Epiphytic lichen responses to environmental change due to clear-cutting differ among tree taxa

Question Many species-rich communities are associated with a foundation species. While we often have detailed information about the foundation species, we know less about its associated species. We explore such a situation, comparing the responses of lichen species associated with different tree taxa, which differ in successional strategy, to the environmental change that takes place when the surrounding trees are clear-cut. Location Boreal forests in Sweden. Methods We illustrated general differences in lichen species composition among four tree taxa and three stand categories using ordination of species occurrences. To analyse responses to clear-cutting we modelled the occurrence probability individually for 144 epiphytic lichen species from the lower 2 m of 2,400 tree trunks of four tree taxa in 130 stands, and compared trees in closed-canopy forests with those retained in logged stands, using Bayesian hierarchical models. Results The composition of lichens on aspen trees deviated clearly from that on the other tree species. Also lichen responses to logging differed among main host tree taxa, where lichen species associated with birches, European aspen, and Scots pine increased in probability of occurrence on trees in logged areas compared to intact forest, while lichen species associated with Norway spruce decreased. We found that time lags for changes in occupancy existed primarily in the increase, but not in the decline, of the groups of lichens associated with different tree taxa. Conclusions Lichens associated with different tree taxa vary in their response to the environmental change brought about by logging, but in a way that differs from the differences in species composition among host trees. Our results highlight the importance of considering the taxa of trees in forest management for the conservation of their associated lichen species. The extent to which the ecology of foundation species influences their associated species merits further inquiry, since such knowledge may facilitate predictions of responses of associated species also in other species-rich communities.