Higher cutting frequency can restore semi‐natural habitat quality on farmland

Abstract In agricultural landscapes, semi‐natural habitats such as field margins play an important role in maintaining biodiversity. However, they are generally highly productive and merely support species‐poor vegetation, which may impair their conservation value and ecological functioning. Ecological theory originally predicted that productive habitats cannot support species‐rich vegetation; however, more recent studies suggest that regular defoliation of herbaceous vegetation types can maintain species‐rich plant communities also under productive conditions. Here we ask whether applying appropriate cutting regimes can restore the species richness of species‐poor vegetation even under productive conditions. We carried out a 6‐year experiment with three productivity levels induced by artificial fertilizer applications (NPK; equivalent to 0, 55, 110 kg N ha −1 year −1 ) and four cutting frequencies (one to four times a year). We examined the response over time of plant species richness and cover of dominant forbs and non‐dominant forbs, grasses and Fabaceae species. The negative effects of productivity on plant species richness were moderated by the effects of cutting frequency. At the low productivity level, species richness increased under all cutting frequencies. At the highest productivity level, cutting once or twice per year resulted in a decline in species richness, while cutting three or four times per year produced increases in species richness. The cover of dominant forbs showed a pattern that was largely opposite to that of species richness. After the first year, a clear and consistent negative relationship was observed between plant species richness and dominant forb cover. The non‐dominant forbs showed the most pronounced positive response to increasing the cutting frequencies. Synthesis and applications . Rather than productivity per se, the cover of dominant plant species drives plant species richness. Breaking the dominance of these species through defoliation can restore the species richness of the vegetation. Because dominant plant species can tolerate more defoliations at higher productivity, the number of times a vegetation needs to be cut to restore and maintain species‐rich vegetation increases with the productivity of the habitat. Our results indicate that the quality of herbaceous vegetation types in semi‐natural habitats on farmland can effectively be restored through cutting regimes that are tailored to the productivity levels of the vegetation.