Floristic composition's dynamics of a natural grassland was evaluated to estimate the effects of grazing systems and introduction of cool season species. The experiment was held in São Gabriel, in the region of Depressão Central, Rio Grande do Sul, Brazil. The grazing period was from 01/11/2004 to 23/12/2004, totaling 53 days. Floristic composition were evaluated before the beginning of the grazing period (23/09/2004) and after its end (27/01/2005). Tested treatments were: natural grassland improvement with introduction of cool season species under rotative grazing (CNM); natural grassland under continuous grazing (CNC) and natural grassland under rotative grazing (CNR), distributed in an entirely randomized design, with two replicates. Corriedale breed ewes, with their lambs, were tester grazing animals. Data were submitted to multivariate analysis based in ordination and randomization testing. In the first survey, the treatment CNM differed (P=0.0001) from CNC and CNR due to the high contribution of the introduced species, while CNC and CNR were similar (P=0.6742) in species' composition. Treatments CNM and CNC were different (P=0.0017) in the second evaluation. The effect of rotative grazing, introduction of species and fertilization seems to be decisive for changes in floristic composition. Vegetation under rotative grazing presented trajectories that converge to a situation of similarity in the species' composition.
floristic composition; grazing methods; improvement; sheep
