VEGETATION CHANGE IN A TOPOGENIC BOG FOLLOWING BEAVER FLOODING

Vegetation change was documented along three permanent transects after nearly three decades of beaver flooding. The anchored forested wetland community was killed and replaced by a minerotrophic fen vegetation, whereas minimal change occurred within the tall scrub-shrub, dwarf shrub and open meadow communities. Along all transects, tree cover was reduced two- to five-fold, whereas low heath shrub cover, especially Chamaedaphne calyculata and Kalmia angustifolia, increased. Herbaceous cover, primarily sedges, increased, especially in the newly created fen. Within the floating mat communities the evergreen ericaceous shrubs and scattered stunted Picea mariana and Larix laricina persisted as did the herbaceous bog flora. Species richness showed little change from 1960-1988 although there was a floristic shift toward more hydric species. Flooding differentially affected the vegetation pattern favoring more minerotrophic species in some areas, but did not appear to threaten the typical bog flora. Historically, beaver and other environmental influences have probably modified the vegetation development over millenia, including prolonged quiescent periods interrupted by periodic disturbances as documented in this study. For most peatlands this dynamic model appears more realistic than any orderly successional dogma.