Relative importance of environmental factors and farming practices in shaping weed communities structure and composition in French vineyards

Understanding the relative importance of spatial, temporal variables, environmental conditions and management practices as filters for weed assemblages is essential to promote biodiversity in agrosystems. In this study, we used a unique data set covering 46 vineyard plots in France (Champagne, Beaujolais and Languedoc winegrowing areas) with 883 flora surveys performed between 2006 and 2012. The three objectives of the present study were: (1) to characterize weed communities composition and structure (richness and abundance) in vineyards from three traditional winegrowing areas in France; (2) to evaluate the relative importance of spatial, temporal variables, environmental conditions and management practices on weed species composition and structure; (3) to determine whether or not weed composition and structure are affected by the same factors. The results of the study revealed that season (including timing of management practices) was the most important filter for weed communities in vineyards, opposing in each plot a spring community and a summer-autumn community. Furthermore, spatial variations between regions (latitude), soil types (pH) and inter-annual variations (2006 to 2012) were also seen to have a strong effect on species turnover. Farming practices explained an overall low variation in composition of weed communities but some species showed a high and consistent fit to contrasting practices. For example, herbicide applications (mostly glyphosate) promoted some species such as Malva sylvestris and Sorghum halepense whereas tillage in inter-rows selected typical annual weeds such as Cerastium glomeratum and Galium aparine. Farming practices had a much higher influence on species richness and abundance with equal effect of both herbicides and soil tillage for controlling weed species richness and abundance in inter-rows, but stronger effects of herbicides were observed on species abundance in the rows. Tillage along the rows and a combination of mowing and tillage along the inter-rows were associated to the highest level of weed richness and abundance. Our study suggests that grapevine growers have a limited ability to influence species composition (mostly determined by abiotic factors) but their choice of management can modulate the level of weed richness and abundance. Our results will contribute to guide farmers towards more integrated management practices, ensuring both an optimal management of the spontaneous vegetation in vineyards and allowing this vegetation to provide various ecosystem services.