Decline of the flora in Danish arable fields.
Surveys of the weed flora in Danish arable fields were conducted during 1967-70 and 1987-89. Frequencies of 67 common weed species in spring barley, spring rape, winter rye, winter wheat and grass ley were compared. The comparison showed that the occurrence of common weed species has generally decreased during the last 20 years. The frequency of some species such as Anagallis arvensis, Arenaria serpyllifolia, Atriplex patula, Cerastium caespitosum [C. fontanum], Galium aparine, Plantago major and Silene noctiflora has decreased markedly, possibly because of intensive chemical weed control. The dominating weed species in the 1987-89 survey were largely the same as in the 1967-70 survey, namely Capsella bursa-pastoris, Chenopodium album, Elymus repens, Myosotis arvensis, Poa annua, Polygonum aviculare, P. convolvulus [Fallopia convolvulus], P. persicaria, Stellaria media, Taraxacum, Veronica arvensis, V. persica and Viola arvensis. Some species occurred more frequently in 1987-89 than in 1967-70, but only Stellaria media increased significantly and only in grass ley.