moreover, we found models generally overestimated observed seasonal net ecosystem exchange (NEE) and respiration (Re) at equatorial locations. In contrast, a southern Amazon forest (Jarú RJA) exhibited dry-season declines in GPP and Reconsistent with most DGVMs simulations. While water limitation was represented in models and the primary driver of seasonal photosynthesis in southern Amazonia, changes in internal biophysical processes, light-harvesting adaptations (e.g., variations in leaf area index (LAI) and increasing leaf-level assimilation rate related to leaf demography), and allocation lags between leaf and wood, dominated equatorial Amazon carbon flux dynamics and were deficient or absent from current model formulations. Correctly simulating flux seasonality at tropical forests requires a greater understanding and the incorporation of internal biophysical mechanisms in future model developments.
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, NSW, Australia.|Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA.
authors.forename: Natalia
authors.identifier: 0000-0003-3921-1772
authors.initials: N
authors.lastname: Restrepo-Coupe
authors.affiliation: Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA.|Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
authors.forename: Naomi M
authors.identifier: 0000-0002-4963-0535
authors.initials: NM
authors.lastname: Levine
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA.|Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, USA.|Department of Atmospheric Sciences, University of Arizona, Tucson, AZ, USA.
authors.forename: Bradley O
authors.initials: BO
authors.lastname: Christoffersen
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA.
authors.forename: Loren P
authors.initials: LP
authors.lastname: Albert
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA.|Biological, Environmental & Climate Sciences Department, Brookhaven National Lab, Upton, NY, USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Agricultural Engineering, Federal University of Vicosa, Vicosa, Brazil.
authors.forename: Marcos H
authors.initials: MH
authors.lastname: Costa
authors.affiliation: School of Geography, University of Leeds, Leeds, UK.
authors.forename: David
authors.initials: D
authors.lastname: Galbraith
authors.affiliation: Department of Agricultural Engineering, Federal University of Vicosa, Vicosa, Brazil.
authors.forename: Hewlley
authors.initials: H
authors.lastname: Imbuzeiro
authors.affiliation: Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Brazil.
authors.forename: Giordane
authors.initials: G
authors.lastname: Martins
authors.affiliation: Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Brazil.|Embrapa Amazônia Oriental, Belem, Brazil.
authors.forename: Alessandro C
authors.initials: AC
authors.lastname: da Araujo
authors.affiliation: Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK.
authors.forename: Yadvinder S
authors.initials: YS
authors.lastname: Malhi
authors.affiliation: Department of Atmospheric Sciences, University of Arizona, Tucson, AZ, USA.
authors.forename: Xubin
authors.initials: X
authors.lastname: Zeng
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Moorcroft
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA.
authors.forename: Scott R
authors.initials: SR
authors.lastname: Saleska
mesh_terms: D001938:Brazil; D002244:Carbon; D057486:Carbon Cycle; D057231:Climate Change; D017753:Ecosystem; D065928:Forests; D010788:Photosynthesis; D012621:Seasons; D014197:Trees
chemical_list: D002244:Carbon
keywords: Amazonia; carbon dynamics; dynamic global vegetation models; ecosystem-climate interactions; eddy covariance; seasonality; tropical forests phenology