Rates, patterns, and impacts of Phragmites australis expansion and effects of experimental Phragmites control on vegetation, macroinvertebrates, and fish within tidelands of the lower Connecticut River

Phragmites expansion rates (Linear at 1-3% yr(-1)) and impacts of this expansion on high marsh macroinvertebrates, aboveground production, and litter decomposition from Phragmites and other marsh graminoids were studied along a polyhaline to oligohaline gradient. These parameters, and fish use of creeks and high marsh, were also studied in Phragmites control sites (herbicide, mowing, and combined herbicide/mow treatments). Phragmites clones established without obvious site preferences on oligohaline marshes, expanding radially. At higher salinities, Phragmites preferentially colonized creekbank levees and disturbed upland borders, then expanded into the central marsh. Hydroperiods, but not salinities or water table, distinguished Phragmites-dominated transects. Pooled samples of Phragmites leaves, stems, and flowers decompose more slowly than other marsh angiosperms; Phragmites leaves alone decompose as or more rapidly than those of cattail. Aboveground Phragmites production was 1,300 to 2,400 g m(-2) (about 23% of this as leaves), versus 600-800 g m(-2) for polyhaline to mesohaline meadow and 1,300 g m(-2) for oligohaline cattail-sedge marsh. Macroinvertebrates appear largely unaffected by Phragmites expansion or control efforts; distribution and densities are unrelated to elevation or hydroperiod, but densities are positively related to litter cover. Dominant fish captured leaving flooded marsh were Fundulus heteroclitus and Anguilla rostrata; both preyed heavily on marsh macroinvertebrates. A. rostrata and Morone americana tended to be more common in Phragmites, but otherwise there were no major differences in use patterns between Phragmites and brackish meadow vegetation. SAV and macroalgal cover were markedly lower within a Phragmites-dominated creek versus one with Spartina-dominated banks. The same fish species assemblage was trapped in both, plus a third within the herbicide/mow treatment. Fish biomass was greatest from the Spartina creek and lowest from the Phragmites creek, reflecting abundances of E heteroclitus. Mowing depressed Phragmites aboveground production and increased stem density, but was ineffective for control. Phragmites, Spartina patens, and Juncus gerardii frequencies after herbicide-only treatment were 0.53-0.21; total live cover was < 8% with a heavy litter and dense standing dead stems. After two growing, seasons Agrosti's stolonifera/S. patens/J. gerardii brackish meadow characterized most of the herbicide/mow treatment area; Phragmites frequency here was 0.53, contributing 3% cover. Both values more than doubled after four years; a single treatment is ineffective for long-term Phragmites control.