Asynchronism in leaf and wood production in tropical forests: A study combining satellite and ground-based measurements

摘要

The fixation of carbon in tropical forests mainly occurs through the production of wood and leaves, both being the principal components of net primary production. Currently field and satellite observations are independently used to describe the forest carbon cycle, but the link between satellite-derived forest phenology and field-derived forest productivity remains opaque. We used a unique combination of a MODIS EVI dataset, a climate-explicit wood production model and direct litterfall observations at an intra-annual time scale in order to question the synchronism of leaf and wood production in tropical forests. Even though leaf and wood biomass fluxes had the same range (respectively 2.4 ± 1.4 Mg C ha?1yr?1 and 2.2 ± 0.4 Mg C ha?1yr?1), they occured separately in time. EVI increased with the magnitude of leaf renewal at the beginning of the dry season when solar irradiance was at its maximum. At this time, wood production stopped. At the onset of the rainy season when new leaves were fully mature and water available again, wood production quickly increased to reach its maximum in less than a month, reflecting a change in carbon allocation from short lived pools (leaves) to long lived pools (wood). The time lag between peaks of EVI and wood production (109 days) revealed a substantial decoupling between the irradiance-driven leaf renewal and the water-driven wood production. Our work is a first attempt to link EVI data, wood production and leaf phenology at a seasonal time scale in a tropical evergreen rainforest and pave the way to develop more sophisticated global carbon cycle models in tropical forests. (Résumé d'auteur)