Where are threatened ferns found? Global conservation priorities for pteridophytes

Recent efforts to improve the representation of plant species included on the IUCN Red List of Threatened Species through the IUCN Sampled Red List Index (SRLI) for Plants have led to the assessment of almost 1000 additional species of pteridophytes and lycophytes under IUCN Red List criteria. Species were selected at random from all lineages of pteridophytes and lycophytes and are taxonomically as well as ecologically representative of pteridophyte and lycophyte diversity. 16% of pteridophyte and lycophyte species are globally threatened with extinction and 22% are of elevated conservation concern (threatened or Near Threatened); of species of pteridophytes and lycophytes previously included on the Red List, 54% were considered threatened. Over half of pteridophyte and lycophyte species assessed for the SRLI use estimates of range size; therefore the method used to measure range may affect the Red List category assigned. We evaluated this using two alternative metrics for estimating range, species distribution modelling (SDM) and ecologically suitable habitat (ESH), for 227 species endemic to the Neotropical biogeographic realm. Differences between range estimates were small when ranges were small but increased with increasing range size. For 58 (25.6%) species alternative modelling techniques result in the species meeting the threshold for a different IUCN Red List category from using extent of occurrence. Modelling threatened species distributions also highlights priority areas for conservation in tropical and subtropical montane forests that are the most species-rich habitat for small-range pteridophyte and lycophyte species, but which are now increasingly subject to rapid conversion to agriculture.