THE DISTRIBUTION OF DICOTYLEDONOUS ARABLE WEEDS IN RELATION TO DISTANCE FROM THE FIELD EDGE

1. Three surveys were carried out in cereal crops during 1988 and 1989 . In the first, numbers of dicotyledonous weed seedlings and seeds in the seed-bank were determined at 10 distances from the crop edge. In t he second and third, only the numbers of seedlings were counted. 2. In the first survey of spring cereals, numbers of seedlings of 13 specie s and numbers of seeds of 11 species decreased significantly as distan ce from the crop edge increased. Viola arvensis was the only species f or which numbers increased. 3. The proportions of the seed-bank repres ented by the germinated seedlings of 21 species varied from 0.4% (Sonc hus spp.) to 55% (Fumaria spp.). The half-life of the seed-bank was hi ghly variable between species. 4. In the second survey of spring cerea ls, numbers of seedlings of 17 species decreased significantly as dist ance from the crop edge increased. Polygonum aviculare was the only sp ecies whose numbers increased. 5. In the survey of autumn-sown cereals , numbers of seedlings of 14 species decreased significantly as distan ce from the crop edge increased. Viola arvensis was the only species w hose numbers increased. 6. These distributions have implications for t he conservation of endangered weed species.