Climate emergency is a significant threat to biodiversity in the 21st century, but species will not be equally affected. In summing up different species’ responses at the local scale, we can assess changes in the species quantity and composition of biotic assemblages. Here we investigated climate change driven variation in species richness and spatial beta-diversity using modelled distributions of 2,841 plant species in Caatinga, the largest dry forest region of South America. More than 99% of plant assemblages were projected to lose species by 2060, with biotic homogenisation ─ the decrease in spatial beta-diversity forecasted in 40% of the Caatinga. Replacement of narrow-range woody species by wide-range non-woody ones should impact at least 85% of Caatinga plant assemblages. The future increase in aridity will change patterns of woodiness and ecological generalism of tropical dry forest plant assemblages, and ultimately erode ecosystem services linked to biomass productivity and carbon storage.

1. Climate emergency is a significant threat to biodiversity in the 21st century, but species will not be equally affected. In summing up the responses of different species at the local scale, we can assess changes in the species quantity and composition of biotic assemblages. 2. We used more than 420K curated occurrence records of 3060 plant species to model current and future patterns of plant species distribution in one of the world's largest tropical dry forests-the Caatinga. While allowing different model extrapolation scenarios, we estimated potential changes in the species richness and composition of dryland plant assemblages in response to projected climate change, and assessed how the ecological generalism and woodiness of plant assemblages can be impacted by the climate crisis. 3. More than 99% of plant assemblages were projected to lose species by 2060, with biotic homogenisation-the decrease in spatial beta diversity-forecasted in 40% of the Caatinga. The replacement of narrow-range woody species by wide-range non-woody ones should impact at least 90% of Caatinga plant assemblages. The exacerbated species loss in the dryland plant assemblages was connected to the heterogenisation and homogenisation of biotic assemblages. Still, the magnitude of climate change impacts on ecological generalism and woodiness patterns of dryland plant assemblages differ according to the direction of the biotic change process. 4. Synthesis. The future increase in aridity will change the patterns of woodiness and ecological generalism of tropical dry forest plant assemblages by decreasing vegetation diversity and complexity. The projected biotic changes in dryland plant assemblages indicate the erosion of ecosystem services linked to biomass productivity and carbon storage. We highlight the importance of long-term conservation planning for maintaining tropical dry forests.

Resumo Descrita no ano de 2015, o conhecimento da biogeografia de Pleurophora pulchra é limitado, fato que impossibilitou sua inclusão na primeira avaliação sobre Áreas Prioritárias para Conservação da Flora do Domínio Caatinga (APCFCs) e Unidades de Conservação (UCs). Nesse contexto, propusemos descrever o potencial biogeográfico de P. pulchra na Caatinga através de modelagem de distribuição de espécies (MDE), visando ampliar as discussões sobre APCFCs e UCs. Utilizamos o algoritmo Maxent para computar o modelo final (MDEf), e o teste Binomial para avaliar o desempenho dos mesmos. Constatamos que P. pulchra está ajustada a ambientes de elevada aridez, com baixa precipitação anual, grande sazonalidade na precipitação, temperaturas estáveis nos meses mais frios e solos pouco espessos, variando de imperfeitamente à bem drenados. O MDEf revelou áreas com adequabilidade ambiental predominantemente na depressão sertaneja meridional da Bahia, Pernambuco e Paraíba, além de áreas do planalto da Borborema da Paraíba. As UCs APAs Cariri e Lago de Sobradinho, APCFCs Jatobá e Cariri Paraibano se destacaram pela representatividade da área com adequabilidade ambiental superior a 0.5. O resultado do teste binomial indicou bom desempenho de MDEf (p < 0.001 t =1) e, portanto, reforçou a possibilidade de novos registros de P. pulchra nas áreas supracitadas.

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