Impacts of agricultural intensification on weed floral and competitive traits: A spatiotemporal study in French vineyards and annual crops

Weeds play a dual role in agroecosystems, offering both ecosystem services and disservices. Agricultural intensification, particularly herbicide use, has reshaped weed communities, with distinct effects in annual and perennial cropping systems. However, how intensification influences weed multifunctionality—especially in terms of competition and pollination—remains limited. This study explores how weed communities respond to agricultural intensification along spatial and temporal gradients, focusing on traits related to competition and pollination. Specifically, (1) the variation in floral and competitive traits across cropping systems, (2) their responses to management practices, especially herbicides, using national weed surveys from annual crops and vineyards, and (3) long-term changes in floral functional diversity, using two diachronic weed survey datasets, are examined. The results show that vineyards support weed communities more favourable to pollinators than annual crops. While herbicides reduce floral resources in annual systems, practices such as tillage and mowing in vineyards can help maintain floral diversity. In contrast, competitive traits showed no consistent response to herbicide use, highlighting context-dependent effects. Over time, diverging trends in weed floral diversity were observed: a decline in annual crops from the 1970s to 2020 s, and an improvement in vineyards from the 1980s onward. These results underscore the importance of considering both functional roles of weeds and their management context. To fully grasp the contribution of weeds to agroecosystem multifunctionality, long-term monitoring of weed–pollinator interactions and farming practices is essential. • Vineyards support weed communities more favourable to pollinators than annual crops. • In annual crops, herbicides reduce floral diversity while in vineyard tillage or mowing may sometimes support it. • No consistent trends were observed in competitive traits in annual crops or vineyards, regarding their response to herbicides. • Weed floral diversity declined in annual crops between the 1970s and the 2000s, but increased in vineyards since the 1980s.