Grassland nature reserves safeguard a high species richness and biomass of grasshoppers

Abstract

In the course of land‐use change, especially since the mid‐20th century, the area of semi‐natural (unimproved) grasslands has dramatically decreased. One way to counteract this process is to designate nature reserves. However, the effectiveness of nature reserves is controversial. The aim of our study was to evaluate the environmental drivers of species richness and biomass of Orthoptera (hereinafter termed ‘grasshoppers’) in grasslands inside nature reserves and within the intensively used agriculture landscape (hereinafter termed ‘wider countryside’). For this purpose, we sampled the grasshoppers at the landscape scale in 45 randomly selected plots. Each plot had a size of 5 ha. The abundance of grasshoppers, as a basis for the biomass calculation, was recorded at the habitat scale in 20 meadow patches (500 m2 each). In addition, various environmental parameters such as habitat diversity, mowing intensity and vegetation structure were determined at the landscape and habitat scale. Our results illustrate the importance of nature reserves for the conservation of grasshoppers. Control plots in the wider countryside harboured fewer species than plots within nature reserves. The differences were even clearer among threatened species. On average, plots in nature reserves had almost twice as many threatened species than control plots in the wider countryside. The comparison revealed similar patterns at the habitat scale: both the number of species and biomass were higher in nature reserves. At the landscape scale, number of species were best explained by the amount of wet grassland and habitat diversity. We identified mowing intensity and to a lower extend the degree of drainage as the key drivers of species richness and biomass at the habitat scale. Synthesis and applications: To preserve biodiversity in nature reserves, we recommend (i) leaving uncut refuges during mowing and (ii) blocking drainage to stabilise the water level. Both measures contribute to a high species number and abundance of grasshoppers and many other insects. An effective conservation measure to promote species richness in the wider countryside would be to increase habitat diversity. This can be done by creating or restoring fallow islands, field margins, fringes and hedgerows.