Towards a calibration of the Index of Lichen Potential Biodeteriogenic Activity: the case of schist in the Upper Douro Region (NE Portugal)

| Resumo Lichen communities are the most abundant colonizer of the vertical schist surfaces in the Upper Douro Region. Lichen organisms are closely connected to the substrate, establishing relationships with it, and they could led to modification more or less significant. Lichen action on the rock surfaces in the Upper Douro region and especially in the Côa valley requires special attention since, in this area, the world’s largest collection of open-air rock-art sites is found and the need of its conservation and preservation requires particular attention and investigation. This action could be either degradative or protective and when the substrate modification occurs, it could occur in two ways, physical or chemical, and each one is related to the colonizing species and the intrinsic substrate properties, and this phenomenon is labelled as biodeterioration. However, oversimplification and the interpretation of lichen action as exclusively degradative should be avoided once there are reports of protective action of lichen thalli and acting as a shield-like barrier between the substrate and the influence of external weathering agents (e.g.: water, wind, temperature) occurring, therefore, bioprotection. To understand how rock deterioration is related to lichen action in the study area, this work aimed to answer to various issues as: which climatic factors are related to the species occurrence and in which spatial scale would be more significant; in which way lichen colonization of surfaces is related to chemical weathering and which species contribute in a major way to that process and, lastly, in which way the index of Lichen Potential Biodeteriogenic Activity could be applied to the schist surfaces of the Upper Douro region as an evaluation tool of lichen action as biodeterioration agent. To perform more practical and less time-consuming evaluations of the lichen action in the schist surfaces in the Upper Douro Region, four dominant species were used as representative species of the lichen assemblages present in the area. Thus, the dominant species present in the study area are the crustaceous Aspicilia contorta subsp. hoffmanniana, Caloplaca subsoluta, Lecanora pseudistera and the squamulose Peltula euploca. The results acquired showed that the climatic factors that influence the most in lichen occurrence are at the micro-scale level (temperature and relative humidity). Element mobilization in colonized schist surfaces was also evaluated and the results showed that there is an aspect-related activity in element changes. In northfacing surfaces there was no evidence of lichen-induced element change. On the other side, in south-facing revealed an intense mobilization of elements being the surfaces colonized by Caloplaca subsoluta the ones with more statistically significant differences detected. vi Abstract | Resumo Allowing an evaluation of lichen action on the schist surfaces in the Upper Douro Region, the implementation of Lichen Potential Biodeteriogenic Activity was tested. The results enhanced a strong dependence of the species abundance and an improvement in the calculation of the index was proposed. Climatic variables could be incorporated to the calculation and, therefore, fill gaps related to physical and chemical action of lichens, once, often, these parameters are hard to obtain.