Grassland irrigation and fertilisation alter vegetation height and vegetation within temperature and negatively affect orthopteran populations

Abstract

European mountain meadows are hosting an exceptionally rich biodiversity. While they have long been exposed to land abandonment, they are nowadays additionally threatened by agriculture intensification through aerial irrigation and slurry application. The consequences of this intensification on arthropods are not well documented and studies are needed to fulfil this knowledge gap. Six experimental management treatments combining a full factorial design and a gradual level of fertilisation and irrigation were implemented in 2010 in twelve different montane and subalpine Swiss meadows. In 2013, orthopterans were sampled to assess the influence of the management practices on their population. In addition changes in vegetation height and temperature induced by intensification were recorded in order to better appraise underlying mechanisms. Intensification had a negative impact on Caelifera (grasshoppers); with decreases of up to 70% in densities and 50% in species richness in the most intensively managed treatment plots. In parallel intensification induced an increase in mean vegetation height and a cooling of up to 4.2 {degrees}C (10 cm aboveground) within most intensively managed plots. These microhabitat and microclimate changes are likely to have affected Caelifera development, in particular thermophilous species. In contrast, Ensifera (bush crickets) densities and species richness did not respond to the management treatments. The use of irrigation (without fertilisation) had limited impacts on orthopterans and microclimate. In conclusion, orthopterans, in particular Caelifera, are relatively sensitive to grassland intensification and to conserve the full community, mountain agricultural systems need to maintain extensively managed meadows.