Riparian bryophyte vegetation in the Cascade mountain range, Northwest U.S.A.: patterns at different spatial scales

Riparian forests are productive and species rich ecosystems where the vegetation is structured by sharpenvironmental gradients. The study describes community patterns of bryophytes in stream-side forests, relates thesepatterns to major environmental gradients, and compares within-site factors with site level variables. Samples werecollected from 360 plots 2 x 4 in in size distributed among 42 sites in old-growth Pseudotsuga—Tsuga forests. Thesites ranged from 420 to 1250 m asl and stream size from 1st to 5th order streams. There were significant changes inspecies richness and composition along several environmental gradients. Richness within sites varied among differentgeomorphic surfaces with the highest number of species on areas periodically flooded. Richness was also higher in plotswith high abundance of woody debris. No site level factors influenced richness at the sample plot level, while the highestspecies number at the site level was for large streams. The main gradients in the species composition within sites werechanges with increasing distance from the stream and amount of woody debris. Both elevation and stream size significantlyinfluenced species composition. The complex set of factors that influenced species richness and composition implies thatmanagement of riparian vegetation must be based on both coarse scale considerations such as regional distribution ofdifferent stream types and fine scale factors such as spatial availability of different substrate types.
Key words: old-growth forest: CCA analysis; fluvial disturbance; bryophytes: elevation effects; coarse woody debris.