Non-linear relationships between grazing pressure and conservation of soil resources in Patagonian Monte shrublands

Grazing effects on soil organic carbon (C) and nitrogen (N) have not been consistent in different studies. Whereas several authors have found changes in the quantity and/or spatial distribution of these soil resources as a consequence of grazing, others have not found any effect. We hypothesised that these responses are due to non-linear relationships between grazing pressure and conservation of soil resources. Therefore, our aim was to identify alternative responses of soil resources (soil organic-C and soil-N) to grazing pressure in a Patagonian Monte shrubland, and their probable causes. We evaluated the amount and distribution of soil resources, the development of soil mounds associated to shrub patches, and the display of signs of wind erosion in six sites under different grazing pressure. Our results show alternative responses of soil resources to grazing in different paddocks, and indicate that the conservation of soil resources was not linearly related to grazing. In a first stage of ecosystem degradation, grazing causes the remobilisation of fine sediments and soil resources and their accumulation in shrub patches. In a second stage, after plant cover is further reduced, soil resources are lost from the system, presumably by wind erosion.