Management of Phragmites australis in Swiss fen meadows by mowing in early summer

Published source details Güsewell S. (2003) Management of Phragmites australis in Swiss fen meadows by mowing in early summer. Wetlands Ecology and Management, 11, 433-445.
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Summary

Common reed Phragmites australis has been spreading Swiss fen meadows; these are species-rich, unfertilized, wet grasslands which are traditionally managed by cutting in autumn or winter. Because an increasing dominance of P.australis might negatively affect fen plant and animal diversity, managers try to control reed by mowing the meadows more frequently, e.g. a first cut in early summer and a second cut in autumn. The present study tested the effectiveness of this mowing regime in reducing the abundance and dominance of P.australis.

Study sites: The reed mowing experiments were under taken at three wetlands Greifensee, Katzensee and Glatt (Swiss National Grid refs: 692'550/247'750; 680'550/254'100; and 691'950/247'650 respectively) near Zurich, Switzerland.

Mowing experiments: Experimental plots (10 m x 10 m, n = 18) were established in 1995-1996 in the three study wetlands. Six plots were mown in late June every year, six were mown in June every two years, and six control plots were never mown in June; all plots were mown in September as part of the regular management.

The shoot number and shoot size of P.australis was recorded in permanent quadrats every year from 1995 through 2001 in late June, right before the first cut of treated plots, and used for non-destructive estimation of above-ground biomass. Samples of the vegetation were taken outside the permanent quadrats every two years to determine total above-ground biomass and nutrient exports caused by mowing.

Until 1997 (third year), the additional cut had no effect on the above-ground biomass of P. australis. As from 1998, the shoot size and above-ground biomass of P.australis was 25–30% lower in the plots with annual June cut than in the control plots. However, the pooled biomass of all other plant species decreased similarly, so that the degree of dominance of P.australis was not reduced. An additional June cut every two years had no effect on the biomass or dominance of P.australis.

The additional June cut increased the total export of N with the hay in 2001 by 18%, and that of P by 50%. These additional nutrient exports were similar for P.australis and for the remainder of the vegetation. Together, the results suggest that a depletion of below-ground stores caused P.australis to decrease after several years of annual mowing in June.

Eighty further permanent quadrats in fen meadows with normal management (mown annually in September) were surveyed in 1995–96 and in 2001. The above-ground biomass of P.australis increased during this time in 49 out of 80 plots, with a mean relative difference of +35.5%.

Conclusions: Additional mowing in early summer only slightly reduced the performance of Phragmites compared to plots mown only in September, but this treatment might help to prevent the species from spreading under the current conditions in Swiss fen meadows.

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