Land use effect on carbon stocks in semiarid ecosystems.

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

Chania, Grecia

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

International Association for Vegetation Science

The Gran Chaco is the most geographically extensive seasonally dry forest in South America. Land use is causing a change in land cover and an associated change in carbon (C) stocks. Some of the primary causes of change in land cover from arid and semiarids ecosystems in South America are deforestation, grazing and agricultural expansion The capacity of the woody ecosystems to provide multiple local and global benefits to society, make  them relevant from an ecological, social and political perspective. The objectives of this study were:         i)            Characterize trends in C storage and distribution in ecosystems components on six differents land use systems in semiarid central western Argentina.       ii)            Understand the influence of land use change on C storage. We compared six different land-uses: old growth native forest (PF), well preserved native forest (SF), species-rich native shrubland (SRS), species-poor Larrea shrubland (LS),  savannah like pastureland (SP) and irrigated soybean culture (SY), all under the same conditions of climate and substrate. The aboveground and belowground C stocks were assessed using vegetation relevés, local and general allometric relationships (tree, shrub and root biomass), and direct harvest (herbaceous layer). We estimated soil C stocks by Walkley & Black method of soil samples collected from four different depths (0-10, 10-30, 30-100 and 100-200 cm). Conclusions Land use change caused by agriculture expansion, deforestation, overgrazing or a combination of them, significantly change de carbon stored in the ecosystems, from values near 200 to 100 Mg/ha. The main change was found in the vegetation  (above and belowground biomass) and  secondly in the carbon stored in the surface layer. Unexpectedly high values in the SOC content in the savannah like pastureland system could be more directed related to soil properties, like texture, than to land use. 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.