The effects of organic and integrated farming on rare arable weeds on the Forschungsverbund Agrarokosysteme Munchen (FAM) research station in southern Bavaria

Since the compensation for unsprayed field margin strips was recently reduced in Germany, the area used in this way has rapidly declined. These experiences show that management restrictions for the sake of species conservation are only accepted when high compensation is paid and efficiency is regularly controlled. The aim of the present investigation was to determine if conservation of arable weeds could be reached by management systems without imposing such restrictions; Therefore, 110 ha farmland, situated in the Tertiarhugelland in southern Bavaria, was investigated to compare the effects of a change from conventional farming to an organic and an integrated cultivation system. Four years after the change to the integrated farming system, the number of rare species had decreased at 90% of all sampling points where they occurred. This development seems mainly to be caused by minimum tillage, which was applied to prevent soil erosion. In the organic management area, rare weed species were observed at 94 grid points. At 33% of them weeds decreased, at 41% they remained unaffected, and at 26% weeds increased in number. Among the species occurring often enough for a statistical analysis, four did not change significantly, while Legousia speculum-veneris was found more frequently. Investigations in the population development at selected points showed a differing response of individual species to these management changes. Nevertheless, frequencies as well as densities of the rare weeds stayed constant within the fields under organic management. This and the respective literature lead to the conclusion that the influence exerted on rare weed species by the organic cultivation system is neutral to positive. Thus, organic management could be at least a way to prevent further decline in rare weeds. (C) 1998 Elsevier Science Ltd. All rights reserved.