Climate dynamics and conservation of Atlantic Forest endemic filmy ferns

Abstract

The Atlantic Forest harbors exceptional fern diversity and endemism, largely supported by climatic refugia that buffered environmental changes through time. These refugia remain crucial under ongoing climate change, particularly for endemic and climate-sensitive taxa such as Hymenophyllaceae ferns. We modeled the distribution of Atlantic Forest endemic Hymenophyllum species over the past 140,000 years and under future climate scenarios to identify climatic refugia and to evaluate the effectiveness of protected areas. Our results show that Hymenophyllum species are strongly associated with the major mountain ranges of the Atlantic Forest and depend on the persistence of their current habitats. Under paleoclimatic scenarios, suitable habitats generally expanded, especially during the Last Glacial Maximum. In contrast, all species showed habitat loss under future projections. By the end of the century, suitable habitats are projected to decline by 17–65% under the optimistic scenario and by 51–98% under the pessimistic scenario. Less than 10% of climatically stable areas are currently protected, and these areas may lose an additional 30% and 75% of their suitability under optimistic and pessimistic scenarios, respectively. These reductions substantially increase extinction risk, with all species potentially qualifying as Threatened or Critically Endangered under pessimistic climate projections by 2100. Based on the overlap between refugial areas and species richness, we identified two priority regions for in situ conservation in southeastern and southern Brazil. Our findings highlight the urgent need to expand and strengthen protection in these areas to safeguard not only Hymenophyllum species but also broader Atlantic Forest biodiversity under climate change.

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