PHYTOSOCIOLOGY OF SOWN PASTURE WEEDS UNDER TWO LEVELS OF DEGRADATION IN BRAZILIAN SAVANNA AREAS, MATO GROSSO DO SUL STATE, BRAZIL

Abstract

Cultivated pastures, in general, go through a decline process, associated with the occurrence of weeds, whose successful management begins with the survey of species and their biology. This study aimed to carry out phytosociological surveys, during the rainy and dry seasons, in two pastures cultivated with Brachiaria (Urochloa) spp., with cattle (AI) and without cattle (AII), in Cerrado (Brazilian savanna) areas of the Mato Grosso do Sul State, Brazil. The occurrence of 104 weedy herbaceous and subshrubby Phanerogams species was recorded. The families with the highest number of species were Fabaceae (23 species), Poaceae (16), and Asteraceae (15). Hemicryptophytes predominate with 41% of the species. The species with the highest importance value and relative coverage are B. decumbens and Sida rhombifolia, in AI, and B. brizantha and Desmodium incanum, in AII, plus Paspalum notatum, in both pastures. The Shannon diversity index was 4.19 and 4.43 nats, for AI and AII, respectively, indicating considerable weed species richness. The floristic dissimilarity index between AI and AII, obtained from the Euclidian distance, is 0.7468, indicating just a few species in common (44%). In the dry season, the number of species in AI decreased 10% while in AII it increased 4%.

KEY-WORDS: Agroecosystem; Brachiaria; flora; plant ecology; Urochloa.