A triple tree-ring constraint for tree growth and physiology in a global land surface model

Jonathan Barichivich,Valerie Daux,Sebastiaan Luyssaert,Jina Jeong,Philippe Peylin,Camille Risi,Thomas Launois

doi:10.5194/bg-18-3781-2021

Abstract

Abstract. 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 (Δ13C) and oxygen (δ18O) 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 Δ13C (r=0.31–0.80) and δ18O (r=0.36–0.74) 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 Δ13C and δ18O variability, but the origin of the correlations with tree-ring δ18O 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.

Highlights

A major challenge for the land surface model (LSM) component of Earth system models is to accurately simulate the historical and future dynamical coupling between the global biosphere and climate (Friedlingstein et al, 2014)
The aims of this study are to (i) integrate key developments and identify the critical processes to concurrently simulate the interannual variability of tree-ring width and its carbon ( 13C) and oxygen stable isotopes in the ORCHIDEE global land surface model, (ii) develop a conceptual triple tree-ring constraint for simulated growth and physiology that exploits the mechanistic relationships among tree-ring variables, and (iii) evaluate the simulated relationships between productivity and tree-ring carbon and oxygen stable isotopes
We demonstrated the potential of a tree-ring triplet based on tree-ring width and 13C and δ18O stable isotopes to constrain the representation of tree growth and physiology in the global land surface model ORCHIDEE (r898), bridging the long-standing gap between the tree-ring and land surface modeling communities

Summary

Introduction

A major challenge for the land surface model (LSM) component of Earth system models is to accurately simulate the historical and future dynamical coupling between the global biosphere and climate (Friedlingstein et al, 2014). LSMs are skillful at reproducing short-term (< 20 years) contemporary observations of plant water and carbon cycling, their simulated responses to environmental changes at longer timescales from decades to centuries are still highly uncertain and contribute to the spread in current climate change projections (Ciais et al, 2013; Friedlingstein et al, 2014) Some of these models project that the terrestrial biosphere will continue behaving as a carbon sink of anthropogenic emissions during the course of the century, while others simulate that it will turn into an additional carbon source to the atmosphere that will accelerate climate change (Friedlingstein et al, 2006; Jones et al, 2013; Friedlingstein et al, 2014). Barichivich et al.: Tree rings in ORCHIDEE els limits confidence in future climate projections (Ciais et al, 2013)

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