Ecology of an atlantic liverwort community

The Atlantic hepatic mat is an assemblage of large leafy liverworts. The component species are Herbertus aduncus (ssp. hutchinsiae), Pleurozia purpurea, Mastigophora woodsii, Bazzania tricrenata, B. pearsonii, Anastrepta orcadensis, Mylia taylorii, Scapania gracilis, S. ornithopodioides, S. nimbosa, Plagiochila carringtonii, P. spinulosa, Lepidozia pearsonii, Anastrophyllum donnianum, A,. Joergensenii and Adelanthus lindenbergianus. Up to 15 of these species can grow together in mixed mats.

These species need a climate with heavy and frequent rainfall and equable temperatures. They grow mainly in north-west Europe, north-west America and the Himalayas. The hepatic mat community was once thought to be confined to western Scotland and western Ireland but this study has shown that it also occurs in the Lake District and North Wales. Hepatic mats similar to the British ones, but with fewer species, occur on the Faroe Islands and in western Norway. The community is most extensive and species-rich in the mountains of western Scotland. It occurs on a variety of substrates from quartzites to mica-schists and basalt. Members of the community occasionally grow close to strict calcicoles, showing that they can tolerate basic substrates. The community is usually on steep, well-drained slopes in the British Isles, but there are good patches on level, peaty ground on Beinn Eighe in West Ross and in blanket-bog in Sutherland. The community is especially luxuriant on shaded slopes facing between north-west and east, but can develop in favourable spots on slopes facing all ways but south-west. Hepatic mats occur in a range of vegetation including woodlands, dwarf-shrub heaths, montane heaths and grasslands, snow-beds and cliff-ledge communities.

The diversity of species within individual stands of the community can be very great, with as many as 10 species occurring together in a 5cm x 5cm quadrat in the north-west Highlands. The typical mountain-side habitat is not particularly stable over time and the community is probably a dynamic one with a high turnover of individuals.