How to decrease the negative effects of medium intensity disturbances on arthropod communities

Abstract. One of the major goals in nature conservation practice is to optimise the timing or the method of treatments or both. We studied the response of the Auchenorrhyncha (Insecta: Homoptera) assemblage to annual mowing in three different locations along an elevation gradient of a mesic grassland. Several weeks after mowing, the total number of imagoes and larvae decreased considerably, and the relative abundance differences between populations at different elevations also decreased, reflecting the density dependent effect of this treatment. The rate of changes in species composition was greatest in the microhabitats with more comfortable microclimates, in the opposite direction of the alteration of abundance, perhaps interfering with the migration. By the next spring the fauna of the wettest habitat proved to be the most sensitive to mowing and the most different from the others. The overall similarity of the insect communities increased, i.e. the community-level biodiversity decreased due to homogenising effect of mowing. In a heteromorphous habitat, the variability of spatio-temporal dynamics of the populations makes it impossible to find either single optimal time or optimal rotation plan for treatment based on the habitat types. For this reason, we suggest mowing in stripes parallel to the elevation gradient, which would mean synchronous treatment of each microhabitat instead of randomly chosen patches, where the execution is problematic. It is easier to keep the ratio of treated to untreated areas at 50%. Stripes should be narrow enough to provide the possibility of migration to favourable habitat patches, and should not hinder mechanical mowing. Suggested width of stripes is 10–15 m for Auchenorrhyncha.