Lichen saxicolous communities on granite churches in Galicia (NW Spain) as affected by the conditions of north and south orientations

Lichens constitute the largest organisms among the stone colonisers. Several studies have shown that lichen species and their traits respond to environmental changes, but none of them focused on saxicolous communities. Five granite Galician churches were studied to characterize the lichen saxicolous communities established in the four facades. In four of the churches two climatic stations were placed, on the N and the S facades. Sampling was also more systematic on N and S walls, as these tend to show the most extreme microclimatic characteristics: relatively cool and humid in the N vs. warm and dry in the S. We aimed at identifying the species and traits associated with these conditions, so as to predict the possible evolution over time in these communities in the prospect of further climate warming in the future. Climatic data were subjected to two-way analyses of variance (ANOVA). We computed species accumulation curves and species richness estimators with EstimateS, analysed the effect of the church, the aspect (N vs. S) and the position of sampling squares on the number of lichen species and on lichen abundance, and community composition in terms of species and lichen traits. Richness analysis showed that only orientation had a significant effect on the number of species present on the walls. Lichen cover was always higher in the N, but the difference was not significant, and only the church factor had a significant effect. Taxa characterizing the N facades were the two varieties of Haematomma ochroleucum, Ochrolechia parella, together with the lichen species with Trentepohlia as photobiont. On the S facades, the characteristic species were Candelariella vitellina and Lepra leucosora; there was a higher diversity of biotype, size and color; with a total absence of sorediate species or with Trentepohlia as photobiont. There was a clear difference between the lichen species requirements in sunlight and aridity on the N and S facades. We hypothesize that a warmer and more arid climate may result in an expansion of the S-dominant lichen species and/or lichen traits to the detriment of those N-dominant.