Annually resolved tree-ring records extending back to pre-industrial conditions have the potential to constrain the responses of global land surface models at interannual to centennial timescales. Here, we demonstrate a framework to simultaneously constrain the representation of tree growth and physiology in the ORCHIDEE global land surface model using the simulated variability of tree-ring width and carbon ("13C) and oxygen (18O) stable isotopes in six sites in boreal and temperate Europe. We exploit the resulting tree-ring triplet to derive integrative constraints for leaf physiology and growth from well-known mechanistic relationships among the variables. ORCHIDEE simulates "13C (rCombining double low line0.31-0.80) and 18O (rCombining double low line0.36-0.74) better than tree-ring width (r<0.55), with an overall skill similar to that of a tree-ring model (MAIDENiso) and another isotope-enabled global vegetation model (LPX-Bern). The comparison with tree-ring data showed that growth variability is not well represented in ORCHIDEE and that the parameterization of leaf-level physiological responses (stomatal control) to drought stress in the temperate region can be constrained using the interannual variability of tree-ring stable isotopes. The representation of carbon storage and remobilization dynamics emerged as a critical process to improve the realism of simulated growth variability, temporal carryover, and recovery of forest ecosystems after climate extremes. Simulated forest gross primary productivity (GPP) correlates with simulated tree-ring "13C and 18O variability, but the origin of the correlations with tree-ring 18O is not entirely physiological. The integration of tree-ring data and land surface models as demonstrated here should guide model improvements and contribute towards reducing current uncertainties in forest carbon and water cycling.
Bibliographical noteFunding Information:
IFY grant from the European Commission, Horizon 2020 frame-work program (grant no. 776810).
Financial support. This research has been supported by the VER-
Acknowledgements. This research is part of a post-doctoral grant to Jonathan Barichivich from the presidential program “Make Our Planet Great Again” (MOPGA) conducted through the Centre National de la Recherche Scientifique (CNRS) of France. We thank Joel Guiot for sharing the simulations of MAIDENiso for Fontainebleau, Fortunat Joos, and Martin Werner for kindly sharing the isotopic forcing used for their LPX-Bern simulations and Manuel Gloor and Roel Brienen for discussions on isotopic theory. We also thank John Marshall and the two other anonymous reviewers for their constructive comments that improved the paper.
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