Old Growth Forest Indicators
Some lichens are poor dispersers and are slow to populate new habitats. Such species tend to stay and flourish in a single habitat such as a forest. These lichens are called old-growth forest indicators. When they are found, their presence can be interpreted as indicating that their current habitat was once part of an ancient forest. Ireland has no forests today, and just a few unpolluted woodlands. Finding an old-growth forest lichen implies that this area may have been part of an ancient forest.
The following species are selected old-growth forest indicators. For a complete list see the West Of Ireland Index of Ecological Continuity published by the British Lichen Society.