Lichen species richness on retained aspens increases with time since clear-cutting

► We made a lichen inventory on 720 retained aspens in two ages of clear-felled areas. ► Retained aspens function as lifeboats and provide habitat for colonizing species. ► The epiphytic lichen flora connected to aspen in boreal forest is very species rich. ► Several successional stages are needed to promote the total lichen diversity. In modern forestry, attempts to mitigate negative effects on biodiversity include the integration of conservation actions into forestry activities, e.g. by leaving trees at harvesting. This practice has been used on a large scale for more than two decades without solid scientific support of whether desirable effects are achieved or not. To increase the knowledge of changes in the lichen flora on retained aspen trees (Populus tremula) with time since clear-cutting we made a study in boreal Sweden where 720 retained aspens in 24 stands were surveyed. Twelve stands were clear-felled 0–4years and 12 where clear-felled 10–16years prior to the inventory. Total lichen species richness increased with time since clear-cutting, as did richness of aspen-dependent lichens and lichens adapted to open environments. There was no difference between the age classes regarding the number of cyanolichens. We show that retained aspens function as lifeboats for old-forest lichens and as a new habitat for lichens adapted to open, sun-exposed habitats. Our results indicate that epiphytic species richness on retained trees is higher after the logging, due to coexistence of remaining species and colonizing species. We suggest that the retention of old aspen and the promotion of aspen generation in the production forest would benefit epiphytic lichens and are thus important conservation measures.