Question: How is grazing intensity associated with species and morpho-functional traits (MFTs) composition, productivity and richness of annual dominated grasslands? Have native and exotic species similar associations to this gradient?
Location: Anthropogenic grassland in the Espinal vegetation in the sub-humid area of the mediterranean type climate region of Chile (35°58′ S, 72°17′ W).
Methods: Data were obtained from a long-term (eight years) experiment with six stocking rates (1 to 3.5 sheep/ha). Detrended Correspondence Analysis (DCA) and regression analysis were used to determinate the relationship between grazing intensity and biomass, richness, abundance and traits of the species.
Results: The first DCA axis was related to grazing intensity and explained most of the floristic variation (69.3%); the abundance of some non-native species, e.g. Vulpia megalura were highly correlated with this axis. In the DCA for MFTs the first axis explained 87% of the variance and was also related to grazing intensity; the abundance of small size plants and shallow roots increased with grazing intensity. The relative abundance of grasses and composites, but not of legumes, changed with stocking rate: as grazing intensity increased composites became the predominant species to the detriment of grasses. The above-ground biomass measured in exclusion cages declined with increasing grazing pressure. The richness of exotic species was greater compared to native ones at low stocking rates, but they converge to similar values at higher stocking rates. However, the relative abundance of exotic species was greater than 75% in all stocking rates.
Conclusions: Grazing intensification has large effects in the structure of grassland in central Chile. With grazing intensities greater than 1 sheep/ha species characteristics change; evolving in a few years (6–8) towards a similar community regardless of the stocking rate. The overgrazed community has more native than exotic species richness, possibly due to greater defence traits against herbivory of this group of species.
Nomenclature: Marticorena & Quezada (1985).