Impacts of an agri-environment field margin prescription on the flora and fauna of arable farmland in different landscapes

The hypothesis that sown 6 m grass margins strips at the edges of arable fields have a positive impact on farmland biodiversity was tested using a paired field approach in southern England. A total of 42 fields were investigated, half with at least 3-year-old margin strips created under the UK agri-environment scheme Countryside Stewardship and half nearby control sites. The sites were grouped on the basis of average field size into small, intermediate or open landscape locations to examine landscape structure effects. Assessments of the flora, bird and territory numbers, bees, spiders, Orthoptera and Carabidae were made in early to mid-summer 2003. There were positive impacts on diversity or abundance for the flora, bees and Orthoptera. The herbaceous flora of the pre-existing boundary adjacent to sown 6 m strips was significantly more species-rich than controls, probably reflecting a buffer effect of the strip. Bees and Orthoptera, the latter of which were only found in field boundaries, were more abundant where strips were sited, reflecting added habitat resources. Bee numbers were significantly lower in field centres where there were no 6 m margin strips. There were no significant effects of sown strips on numbers of birds observed or bird territories, spiders or Carabidae, but also no negative impacts. Lycosid spiders were consistently more abundant in boundaries of small fields with 6 m margin strips. Linyphiidae were more abundant within the crop area of smaller fields. Amongst birds, wrens (Troglodytes troglodytes) were also more abundant in small fields, while yellowhammers (Emberiza citrinella) were more abundant in open landscapes. The results confirm there are benefits to farmland biodiversity from introducing new margin strips at the edges of arable fields. More significantly, the success of agri-environment schemes, which will vary between taxa and species, can be dependent on landscape structure. Scheme administrators may need to address landscape structure and mean field size to achieve significant enhancement of populations of declining farmland species.