Distribuição espacial de leguminosas herbáceas em duas áreas de savana de Roraima

Abstract

The objective of this study was determining distribution patterns of herbaceous legumes (Fabaceae) in two savanna areas of Roraima, northernmost of Brazilian Amazonia (Monte Cristo -MC and Água Boa-AB). The basic purposewasidentifying environmental edaphic factors (chemical and physical properties of soil)to determinethe presence and distribution of this group in these areas. The study inventoried all species of herbaceous legumesin 12 permanent plotsin MC and 22 ones in AB (2 m x 250 m each one). Total richness was25species (4 Caesalpinoidae; 20 Faboidae; 2 Mimosoidae)in the total, with 24in MC and 19in AB(18species were common). The diversity in MC (H' = 1.07) was larger than in AB (H' = 0.71). Similarity (Sij) was> 84%, indicating that geographical distance (~50 km) did not haveinfluence in the composition of the legumesspecies. Chamaecrista desvauxiiCollad. Killip. wasthe most abundant species in the two fields. The higher IVI(Importance Index Value) were to Eriosema crinitumH.B.K. (AB)and Chamaecrista hispidulaVahl. (MC). The Cluster analysis (Generic) determined four groups in AB, being a monoespecific represented by C. desvauxii, present in almost environments of that place. In MC were formed five groups, being the richest (10 species) formed by species of higher IVI (C. hispidula, E. crinitumand C. desvauxii). This group combined no influences of water table, with low concentrations of Fe(<30 mg.kg-1) and high of Mn(30-80 mg.kg-1), besides middleclay concentrations (15-20%). The results of the two areas suggest that there is a pattern of distribution of species of herbaceous legumes in the two savannaareas surveyed associated to water table seasonality and, in some cases, fertility and granulometryof the soil. The amplification of this study inother savanna areas of Roraima can supply important information for conservation process of this ecosystem in the Amazonia.