THE IMPACTS OF SURROUNDING MEADOWS AND WO ODS ON ARABLE WEED COMMUNITIES AND THEIR PHENOLOGY UNDER CONVENTIONALLY BIOLOGICALLY FARMING CONDITIONS/

In 1989, we investigated the arable weed vegetation on conventionally and organically farmed bur. otherwise fully comparable barley fields a nd their connecting meadow and wood habitats near lake Ammersee (Upper Bavaria). Special attention was paid to species diversity, weed cover age, distribution, and phenology on inner and outer field edges. Organ ic farming led to fairly higher degrees of species diversity, to a nat ural development of weed cover degrees during the growing season due t o being cut during harvest time only, not affected by occasional herbi cide impacts, and to intensively fructifying weeds. Weeds found on the conventionally farmed field mostly occurred in surrounding habitats, too; while 35 of 46 weed species growing in the organically farmed fie ld were restricted to the field itself. From among the surrounding hab itats, only an extensively used meadow with newly planted small trees and bushes was found to be a refugium for arable weed species. Fructif ication on this area of only 0.5 ha had double the generative reproduc tion success of the neighbouring 6 ha conventionally farmed barley fie ld. Local weed distributions were used to differentiate between ecolog ical weed groups prefering field, fallow strip, meadow wood habitats, and the ecotones between. Weed fructification on the conventionally fa rmed field mostly could be completed only at field edges where the bar ley suffered from failing fertilizers more than arable weeds did from herbicide impacts. Strips adjacent to fields or weedy and grassy edges of hedges and small woods should be mowed irregularly, both to promot e annual arable weed species, which prefer low and sparse vegetation d uring the year, but also to enable fructification of perennial species in another.