Reconstructing the history of a Great Lakes coastal wetland with pollen analysis

Aggressive plant invaders such as Typha x glauca threaten wetland ecosystems by reducing biodiversity and causing often irreversible, edaphic modifications. Cheboygan Marsh on the coast of Lake Huron in northern Michigan is currently undergoing invasion by T. x glauca, and soils associated with the invader have significantly higher soil organic matter (>85%) than soils in areas of native vegetation (<25%). In this study, we used fossil pollen assemblages, satellite imagery, historic water-level data, lead-210 and cesium-137 dating to reconstruct the history of invasion by T. x glauca in Cheboygan Marsh. We wanted to 1) determine an approximate date when invasion began, 2) correlate organic matter accumulation to the rise in T. x glauca pollen, and 3) examine the effect historical water-level fluctuations have on T. x glauca using its pollen as a proxy. We found that T. x glauca became the dominant species in Cheboygan Marsh by the late 1950's, following the highest peak in water level over the last 100 years. Two decades after T. x glauca was established in the marsh, soil organic matter rose dramatically and reached current levels by the 1980's. This study suggests that organic matter and water-level fluctuations are important controls in wetland invasions by T. x glauca and should be considered in their management.