Treefall gaps are a ubiquitous feature of forested ecosystems and provide regeneration opportunities for many forest mosses which are dependent on microsites created by disturbance. Bryophyte communities on treefall mounds present an excellent opportunity to explore the extent to which community composition is influenced by dispersal patterns and establishment success. The goals of this paper are to 1) determine the bryophyte community structure of treefall mounds in the Adirondack forests and 2) to evaluate the extent to which community structure of treefall mounds is a consequence of dispersal limitation and establishment success and 3) to assess the role of microsite in successful establishment by sown spores and vegetative fragments. Bryophyte communities were described from field census of treefall mounds differing in age class. Most mounds support only 1–2 species, of the possible 13 species that colonize treefall mounds in the study area, the Adirondack Mountains of New York State. Moss species composition and diversity does not change with age of the mound, although cover increases significantly. Experimental treefall mounds varying in substrate and canopy type were created and sown with spores or vegetative fragments of five species: Polytrichum ohioense, Dicranella heteromalla, Atrichum angustatum, Diphyscium foliosum and Pogonatum pensylvanicum. The highest establishment success occurred with fragments sown on humus substrates in canopy gaps. Establishment success was significantly higher when propagules were sown than on the unsown controls. Colonization was very low in the absence of sown propagules. The data suggest that community composition of treefall mounds is strongly influenced by dispersal limitation.