Bryophyte response to forest canopy treatments within the riparian zone of high-elevation small streams

Abstract

Riparian buffer strips are increasingly used to mitigate disturbance effects on terrestrial biota found adjacent to streams, yet it is unclear how the effects of canopy treatment (clear-cut, buffer, or intact forest) will interact with pre-existing stream–upland gradients. We questioned whether proximity to the stream would influence bryophyte richness and whether the effects of canopy treatment on bryophyte composition and functional group representation would differ along the stream–upland gradient. Bryophyte richness, abundance, and composition were sampled in continuous forest (n = 6), two-sided buffers (buffer width approximately 15 m on both stream sides; n = 10), and clear-cuts (n = 7) in the southern interior of British Columbia. At each site, bryophyte functional group frequency was sampled within 10 × 2 m belt transects located at 1, 5, and 10 m from the stream edge. Both distance from the stream and canopy treatment were strongly associated with bryophyte community variation. The richness of many functional groups was highest immediately adjacent to the stream. The richness and frequency of forest-associated species, as well as the overall extent of the bryophyte mat, had the highest values in continuous forests, intermediate values in buffers, and lowest values in clear-cuts. Although significant differences in bryophyte communities occurred between buffers and clear-cuts at all distances from the stream, differences between buffers and continuous forest were nonsignificant. These results indicate that riparian buffers can play an important role in the mitigation of harvesting effects on the bryologically rich communities along small headwater streams.