Questions To what extent do changes in management (abandonment and fertilization) affect plant functional and taxonomic diversity in wet meadow communities? To what extent do the changes in functional and taxonomic diversity depend on site productivity? Location Železné hory Mts., Czech Republic. Methods Experimental plots were established on 21 wet meadows differing in productivity and species composition. In each meadow, in 2007, four 1 × 1 m plots were established, representing a full factorial design with abandonment and fertilization as the factors. In each plot, the number of species present was recorded in 100 subplots (0.1 × 0.1 m) in the years 2007, 2009 and 2011. Different indicators of functional diversity (functional richness, functional evenness, and Rao′s quadratic entropy) were calculated using five functional traits (SLA, LDMC, seed mass, plant height and clonality). Both abundance‐weighted and non‐weighted diversity indices were calculated. Randomization tests (conducted with PERMANOVA) were used to assess the effect of site productivity and management on both α‐ and β‐diversity components. Results Meadows along the productivity gradient differed in functional and taxonomic diversity. Both abandonment and fertilization decreased taxonomic diversity. Whereas fertilization decreased functional richness and Rao′s quadratic entropy, abandonment decreased functional evenness. The changes in both taxonomic and functional diversity caused by abandonment and fertilization occurred faster in more productive meadows. Conclusions The increased dominance of tall species with abandonment and fertilization, followed by the loss of species and the decrease in various indicators of functional diversity, suggest that increased competition for light resulted in increased trait convergence among co‐existing species. In addition, many processes occurring after abandonment and fertilization depend on meadow productivity. Results suggest that abundance‐ and non‐abundance‐weighted diversity indices give complementary insights on community structure. These results imply that changes are needed in current meadow management and conservation.

Semi‐natural meadows host a great number of species coexisting at fine spatial scales. Different assembly mechanisms, related to differences in functional traits between species, can influence such coexistence. Coexisting species could be either functionally dissimilar to occupy different niches (‘divergence’) or functionally similar due to exclusion of species with traits less adapted to the prevailing abiotic and biotic conditions (‘convergence’). Various theories differently predict how trait convergence and divergence should differ due to disturbance, along productivity gradients, and across different functional traits. We tested such theories in 21 wet meadows of different productivity in central Europe. In each meadow, four 1 × 1 m plots were established in which disturbance by mowing was combined with fertilization. Species presence was recorded in 100 quadrats 10 × 10 cm in size within the plots over five years. Convergence and divergence were assessed at very fine spatial scales (10 × 10 cm) to focus on the processes driven by the interactions for similar resources. Convergence emerged as the dominant pattern for all traits and across all years. It was particularly strong in the least productive conditions while divergence emerged in some of the most productive meadows. Mowing increased convergence in meadows with low productivity, but increased divergence in productive meadows. Fertilization generally increased convergence, with this increase being more pronounced in mown plots. Convergence in unproductive conditions could be caused by either higher fitness of stress‐tolerant species (more abundant in the species pool of these sites) or by functionally similar species sharing similar patches within fine‐scale heterogeneous plots. This outcome also suggests abiotic filters can have an important role at fine scales, where plant‐ecological theory usually predicts the prevalence of biotic processes.

Summary 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. 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. 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. 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. 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.

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