Lichens and Their Impact on Rock Substrates at Persepolis Unesco World Heritage Site

Mohammad Sohrabi

The ancient stone structures of Persepolis, a UNESCO World Heritage Site, are home to a diverse array of lichens that thrive in the site's harsh, arid climate. These symbiotic organisms, composed of a fungus and a photosynthetic partner, are well-suited to extreme environmental conditions, including high temperatures, limited moisture, and intense sunlight. Lichens colonize the surfaces of Persepolis' monumental architecture, such as intricate carvings, columns, and inscriptions, where they play a dual role. On one hand, they contribute to biodeterioration through mechanical and chemical weathering, and on the other, they provide valuable ecological insights. Lichens are highly sensitive to environmental conditions and act as indicators of air quality, offering a natural barometer for both the preservation of cultural heritage and the surrounding ecosystem.

The lichen mycota of Persepolis can be categorized based on their ecological niches and the impact they have on rock substrates. Epilithic lichens, which grow on the surface of rocks, are the most prevalent on the exposed stone structures. These lichens secrete organic acids that break down the rock matrix, leading to physical weathering and chemical alteration of the substrate. Genera such as Acarospora, Circinaria, and Calogaya are commonly found in these areas, particularly in locations with high sun exposure and temperatures. Endolithic lichens, on the other hand, penetrate the rock's surface, colonizing the pores and crevices, where they cause deeper, more insidious damage. Species like Bagliettoa and some species of Rinodina are typically found in shaded or sheltered locations, where moisture accumulates within the rock. These lichens contribute to the weakening of the stone over time, often leading to long-term structural damage. Additionally, soil lichens found in rock cracks and fissures further exacerbate the deterioration process. Genera such as Peltula and Psora colonize these microhabitats, where their roots and hyphal networks infiltrate the rock surface in search of nutrients. Together, these various lichen groups—epilithic and endolithic —play a significant role in the biodeterioration of the rock surfaces at Persepolis, highlighting the need for integrated conservation strategies that address both the preservation of the site's cultural heritage and its natural biodiversity.