Biodeterioration of monuments in relation to climatic changes in Rome between 19–20th centuries

A decrease in the biodeterioration phenomena of Roman monuments during the last two centuries is shown, by comparing historic and recent data. During this period, an increase in air pollution, a reduction of humidity, and recently a reduction of rainfall, has taken place. Pollution reduces the diversity of the flora, i.e. the number of different organisms (especially lichens), but it hardly reduces the total biological cover. On the other hand, an unfavourable bio- and microclimate dramatically reduces the survival of the biological species on a xeric substrate such as stone material. In fact, when the microclimate is favourable, organisms resistant to pollution (especially cyanobacteria) can grow abundantly even in very polluted environments. A reduction of the water supply seems the most important limiting factor for the lithophytic microflora.