Environmental and historical controls of floristic composition across the South American Dry Diagonal

Abstract

Aim The aim of this study was to test the role of environmental factors and spatially autocorrelated processes, such as historical fragmentation and dispersal limitation, in driving floristic variation across seasonally dry tropical forests (SDTFs) in eastern South America.Location SDTFs extending from the Caatinga phytogeographical domain of north-eastern Brazil to the Chaco phytogeographical domain of northern Argentina, an area referred to as the Dry Diagonal.Methods We compiled a database of 282 inventories of woody vegetation in SDTFs from across the Dry Diagonal and combined this with data for 14 environmental variables. We assessed the relative contribution of spatially autocorrelated processes and environmental factors to the floristic turnover among SDTFs across the Dry Diagonal using variation partitioning methods. In addition, we used multivariate analyses to determine which environmental factors were most important in explaining the turnover.Results We found that the environmental factors measured (temperature, precipitation and edaphic conditions) explained 21.3% of the variation in species composition, with 14.1% of this occurring independently of spatial autocorrelation. A spatially structured fraction of 4.2% could not be accounted for by the environmental factors measured. The main axis of compositional variation was significantly correlated with a north-south gradient in temperature regime. At the extreme south of the Dry Diagonal, a cold temperature regime, in which frost occurred, appeared to underlie floristic similarities between chaco woodlands and southern SDTFs.Main conclusions Environmental variables, particularly those related to temperature regime, seem to be the most significant factors affecting variation in species composition of SDTFs. Thus historical fragmentation and isolation alone cannot explain the turnover in species composition within SDTFs, as is often assumed. Compositional and environmental heterogeneity needs to be taken into account both to understand the past distribution of SDTFs and to manage and conserve this key tropical biome.

Plant diversity patterns in neotropical dry forests and their conservation implications

“…3). The relationship of the Caatinga and central Brazil dry forests, which share almost 700 species, has been highlighted previously (2,14,31), but what is striking elsewhere is the low levels of floristic similarity, even among geographically proximal floristic groups (e.g., northern and central interAndean valleys).…”

Inserting Tropical Dry Forests Into the Discussion on Biome Transitions in the Tropics

“…These are dry forests found in the Cerrado region and around the Pantanal and Chiquitania regions of Brazil and Bolivia. Within the Cerrado, dry forests are known to occur on and around calcareous outcrops, where soils have higher phosphorus and base cation concentrations (Ratter et al, 1978;Furley and Ratter, 1988;Oliveira-Filho and Ratter, 2002;Neves et al, 2015). On these soils, trees can grow more quickly, have better chances of escaping the "fire trap" and are more likely to FIGURE 1 | Map of biomes across lowland tropical South America (after Silva de Miranda et al, in press).…”

“…However, it is likely that soil fertility is relevant for the presence of dry forests around calcareous outcrops as a different vegetation, cerrado rupestre, which is floristically related to savanna vegetation, is found on noncalcareous outcrops in the Cerrado (Ribeiro and Walter, 1998). Whichever factor is more important (soils with high fertility or low water-holding capacity), it is evident that the same drought-tolerant, fire-intolerant tree species and lineages that dominate vegetation in the arid Caatinga are also found in dry forest patches in the moister Cerrado (Prado and Gibbs, 1993;Neves et al, 2015;DRYFLOR, 2016;Silva de Miranda et al, in press). …”

Effects of soil and space on the woody species composition and vegetation structure of three Cerrado phytophysiognomies in the Cerrado-Amazon transition

“…Legendre et al, 2002;Peres-Neto and Legendre, 2010;Moro et al, 2015;Neves et al, 2015;Mews et al, 2016), although Mews et al (2016) used an approach of this type. This new approach may help improve the understanding of the factors and mechanisms that mold the distribution of the flora and the structure of the vegetation of the Cerrado.…”