Livestock removal is not enough to recover functional diversity in arid ecosystems of the Patagonian Monte (Argentina)

Abstract

Sheep grazing induces the replacement of preferred plant species with lowdefences by others well defended against herbivory, affecting thevariance of trait distributions related to resource capture and utilizationwithin plant communities ("functional diversity"). High functional diversitymay reflect high species complementarity in resource use, improving ecosystemfunctioning. We analysed whether the removal of domestic herbivores (disturbance agent) enhances the functional diversity of traits related to light capture in Patagonian Monte rangelands. We selected two contrasting sites in relation to grazing disturbance: La Elvira (EL) which has been grazed by sheep from the beginning of the past centuryuntil present with a stocking rate of 0.11-0.14 sheep/ha and La Esperanza (ES)subjected to the same grazing history but until 2003, when livestock was removed. At each site, we identified two areas with contrasting signs of grazing disturbance (high and low grazing impact), and we assessed the plantcover and the functional diversity of plant height, specific leaf area and N concentration in green leaves in August 2010. Plant cover was higher in ES (past grazing) than in EL (past and present grazing), and the difference between areas (low and high grazing impact) was higher in ES than EL. Functional diversity did not vary between sites being higher at areas with low than high grazingdisturbance. Accordingly, changes in functional diversity induced by grazing persistedafter livestock removal despite of increased plant cover. In conclusion, short-mediumterm livestock exclusion is not enough to restore functional diversity in the Patagonian Monte.