Diversity patterns reveal the singularities of the savanna woody flora in the Cerrado-Amazonia transition

Transitional vegetation zones in the neotropics harbor high biodiversity and are threatened by advancing deforestation and climate change. Besides, the diversity patterns at multiple spatial scales are little understood. We investigated the woody flora of eight savanna sites over 700 km along the transition zone between the Cerrado and Amazonia. We assessed plant diversity at three spatial scales: alpha (α = local richness), beta (β_Jac = Jaccard mean dissimilarity of species composition between sites), and gamma (γ = regional diversity). We also measured the sites’ contribution to beta diversity (LCBD) to unveil the ecological singularity of the transition. We found high local richness (α = ∼80 species per hectare) and high between-site dissimilarity (β_Jac = 0.651; LCBD = 0.354), which together contributed to high regional diversity (γ = 167). There was no relationship between floristic composition and proximity between sites or proximity to Amazonia. The locally dominant species (representing 80% or more of the total abundance) also differed across sites, indicating the unique composition of each community. This high floristic diversity at different spatial scales is severely threatened by extensive deforestation in recent decades and a paucity of protected areas, stressing the need for protected areas and conservation actions.