Individual study: Dynamics of common reed Phragmites australis under different mowing regimes in lowland fens of Switzerland
Güsewell S., Le Nédic C. & Buttler A. (2000) Dynamics of common reed (Phragmites australis Trin.) in Swiss fens with different management. Wetlands Ecology and Management, 8
Reed Phragmites australis has been reported to become increasingly abundant in Swiss fens and wet grasslands, which are traditionally managed by mowing in autumn or winter. Because an increased dominance of P.australis might negatively affect fen plant and animal diversity, managers try to control reed through earlier or more frequent mowing. This study tested whether the abundance of P.australis is still increasing and to what extent its dynamics is influenced by the mowing regime.
Four separate studies in base-rich fens of the Swiss lowlands were undertaken. The shoot number, shoot size and above-ground biomass of P.australis was monitored in permanent quadrats within plots with various mowing regimes over a period of 4 to 15 years. The first study compared plots left unmanaged with plots mown in winter in a triennial rotation; the second one included unmanaged plots, plots mown in summer, and plots mown in winter; the third one compared plots mown in June and September with plots mown only in September; the fourth study investigated only plots mown in September.
In all studies the above-ground biomass of P.australis fluctuated without trend or tended to decrease during the period investigated. The decreasing tendency concerned shoot size rather than shoot number, and within a given study it was stronger for plots with initially taller shoots.
The mowing regime hardly influenced the dynamics of P.australis. Mowing in winter every three years reduced shoot size in the year after mowing, but not in the long term. Mowing every year in late summer initially reduced the shoot size compared with unmown plots, but this effect almost disappeared in the long term, after mowing had become biennial. Mowing in June (in addition to September) caused no noticeable effects. Other factors (e.g. weather conditions, competition, or population processes) were apparently more important than management in determining the abundance of P.australis in the fen communities investigated here, although long-term effects of mowing in summer still need more investigation.
Conclusions: As a practical consequence, it is suggested that at sites which are not strongly dominated by P.australis, as most of those investigated here, reducing the performance of this species should not constitute a major target of nature conservation management, nor can its dynamics be used as an indicator for management success before underlying causes are better understood.
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