Epiphytic bryophytes of an urban forest : diversity, ecology, and host tree preference in Maksimir Forest Park, Zagreb

Epiphytic bryophytes of Maksimir Forest Park were investigated during the winter of 2023 and the spring of 2024. Sampling included five tree species: sessile oak, common hornbeam, European beech, black locust, and European spruce, each represented by five individuals. A total of 35 bryophyte taxa were recorded, of which 31 were mosses and 4 were liverworts. The tree species harbouring the highest bryophyte diversity was beech, while black locust and spruce were species-poor and had low bryophyte cover. The most frequent and abundant bryophyte was Hypnum cupressiforme , followed by Metzgeria furcata , Platygyrium repens , Frullania dilatata and Radula complanata . During the research, a NATURA 2000 target species Dicranum viride was found on beech and oak. The predominant life form on all tree species was the smooth mat, which provides more photosynthetic surface and is thus advantageous in shaded forest habitats, while the most common life strategy was stress-tolerant perennial, indicating that most of the sampled environment is stable with minor stressors. The ANOSIM testrevealed that bryophyte assemblages on different tree species differed significantly, however, with considerable overlap, with those on black locusts being the most distinct, with Dicranoweissa cirrata being characteristic of this tree species. The DCA analysis with host tree parameters (bark roughness, tree trunk circumference, total/dominant bryophyte coverage) and Ellenberg indicator values passively projected as vectors revealed no discrete separation of tree species based on epiphytic bryophyte composition; however, some patterns were evident. Black locusts and certain species-poor oak trees formed a loose group associated with rougher bark and pleurocarpous species such as Hypnum cupressiforme and Platygyrium repens . Beech and hornbeam, grouped on the opposite side of the ordination, shared similar bryophyte assemblages associated with smoother bark and higher ecological indicator values for light, nitrogen, and substrate reaction, with beech additionally harbouring bryophytes indicative of higher moisture. This was true for species-rich oak individuals as well.