Index of Lichen Potential Biodeteriogenic Activity (LPBA): A tentative tool to evaluate the lichen impact on stonework

An index of Lichen Potential Biodeteriogenic Activity (LPBA) is proposed to quantify the overall lichen impact on stonework on the basis of the volume of influence of each species, quantified both on the surface of and within the substratum, and of other parameters related to reproduction, physico-chemical action, and bioprotection. Ordinal scales are introduced for each parameter with reference to experimental data and literature on the current evaluation approaches. The index was designed to obtain that a lower knowledge of the colonization phenomena may yield an overestimation of the lichen impact, but not an underestimation, thus assuring a precautionary approach, which is functional to conservation programs. Representative case studies from the north-western Italy were examined to highlight the range of applicability of the index from small-sized stone substrata, to buildings, to whole archaeological areas. The application of the index shows that the consideration of the different factors involved in the lichen biodeteriogenic activity gives a different and more exhaustive evaluation of biodeterioration with respect to cover only and confidently describes the lichen effect on stonework with reference to the substratum damage. The necessity of a wide research network which extends the index application to more case studies, allowing the calibration of the parameter scales and the elaboration of an interpretative index scale, is invoked to move towards a statistical validation of the index.