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Soil characteristics are important drivers of variation in wet tropical forest structure and diversity, but few studies have evaluated these relationships in drier forest types. Using tree and soil data from 48 and 32 1 ha plots, respectively, in a Bolivian moist and dry forest, we asked how soil conditions affect forest structure and diversity within each of the two forest types. After correcting for spatial effects, soil-vegetation relationships differed between the dry and the moist forest, being strongest in the dry forest. Furthermore, we hypothesized that soil nutrients would play a more important role in the moist forest than in the dry forest because vegetation in the moist forest is less constrained by water availability and thus can show its full potential response to soil fertility. However, contrary to our expectations, we found that soil fertility explained a larger number of forest variables in the dry forest (50 percent) than in the moist forest (17 percent). Shannon diversity declined with soil fertility at both sites, probably because the most dominant, shade-tolerant species strongly increased in abundance as soil fertility increased.

Floristic variation is high in the Neotropics, but little is known about the factors shaping this variation at the mesoscale. We examined floristic composition and its relationship with environmental factors across 220 1-ha permanent plots in tropical lowland Bolivia. For each plot, abundance of 100 species (93 tree and 7 palm species =10 cm diam) was obtained. Climatic data, related to rainfall seasonality and temperature, were interpolated from all available weather stations in the region, and soil properties, related to texture and fertility, were obtained for each plot. Floristic variation was strongly associated with differences in water availability and temperature, and therefore the climatic gradient shaped floristic variation more strongly than the edaphic gradient. Detrended correspondence analysis ordination divided lowland Bolivia primarily into two major groups (Southern Chiquitano region vs. the Amazon region) and a multiple response permutation procedure distinguished five floristic regions. Overall, the tested environmental variables differed significantly among the five regions. Using indicator species analysis, we distinguished 82 strong indicator species, which had significant environmental preferences for one floristic region. These species can be used as indicators of environmental conditions or to determine which floristic region a certain forest belongs. Given the predicted decreases in rainfall and increases in temperature for tropical lowland forests, our gradient approach suggests that species composition may shift drastically with climate change

Background: It has been proposed that the interaction between herbivory and soil nutrient availability drives habitat association of tree species in Peruvian Amazonia. Nevertheless, there is no empirical evidence that this interaction holds across other Amazonian regions. Aims: We address this knowledge gap by testing whether the interaction between herbivory and soil nutrient contributes to habitat association of tree species in white-sand and terra-firme forests in the upper Rio Negro, Brazil. Methods: We conducted a reciprocal transplanting field experiment in which we controlled for the presence of herbivores. We tested for differences in tree-seedling growth and herbivory among seven white-sand and seven terra-firme habitat-specialist species. Additionally, we assessed whether tree seedlings differed in their functional traits. Results: We found no empirical evidence that an interaction between herbivory and soil nutrients shapes habitat association in white-sand and terra-firme forests of the upper Rio Negro. Tree seedlings showed higher mortality when growing in their non-typical habitat. Growth and herbivory were similar regardless of the presence or absence of herbivore protection and type of soil. Conclusions: We suggest that the overall differences in soil nutrient status between white-sand and terra-firme forests in the upper Rio Negro are insufficient to trigger an interaction between herbivory and soil nutrient availability.

Soil characteristics are important drivers of variation in wet tropical forest structure and diversity, but few studies have evaluated these relationships in drier forest types. Using tree and soil data from 48 and 32 1 ha plots, respectively, in a Bolivian moist and dry forest, we asked how soil conditions affect forest structure and diversity within each of the two forest types. After correcting for spatial effects, soil-vegetation relationships differed between the dry and the moist forest, being strongest in the dry forest. Furthermore, we hypothesized that soil nutrients would play a more important role in the moist forest than in the dry forest because vegetation in the moist forest is less constrained by water availability and thus can show its full potential response to soil fertility. However, contrary to our expectations, we found that soil fertility explained a larger number of forest variables in the dry forest (50 percent) than in the moist forest (17 percent). Shannon diversity declined with soil fertility at both sites, probably because the most dominant, shade-tolerant species strongly increased in abundance as soil fertility increased.

Floristic variation is high in the Neotropics, but little is known about the factors shaping this variation at the mesoscale. We examined floristic composition and its relationship with environmental factors across 220 1-ha permanent plots in tropical lowland Bolivia. For each plot, abundance of 100 species (93 tree and 7 palm species =10 cm diam) was obtained. Climatic data, related to rainfall seasonality and temperature, were interpolated from all available weather stations in the region, and soil properties, related to texture and fertility, were obtained for each plot. Floristic variation was strongly associated with differences in water availability and temperature, and therefore the climatic gradient shaped floristic variation more strongly than the edaphic gradient. Detrended correspondence analysis ordination divided lowland Bolivia primarily into two major groups (Southern Chiquitano region vs. the Amazon region) and a multiple response permutation procedure distinguished five floristic regions. Overall, the tested environmental variables differed significantly among the five regions. Using indicator species analysis, we distinguished 82 strong indicator species, which had significant environmental preferences for one floristic region. These species can be used as indicators of environmental conditions or to determine which floristic region a certain forest belongs. Given the predicted decreases in rainfall and increases in temperature for tropical lowland forests, our gradient approach suggests that species composition may shift drastically with climate change