The effects of salinity and flooding on Phragmites australis

  • Published source details Hellings S.E. & Gallagher J.L. (1992) The effects of salinity and flooding on Phragmites australis. Journal of Applied Ecology, 29, 41-49.


The need to control common reed Phragmites australis in the tidal marshes of Delaware and other mid-Atlantic US states became a priority of coastal zone managers due to a dramatic expansion in the area occupied by this robust grass. Mowing and burning has been attempted as a means of control but has usually resulted in little or no success. Herbicide control may be effective but may not be compatible with other marsh management objectives. This study examined the effects of water salinity, flooding and cutting on P.australis growth in an outdoor experimental trial.

Study site: The outdoor experimental trial was undertaken at the Halophyte Biology Laboratory in Lewes, Delaware, USA.

Experimental design: In June 1988, two plastic swimming pools (1.82 m diameter, 0.30 m deep) were filled either with fresh or brackish (10 g/l salinity) water. Pots of healthy P.australis (about 1.5 m tall) were placed in the pools such that the pot was either 5 cm exposed or 5 cm below the water. The reeds were cut twice (June and August 1988) or left uncut (giving eight treatments in total, five pots/treatment). Water level and more or less constant salinity, were maintained throughout.

Growth: Culm density data was collected in October 1988 (end of growing season) and September 1999 (after flowering for the second year).

In October 1988 at the end of the first growing season, little effect of salinity on culm density (c. 450/m² in freshwater; 410/m² in brackish water) was evident. However culm density was significantly less in submerged pots (c.360/m²) compared with those above the surface (c.500/m²), and also far less in pots where the reed had been cut (c.180/m²) compared with uncut plants (c.680/m²).

The most significant result came in the second year, in September 1989. When plants were cut and the stubble flooded with brackish (salinity 10 g/l) water, there was no further above-ground growth for 18 months, i.e. all plants had apparently died. In addition, submerged pots contained half as many stems as those 5 cm above the water surface.

Conclusions: Salinity, cutting and flooding of P.australis plants all reduced growth and survival in this outdoor experiment. The results suggest that substantial reed control could be achieved if appropriate timing of flooding affected marshes could be undertaken, with results perhaps enhanced in combination with cutting.

Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at:


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