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 wetlan d community was killed and replaced by a minerotrophic fen vegetation, whereas minimal change occurred within the tall scrub-shrub, dwarf sh rub and open meadow communities. Along all transects, tree cover was r educed two- to five-fold, whereas low heath shrub cover, especially Ch amaedaphne calyculata and Kalmia angustifolia, increased. Herbaceous c over, 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 di d the herbaceous bog flora. Species richness showed little change from 1960-1988 although there was a floristic shift toward more hydric spe cies. Flooding differentially affected the vegetation pattern favoring more minerotrophic species in some areas, but did not appear to threa ten the typical bog flora. Historically, beaver and other environmenta l influences have probably modified the vegetation development over mi llenia, including prolonged quiescent periods interrupted by periodic disturbances as documented in this study. For most peatlands this dyna mic model appears more realistic than any orderly successional dogma.