Weed species richness in winter wheat increases with landscape heterogeneity

There is empirical evidence that landscape composition and structure can affect the distribution and long-term dynamics of the organisms that live in it. Weeds are no exception and in this paper, we investigated how weed richness and diversity in 123 winter wheat fields within a small agricultural region were affected by the landscape surrounding each field (radii ranging from 100 to 1000 m) and the field properties such as its size and the preceding crop. Landscape was described by its proportion (cover of spring crops, winter crops, woodland, grassland, set-aside) and its structure (number of fields, number of land use types). Akaïke criterion-based models indicated that variations in weeds were best explained at the 200 m radius. At that scale, hierarchical partitioning shows that the independent contributions of field level and landscape level variables were significant for two variables. Weed richness and weed diversity increased significantly as field size decreased and as the number of fields within 200 m increased. This suggests that weed richness and diversity are higher in landscapes that have a finer grain, probably because these landscapes offer more habitat heterogeneity within cultivated areas and contain more crop edges that can shelter many weed species.