Risk, hazard, and vulnerability for stone biodeterioration due to higher plants: The methodological proposal of a multifactorial index (RHV)

The growth of higher plants on buildings and stone monuments can cause various biodeterioration phe- nomena. Along with careful management of higher plants in archeological sites and monumental areas, a comprehensive method for assessing the risk they pose to stone conservation still needs to be de- veloped. We propose, therefore, a multi-factorial index of risk from higher plants which will evaluate relevant threats to stone structures and local conditions of vulnerability (RHV). We suggest associating such threats with the environmental conditions (defined by bioclimate and environmental context) and with the plant growth characteristics (defined by life forms, root systems and stem development fea- tures, ecological preference, and physiological characteristics). We also suggest associating vulnerability with edaphic factors (stone typology and colonization microsites) and with conservation status, including management activities. The proposed index was tested at a number of international sites in a biocli- matic gradient varying from a temperate climate (Lucca, Italy) to Mediterranean (Rome, Italy) and sub- Mediterranean xeric (Pasargadae, Iran) and tropical (Angkor, Cambodia) conditions. The results show how useful such an index can be in performing analytical assessments of the risk posed by ruderal plants in cultural heritage sites.