COLONIZATION BY LICHENS OF GRANITE DOLMENS IN GALICIA (NW SPAIN)

We studied colonization by lichens of five granite dolmens in Galicia (NW Spain). A total of 60 species, 3 subspecies and 2 varieties (some cited for the first time in Galicia) were identified, and the positions in which they occurred on the dolmens were mapped. The factors most strongly influencing colony initiation and position were degree of exposure to rain, insolation, substrate verticality/horizontality, humidity and location (on the inside or outside of the chamber). We also evaluated microscopic-level effects of colonization by five species of lichen (Xanthoria parietina, Aspicilia cinerea, Diploschistes scruposus, Pertusaria coccodes and Ochrolechia parella) in samples taken from nearby outcrops of the same granite as the dolmens. Hyphae were observed to penetrate almost exclusively through intermineral voids, except in the case of micas which were penetrated between layers. The only mineralogical effect observed was degradation of micas to mica-aluminium hydroxy vermiculite intergrades.