Efecto de los gradientes de pastoreo ovino sobre la vegetación y el suelo en Península Valdés, Patagonia Argentina

Abstract

The introduction of domestic livestock in the arid Patagonia produced changes in vegetation and soil that altered fundamental ecosystem processes, increasing desertification and biodiversity loss. In this region, it is common to observe gradients of decreasing animal activity from watering points where livestock impact is greatest near the watering sites, called piospheres, particularly suitable for assessing the effect of grazing on arid ecosystems. The aim of this study was to evaluate the effect of sheep-grazing intensity using piospheres on the structure of the vegetation and soil in shrubby steppes of Peninsula Valdes, Argentina. Variation of plant cover, vertical complexity of the vegetation, number and area of vegetated patches, micro-topography and soil compaction in relation to piosphere gradients were studied using Generalized Linear Mixed Models (GLMM) and multivariate analyses. Grazing intensity decreased according to increasing distance to the watering point. This fact, explaining more than 50% of the overall environmental variability, confirmed the existence of a piosphere gradient on each studied site. Such environmental changes were characterized by a gradual increase in grass and litter cover, vertical complexity of vegetation and soil microtopography at increasing distances from the watering point. Percentages of bare soil and gravel, cover of annual grasses and soil compaction showed the opposite pattern. This study demonstrates, for the first time, the existence of sheep piospheres in the shrubby steppes of Peninsula Valdes. Our results indicate that sheep-grazing intensity is associated with changes in the structure and composition of the vegetation and the soil characteristics that are compatible with degradation processes in the study region. Taking into account the importance of Peninsula Valdes in the context of biodiversity conservation, more studies of this type are required to implement effective management actions integrating livestock and conservation efforts on the terrestrial ecosystems of the region.