Unravelling the influence of environment and development on intra-annual dynamics of wood formation and resulting tree-ring structure and isotope ratios

PI : Cyrille Rathgeber (UMR 1092 Laboratoire d’étude des Ressources Forêt-Bois – LERFOB)

Co-applicants : Stéphane Ponton (UMR 1137 Ecologie et Ecophysiologie Forestières – EEF), Julien Ruelle (UMR 1092 Laboratoire d’étude des Ressources Forêt-Bois – LERFOB)

Collaborations : Patrick Fonti, Kerstin Treydte (WSL Zürich, Switzerland); David Frank (LTRR, University of Arizona, USA); Henri Cuny (IGN, Champigneulles, France)

________________________________________________

Context — Tree rings play a major role in documenting past and on-going climatic changes along with their impacts on forest ecosystems. However, past climate reconstructions and future growth projections both remain hampered by a poor understanding of the influence of the environmental and developmental factors on the physiological processes ruling wood formation.

Objectives — The WoodIsotop project aims at advancing our knowledge on the interactions among environmental factors, developmental constraints, and physiological processes involved in wood formation. Our investigations will concentrate on better understanding the mechanisms through which seasonal climatic variations and extreme events leave permanent imprints in tree rings. In particular, we will focus on unravelling which, when, and how environmental factors influence intra-annual wood formation dynamics and the resulting tree-ring characteristics (e.g. tree-ring micro-density profiles, wood anatomy features, and high-resolution isotope ratios).

Approaches — To carry out this project, we will capitalize upon two existing networks of instrumented mixed coniferous forests: the Donon (composed of 3 stands, containing 3 species, monitored over 3-4 years, and distributed along an altitudinal gradient, in the Vosges Mountains, France); and the Lötschental (composed of 8 stands, containing 1-2 species, monitored over 9 years, and spread along two altitudinal gradients in the Valais, Switzerland). The two datasets will be supplemented to contain the same information about wood formation dynamics, quantitative anatomy, and chemical composition. Moreover, we will further develop our model of intra-annual dynamics of xylogenesis to accurately link cell differentiation kinetics, tracheid morphology, and isotope ratios to co-occurring environmental conditions.

Expected results and impacts — By connecting causes (environmental and developmental conditions) and consequences (tree-ring features and wood isotopic signature) thanks to a mechanistic understanding of the physiological processes involved in wood formation, the WoodIsotop project will not only strengthen the reliability of the tree-ring variables used for climatic reconstructions, but will also reduce uncertainties of future assessments of climatic change impacts on tree growth, forest ecosystem functioning, and flux exchanges between the terrestrial biomass and the atmosphere.