CONICET | Buscador de Institutos y Recursos Humanos

Question: What are the changes in vegetation structure, soil attributes and mesophauna composition associated with grazing removal in mesic grasslands? Location: Southern Campos of the Río de la Plata grasslands, in south-central Uruguay (Lat 31º54´S, Long 58º15´W). Methods: We surveyed seven continuously grazed (G) and ungrazed (U) paired plots. Plant and litter cover were recorded on three 5-m-long interception lines placed parallel to the fence in each plot. We also extracted soil fauna out of a 10 cm depth composite sample and we determined species composition and abundance of oribatid taxa. The soil attributes measured included soil bulk density, soil water content, soil organic carbon and nitrogen content and root biomass at different depths. Soil organic carbon was estimated in two organic matter (OM) fractions (particulate and mineral associated OM). Changes in floristic, PFT and mesofauna composition were analyzed by Non-metric Multidimensional Scaling. Results: Richness was lower in U than in G plots. From a total of 105 species recorded in grazed plots only 3 were exotics. Shrub and litter cover were significantly higher inside the exclosures, while Cyperaceae-Juncaceae was lower than in grazed plots. Grazing treatments differed significantly in plant and oribatid species composition. Grazing exclusion significantly reduced soil bulk density and increased soil water content. Carbon content in particulate organic matter (POM) was lower in the upper soil of ungrazed sites. However, deeper in the profile grazing exclosures had 8% more carbon in the mineral associated organic matter. Conclusions: Our results agree with previous studies showing a strong influence of grazing on vegetation structure, soil fauna and soil attributes. However, three results were particularly interesting because they differed from the results of previous analyses: the increase of shrub cover in ungrazed sites, the redistribution of the soil organic carbon in the profile and the low invisibility of the prairies regardless of grazing regime.

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