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Forest water use and water use efficiency at elevated CO 2 : a model‐data intercomparison at two contrasting temperate forest FACE sites
Author(s) -
Kauwe Martin G.,
Medlyn Belinda E.,
Zaehle Sönke,
Walker Anthony P.,
Dietze Michael C.,
Hickler Thomas,
Jain Atul K.,
Luo Yiqi,
Parton William J.,
Prentice I. Colin,
Smith Benjamin,
Thornton Peter E.,
Wang Shusen,
Wang YingPing,
Wårlind David,
Weng Ensheng,
Crous Kristine Y.,
Ellsworth David S.,
Hanson Paul J.,
Seok Kim Hyun,
Warren Jeffrey M.,
Oren Ram,
Norby Richard J.
Publication year - 2013
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.12164
Subject(s) - environmental science , transpiration , atmospheric sciences , canopy , interception , water content , canopy conductance , eddy covariance , stomatal conductance , temperate forest , precipitation , temperate climate , water use efficiency , forest ecology , ecosystem , photosynthesis , meteorology , ecology , vapour pressure deficit , botany , biology , geotechnical engineering , physics , engineering , geology
Predicted responses of transpiration to elevated atmospheric CO 2 concentration ( eCO 2 ) are highly variable amongst process‐based models. To better understand and constrain this variability amongst models, we conducted an intercomparison of 11 ecosystem models applied to data from two forest free‐air CO 2 enrichment ( FACE ) experiments at Duke University and Oak Ridge National Laboratory. We analysed model structures to identify the key underlying assumptions causing differences in model predictions of transpiration and canopy water use efficiency. We then compared the models against data to identify model assumptions that are incorrect or are large sources of uncertainty. We found that model‐to‐model and model‐to‐observations differences resulted from four key sets of assumptions, namely (i) the nature of the stomatal response to elevated CO 2 (coupling between photosynthesis and stomata was supported by the data); (ii) the roles of the leaf and atmospheric boundary layer (models which assumed multiple conductance terms in series predicted more decoupled fluxes than observed at the broadleaf site); (iii) the treatment of canopy interception (large intermodel variability, 2–15%); and (iv) the impact of soil moisture stress (process uncertainty in how models limit carbon and water fluxes during moisture stress). Overall, model predictions of the CO 2 effect on WUE were reasonable (intermodel μ = approximately 28% ± 10%) compared to the observations (μ = approximately 30% ± 13%) at the well‐coupled coniferous site (Duke), but poor (intermodel μ = approximately 24% ± 6%; observations μ = approximately 38% ± 7%) at the broadleaf site (Oak Ridge). The study yields a framework for analysing and interpreting model predictions of transpiration responses to eCO 2 , and highlights key improvements to these types of models.