An Ecological Study of Ysgolion Duon, a Mountain Cliff in Snowdonia

Abstract

Species distributions on a mountain cliff was related with environmental factors. Ysgolion Duon is in the Carneddau mountain group of Snowdonia, between 600 and 900 m, and is composed of rhyolite and dolerite. The cliff experiences lower temperatures and higher humidities tnan the surrounding grassland. Many species are confined to the cliff by grazing pressure in the grassland. The ordination procedure used was that of Orloci (1966). The principal axis of the ordination was from stands containing mesophilous and arctic-alpine species to those with heath species, corresponding with a gradient from wet eutrophic to dry oligotrophic conditions. The former occur on the lower cliff and in gullies, whereas the latter are on the upper cliff and buttresses. The importance of ground water is due to leaching of dolerite and subsequent transfer of nutrients into the gullies of the lower cliff. The isolation of the cliff from many biotic influences and the number of relict species in the flora suggests that the vegetation is relatively constant.