GARIBALDI Lucas Alejandro
congresos y reuniones científicas
Impact of introduced herbivores on plant biodiversity and ecosystem function in cool-temperate Patagonian forests.
Congreso; INTECOL; 2013
Institución organizadora:
The introduction of large exotic herbivores constitutes a major threat to the conservation of the few remaining forested regions that have been spared from intensive logging. Large-herbivore effects on plant biodiversity and key ecosystem processes have been extensively documented in grasslands and savannas. Less is known about the impact of introduced grazers on understorey plant communities and the functioning of native forest ecosystems. Herbivory effects on plant diversity and species composition have been found to vary along gradients of primary productivity and resource availability. But how  concomitant effects on carbon and nutrient cycling might change along environmental gradients remains largely untested. Here we examine the long-term effects of introduced domestic herbivores on understorey plant composition, species diversity and litter decomposition in cool-temperate forests of southern South America. Our study compared historically (>50 years) grazed and ungrazed sites (n = 5) paired along a region-wide moisture gradient (PP = 1400?1800 mm/year; PP/PET = 2.5?4.5) in Nahuel Huapi National Park, northwestern Patagonia, Argentina. Nothofagus dombeyi was the main canopy species across all sites. Vegetation sampling and litterbag decomposition experiments were replicated for three plots nested within sites. Data were analysed using hierarchical mixed-effect models. Compositional dissimilarity (Bray-Curtis index) between grazed and ungrazed sites was generally greater than 60%, and increased with increasing environmental moisture. Large herbivores reduced woody plant cover (50%) and species evenness (30%) throughout the moisture gradient, but there was no overall consistent effect on plant species richness per site. In addition, grazing reduced species diversity (40%) within the leaf-litter pool, which contained a greater proportion of N. dombeyi leaves in grazed than in ungrazed sites. Decomposition rate of N. dombeyi leaf litter over 18 months was higher in ungrazed than in grazed sites, irrespective of site moisture. Further, the leaf-litter pool of understorey species from ungrazed sites decomposed faster than the corresponding litter pool of grazed sites, but only when incubated in ungrazed forests towards the drier end of the gradient. Our results show that the presence of domestic herbivores altered understorey community structure and diversity, which resulted in a significant functional shift in the litter pool composition. Long-term increase in large herbivore densities also decelerated organic matter decomposition, by primarily modifying the forest soil environment rather than the quality of aboveground litter inputs. Importantly, grazing-induced changes in forest biodiversity and ecosystem function were not restricted to certain environmental conditions, but were manifested across a broad-scale moisture gradient.