PARENT SESSION
Poster Session 3: Aquatic Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 210 D, Level 2, Palais des congrès de Montréal
A Rapid Expansion of Phragmites australis in a Great Lakes Coastal Wetland.
Tulbure, Mirela1, Johnston, Carol1, 1 South Dakota State University, Brookings, SD, USA
ABSTRACT- Great Lakes Coastal wetlands are subject to water level fluctuations that promote the maintenance of coastal wetlands. Plant communities are not only adapted to these fluctuations, different communities being favored at different water levels, but the natural cycle of emergent wetland formation, inundation, and recession is beneficial to plant biodiversity, and is considered essential to maintaining coastal wetlands in good condition. This presentation documents a dramatic change in emergent wetland vegetation communities at Point au Sauble peninsula, a Lake Michigan coastal wetland. Herbaceous vegetation was sampled in 1 X 1 m2 quadrats along a north-south trending transect placed across the lagoon in 2001 and again in 2004. In 2004 half of the transect was covered by a monospecific, 3m tall, invasive Phragmites community; in 2001 Phragmites was present but its cover was very sparse. Percent similarity between plant species present in 2001 vs. 2004 was only 19% (Jaccard coefficient), indicating the dissimilarity and therefore the changes that took place in only three years. Water depth, the height of the dominant herbaceous plants and coverage by invasive species differed significantly between 2001 and 2004, being higher in 2004. The water level had dropped 1.25 m in Lake Michigan since 1997, the largest drop since data records were kept. This lead to the emergence of exposed lake mud flats, which created favorable conditions for Phragmites invasion. Based on morphological characters, Phragmites from Point au Sauble was found to belong to the more aggressive, introduced genotype. It displaces native vegetation and is tolerant of a wide range of water depth. Therefore it may disrupt the natural cycles of vegetation replacement that occur under native plant communities in healthy coastal wetlands.
Key words: Great Lakes Coastal wetlands, Phragmites australis, vegetation replacement, invasion