Lichens as indicators of air pollution in a steel producing town in South Wales

Abstract

The lichen flora of a given region depends upon a multiplicity of factors. Some factors act directly or indirectly upon the lichen thallus; in addition the lichen thallus is capable, to some extent at least, of exerting a modifying influence upon the macro- and micro-environment. The polluted centre of Port Talbot, a steel town, has a restricted number of crustose and rather depauperate species. This ‘lichen desert’ is quite small possibly because either (a) the atmosphere is not heavily polluted, or (b) there is a rapid dilution of pollutants. With distance away from Port Talbot there is an increase in the number of lichen species and a change in the proportion of the various growth forms. Abutting the ‘lichen desert’ is a zone in which Parmelia sulcata, P. saxatilis, Cladonia coniocraea, and C. fimbriata are the most widely represented species. This is followed by a further zone dominated by Usnea comosa, U. florida, Cetraria glauca, and Cladonia impexa in particular. It must be noted that these zones are not clearly defined; there is a gradation in growth forms and a gradual change in the abundance of various species.