Increasing weed flora in Danish beet, pea and winter barley fields

In Denmark, several political initiatives have been taken to reduce use of pesticides and fertilizer in order to avoid unwanted side effect of the increasing cropping intensification. Based on two nation wide surveys we investigate flora changes and discuss the changes in relation to biodiversity, crop yield, agricultural management and climate. Our assumption is that the surveys are representative for the country. We present frequency analyses of 90 species recorded in 157 fields surveyed in 1987-89, and in 167 fields surveyed in 2001-04. Based on 4910 circular sample plots in unsprayed areas, we studied flora changes in four crops and showed that the frequency of many weed species have increased. Particularly some winter annual species (e.g. Veronica arvensis L. and Viola arvensis Murray), grass weeds (Poa annua L.. Apera spica-venti (L) P. Beauv.) and nitrophileous species (e.g. Capsella bursa-pastoris (L) Medik, Cirsium arvense (L Scop.), Galium aparine L, Fallopia convolvulus (L) A. Lowe, Tripleurospermum inodorum (L) Sch. Bip.) have been favoured. Some weeds have declined in some crops but increased in other crops (e.g. Chenopodiurn album L, Geranium pusillum L), while only a few species declined in one crop without increasing in other crops (e.g. Elytrigia repens (L) Desv. ex Nevski; Sinapis arvensis L). Our data indicate that continuously increasing productivity (increasing yields) seems to be possible simultaneously with enhancing the frequency of the wild flora in arable crops. (C) 2012 Elsevier Ltd. All rights reserved.