Bocage landscapes are characterized by a network of hedgerows that delimits arable fields. Such landscapes provide many ecosystem services, including biodiversity conservation, but their effects on weed communities remain largely unknown. Bocage landscapes could affect weed communities through two main processes: plant spillover from hedgerows and increased environmental heterogeneity in arable fields. These bocage effects are also likely to vary between farming systems (conventional vs. organic) due to differences in management practices. We sampled weed communities more than 20 m from field margins in 74 arable fields (37 per farming system). Fields were located along two independent landscape gradients of total length of hedgerows (with or without a shrub layer) and organic farming cover, in Brittany (France). We analysed the effect of ‘bocage’ (i.e. the density and complexity of hedgerow networks) and farming systems at field and landscape scales on species and functional diversity of weed communities. Further, we used fidelity to non‐crop habitats and Ellenberg indicator values to assess the ‘plant spillover’ and ‘environmental heterogeneity’ hypotheses, respectively. Weed communities were more diverse and more abundant in organic farming systems. In addition, weed communities were more diverse, but not more abundant, in denser and more complex bocage landscapes. ‘Bocage’ increased species diversity of weeds, but also community‐weighted variance of specific leaf area, plant height and seed mass. Positive effects of ‘bocage’ on weed diversity were driven by increased environmental heterogeneity rather than spillover of transient species from hedgerows. ‘Bocage’ effects were independent of farming systems at field and landscape scales. Synthesis and applications. Maintaining diverse weed communities is key to agroecological weed management and biodiversity conservation in agricultural landscapes. Farmers are often concerned that hedgerows harbour competitive plants spreading into field edges, thereby increasing weed pressure. However, our study shows that dense and complex bocage landscapes promote weed diversity in field cores, most likely by increasing environmental heterogeneity. Thus, bocage landscapes could actually enhance ecosystem services provided by weed communities and reduce weed‐crop competition.
The relative contributions of agricultural intensity and semi‐natural habitats to the multifunctionality and sustainability of ecosystems at different spatial scales remain largely under‐investigated. In this study, we assessed the multifunctionality of 40 winter cereal fields and 40 hedgerows based on ecological, agronomic and socio‐economic performance using data from field surveys and interviews with farmers. We specifically focused on the effects of local farming systems (organic vs. conventional) and management (cereals intercropped with legumes vs. monocrops), the effects of landscape heterogeneity related to hedgerow density, and the spatial extent of semi‐natural habitat and organic farming. Multifunctionality indices associated with increased values of proxies for biodiversity conservation and pest control functions were higher for hedgerows than crop fields. Agroecosystem multifunctionality was similar between organic and conventional farming as a consequence of antagonistic responses of individual function proxies. While organic farming promoted the ecological performance of crops, conventional farming resulted in higher agronomic performance (i.e. yield). Interestingly, lower yields of organic crops were not systematically associated with reductions in socio‐economic performance in terms of farmer income and labour. At the landscape scale, hedgerow density and the extent of semi‐natural habitats and organic farming had little influence on agroecosystem multifunctionality or individual function proxies. Synthesis and applications. Our results confirm the high value of hedgerows and organic farming at the local scale for the ecological performance of ecosystems. Our study suggests that, among existing agri‐environment schemes in Europe, hedgerow planting and organic farming are appropriate tools to optimise the ecological performance of ecosystems at the local scale even if antagonistic effects with agronomic performance should not be neglected.
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