Weed colonization of experimental gaps in the canopy of a wheat crop

Abstract

Gaps of different sizes were opened in the canopy of a wheat crop by removing all above ground vegetation in August and October. Half of the gaps opened in August were reopened in October. Composition of the weed community and abundance of individual species were measured in September and in November just before crop harvest. In September there were very little differences between treatments, and in November the most important differences were due to time of gap opening but not between gaps of different sizes. Most weed species are synchronous with the crop and are well adapted to coexist with it, so there is a marked negative effect of late opening of gaps on most of them. Gaps have a positive effect on weeds asynchronous with the crop and perhaps on rarities, i.e. species which are neither constant nor abundant.