Abstract

Numerous studies have documented the invasion of wetland plants, yet few have tracked the invasion process from its early stages to subsequent large-scale, plant-community changes. The invasion of Phragmites australis (common reed) into the Great Lakes region is a recent phenomenon, facilitated by a decline in water lake levels. The spread of P. australis was tracked in the Old Woman Creek National Estuarine Research Reserve, a 60-ha Lake Erie coastal wetland, using a combination of low-altitude aerial photography and ground surveys during the period from 1993 to 2005. Since the late 1990s, the Old Woman Creek wetland has shifted from a predominantly open-water system to a shallow, water-emergent system. This shift has coincided with a decline in Lake Erie water levels, which are now closer to the long-term mean water level. Aerial photographs for the period 1993–2005 show a transition from the floating leaf Nelumbo lutea (American lotus), to a mixed-emergent community, to increasingly large monotypic beds of P. australis. This wetland perennial grass currently occupies about 22% of the lower wetland and is also a significant component of the emergent community that covers approximately 30% of the lower wetland. The emergent community and P. australis comprised less than 1% of the wetland area in 1993.

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