Cattail Invasion of Sedge Meadows Following Hydrologic Disturbance in the Cowles Bog Wetland Complex, Indiana Dunes National Lakeshore

Abstract

The vegetation of the 80.7 hectare Cowles Bog Wetland Complex has been altered from its historic mixed sedge-grass domination (Carex stricta, Calamagrostis canadensis) in lower areas and woody growth in slightly elevated areas , as based on archival aerial photographs from 1938-1982 and recent field data. Cattails (Typha spp.) were present in 1938 and made minor gains in cover through 1970. However, the major invasion of cattails appears to be associated with stabilized, increased water levels caused by seepage from diked ponds constructed upgradient from the wetland in the early 1970s. The water level increases are assumed to have been of a magnitude which adversely affected the sedge-grass community but did not preclude cattail growth. The cattail vegetation type increased in cover from 2.0 ha in 1938 to 9.7 ha in 1970 to 37.5 ha in 1982. The sedge-grass vegetation type correspondingly decreased from 56.4 ha to 43.0 ha to 5.7 ha. Cattail invasion appears to have occurred through establishment of disjunct colonies by seed reproduction; followed by vegetative expansion and merging of the colonies.