The effect of environment on assemblages of lichens growing on rock surfaces

Summary The influence of environment on lichen assemblages of known age is examined. The main cause of variation seems to be the response of the lichens to the rock aspect providing the most favourable moisture conditions. this being dependent on the orientation of each surface to the prevailing wind. However, no really consistent patterns could be found and no specific correlations could be made with anyone climatic factor. The significance of lichens for dating rock surfaces is discussed with reference to the two main causes of variation: stone size (Orwin, 1970) and environment. Definite correlations of lichen patterns with time give lichens some value for comparative dating within one general climatic area.