Phorophyte preferences of epiphytic bryophytes in a stream valley in the Carpathian Basin

Epiphytic bryophytes were studied on two tree species with different bark characteristics (Alnus glutinosa and Carpinus betulus) in two vertical ranges (0–60 and 60–200 cm height above ground on the trunk) in a stream valley in the Carpathian Basin (N.W. Hungary). There is a significant difference in the species composition of the trees. Dicranum montanum and Platygyrium repens occurred significantly more often on Alnus glutinosa, whereas Frullania dilatata and Radula complanata were more often on Carpinus betulus in both vertical ranges. Orthotrichum species were typical only in the vertical range 60–200 cm on Carpinus betulus, whereas Plagiothecium nemorale and Metzgeria furcata were typical of Alnus glutinosa and Carpinus betulus, respectively, in the vertical range 0–60 cm. Although most of the bryophyte species have significant phorophyte preferences, Hypnum cupressiforme (in both vertical ranges) and Isothecium alopecuroides (in vertical range 0–60 cm) are indifferent in this respect. Our findings showed clearly that phorophyte preference and vertical position on the trunk are not independent variables. We investigated the independence of the frequencies and abundances of bryophyte species in the two vertical ranges separately on the two tree species. The species form four different groups: (1) species with greater abundance in the higher vertical range; (2) species with smaller abundance in the higher vertical range; (3) indifferent species with nearly uniform abundances in both vertical ranges; (4) species present only in one vertical range. It was found that even a single bryophyte species can show different vertical preferences depending on tree species. No significant relationships were found between the abundances of bryophytes and distance from the stream, slope of the bark surface and trunk circumference. Species-specific traits appear to explain individual phorophyte preferences; however, in several cases chemically mediated effects of the bark appeared to be important.