Impact of windthrow on distribution of bryophytes in hemlock-hardwood forests

The community concept, first articulated in the early 20 th century, continues to be refined and reshaped by contemporary ecologists. In particular, the applicability of community concept to bryophytes has been questioned. The bryophyte ecology literature shows some evidence for similarities between typically studied plant communities and bryophyte communities, although other studies point out important differences in relationships between species. The poikilohydric physiology of bryophytes is frequently cited as a reason for these differences. As a result, the community concept can be useful for studying bryophytes, but does not apply at every scale and group of species.; Bryophyte communities in northern Wisconsin hemlock-hardwood forests are proposed to change after windthrow removes the canopy. Cover estimates of bryophyte species, canopy cover estimates and substrate types were collected under three canopy cover conditions to explore the hypothesis that canopy removal created different bryophyte communities. In addition, number of tree seedlings and distance to potential residual populations were recorded to explore potential effects on overall abundance of bryophytes. Analysis using NMS ordination did not show distinctive bryophyte communities under the different canopy cover conditions. Inverse analysis of bryophyte species showed changes in substrate occupation with changes in canopy cover condition, however. This shows that interaction between species only occurred in individual patches on specific substrate types.; A common garden experiment over one growing season tested species response to different canopy conditions on soil substrate. Polytrichum juniperum and Ceratodon purpureus were frequently found in areas of complete canopy removal. Ceratodon purpureus was also found under partial canopy removal conditions along with Mnium sp., but Polytrichum juniperum was not present. Mnium sp. was the only bryophyte found on exposed soil under full canopy cover conditions. Each species increased cover under the expected conditions with the exception of Ceratodon purpureus. In contrast to the field conditions, this common weedy species survived under all conditions. Canopy conditions offer a secondary constraint to substrate type for some bryophyte species in hemlock-hardwood forests of northern Wisconsin. Understanding changes in vegetation caused by the natural disturbance regime will aid forest managers in maintaining forests with multiple-use goals.