CONSERVATION ASSESSMENTS

Provisional IUCN conservation assessments of all species of ferns occurring in Thailand, Laos and Cambodia have been calculated using the IUCN (2001) Red List Categories and Criteria.

The large majority of species have been assessed as Least Concern. Five species have been listed as Vulnerable (Adiantum gomphophyllum, Adiantum membranifolium, Adiantum thongthamii, Hymenasplenium inthanonense, Lepisorus oosphaerus), two species as Endangered (Adiantum siamense, Microsorum thailandicum) and one species as Critically Endangered (Heterogonium hennipmanii). A further 32 species have been listed as Data Deficient (due to insufficient knowledge on current distribution in most cases but also due to questions on taxonomic status in a few species).

The many Adiantum species amongst the threatened species is largely due to the fact that several species are rather locally endemic in karst limestone habitats. Karst limestone habitats are under pressure throughout Southeast Asia, particularly due to exploitation of the limestone for cement (see Clements et al., 2006).

On the whole fern species have rather lower numbers of threatened species than many other groups of vascular plants. This is largely due to the fact that local endemism is rather rare and that many species have very widespread distributions or very large disjunct distributions, presumably due to the very light windborne spores. Under the B criteria most species have an Extent of Occurrence and Area of Occupancy that is much too large to fall into any of the threatened categories. However, this should constantly be monitored as deforestation may lead to the loss of current ranges of distribution of many species.