Tillage intensity or landscape features: What matters most for wild bee diversity in vineyards?

Vineyard inter-rows can provide habitats for a range of plant and animal species especially when covered with vegetation. However, frequent tillage results in the degradation of habitat quality and the provision of biodiversity-based ecosystem services. Wild bees are important pollinators of crops and wild plants and depend on both, floral resources and suitable nesting sites, which are influenced by the landscape configuration. We examined effects of field and landscape parameters on wild bee species' richness, abundance and functional traits in Austrian vineyards over two years using Generalised Linear Mixed models, Detrended Correspondence Analysis and Random Forests. Alternating tillage was compared with no tillage in two inter-rows per vineyard. Forage availability in these inter-rows was estimated by flower coverage at each sampling date, and landscape features were analysed within a radius of 750 m around the vineyards. Across all vineyards we found 84 wild bee species with a mean abundance (+/- SD) of 29 (+/- 16.6). Forage availability had the strongest positive effect on wild bee diversity and abundance. In comparison to no tillage, alternating tillage slightly increased wild bee diversity and abundance. Eusocial wild bees were more abundant in untilled inter-rows, whereas solitary wild bees were more closely associated with alternating tilled vineyards. At the landscape scale, the percentage of artificial areas (mostly villages) and distance to semi-natural elements raised wild bee diversity and abundance. The proportion of woodland increased the abundance of wild bees, in particular of eusocial taxa. Solitary wild bee abundance was enhanced by the number of solitary trees. Pollination provided by wild bees in viticultural areas can be enhanced by maintaining a diversity of different soil management strategies to improve forage availability in vineyards. Furthermore, semi-natural elements such as fallows or solitary trees providing floral resources and nesting habitat should be preserved within viticultural landscapes.