SOIL EROSION IN THREE GRAZED PLANT COMMUNITIES IN NORTHEASTERN PATAGONIA

Grazing has been identified as the main cause of land degradation in Patagonia. However, land degradation is highly variable among areas, even within the same paddock. This strongly suggests that different plant communities differ in their resistance to land degradation. In this study, we have evaluated soil erosion at both microsite and community scales in coexisting plant communities subject to sheep grazing in northeastern Patagonia. Three plant communities coexist in the area: two shrub steppes dominated by Chuquiraga avellanedae Lorentz and Nassauvia ulicina (Hook. f.) Macloskie, and a grass steppe dominated by Nassella tenuis (Phil.) Barkworth. At a community scale, our results indicate that shrub steppes generally experienced soil erosion, whereas the grass steppe commonly did not show signs of soil erosion/deposition. At a microsite scale, non-vegetated soil surface types and degraded mounds never accumulated sediments, regardless of plant community. In contrast, we found that in some sites, the intact mounds and grasses entrapped sediments, but in other sites, soil erosion prevailed. Our results highlight the fact that soil erosion measurements are scale dependent, because results at microsite and community scales often differ. When comparing among communities, grass steppe is more intensely grazed, but at the same time, it shows less evidence of past and present erosion. In contrast, the N. ulicina community showed a direct relationship between grazing and soil erosion. Finally, soil erosion was not related to grazing in the C. avellanedae community. Our results demonstrate that the grass steppe is more resistant to land degradation than shrub steppes. Copyright (c) 2014 John Wiley & Sons, Ltd.