Abstract
In South America, the largest seasonal savanna region is the Brazilian cerrado. Our aim was to study temporal changes in some community descriptors, such as floristic composition, richness, species density, plant density, and cylindrical volume, in a seasonal cerrado, comparing it to a nearby hyperseasonal cerrado. In four different seasons, we placed randomly ten 1 m(2) quadrats in each vegetation form and sampled all the vascular plants. Seasonal changes in floristic composition, species density, and plant density were less pronounced in the seasonal than in the hyperseasonal cerrado. Floristic similarity between the vegetation forms was lower when the hyperseasonal cerrado was waterlogged. Richness and species density were higher in the seasonal cerrado, which reached its biomass peak at mid rainy season. The hyperseasonal cerrado, in turn, reached its biomass peak at early rainy season and, despite the waterlogging, maintained it until late rainy season. In the hyperseasonal cerrado, waterlogging acts as an environmental filter restricting the number of cerrado species able to withstand it. The seasonal cerrado community was more stable than the hyperseasonal one. Our results corroborated the idea that changes in the environmental filters will affect floristic composition and community structure in savannas.
Highlights
Plant-available moisture (PAM) is one of the crucial ecological limitations for the growth of savanna plants, varying both spatially, according to depth, and temporally, as a result of seasonal rainfall (Sarmiento, 1996; Silva, 1996)
Soil water potentials are above the permanent wilting point during the rainy season and, water is available for any plant species (Sarmiento, 1996; Quesada et al, 2004; Oliveira et al, 2005)
We tried to answer the following questions: i) does the floristic composition vary in the same way throughout the year in the seasonal and hyperseasonal cerrados?; ii) is the floristic composition of the hyperseasonal cerrado (Cianciaruso et al, 2005) less similar to the seasonal cerrado when the former is waterlogged?; iii) is the seasonal cerrado savanna richer in species than the hyperseasonal cerrado?; iv) does species richness vary throughout the year in seasonal and hyperseasonal cerrados?; and v) do species density, plant density, and cylindrical volume vary in the seasonal cerrado as we previously found in the hyperseasonal cerrado (Cianciaruso et al, 2005)?
Summary
Plant-available moisture (PAM) is one of the crucial ecological limitations for the growth of savanna plants, varying both spatially, according to depth, and temporally, as a result of seasonal rainfall (Sarmiento, 1996; Silva, 1996). Soil water potentials are above the permanent wilting point during the rainy season and, water is available for any plant species (Sarmiento, 1996; Quesada et al, 2004; Oliveira et al, 2005). Soil water potentials may remain for some months at values as low as the permanent wilting point, still within the reach of woody plants, but not of herbaceous ones (Franco and Nobel, 1990; Sarmiento, 1996; Franco, 2002). Drought causes water deficit in plants, affecting metabolism and morphology, reducing growth, and arresting development (Baruch, 1994).
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