Restricted geographic distribution of tree species calls for urgent conservation efforts in the Subtropical Atlantic Forest

The Atlantic Forest encompasses a high level of biodiversity, endemism and degradation; hence, it is a biome of particular interest for biological conservation. We aimed to investigate the actual geographic distribution of tree species and, among the indicator species of each vegetation type, the conservation status and potential distribution of each species along a vegetation gradient of the Subtropical Atlantic Forest. We analysed the species’ relative constancy to determine their actual distribution, obtained 21 indicator species of the different vegetation types and modelled their potential distribution using the maximum entropy algorithm. The potential distribution models were pooled to yield a single map, which was used to predict the distribution of climatic suitability for these species in South America. Our results showed that the actual geographic distribution is restricted for most species (~72 %). Araucaria angustifolia and Euterpe edulis were categorized as threatened species. The sum of the indicator-species maps showed reduced climatic suitability across most of South America. The southern region of Brazil and the southeastern Brazilian highlands, as well as a few areas of seasonal forests on higher elevations of the Bolivian Chiquitanía and Andean Piedmont, exhibited the best climatic suitability. Elevation was the most important variable in our models. Given the concerning level of forest degradation and the presence of endangered and geographic restricted species, our results are a relevant contribution to biodiversity conservation in the Subtropical Atlantic Forest areas, highlighting their floristic and environmental uniqueness and, therefore, the urgent necessity of preserving their biological heritage.