ABSTRACT We surveyed two savanna sites, one on flat terrain with deep soil (DS), and the other on hilly terrain with rocky outcrops and shallow soil (RS), before and after an accidental fire. We found that the fire did not cause any significant changes in the species composition or diversity of either community, and did not result in floristic homogenization. However, we did record a reduction in the density of plants and in basal area in the DS savanna in comparison with the RS savanna, as well as a higher rate of basal sprouting, which indicates a trade-off between mortality and sprouting. We conclude that, whereas post-fire changes in vegetation structure were more pronounced in the DS savanna than in the RS, the difference in the underlying substrate did not have a direct influence on the post-fire composition of woody species. The greater grass biomass found in the DS savanna in comparison with the RS savanna appears to have been the principal modulator of the severity of the fires in the two phytophysionogmies, and accounts for the distinct responses to fire we observed in the two woody communities.

ABSTRACTWe investigated the existence of an ecotone in the species composition, diversity and vegetation structure in the transition between gallery forest and cerrado sensu strictoin central Brazil. We tested two hypotheses: 1) a ecotone can be found between gallery forest and cerrado; 2) a gradient exists in the species composition of the cerrado. We established three parallel transects of 5 m × 350 m running between gallery forest and cerrado, which were divided into subplots of 5 m × 10 m, perpendicular to the margin of the Bacaba stream in Nova Xavantina (Mato Grosso, Brazil). We identified and measured the height and diameter of individual plants in the plots with a diameter of at least 3 cm at 30 cm above the ground. We recorded 140 species, of which 26 were exclusive to the gallery forest, and 95 to the cerrado. The cerrado presented higher species richness (observed and estimated) and diversity (diversity profiles) than the gallery forest. Both hypotheses were accepted: a distinct ecotone was observed between gallery the forest and cerrado, and a pronounced gradient was found in species composition among the cerrado plots, apparently in response to the variation in soil moisture content, probably related to topography.