Differential effects of semi-natural habitats and organic management on spiders in viticultural landscapes

Organic management has the potential to mitigate negative impacts of intensive farming on biodiversity. We aimed to determine the effects of management system (organic vs. conventional), local habitat conditions and the surrounding landscape on ground-dwelling spiders (Arachnida: Araneae) in vineyards. We studied spider species richness, abundance and community composition in fifteen pairs of conventional and organic vineyards along a gradient of landscape composition in Germany. In spite of positive effects of organic management on the inter-row vegetation and soil organic matter, this management system only moderately enhanced species richness of spiders compared to conventional vineyards and did not have the strong positive effects on spider densities known from other cropping systems. Instead, due to high densities of the dominant species Pardosa agrestis, spider abundance was highest in landscapes with high vineyard cover. Densities of spiders other than P. agrestis increased with proximity to semi-natural habitats (SNH). Spider community composition was shaped by management system and cover of SNH. Our results suggest that organic vineyards still promote spiders relative to conventional vineyards, but less strongly than in other cropping systems. In addition, semi-natural habitats enhance the spider fauna in viticultural landscapes and may thus facilitate natural pest control.