Seasonally dry tropical forests of the Gulf of Mexico: A degraded landscape undergoing homogenization or a promising, resilient reservoir?

Seasonally dry tropical forests are amongst the most threatened ecosystems in the world due to severe and long-lasting anthropic disturbances. In this study, the spatial variation in plant diversity for the seasonally dry tropical region in central Veracruz was assessed at three different scales: among forested vegetation types, within each vegetation type and within forested patches. This region is characterized by extensive deforestation and today only 12% of its original forest cover remains. Of this, more than a third is early secondary forest. Woody vegetation was sampled in 29 forested patches (three 20 × 50 m transects per patch: 8.7 ha in total) belonging to six vegetation types. A total of 157 species were recorded (sample coverage >97%). Richness per patch was 3–33 spp., and 9 to 88 spp. per vegetation type. Species composition varied greatly across the region as indicated by the low values of compositional similarity (<35%) detected among all six vegetation types, particularly for the most abundant species. Also, relatively low similarity was detected between patches, including small patches of secondary vegetation that are contributing different species to regional diversity. The latter, when allowed to grow over 20 years contributed greatly to β-diversity. Thus, the spatial turnover of species at different scales is remarkably high, favoring the maintenance of a rich species pool at both the local and the regional scales and at the same time indicates that crucial ecological processes such as natural regeneration are still occurring within the region. This could indicate that despite the pervasive landscape modification and long history of forest fragmentation, the region is not currently experiencing the homogenization of its still remarkably rich woody flora.