The influence of nonnative angiosperm trees on epiphytic bryophyte diversity is a major gap in invasion ecology. Two prominent invasive species, Acer negundo and Prunus cerasifera, are expanding rapidly into temperate forests, and, therefore may have the potential to impact epiphytic bryophyte communities. In this study, we compared the effects of tree diameter at breast height (DBH) on epiphytic bryophyte diversity among two native (Quercus robur and Acer platanoides) and two invasive (A. negundo and P. cerasifera) tree hosts, and assessed the ecological mechanisms shaping the community assembly of bryophytes colonizing their bark. We conducted our study in the surroundings of the Białowieża National Park by surveying epiphytes inhabiting the studied tree species, with 25 individuals per tree species selected, each varying in DBH. Using ordination and linear regression methods, we found that interspecific competition could play a similarly important role in shaping the assembly processes of bryophyte communities on A. platanoides and A. negundo, as indicated by a negative relationship between DBH and functional diversity metrics. This pattern corresponds with the highest mean water capacity of bark observed for A. negundo, as well as the relatively higher mean bark pH of A. negundo compared to native tree hosts – A. platanoides and Q. robur. Larger P. cerasifera trees may support more competitive bryophytes, as revealed by the negative relationship between DBH and functional richness. However, habitat filtering appears to play a prominent role in community assembly on P. cerasifera, as evidenced by its bark's lowest mean pH and water capacity among the surveyed phorophytes, and by increasing the proportion of pioneer and light-demanding epiphytes with tree size. For Q. robur, with close-to-neutral bark pH and low water capacity, the influence of interspecific competition on bryophyte community assembly across the DBH gradient was less pronounced compared to other phorophytes, likely due to the slower development of suitable microhabitats for epiphyte colonization. The ability of nonnative A. negundo and P. cerasifera to support functionally diverse bryophyte communities, similar to native hosts, highlights their potential as key hosts for restoring and persistence of epiphytic biota in tree plantations and urban ecosystems. Our study offers new insights into the impact of invasive trees on a largely underexplored group of dependent organisms, expanding the functional and phylogenetic scope of nonnative trees assessed for impact on bryophytes.