Suppressing competitive dominants and community restoration with native parasitic plants using the hemiparasitic Rhinanthus alectorolophus and the dominant grass Calamagrostis epigejos

1. Dominance of native or alien competitive plants causes competitive exclusion of subordinate species and represents a major mechanism reducing biodiversity following land-use changes. The successful competitive strategies may, however, be interfered with by parasitic plants, which withdraw resources from other plants' vasculature. Parasitism may strongly reduce the growth of the dominants, which may facilitate regeneration of other species and consequently trigger restoration of natural communities of high diversity. 2. Here, we aim to provide robust empirical evidence demonstrating this restoration potential of parasitic plants. We present a case study testing suppressive effects of hemiparasitic Rhinanthus alectorolophus on competitive grass Calamagrostis epigejos. In recent decades, C. epigejos has invaded many high-nature-value semi-natural grasslands of Central Europe, which is one of the prominent factors causing their biodiversity decline. 3. We conducted three manipulative field experiments testing the effect of sowing of R. alectorolophus in different vegetation types infested by C. epigejos. Rhinanthus sowing was compared to different mowing treatments recommended as the 'best practice' management at respective sites. 4. Rhinanthus alectorolophus established itself in most C. epigejos-dominated plots where sown. Calamagrostis epigejos was virtually exterminated in 2 years in two of the experiments (dry meadow and industrial area). In the wet-meadow experiment, the suppressive effect was variable as a result of uneven establishment success of Rhinanthus. In this experiment increased mowing intensity had an additional suppressive effect on C. epigejos. Rhinanthus also increased regeneration potential of other species by a temporary reduction of vegetation density. Restoration of target vegetation composition was, however, dependent on community context. 5. Synthesis and applications. We demonstrated that hemiparasitic Rhinanthus alectorolophus is an accessible and efficient tool for targeted biological control of Calamagrostis epigejos, with a great potential to restore infested grassland vegetation. The strong effect of Rhinanthus is caused by interference with the underground storage and clonal growth strategy of Calamagrostis epigejos, which are both traits that underlie its competitive ability. The potential of native parasitic plants should be considered in restoration management of sites infested by competitive dominants, either alien or native.