Lichen assemblages on Scots pine stumps and fine woody debris in hemiboreal post-harvest sites: the impact of site age and green tree retention

Retention of live trees and dead wood structures in clear-cut sites is a common sylviculture measure for biodiversity purposes. We studied lichen assemblages on pine stumps and fine woody debris (FWD) in 16 post-cut (4-6 and 9-11 yr. old) dry boreal pine stands in Latvia to explore what type of substrata and stand-scale characters (e.g., retention level, time since harvest) are related to lichen species richness and differences in composition. We found 48 lichen species on stumps and 43 species on FWD. Majority of the species (except Cladonia parasitica) were common lichens of coniferous forests in hemiboreal regions. Time since harvest and retention level had positive impacts on richness on stumps, but not on FWD. Increase in total species richness on stumps in older post-harvest sites compared to the younger ones was strong and relatively rapid. Notwithstanding species richness, assemblages on FWD and on stumps were distinct between older and younger cut sites. The impact of time also emerged when assemblages on vertical and horizontal stump surfaces were separated. We conclude that pine stumps are important to lichen richness and post-harvest recovery of the epixylic lichen biota, especially in the face of alarming scarcity of snags and logs in cut-over sites in Latvia, where dead wood legacies (particularly snags) are not retained in sufficient amount.