The first half of the project has focused on (1) consolidating new modelling developments to integrate wood formation with tree-ring stable isotopes into the ORCHIDEE global land surface model, (2) establishing a network of standardised intra-annual tree growth monitoring at existing flux tower sites (supersites) in Europe and South America, complemented by non-monitored locations across both Northern and Southern Hemispheres, and (3) developing multi-species records of wood formation for the Southern Hemisphere.
We advanced the process-based integration of carbon source-sink growth dynamics in tree rings and stable isotopes within the ORCHIDEE land surface model, successfully implementing the simulation of dynamic wood density. The inclusion of dynamic wood density did not result in numerical instabilities by altering the functional equilibrium of carbon flows, allowing us to proceed with integrating the full wood formation module as the next step as envisioned in our model development activities. We have tested several mechanistic frameworks for wood formation with different levels of complexity and have adapted the most suitable for the structure of ORCHIDEE, which will improve the realism of biomass growth in the model.
A great effort was also dedicated to assembling the integrative tree-ring observation database for the novel model-data framework of the project. Our first major achievement was the rapid establishment of a dendrometer-based growth monitoring network with sites across several forest biomes from temperate Europe to the whole length of South America and southern Africa. Initially, growth monitoring was planned for supersites equipped with flux towers. After improvement of the methodology, we expanded growth monitoring using dendrometers beyond these supersites to capture a broader range of biomes and environmental conditions. This expansion was made possible through the dedicated collaboration and enthusiasm of a wide network of colleagues from the tree-ring and eddy covariance communities. The network continues to expand, with new efforts focused on North America.
Beyond supersites, many new tree-ring triplet datasets (ring width and ring carbon and oxygen stables isotopes) are available for the project through collaboration with French, Chilean, Argentinean, German and Spanish collaborators for South America and Europe. Efforts are also underway to incorporate tree-ring and isotope sites from tropical forests in South America and Africa, as these regions remain highly underrepresented in global tree-ring datasets. A significant milestone of the project has been the establishment of dendrometer and xylogenesis monitoring together with the updating of the only multi-centennial tree-ring record existing in Southern Africa.
Another key achievement of the project is the development of xylogenesis records for the Southern Hemisphere, including mutiple species. To support this scientific effort, we established new laboratory facilities and capabilities at the host institute (LSCE) by founding the “Wood Numerics Lab”—the second lab in France capable of high-throughout xylogenesis measurement and the first in Europe to integrate xylogenesis and tree-ring stable isotope measurement with land surface modeling.
