In total 235 ha of the Beinn Eighe National Nature Reserve are covered in ancient woodlands, which grows in areas between 12 and 300 metres above sea level, and the woodland at Coille na Glas Leitir on the northern side of the mountain is the largest fragment of ancient Caledonian pinewood remaining in north-west Scotland. The Scots pine in this area show genetically differences to those in eastern parts of Scotland, and are more similar to those growing in southern Europe. It is thought that this results from the fact that western Scotland became ice-free first at the end of the last ice-age, allowing pine to move north along the western fringe of Europe. Pines reached Eastern Scotland from more northerly areas during a later period, as the ice sheets retreated further. In March 2019 a "genetic reserve" was established at Beinn Eighe as part of the European Forest Genetic Resources Programme in order to coordinate investigation and protection of the unique DNA fingerprint of the area's pines.