Edaphic properties as key drivers for woody species distributions in tropical savannic and forest habitats

Edaphic gradients can explain plant species distribution at a local scale in the neotropics and elsewhere, but few studies have evaluated the individual responses of species to such gradients. We collected data on species and soils in open savannic and forest formations (totalling five habitats in each formation), aiming to evaluate the importance of edaphic factors on the distribution of woody plant species in tropical habitats. Logistic regression was used to test the influence of predictor variables (soil texture and fertility) on plant occurrence (presence or absence). Most species (73%) responded to the edaphic gradients. However, the edaphic gradients did not explain the distribution of the remaining 27% of species, which implies the existence of other factors determining their occurrence. Soil fertility (nutritional status) was the major factor in forest habitats (65% of the species which showed significant response), while soil texture was the most explanatory factor for species occurrence in open habitats (55% of the species that showed a significant response). Thus, nutrient status was less limiting and soil texture was more limiting in savannic formations, whereas the opposite was observed for forest formations. Most species showing a relationship with edaphic gradients had a unimodal response, which is in accordance with the literature. Our study showed that soil properties largely regulate the distribution of plant species in tropical habitats, despite other factors not investigated here also having an effect on several of the studied species. Models of species distribution that take into account environmental heterogeneity are key for the elaboration of strategies for the conservation and restoration of ecosystems.