Seasonal changes in carbon and water fluxes under different land uses in the Orinoco lowlands

Land use change in the savannas of the Orinoco lowlands have resulted in a vegetational mosaic. To elucidate how these changes have affected the energy, carbon and water exchanges, we measured these fluxes using eddy covariance and soil CO₂ efflux systems in contrasting systems: a Andropogon field (S1), a herbaceous savanna derived from tree savanna (S2), a tree savanna (S3) and a relatively undisturbed savanna woodland (S4). In the wet season there were differences in the radiation budget. The seasonally averaged daily albedo for the Andropogon field (0.15-0.16) exceeded that of the savanna stands (0.12-0.14). The herbaceous savanna showed a reduced seasonally average daily flux latent heat (6.52 MJ m^-2 day^-1) as compared with that for the fallow savanna woodland (8.65 MJ m^-2 day^-1). The annual Net ecosystem productivity (NEP) over the S1-S4 was 323, 15, 145 and 161 g C m^-2 yr^-1, respectively. For the whole annual course, the gross primary production over the S1-S4 stands was 1213, 957, 1477 and 1479 g C m^-2 yr^-1 respectively. The Net Primary Productivity of the S1-S4 stands calculated as the summation of the net ecosystem exchange and heterotrophic respiration in the day and night. This net flux when integrated over time was 432, 264, 344 and 449 g C m^-2 yr^-1, respectively. In the analysis the results indicate that the controls and physiological functions of the ecosystems in relation to land-use practices may be generalized to savannas.