Rubber flux : CO2, water and energy budget of rubber plantations in Thailand

Rubber Flux aims at providing a complete picture of CO2, water and energy budget of a rubber plantation in Eastern Thailand. Beyond the evaluation of the fluxes, our purpose is to partition them among the different components of the plantation ecosystem (canopy, trunks, roots, under storey, soil) and the different functions (photosynthesis, respiration. evapotranspiration ) in order to understand the factors controlling the carbon, water and energy budgets of the ecosystem. The experiment is situated at the Chachoengsao Rubber Research Station located in Phanom Sarakham district, about 140 km east of Bangkok The observation site is located in a 6 ha plot at the center of the 350 ha station. The plot itself is planted with a monoclonal stand (clone RRIM 600). Trees were 13 years old in 2007. The average height was 20 m and average girth at 1.7 in was 60 cm. Initial planting density was 500 trees/ha and actual stand density was 454 trees/ha in June 2006. Trees are tapped for latex production for 5 years. Carbon fluxes of rubber plantation ecosystem are continuously measured by the eddy covariance method (ED). Evapo-transpiration (ET) is measured by ED and water balance together. Meanwhile, amounts of carbon (C) stored in the trees will be evaluated by measuring biomass increment of the plantation, in combination with estimations of the carbon content at the different compartments. ED methodology was adapted from a similar experiment developed by our research group on another tropical tree crop plantation, coconut tree, in Vanuatu islands. The flux tower is 25 in high. Three-demensional (3-D) sonic anemometer Young 81000V 20 Hz is used together with alt open path gas analyser (LI-7500; LI-COR, Inc., Lincoln, Nebraska, USA). Raw data are collected and pre-processed by the "Tourbillon" software (INRA-Bioclimatologie, Bordeaux, France) for a time-integration period of 300 s. Raw data are post-processed using EdiRe software (University of Edinburgh, UK) into half-hourly values. All data are despiked according to variance filters, planar fit is applied (parameters are calculated monthly), and vapour is corrected for buoyancy. Weather station measures semi-hourly net radiation (Rn), photosynthetically active radiation (PAR), diffuse PAR (PARdiff), reflected PAR (PARreflected), global radiation (Rg), Air temperature (Ta), Relative humidity (Rh), wind speed, wind direction, rainfall, vertical profile of air temperature (TCs). Energy balance will be assessed by measurements of net radiation (Rn) and estimation of the energy partitioning among heat fluxes and heat storage. Results obtained at the ecosystem scale by these methods will be compared to gas exchanges measured at the level of the different compartments (canopy, trunk, root system, soil, etc). Thereby, the validated CO2 and H2O fluxes will be used to model gas exchanges of rubber plantation ecosystem according to climate and other environmental parameters as well as crop management. (Résumé d'auteur