Effects of low-input farming systems on carabids and epigeal spiders – a paired farm approach

Abstract

We compared the effects of different low-input farming systems on carabids and spiders. The study was performed in a 3-year field survey using a paired-farm approach in six different landscapes units in northwestern Switzerland considering also the nearby semi-natural habitats. Carabids and spiders were sampled in 24 winter cereal crops and 18 semi-natural habitats using five funnel pitfall traps per site. Considering all cereal sites, in low-input ICM fields (= no insecticides, fungicides and growth regulators; ICM: Integrated crop management) 36% less carabids and 8% less spider specimens were found. In several cases, carabid populations of organic fields were significantly richer in species and abundance than in the low-input integrated crop management farmed plots. Endangered, stenoceous carabids (e.g. xero-thermophilous) and top-predators were more abundant in the organic fields. Spider communities differed less in mean number of species and abundance between the two low-input agricultural systems. Multivariate analysis showed that farming method and weed abundance were significant factors altering the carabid fauna and weed diversity influence spider fauna. Wolfspiders such as Pardosa agrestis, P. palustris and Trochosa ruricola seem to be enhanced by organic management. Linyphiids (Erigone atra, Oedothorax apicatus) were more abundant in lowinput ICM fields. Several carabid species and wolfspiders which have their main distribution in semi-natural habitats occurred more abundant in organic fields. This indicates that seminatural habitats in combination with organic farming may be an important factor for the conservation and enhancement of the species rich assemblages on agricultural land. Auswirkungen von zwei extensiven Anbausystemen auf die Laufkafer- und Spinnenfauna wurden unter Berucksichtigung der im Umfeld liegenden naturnahen Habitate untersucht. Sechs vergleichbare Paarbetriebe in sechs Landschaften der Nord-Westschweiz wurden wahrend einer 3-jahrigen Untersuchung dazu ausgewahlt. Die epigaischen Nutzarthropoden wurden mittels 5 Trichterbodenfallen in 24 Wintergetreideflachen und 18 naturnahen Flachen erfasst. Uber alle Ackerstandorte betrachtet wurden in den extensiv, integriert (IP) bewirtschafteten Getreideflachen (keine Anwendung von Fungiziden, Insektiziden und Wachstumsregulatoren) 36% weniger Laufkafer und 8% weniger Spinnentiere gefunden. In einigen Vergleichsfallen waren die durchschnittliche Artenvielfalt und Aktivitatsdichte der Laufkafer in den biologisch bewirtschafteten Wintergetreideflachen signifikant hoher als in den IP-Extenso Flachen. Gefahrdete, stenoke (z.B. xero-thermophile) Laufkaferarten und Top-Pradatoren waren in den biologisch bewirtschafteten Flachen zahlreicher. Bei der Spinnenfauna ergaben sich weniger deutliche Unterschiede betreffend durchschnittlicher Artenzahl und Aktivitatsdichte. Multivariate Analysen zeigten, dass die Anbaumethode und die Dichte der Begleitflora die Laufkafer signifkant beein