Long‐term species change in a Uruguayan grassland

Abstract. This paper reports on species changes which occurred in plots in a Uruguayan grassland after 55 yr of continuous grazing. The study was based on the pioneering work of B. Rosengurtt who sampled 10 plots in 1935; in 1990 we re‐sampled five of them. Comparative studies were based on rank‐frequency, diversity, evenness and multivariate analyses. Diversity was measured as species richness S , Shannon's index H and its exponential form N = e H , evenness E = N/S and Gini's coefficient of hierarchy G . Species‐richness of the plots increased significantly. Species which entered the sites are mostly weedy species, while those that have decreased are mostly palatable forage species. Evenness, however, remained constant. Floristic change was chiefly associated with time, and secondarily with plot soil‐type. During the 55 yr that elapsed between both observation periods, a dramatic floristic change has occurred in this grassland site.