Indicator Species and Structure of Natural Grasslands on Basaltic Soils with Contrasting Sheep Stocking Rates

Abstract

The stocking rate adjustment is one of the most important management tools in grasslands ecosystems, since it determines the relationship of forage offer with animal demand, and thereby affects animal production. A field experiment assessed the effect of 5.4 vs 10.8 wether ha-1 on the structure of grasslands of red and black basaltic shallow soils of Uruguay. Forage availability and height, species composition and floristic diversity were evaluated, and indicator species of stocking rate levels were identified. The increase of the stocking rate decreased the offered forage biomass, but no changes were detected in species richness and diversity. The soil type factor explained most of the botanical composition differences, while the response to stocking rates was of smaller magnitude. The vegetation response to the stocking rate increase was different between soil types. For the evaluated stocking rates, Black Lithosols showed two different vegetation states characterized one by the dominance of cool season tall grasses and the other by prostrate species. On the other hand, the botanical composition on the Red Lithosols was little affected. Twelve indicator species related to stocking rates levels were identified, which can be used as indicators of the recent history of grazing. The evaluation of this species will facilitate the development of management and monitoring plans of Basaltic grasslands.