Changes in soil organic carbon after roller-chopping in dry forests of san luis (Argentina)

Abstract

Soil organic carbon (SOC) is a fundamental component of the global carbon cycle, with influence on different ecosystem services. Although abrupt changes in vegetation cover, such as deforestation, can modify the stock and dynamics of SOC, other subtler changes may also be of importance. In this work, we evaluate the effects of a technique widely used in rangelands of the Chaco region, such as roller-chopping (i.e., partial mechanical destruction of woody vegetation) on the SOC content in dry forests of San Luis province. For this, we sampled the surface soil (<40 cm) in three sites with native forest and roller-chopped paired plots and analyzed their contents of organic carbon and total nitrogen. In addition, we quantified the proportion of different vegetation covers (i.e., tree, shrub, and grass) and analyzed the NDVI dynamic. On average, roller-chopped stands stored almost 5 Mg/ha more SOC than dry forests (+13%). The greatest contrasts were found in the surface soil (0-20 cm depth), where roller-chopped stands exceeded dry forests by up to 30%, while no significant differences were found deeper in the soil profile (20-40 cm depth). Roller-chopped stands also showed higher total nitrogen content in the surface soil (0-10 cm depth, +20%). Dry forests stands showed higher aerial coverage of trees (and less of shrubs) than roller-chopped stands, but this parameter was not related to SOC contents. Our study provides the first results about the effects of roller-chopping on SOC in the region, although the mechanisms behind these changes have not been clarified yet. It is essential to move forward in this aspect in order to design management strategies aimed at increasing SOC levels and the sustainability of agricultural activities in the region.