Biodeterioration on megalithic monuments. Study of lichensʹ colonization on Tapadão and Zambujeiro dolmens (southern Portugal)

A description of the lichen species associated with the granite rocks used as building material in Tapadão and Zambujeiro dolmens (Alentejo, southern Portugal) is presented. The field survey undertaken in both archaeological sites has made possible some correlations between diversity, frequency and distribution of the species, and the climatic conditions, deterioration forms, inclination and exposure to rainfall of the lithic pieces. Only epilithic lichens were studied and, among these, crustose species are the most representative. Preliminary laboratory tests indicate a deep penetration of hyphae into the substrate, resulting in remarkable ‘canalization’ and fragmentation of all granite minerals. The consequent biogeophysical and biogeochemical damage reveals lichens as important weathering agents.