Lichens, algae, and mosses growing on rock surfaces that have prehistoric or historic rock art are a major problem for preserving these fragile remains of the past. Most rock art is surficial or shallowly pecked or incised into the rock surface. Breakdown of the rock by microflora can easily erase these images. The problem is worldwide. Archaeologists have several major issues for site preservation where biodeterioration is a factor. One issue is whether the rock surface is now so deteriorated that the lichen structures are holding it in place. Killing the lichens would release the undermined rock and leave the remaining rock art unprotected. If we kill the lichens, what method should we use? The recent development of dating techniques that analyze rock coatings, such as rock varnish, oxalate, and silica, means that we cannot contaminate the surface with chemicals that would prevent future dating. An associated issue is keeping any chemicals from getting into the environment, such as not contaminating archaeological deposits below the rock art. We cannot just spray on chemicals, but would need to carefully dab them on, time consuming work. A crucial issue is how fast the lichens are growing and whether they will deteriorate more of the panel. A slow growing lichen leaves plenty of time to investigate, conduct experiments, and make decisions. If removed, how fast will the lichen regrow? If removal leaves a fragile, exposed surface, should we use a rock consolidant to preserve the site? All known consolidants alter the rock porosity, which could negatively impact the rock art. Instead of major interventions, can we alter the microenvironment to discourage lichen growth? This ideal solution may be difficult in many settings. A final issue is the ethics of altering the natural environment. Whose sites are these and what is their view?

Key words: archaeology, biodeterioration, lichen, rock art