Effects of livestock exclusion in forests of Uruguay: Soil condition and tree regeneration

Abstract

Livestock intervention, depending on the regime of grazing and the sensitivity of species, could alter the structure, composition and dynamics of forest ecosystems, with negative long-term impacts on plant communities, soil and water quality, and thus on the provision of ecosystem services. We studied here the effects of livestock on forest ecosystems of Uruguay where livestock ranching is the most extensive and traditional production activity. The aim of the present study was to investigate the effects of livestock exclusion on forest dynamics, particularly on tree regeneration and soil properties. We analyzed six grazed–ungrazed (4–17years of exclusion by fences) paired sites, in hillside forests of Uruguay. Our results indicate that exclusion contributes to improve soil conditions by increasing leaf litter cover and tending to reduce erosion. Regeneration was also improved under exclusions, with increased density of tree seedling (+20%) and saplings (+60%). Species composition of regenerating trees was in general not affected by exclusion, but one (i.e., Styrax leprosus) of the 11 sapling species sampled was almost absent in grazed sites. Despite the short-term experiment, our findings indicate that livestock exclusion is a useful tool to protect hillside forests of Uruguay by improving soil conditions and providing opportunities for the regeneration of shade-tolerant and grazing-susceptible species. Light-demanding species, such as canopy-dominant trees Scutia buxiflora and Lithraea brasiliensis presented very low densities of saplings and seedlings, in either grazed or un-grazed sites, suggesting that our enclosure treatment failed to generate adequate microsites for such species. Forest gaps and grassland–forest transitions should be incorporated in future enclosures to benefit light-demanding trees.