Weeds in a changing climate: Competitors or service plants?

Societal Impact Statement Reducing herbicide use and preparing agroecosystems for climate change are two top priorities on the global policy agenda. Here, we explore whether these two challenges can be tackled simultaneously. While weeds are generally considered a threat to crop production, we show that weeds can help overcome climate change challenges in agroecosystems. However, crop–weed interactions need to be carefully managed. Options for this were found to be greater in perennial than in annual systems. These findings provide a new perspective on weeds and call for more research on the appreciation of weeds as service plants, which ultimately may create new avenues for weed management and agricultural policy. Summary Sustainable agricultural production is at risk due to climate change, the increasing herbicide resistance of weeds and pressures to minimise herbicide use. Rather than solely considering weeds as part of the problem, we see this as an opportunity to investigate whether weeds can help overcome climate change challenges in agroecosystems. Using both ecological and agronomic perspectives, we assessed to what extent weeds can support the ecosystem functions water and climate regulation and whether their potential role as service plants would interfere with crop production. Based on ecological trait‐based analyses, we demonstrate that weeds are excellent candidates to support the delivery of water and climate regulation. Despite climate change‐induced shifts in weed communities, weeds continue to support these ecosystem functions. However, weed trait values that promote the ecosystem processes underlying water and climate regulation also tend to increase competition with crops. We show that confining weed–crop interactions is key to allow weeds to operate as service plants and that the spatial and temporal opportunities to manage these interactions vary among annual and perennial cropping systems. Overall, diversified management is recommended in both systems to avoid the selection of weed communities composed of just a few highly competitive weed species. We conclude that weeds could act as service plants in a changing climate rather than being considered a threat to agroecosystems. Weed management and research should thus prioritise the investigation and implementation of this new perspective.