THE ECOLOGY AND CONSERVATION OF THE KILLARNEY FERN TRICHOMANES-SPECIOSUM WILLD IN BRITAIN AND IRELAND

Trichomanes speciosum Willd. (Hymenophyllaceae) is one of the rarest a nd most celebrated species in the British and Irish vascular flora. Th e ecology and habitats of 43 colonies of the sporophyte (fern plant) g eneration are described. Two-way indicator species analysis suggests t hat T. speciosum occurs in four main floristic groups; in very deeply shaded habitats; in large dripping caves; in crevices in cliffs and sm all caves; and on dripping vertical cliffs and rocky banks in wooded r avines. Canonical correspondence analysis shows that altitude and habi tat types are the major environmental variables influencing the floris tic 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 habita ts in western Britain and Ireland are discussed Sporophyte establishme nt appears to be most critical, especially under a climate that is mar ginal for its temperature requirements. The distribution pattern of T. speciosum and its ability to colonise man-made habitats in northern F rance but not in Britain or Ireland suggest that some factor associate d with temperature may be limiting. As each colony may consist of one or two individual plants with many fronds arising from the rhizome mas s, there are only about 50-100 plants of the sporophyte generation kno wn in Britain and Ireland There is thus a need to protect all remainin g colonies in the British Isles from interference, especially collecti ng and habitat alteration. Extreme discretion with information about l ocalities is essential. Translocation and re-stocking in the wild are only considered appropriate in special circumstances.