A framework to estimate the contribution of weeds to the delivery of ecosystem (dis)services in agricultural landscapes

There is a pressing need for indicators and methods to quantify the provision of ecosystem services as a prerequisite to identify management options that optimize trade-offs between services. Arable weeds provide multiple services and are thus a good model to evaluate such trade-offs. This flora provides trophic resources (flowers or seeds) that support pollinators and pest natural enemies (pollination and pest control services) but can also be harmful for crop production (disservice). To date, few indicators are available to quantify the contribution of weeds to ecosystem services or their harmfulness, and no indicators account for intraspecific variability in weed traits that result from contrasting growing conditions, notably the location of weeds within fields (field edge vs field core) and crop type. Here, we developed nine proxies for potential weed harmfulness (competition, harvest difficulties and future weed infestations) and weed contributions to resources provision to pollinators (bees, bumblebees and hoverflies) and pest natural enemies (carabid beetles, birds and parasitoid wasps). These nine proxies accounted for individual weed plant response to growing conditions (combination of within-field location by crop type) for 155 weed species, resulting in 967 unique situations (combinations of species by within-field locations by crop types). Apart from harvest difficulties, all proxies were positively correlated, i.e. harmfulness increased when services increased. Weed plants located on field edges had greater contributions to all proxies than those located in field cores, especially in cereal crops. We identified that small weed species with short life cycles and low competitiveness, presented the optimum proxy combination, i.e. high services and low harmfulness. The development of these proxies and the proposed framework provide new avenues for assessing trade-offs between multiple ecosystem services at different temporal (crop sequence) and spatial scales (landscape).