Colonization by lichens of granite churches in Galicia (northwest Spain)

The colonization of granite churches in Galicia (northwest Spain) by lichens, and the contribution of lichens to weathering, were investigated. Lichens were sampled from 20 rural churches, with the aims of identifying the commonest species and investigating environmental correlates of species distribution. Species composition was basically similar at all 20 sites, but microenvironmental factors (for example, aspect and microsite humidity) had clear effects on the distribution of many species. As regards weathering, the most common effect of lichens was disaggregation associated with hyphal penetration of intergranular voids. Lichens also appear to affect biotite, encouraging transformation to vermiculite and provoking release of Fe which is precipitated as noncrystalline oxyhydroxides. A neoformation mineral (whewellite) was detected in thalli of Ochrolechia parella.