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The epiphyte (lichens and bryophytes) species richness, diversity and composition on basal trunks of Picea abies in spruce swamp-forests were compared to adjacent mesic forests on mineral soil in two southern and two middle boreal sites in old-growth forest patches in Finland. The sampling was carried out along four line transects parallel to swamp-forest margin: 1) in the spruce swamp-forest, 2) at the swamp-forest margin, 3) on mineral soil c. 10–20 m off the swamp-forest margin and 4) on mineral soil at least 50 m off the swamp-forest margin. In the two southern boreal sites there was a decreasing trend in the average species number per tree from the trees in swamp-forests (21–25 species) to the trees on mineral soil (17–18 species), whereas in the two more humid and virgin middle boreal sites a similar trend was not detected (25–28 species on all trees). There were no major differences in the epiphyte flora between the locations or study sites; the dominant species occurred on nearly all sample trees. The crustose lichens Cliostomum leprosum, Arthonia leucopellaea and Lecanactis abietina were the most common species that were mainly confined to the swamp-forests in the southern boreal sites, C. leprosum also in the middle boreal sites. In addition, several rare species occurred exclusively on the swamp-forest trees. Lecanactis abietina extended significantly higher on the swamp-forest trees than on the trees on mineral soil in the southern boreal sites. The spruce swamp-forests proved to be one of the most important habitats for maintaining the epiphyte diversity in the boreal forest landscape.