The ecology and conservation of the Killarney Fern Trichomanes speciosum willd. In Britain and Ireland

Abstract

Trichomanes speciosum Willd. (Hymenophyllaceae) is one of the rarest and most celebrated species in the British and Irish vascular flora. The ecology and habitats of 43 colonies of the sporophyte (fern plant) generation are described. Two-way indicator species analysis suggests that T. speciosum occurs in four main floristic groups; in very deeply shaded habitats; in large dripping caves; in crevices in cliffs and small caves; and on dripping vertical cliffs and rocky banks in wooded ravines. Canonical correspondence analysis shows that altitude and habitat types are the major environmental variables influencing the floristic composition of the 43 colonies. Monitoring data suggest that frond number remains remarkably constant over 13–29 years. Possible reasons for the absence of T. speciosum in so many apparently suitable habitats in western Britain and Ireland are discussed. Sporophyte establishment appears to be most critical, especially under a climate that is marginal for its temperature requirements. The distribution pattern of T. speciosum and its ability to colonise man-made habitats in northern France but not in Britain or Ireland suggest that some factor associated with temperature may be limiting. As each colony may consist of one or two individual plants with many fronds arising from the rhizome mass, there are only about 50–100 plants of the sporophyte generation known in Britain and Ireland. There is thus a need to protect all remaining colonies in the British Isles from interference, especially collecting and habitat alteration. Extreme discretion with information about localities is essential. Translocation and re-stocking in the wild are only considered appropriate in special circumstances.