Tree and shrub floristic variation in the Caatinga.

(a) Quantitative representation of beta diversity as interpolated dissimilarity based on NMDS axes. The colours of the map have no absolute meaning—only the colour differences between locations within the same study site are meaningful. (b) Regionalization of woody plants into nine biogeographical subregions based on the K-means partitioning of the interpolated values of NMDS axes. Maps drawn in 2.5 arc-min resolution.