Grazing without grasses: Effects of introduced livestock on plantcommunity composition in an arid environment in northern Patagonia

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Abstract.Question:How does grazing intensity affect plant density, cover and species richness in an Patagonian arid ecosystem?Location:Monte steppe ecoregion, SW Argentina.Methods:I analysed the effect of grazing on plant density, cover and species richness using a stocking rate gradient within the same habitat. Six paddocks were used with stocking rates ranging between 0.002 - 0.038 livestock/ha. Plant density, species richness, plant cover and percentage of grazed branches were determined by sampling plots within each paddock. The percentage of grazed branches was used as an independent measurement of grazing intensity.Results:Higher stocking rates were related to lower plant density, species richness and plant cover. The paddock with the lowest grazing intensity had 86% more plants per unit area, 63% more plant cover and 48% higher species richness. The percentage of grazed branches and the quantity of dung increased with stocking rate.Conclusions:Introduced livestock seriously affect native vegetation in the Patagonian Monte. The damage observed in this xerophytic plant community suggests that plant adaptations to aridity do not provide an advantage to tolerate or avoid grazing by vertebrate herbivores in this region. Plant degradation in this arid environment is comparable to the degradation found in more humid ecosystems.Nomenclature:Correa (1969-1998).

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