The role of lichens in inhibiting erosion of a soluble rock

Soluble rocks undergo erosion by solution when rain falls on an unprotected rock surface. Lichens may act to protect the surface from such erosion, an d the protected area may subsequently emerge from the surrounding lowering surface to form an area of higher relief. Specimens of Aspicilia calcarea a nd Diploschistes diacapsis act in this way on a gypsum surface, creating co nical or rounded mounds up to 15 mm in height. In the case of Aspicilia, th e lichen centre decays, re-exposing to surface solution the central area, w hich then corrodes to create a cratered gypsum cone. The gradient of the co ne side-slopes is a function of the relative rates of lichen radial growth and rock surface lowering. (C) 2000 The British Lichen Society.