How effective is large landscape-scale planning for reducing local weed infestations? A landscape-scale modelling approach

Abstract Finding efficient and environmentally sustainable methods for arable weedmanagement is a current challenge in agroecosystems. Weedspecies disperse over scales larger than the field. Landscape-scale management could, therefore, reinforce field-scale strategies for innovative cropping systems. In particular, the introduction of semi-natural habitats, such as permanent meadows, which are unsuitable habitats for annual arable weeds, could potentially reduce weeddensities in crops. We developed a spatially explicit, landscape-scale model of annual arable weedpopulation dynamics including the main components of weedmanagement at cropping systemlevel: crop rotation, tillage regime, intensity of herbicide use and mechanical weeding. The variability of responses to these factors for different weedspecies functional typeswas considered by modelling four functional responsegroups. We used this model to investigate the effects of increasing the proportion of permanent meadows in the landscape and of the spatial arrangement of meadows on weeddensity in crops. With this model, increasing the proportion of permanent meadows significantly decreased mean seed density of weedsin crops. Furthermore, weeddensity in cropswas found to be lower for landscapes in which the meadows were scattered, rather than clustered together in large zones. However, these spatial and landscape-scale effects were much weaker than the local effect of cropping systems. Weeddensity in permanent meadows was more sensitive to the proportion of meadows and to their spatial arrangement than weeddensity in crops, although the absolute value of weeddensity remained low in this unfavourable habitat.