Community assembly persists as a key topic in ecology due to the complex variation in the relative importance of assembly forces and mechanisms across spatio-temporal scales and ecosystems. Here we address a forest–savanna vegetation mosaic in the Brazilian Atlantic forest to examine the role played by soil attributes as determinants of community assembly and organization at a landscape spatial scale. We examined soil and plant assemblage attributes across 23 plots of forest and savanna in a 1600 km² landscape exposed to the same climatic conditions in the Atlantic forest region of northeast Brazil. Assemblage attributes included species richness, taxonomic and functional composition (community weighted mean, CWM) and functional diversity (quadratic diversity; Rao’s quadratic entropy index) relative to plant leaf area, specific leaf area, leaf dry matter content, thickness and succulence. Our results suggest that forest and savanna patches exposed to the same climatic conditions clearly differ in terms of soil attributes, plant assemblage structure, taxonomic and functional composition. By selecting particular plant strategies relative to resource economy, soil potentially affects community structure, with forest assemblages bearing more acquisitive resource-use strategies, while conservative plant strategies are more frequent in savannas. Accordingly, savanna–forest mosaics in the Atlantic forest region represent spatially organized plant assemblages in terms of taxonomic and functional features, with a signal of trait convergence in both vegetation types. Soil-mediated filtering thus emerges as a potential deterministic assembly force affecting the spatial organization of savanna–forest boundaries and mosaics.

The proliferation of disturbance-adapted species in human-modified landscapes may change the structure of plant communities, but the response of biodiversity to human disturbances remains poorly understood. We examine the proliferation of the palm,Syagrus coronata, in disturbed forest stands and its impacts on the structure of vascular epiphyte assemblages in a human-modified landscape of Brazilian Caatinga dry forest. First, we comparedS. coronatadensity between old-growth and regenerating forest stands. We then surveyed vascular epiphytes on 680 phorophytes (S. coronataand non-palm/control species) across five habitat types with different disturbance levels. There was an eight-fold increase inS. coronatadensity in regenerating areas compared with in old-growth forest.Syagrus coronotasupported richer epiphyte assemblages at local (i.e. per palm) and landscape (i.e. pooling all palms) scale than control phorophytes, supporting more than 11 times the number of species of control phorophytes at both scales. Epiphyte assemblages were more abundant, species-rich and dominated by abiotically dispersed species in forest sites with intermediate disturbance levels (regenerating forest stands). More than simply operating as an exclusive phorophyte for more than 90% of the epiphyte species we recorded here,S. coronatafavours epiphyte persistence and structures their assemblages across human-modified landscapes of the Caatinga forest.