Wildflower sowings as alternative for conventional inter-row greening in German vineyards

Most European vineyards contribute little to biodiversity preservation due to intensive agricultural practices and a low plant species diversity that has low potential to support benefical insects such as pollinators. Based on specific plant traits, we selected 37 forbs and one grass species, sowing them in the inter-rows of 11 vineyards (biodiversity vineyards) in Germany in autumn 2020 and spring 2021. The aim was to increase native plant diversity and to provide a sufficient vegetation cover for vineyard work. For comparison, we used six vineyards with conventionally greened inter-rows (control vineyards). In both the biodiversity and control vineyards, we recorded the cover and number of all plant species as well as the cover of bare soil in the years 2021 to 2023. Furthermore, we calculated the Pollinator Feeding Index (PFI) to assess and compare the potential of sown and spontaneously emerging forb species occurring in the biodiversity and control inter-rows as food sources for pollinators. Of the 38 sown species, 36 established in the biodiversity vineyards. Already in the first year after sowing, vineyard inter-rows sown with the new seed mixture showed comparable vegetation cover as conventionally greened vineyard inter-rows, thus ensuring suitability for vineyard work. In addition, we found significantly higher forb cover and species number within the biodiversity vineyards, while the control vineyards showed a significantly higher grass cover. We observed significantly higher PFI values in the biodiversity vineyards as compared to the control vineyards. The introduced plant species did not only increase plant diversity, but could also be an important nectar and pollen source for pollinating insects. However, spontaneously established plant species also contributed to the PFI, especially in spring and early summer. Due to the benefits of using high-diversity seed mixtures, subsidizing the use of wild plants for vineyard greening as part of agri-environmental schemes is recommended.