Lichen colonies on surfaces such as stone can attain an age of 9, 000 years, an approximate date being obtainable by measuring the colony's diameter. They can provide indicators of woodland age and continuity. The list of lichen species used to calculate the Revised Index of Ecological Continuity (RIEC) is provided. A select list of typical lowland broadleaved woodlands and their RIEC values includes such woods as Boconnoc Park Cornwall, Holne Chase in Devon, Great Wood Borrowdale in Cumbria among those with high ratings.