Volume 22, Issue No. 2, 1997

A PRELIMINARY SURVEY OF THE VEGETATION AND BIOGEOCHEMISTRY _OF THE MAFIC/ULTRAMAFIC SEQUENCES OF THE CERRO _MANTIQUEIRA, LAVRAS DO SUL, RIO GRANDE DO SUL, BRAZIL

M.C. Lima e Cunha*, D.L. Saldanha**, R.R. Brooks*** and C.E. Dunn****

Keywords: geobotany, biogeochemistry, serpentine flora, Scoparia montevidensis. Rio Grande do Sul, Brazil.

ABSTRACT

This work is concerned with geobotanical and biogeochemical studies of the vegetation over serpentine soils of the Cerro Mantiqueira, Lavras do Sul, Rio Grande do Sul State, Brazil. The object of these studies was to differentiate lithologies of the Cerro Mantiqueira by qualitative and quantitative sampling of plant communities. The data show that vegetation patterns in terms of composition, density and frequency, are distinctly different over serpentinite than over the other lithologies of the sequence. The few shrubs or trees present, show xeromorphic characteristics such as low height, thickened stems and numerous small leaves. From comparison with similar regions of the world, the ultramafic terrain of southern Brazil supports a distinct vegetation conditioned more by environmental geochemistry than by climatic or latitudinal factors. Biogeochemical studies using Baccharis trimera (Asteraceae) showed an increase of nickel and magnesium concentrations in plants growing over the serpentinite compared with the country rock. There was a corresponding reduction in the barium and strontium content of this plant over the same transect. The potential of this species for biogeochemical prospecting deserves further study.