A importância de condições hidrológicas na distribuição e conservação de plantas herbáceas de sub-bosque em florestas amazônicas: uma contribuição em escala regional

Abstract

Although it is know that water conditions are important determinants of species composition in tropical forests, the relationship between hydrology and vegetation is often assessed indirectly through other environmental predictors, such as topography. We investigated the relationship between understory herbs and local and regional hydrological conditions in eighty-eight 250 x 2 m plots over a linear extent of approximately 600 km long in terra-firme forests in the Central Amazon. Nonmetric Multidimensional Scaling was used to order the plots by their floristic dissimilarities and multiple regressions were used to identify the best predictor of species composition. Local hydrological conditions represented by height above the water, either below or above ground, were better predictors of species composition than regional climatic conditions. Soil fertility was consistently low and was a less important predictor than local hydrological conditions. Most of the effect of height above water was due to the inclusion of seasonally flooding sites. When only non-flooding sites were analyzed, the height above water had only a weak effect (quantitative data) or no effect (qualitative data) on species composition. Different taxonomic groups in the herb community respond differently to the hydrological gradient. The Zingiberales showed the strongest association with hydrological conditions. Because local hydrological conditions were the best predictor of species composition in tropical forests, our results have broad applicability. In particular, this predictor can be used to test the efficacy of existing conservation units as refuges for herbs under climate changes.