Land use effect on carbon stocks in semiarid ecosystems

CONTI G; DÍAZ S; BAPTIST F; PÉREZ HARGUINDEGUY N

Chania, Creta, Grecia.

Simposio; 52 Symposium of the International Association for Vegetation Science; 2009

International Association for Vegetation Science (IAVS)

Arid and semiarid ecosystems occupy a large proportion of South America and are being subjected to accelerated land use change. The assessment of the capacity of ecosystems subjected to different uses to provide multiple benefits to society is an essential step to establish conservation, management and policy options. One particularly relevant benefit provided by woody ecosystems is carbon (C) sequestration. Different land-use regimes have the potential to significantly influence C sequestration through direct impacts on the soil and also through the manipulation of the vegetation composition. We assessed aboveground and belowground C stocks in six different land use situations in semiarid central-western Argentina. These included old -growth forest, well-preserved secondary forest subjected to grazing, species-rich mixed shrubland, species-poor Larrea shrubland, savannah-like pastureland with sparse tree cover, and annual crops, all under the same conditions of climate and substrate. We estimated vegetation C stocks using vegetation relevés, allometric relationships (tree, shrub and root biomass), and direct harvest (herbaceous layer). We estimated soil C stocks by loss of ignition on soil samples collected from four different depths. The first results showed significant differences in the total C content of vegetation among different land-use situations, ranging between 74 Mg C ha-1 and c. 5 Mg C ha-1 in aboveground portions and between 48 Mg C ha-1 to 2 Mg C ha-1 in roots. The organic C content in the first 10 cm of soil showed less marked differences among situations, with values varying from 38 Mg C ha-1 to 23 Mg C ha-1. The total C stored in each land use system showed a predictable overall tendency from well-preserved forests to highly disturbed systems. However, the correspondence between vegetation and soil stocks was not tight or easily predictable in all cases. Further analysis of the amount and recalcitrance of the C stored in deeper soil layers will allow a more complete picture of what are the best long-term C sequestration options in the region.