Individual study: Regeneration of native wetland plant assemblages following herbicide control of common reed Phragmites australis at Chapman Pond, East Haddam, Connecticut, USA
Farnsworth E.J. & Meyerson L.A. (1999) Species composition and inter-annual dynamics of a freshwater tidal plant community following removal of the invasive grass, Phragmites australis. Biological Invasions, 1, 115-127
Common reed Phragmites australis has colonized and become dominant in freshwater and brackish marshes throughout much of eastern USA. Although native, it appears to have expanded due to factors including alteration of hydrologic flows, disturbance of sediments through ditching/dredging and reclamation, and increased nutrient inputs.
This study documents the partial restoration of native freshwater wetland plant assemblages following herbicide treatment of two stands of reed at Chapman Pond, East Haddam, Connecticut. The 24 ha pond, alongside the Connecticut River, is fringed by freshwater tidal marsh (approximately 53 ha) of high conservation value due to the flora and fauna that it supports.
Treatments: In August 1995, The Nature Conservancy and the Connecticut Department of Environmental Protection undertook Phragmites herbicide control in northern and middle Phragmites stands around the pond. A 1% solution of Rodeo (Monsanto, Inc; active ingredient glyphosate) was applied to Phragmites stems using a hand-held sprayer in two plots: Plot 1 (northern stand) sprayed from a boat; Plot 2 (middle stand) sprayed from a low-ground-pressure amphibious vehicle. Each plot was mulched during the subsequent spring: Plot 1 was hand-cut and cut stems were left in place; Plot 2 was mown using a Seppi mower, which shredded vegetation into fine pieces. Each treatment removed about 0.4 ha of Phragmites. A third Phragmites stand (plot 3) was left intact in the southern sector as an untreated reference plot.
Monitoring: One year before and for 3 years after the treatments, plant species composition and richness were recorded, and patterns of plant recruitment examined.
Density of live Phragmites stems were similar in the three plots prior to treatment, and remained at 35-45 stems/m² between 1995 and 1998 in plot 3. Stem densities declined greatly in plots 1 and 2 between 1995 and 1996. Although there was a very slight recovery by 1998 (plot 1 = 19/m²; plot 2 = 5/m²) stem densities were still much reduced compared to the original pre-treatment situation.
Phragmites also declined in extent in both treated plots but re-colonization was apparent. In 1995, 100% of quadrats surveyed contained some Phragmites. In 1996, treatments had reduced occurrence to 36% of quadrats in plot 1 and 40% of quadrats in plot 2. In 1998, 64% of surveyed quadrats in plot 1 and 45% in plot 2 contained Phragmites.
Richness, evenness, and density of other wetland plant species increased up to 1997 in all plots. However, species composition in plots 1 and 2 was richer than that of plot 3, and more closely resembled the desired uninvaded wetland assemblage. Rates of recovery of species richness in plots 1 and 2 declined from 1997 to 1998, perhaps reflecting saturation of available colonization space, and/or the gradual return of Phragmites.
This study demonstrates that freshwater tidal marsh plants were able to regenerate following Phragmites invasion and subsequent control. The authors recommend that careful multi-site monitoring is needed to provide convincing measures of success, to detect re-invasion, and hence indicate when further Phragmites control is warranted.
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