Effects of the abandonment of alpine summer farms on spider assemblages (Araneae)

Abstract

In parallel with the current effects and responses to climate change ongoing changes of land use strongly affect alpine areas. The aim of this study was to analyse spider assemblages occurring on farmlands with differing stages of land use intensity. We collected the ground-dwelling spider fauna of semi-natural grasslands in currently farmed and abandoned farmland in the alpine zone of Hardangervidda, Norway, using pitfall traps. Trapping during the whole vegetation period resulted in 1,548 individuals belonging to 39 species of spiders. Linyphiids and lycosids dominated. The total number of species differ little between sites, but there was a general trend of increasing proportions of lycosids, gnaphosids and thomisids individuals and species, and a decrease in the proportion of linyphiids with farmland abandonment. Two main groupings of spider assemblages were found using a principal component analysis: One grouping was characteristic of intensely disturbed sites, mainly dominated by typical pioneer species. The other was characteristic of abandoned and less disturbed sites, dominated by widespread species. The abandonment of summer farms led to a succession in spider assemblages, including a decline in spider species with a high ballooning activity and an increase of species with a larger body size. We suggest that the main reason lies in the absence of disturbance by grazing including differing vegetation architecture and the proportion of bare ground with abandonment. Spider assemblages react quickly to environmental changes that occur in alpine habitats after abandonment. Thus, it is necessary to include spiders and other invertebrate animal indicator groups in field studies and experiments dealing with grazing impacts on alpine habitats.