Simultaneous measurements of carbon dioxide, water and energy exchange above four different ecosystems

Abstract

International audienceOver the last decades many studies have been performed to determine mass and energy budgets of forests, croplands and grasslands. However, most measurements have been made in different geographical regions and at different periods of time. As the results depend on the meteorological conditions and vary in time it is difficult to intercompare them directly and evaluate the relative contribution of each ecosystem to global water and carbon exchanges. Therefore, there is a need to measure fluxes over different types of ecosystem during a given period of time, in a given region with similar meteorological conditions. In the present study we report flux data, as performed above four different canopies submitted to the same climate forcing. As a contribution to the Regional Experiment component of the CarboEurope-IP project, the carbon and energy budgets of four typical ecosystems of Les Landes region in South West of France, a forest clear-cut, a mature forest, a vineyard and an irrigated maize crop, were measured during an entire growing season, from 17 May to 12 October 2005. The energy balance closure is fairly good at all sites. CO 2 flux measurements show that the maize crop before irrigation and the clear-cut behave as sources of CO 2, whereas the vineyard and the mature forest act as sinks. However the maize crop becomes a substantial sink of CO 2 after the start of irrigation and canopy growth, with fluxes three times as large as for the 35- year old forest. Evapotranspiration is largest over the irrigated maize and lowest over the clear-cut, while the vineyard and the mature forest exhibit similar water fluxes. The data collected provides a good basis for a comparative study of the main ecosystems of the region, and for upscaling fluxes at the regional level, in conjunction with all other measurements performed during the 2005 CERES experiment