5 Conclusions

Buffer zones for biodiversity of plants and arthropods: is there a compromise on width?

The effects of buffer zones on plants, insects and spiders are so clear cut that the following conclusions can be drawn:

A buffer width of 6 m in cereal fields is the narrowest width to consistently increase the biodiversity and abundance of plants and arthropods. An additional increase in width will in most cases only lead to marginally more species. Therefore, a 6 m buffer seems to be the best compromise when considering the trade-off between biodiversity gain and buffer zone costs.
While the arthropod fauna within the herbaceous hedge bottom obtains a substantial protection against chemical effects at all tested buffer widths, the arthropod fauna on the woody species in the hedge are affected to a much lesser extent by the tested buffer widths.
The biodiversity benefits within the buffer zone and the hedge bottom are already at a 6 m buffer so remarkably good, that this buffer width is worth considering as a general measure to counteract the decreasing biodiversity in arable landscapes.
Butterflies might be considered a potential biodiversity indicator for assessing the impact of future buffer zone programmes.
Although the present investigation was carried out in spring barley along well established hedges, the biodiversity gains with buffer zones may be regarded valid in cereal fields in general, if these are placed along somewhat similar hedges (bushes and or trees) even less tall and less wide. Furthermore, the importance of a well developed hedge bottom flora (from the hedge out to the crop) was so markedly, that it should be allowed to develop if it is not present along the field edges.
No general conclusion can be drawn on yield value within the buffer zones. But, as the first 6 m of the field is within the competition range of trees and bushes in a hedge, and because weed seed pollution may be a problem within the buffer zones, it may be advisable to regard the yield in a 6 m buffer zone as having low value.