Supervisors: dotsent Tiina Randlane ja teadur Inga Jüriado
Opponent: dr. Christopher J. Ellis (Edinburgi Botaanikaaed, UK)
Semi-natural habitats with long management history, wooded meadows and alvars in northern Europe, are of great importance for nature conservation according to their high contribution to biodiversity including rare, red-listed, and protected lichens for the studied region. Unfortunately these habitats are disappearing from our cultural landscape, mainly due to the cessation of traditional management; they are replaced by cultivated fields or abandoned to brushwoods. The study demonstrates that abandonment of wooded meadows causes changes in stand structure and in the openness of wooded meadows, which impoverishes and alters epiphytic lichen community. Light-demanding lichen communities, rich in foliose and fruticose lichens, will be replaced with impoverished shade-tolerant crustose lichen dominated communities due to encroachment of wooded meadows with trees and shrubs. To support diverse epiphytic lichen communities trees and undergrowth should be cut selectively, retaining a mosaic of semi-open structure of wooded meadows with trees of various species and age classes, and some clumps of bushes. Annual mowing or grazing is important for preserving this semi-open structure.
Similarly, epigeic lichen communities of semi-natural alvar grasslands are strongly affected by cessation of grazing and cutting of junipers. With the increasing herb and shrub cover, the species richness of epigeic lichens diminishes, species composition alters and the proportions of species growth forms change (crustose and squamulose species are replaced with fruticose species). Lichens with a conservation value, especially rare species, are particularly sensitive to the abandonment-induced encroachment of herbs and shrubs. Old abandoned limestone quarries, former military areas or wastelands of failed afforestation attempts appeared to be alternative or temporary substitution habitats (refugia) for ground layer lichens including lichens with a high conservation value. Therefore, in addition to conventional recommendations for alvar restoration including moderate grazing and removal of shrubs, it is suggested to promote small-scale ground cover disturbances and patchy peeling off of the soil layer to expose base rock.