Heuschrecken (Orthoptera) in Biodiversitätsförderflächen der voralpinen kulturlandschaft schönenbergs (Schweiz, Kanton Zürich) mit trends seit 1990

Abstract

Grasshoppers (Orthoptera) in ecological compensation areas of a pre-alpine cultural landscape near Schönenberg (Switzerland, canton of Zürich) with trends since 1990. Our investigations in the pre-alpine cultural landscape of Schönenberg (Switzerland, canton of Zürich) have shown that ecological compensation areas (ECA) such as reeds and extensively managed semi-natural grassland have a highly positive effect on the species diversity and density of grasshoppers compared to conventionally managed cut meadows. ECA reeds showed significantly higher diversities and densities of grasshopper species than ECA meadows and ECA pastures. ECA reeds also contained almost 95% of all observed individuals of the grasshoppers on the Swiss Red List. Within the ECA reeds, significantly higher species diversity was recorded in moor grass meadows and tall forb communities compared to low sedge fens, tall sedge fens and subareas with high density of Phragmites australis. Grasshopper densities in moor grass meadows and tall forb communities proved to be significantly higher than those in tall sedge fens. Compared to previous surveys in Schönenberg ZH from 1990 and 2000, the grasshopper diversity in the conventionally managed meadows did not significantly change, but there were considerable shifts in the relative abundance at species level. For example, the rather xerophilous species Chorthippus biguttulus was more frequent in conventionally managed meadows in 2016 than in 1990 and 2000, while the regionally more hygrophilous species Chorthippus dorsatus showed an opposite trend. Chorthippus albomarginatus, a species which had not been observed in 1990 and 2000, was found in 2016 within some conventionally managed meadows. These findings currently belong to the easternmost sites of the Swiss pre-alpine region. In 2016, a significantly higher species diversity of grasshoppers was found within the ECA reeds compared to 1990. Although the endangered species Conocephalus fuscus suffered a massive decline since 1990, other species significantly increased in their relative abundance, e. g. the potentially endangered species Chrysochraon dispar and Decticus verrucivorus. Measures to promote grasshoppers on ECA grassland are discussed, with a focus on the asynchronous management, the use of compatible mowing techniques and the maintenance of temporally and spatially varying subareas with uncut vegetation.