Environmental factors affecting the distribution of lichens on granitic monuments in the Iberian peninsula

The phytosociology of lichens colonizing granitic churches and dolmens in G alicia (N.W. Spain) and Alentejo (central Portugal) was studied so as to id entify (a) a group of species whose frequency on these structures would mak e them potentially useful as rest: species for the evaluation of biocides u sed for conservation, (b) environmental factors likely to control species d istribution, and (c) species that may be useful as bioindicators of environ mental factors in this kind of construction in the region studied. Chief am ong the factors correlating with species distribution is the class of struc ture (church or dolmen), which is attributed to the probable influence of m is factor on environmental parameters affected by structural complexity, th e presence of non-granitic materials and the influence of man in the immedi ate surroundings. The bioindicator species most sensitive to this complex o f parameters appear to be three species found only on churches (Caloplaca c itrina, Sarcogyne clavus and Verrucaria macrostoma) and the most widespread of the species found only on dolmens (Lasallia pustulata). Other important factors, probably affecting the influence of class of structure, are pH an d the availability of nitrogen and moisture. (C) 1999 The British Lichen So ciety.