Response of invasive common reed Phragmites australis to introducing salt water and other control treatments in an impounded marsh at the Edwin B. Forsythe National Wildlife Refuge, Oceanville, New Jersey, USA
Published source details
Sun H., Brown A., Coppen J. & Steblein P. (2007) Response of Phragmites to environmental parameters associated with treatments. Wetlands Ecology and Management, 15, 63-79
Published source details Sun H., Brown A., Coppen J. & Steblein P. (2007) Response of Phragmites to environmental parameters associated with treatments. Wetlands Ecology and Management, 15, 63-79
Common reed Phragmites australis has expanded greatly in some North American wetlands over the last 50 or so years. Phragmites may form dense monotypic stands reducing habitat value for wildlife and threatening plant biodiversity. Various techniques to control Phragmites have been used, including burning, cutting and herbicide application. This study evaluated the response of invasive Phragmites in a brackish marsh to changes in pore water geochemistry bought about by introducing salt water through tidal enhancement, alone or in combination with other management regimes used by the US Fish and Wildlife Service (USFWS). A pilot study was conducted prior to these experiment that showed a negative correlation between Phragmites growth and concentration of the main cations associated with salinity (i.e. Na, Ca, Mg and Fe).
Study site: The experiment was undertaken in an impounded marsh at the Edwin B. Forsythe National Wildlife Refuge in Oceanville, New Jersey, northeast USA. The flow rate of tidal water can be controlled by tidal gates, and a management aim was to convert Phragmites-dominated marsh to that resembling surrounding tidal salt marsh. In the 216.5 ha (535 acre) brackish-water impoundment (East Pool), continuous tidal exchange with the estuary (tidal range approximately 2 m) was introduced in July 1999 by opening several control gates.
Eight plots were established in the wetland and the following treatments applied:
Plot 1 - tidal enhancement;
Plot 2 - glyphosate application + controlled burn + tidal enhancement;
Plot 3 - tidal enhancement alone, and tidal enhancement followed by a controlled burn;
Plot 4 - glyphosate application + tidal enhancement.
Plots 5, 7 and 8 served as untreated freshwater impoundments (controls); and 6 served as an untreated salt marsh.
Each plot consisted of up to seven subunits. Each subunit consisted of a Phragmites-dominated vegetation patch.
Burning: Burning was conducted in four subunits of plot 2 in winter 1999 prior to tidal enhancement, and two subunits of plot 3 in February/March of 2000 once tidal enhancement had begun. New Jersey state law limits the burning season to October 1 to March 31. The purpose of burning was mainly to reduce dead reed standing biomass.
Glyphosate application: Plots 2 and 4 were treated by aerial applications of glyphosate at 4 pints/acre in September 1998. September applications allowed improved translocation of the herbicide to root masses after the tasseling (seeding) stage when the reed redirects nutrients to the root zone.
Data collection: A pretreatment vegetation, soil and pore water chemistry survey was conducted in the winter of 1998-1999. First year post-treatment surveys were conducted in winter 2000 (14 January -12 February), and in summer/early autumn (4 August to 10 October). A second year post-treatment survey was conducted in August 2001.
Prior to allowing in tidal salt water, salinity in the East Pool averaged 7.1. Tidal water salinity varied around 30 from 2000 to 2002, and average pore water salinity in East Pool was 27 in 2000 and 32 in 2001. It appeared that soil water salinity above about 28 would be needed to maintain a reduction in Phragmites and to enhance replacement by salt marsh species.
There was a reduction in average Phragmites height ranging 25 to 84 % for different treatment combinations, while untreated (freshwater impoundment) sites exhibited a slight height increase. There was a reduction in average live stem density from 51 to 87% for different treatment combinations. The greatest reduction of density and height occurred when tidal enhancement was followed by a winter burn.
Significant negative correlations were observed between Phragmites height and the main cations associated with tidal salt water (Mg2+, Na+ and K+ and to a lesser extent Ca2+). pH changed little. A reduction of soil adhesiveness associated with the decay of Phragmites roots was observed after two months of (unintended) summer flooding in 2001 when plants were submerged in standing water.
Towards the end of 2001 growing season, saltmeadow cordgrass Spartina patens and saltgrass Distichlis spicata had begun to ramify into the centre of the previously Phragmites-dominated, island patches.
These results indicate that tidal exchange, in combination with other management techniques, is promoting a gradual transition from a Phragmites-dominated system to a Spartina system.
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