Analysis of weed dispersal to predict chances of re-colonisation

The protection of rare arable weeds and the restoration of biodiversity in agroecosystems have become an important issue in most European countries. Traditional analyses of weed dispersal focussing on the prediction and control of infestations have to be adapted to the new aim of restoration ecology by quantifying chances of re-colonisation within fields and across field borders. This study analyses within-field spread of weeds under usual arable cultivation whereas between-field colonisation usually not aided by machinery was simulated in undisturbed controls. The experiments were conducted on an arable farm in the central German lowlands 6 years after conversion to organic management. The test species, Lithospermum arvense and Silene noctiflora, have declined in recent decades but belong to the characteristic weed community. Dispersal was analysed by recording seedling emergence around patches of introduced mother plants where the species were absent. Negative exponential models provided a good fit of the dispersal curves from the mode outward. In the "arable" treatment, the percentage seedlings - distance regression line fell below 0.5% at 5 m, in the control this level was reached at a distance of about 2 m indicating that long-distance dispersal is a rare event. Cultivation increased the peak distance of the dispersal curves significantly whereas the slope of the curves from the mode outward was hardly affected. Despite different fruit and propagule morphology, seed shadows of both species were very similar. Spatial distribution of the seedlings in the arable treatment occurred along the axis of management and against the prevailing wind direction. The results may help to improve targeting subsidies in agri-environment schemes and assessing the need for re-introduction by sowing. (c) 2004 Elsevier B.V. All rights reserved.