Effects of livestock management on carbon stocks and fluxes in grassland ecosystems in the Pyrenees

Abstract

Grassland ecosystems can constitute a source or a sink in the global C balance, and their management affect their position in that balance. We aim to assess soil organic carbon (SOC) content and determine how grazing affects C fluxes and stocks in grasslands at high altitude in the Pyrenees. In a preliminary survey we found that total SOC ranges from 65 to 300 Mg ha-1 in these ecosystems, and is partially explained by complex combinations of variables representing topography, macroclimate and bedrock. In a second, more detailed survey, we improved the modelling of SOC by introducing management variables and standing biomass. Preliminary results of this work suggested that abandoned areas had lower SOC than grazed areas, and the higher SOC contents occurred when both sheep and cattle grazed in the area. The importance of management in soil carbon accumulation was confirmed in an experiment developed in two subalpine locations, where we found a sharp increase in active soil organic matter in grazed compared to non-grazed plots. The Eddy covariance method showed that an intensely grazed area was a slight sink for C, in spite of the elevated C efflux in August, when temperatures were very high and vegetation had been heavily grazed.

R. Rodríguez, M. Guardiola, N. Serena, P. Ferrer and others provided much help with sampling and in the lab. This study was funded by the project CARBOPAS, from the Spanish Ministry of Science and Technology; the Vth Framework Projects EMERGE and CARBOMONT; and INTERREG III-A. The Fundació Territori i Paisatge and the Natural Park Cadí-Moixeró offered much support in the development of the projects.