Peat hags are evidence of erosion, either from burning or from water flow eroding downwards into the peat. The exposed area of bare peat associated with peat hags can indicate a problem if the area is extending and actively eroding. However, as seen in this image, areas of bare peat can be quickly colonised and stabilised by common cottongrass (Eriophorum angustifolium) – which is believed to facilitate the growth of peat-forming species of bog moss (Sphagnum app.). In these cases, the problem can be considered historic rather than current.