Ecology and taxonomy of montane lichen vegetation in the British Isles

Factors influencing lichen distribution, principally climate and geology, are discussed. The extreme oceanicity of the British climate is identified as the most influential factor in the development of a distinctive lichen vegetation in the area. Twenty-four species of lichen are recorded for the first time from the British Isles along with, approximately, 50 unidentified taxa. Draft descriptions are provided for 18 undescribed taxa. Keys are provided to difficult groups and genera, i.e. sterile crustose saxicolous and terricolous lichens, Lecidea, Porpidia, Rimularia and Rhizocarpon subgenus Phaeothallus Lichens having the centre of their British distribution in montane areas are listed and assigned to a montane sub-zone. Using this list, a comparison is made between the lichen vegetation of three oceanic areas of the British Isles. The importance of the saxicolous lichen vegetation of the oceanic mountains of western Scotland is emphasised and shown to be important in its own right rather than a species-poor outlier of the Scandinavian flora. The lichen vegetation of those National Vegetation Classification communities in which lichens form a significant part is described. In general, terricolous macro-lichens are shown to correspond with NVC communities but terricolous micro-lichens and saxicolous species do not and need to be treated separately from NVC. Lichen data from areas of prolonged snow-lie are analysed by TWINSPAN and three un-named, apparently endemic, lichen communities identified. One is restricted to areas of prolonged snow-lie throughout the Scottish Highlands whereas the other two are more widespread in the western mountains but confined to snow-beds in drier, eastern parts of the country. Their composition and affinities are discussed. Grazing animals are shown to have a devastating effect on upland/montane lichen vegetation, although this is less pronounced at higher altitudes. Grazing is shown to have a qualitative, as well as a quantitative, effect.