Sammendrag

The abundance of Juncus effusus (soft rush) and Juncus conglomeratus (compact rush) has increased in coastal grasslands in Norway over recent decades, and their spread has coincided with increased precipitation in the region. Especially in water‐saturated, peaty soils, it appears from field observations that productive grasses cannot compete effectively with such rapidly growing rush plants. In autumn–winters of 2012–2013 and 2013–2014, a four‐factor, randomised block greenhouse experiment was performed to investigate the effect of different soil moisture regimes and organic matter contents on competition between these rush species and smooth meadow‐grass (Poa pratensis). The rush species were grown in monoculture and in competition with the meadow‐grass, using the equivalent of full and half the recommended seed rate for the latter. After about three months, above‐ and below‐ground dry matter was measured. J. effusus had more vigorous growth, producing on average 23–40% greater biomass in both fractions than J. conglomeratus. The competitive ability of both rush species declined with decreasing soil moisture; at the lowest levels of soil moisture, growth reductions were up to 93% in J. conglomeratus and 74% in J. effusus. Increasing water level in peat–sand mixture decreased competivitiveness of meadow‐grass, while pure peat, when moist, completely impeded its below‐ground development. These results show that control of rush plants through management may only be achieved if basic soil limitations have been resolved.

Sammendrag

Increasing abundance of Juncus effusus (soft rush) and Juncus conglomeratus (compact rush) in pastures and meadows in western Norway has caused reductions in forage yield and quality in recent decades. Understanding plant development and regrowth following cutting is essential in devising cost-effective means to control rushes. In a field experiment in western Norway, we investigated development of above- and below-ground fractions of rush from seedlings to three-year-old plants, including the impact on vigour of disturbing growth by different cutting frequencies during the period 2009–2012. Each year, the plants were exposed to one or two annual cuts or left untreated and five destructive samplings were performed from March to early December. Juncus effusus showed significantly more vigorous growth than Juncus conglomeratus in the last two years of the study period. The above-ground:below-ground biomass ratio of both species increased mainly in spring and early summer and was reduced in late summer and autumn. Removal of aerial shoots also reduced the below-ground fraction of both species. One annual cut in July effectively reduced biomass production in both species by 30–82%, which was only a slightly smaller reduction than with two annual cuts, in June and August. Mechanical control measures such as cutting can thus effectively reduce rush vigour when performed late in the growing season.