The effect of riparian buffer strips on salmonberry (Rubus spectabilis) community structure in alder stands of the Oregon Coast Range

Graduation date: 1993Salmonberry community structure was examined in alder-dominated\ud riparian buffer strips in the Oregon Coast Range. Salmonberry growing on slopes\ud was found to respond differently, to both characteristics of the buffer strips and\ud to environmental factors, than salmonberry growing on terraces.\ud Salmonberry, as measured by total height, number of ramets or sprouting\ud centers, cover, and estimated biomass, was found to increase with increasing light\ud on the slopes. Salmonberry cover, height and number of ramers were all found\ud to be greater on slopes within buffer strips, than on slopes in undisturbed riparian\ud stands, where the adjacent stand had not been cut and no buffer created. The\ud greater dominance of salmonberry within buffer strips was attributed to increased\ud sidelight into the riparian area, due to the hest of the adjacent stand. None of\ud the four salmonberry characteristics were found to be related to light on the\ud terraces. Salmonberry height, cover, number of ramets, and biomass on terraces\ud did, however, all increase with increasing age of the buffer strip.\ud There did not appear to be any clear edge effect on salmonberry within the\ud buffer strips. An index of herbaceous vegetation was developed, through\ud ordination, to examine the effects of unquantified environmental factors on\ud salmonberry. Disturbance appeared to play a role in the variation seen in the\ud salmonberry population.\ud Salmonberry's aerial stem diameter distribution, both within buffer strips\ud and in undisturbed stands, resembled an uneven-aged distribution. Sairnonberry\ud stem distribution followed the same pattern whether on slopes or terraces. This\ud suggests persistent, self-replacing salmonberry stands in these alder-dominated\ud riparian communities.\ud Salmonberry was found to be negatively correlated with herb, vine maple,\ud and swordfern cover, and also with herbaceous species abundance. There was\ud no relationship between salmonberry and elderberry cover. Tree regeneration\ud was found to be extremely sparse. Only one alder seedling per hectare was found\ud in the undisturbed riparian stands. There were 29 seedlings per hectare found\ud within the buffer strips, 22 of which were conifers.\ud The four salmonberry community variables increased in response to buffer\ud strip creation when growing on both slopes and terraces. Salmonberry was shown\ud to have a self-replacing canopy, and to dominate other shrubs and herbs in the\ud riparian community. These factors, along with the lack of tree regeneration in these alder-dominated riparian areas, all suggest that without silvicultural\ud intervention salmonberry could eventually dominate the riparian community