The agri-environmental schemes to improve biodiversity in Dutch agricultural landscapes are not effective. A profound study which compares fields with management agreements with common managed fields, finds no positive effects on plant and bird species diversity. Meadow birds like the Lapwing, Oystercatcher, Common Redshank and Black-tailed Godwit – four main target species of management agreements – are even less common in grassland with agri-environmental schemes. Hover flies and bees show modest increases in these fields. These are the main results of a field study conducted by Dr. David Kleijn and Professor Frank Berendse of the Nature Management and Plant Ecology Group of Wageningen University, which will be published in Nature of October 18th. The results indicate there is pressing need for a scientifically sound evaluation of agri-environmental schemes.
Agri-environment schemes are very popular and are commonly accepted to counteract the negative impacts of modern agriculture on the environment. The European Union spends 1.7 Billion Euro (4% of the total expenditure on the Common Agricultural Policy) and the expenditures are expected to rise tot 10% in the near future. Most Dutch management agreements restrict the use of fertiliser of postpones the first mowing or grazing date, to support wader populations and plant diversity. The Netherlands has been implementing this type of schemes since 1981, which is considerably longer than comparable EU-based measures. Kleijn and Berendse surveyed plants, birds, hover flies and bees on 78 paired fields that either had agri-environmental schemes or were managed conventionally. The Dutch Stimulation Programme Biodiversity funded the work.
Management agreements designed to enhance the botanical diversity of entire fields or field edges did not have any positive effect on plant species richness. Plant diversity in agriculturally used Dutch grasslands is a marginal matter indeed. On average, edges accounted for 96% of a field’s total species richness and 66% of all encountered species were never found in the field centre. Despite the considerable reduction in fertiliser inputs, the current level may still be too high and seed sources to scarce to promote the development of more species-rich vegetation. Surprisingly, fields with management agreements that aimed to support wader populations by postponing first farming activities had lower counts of the target species Lapwing, Oystercatcher, Common Redshank and Black-tailed Godwit. Kleijn and Berendse think the reduced fertiliser inputs probably adversely affected the abundance of the soil animals (e.g. earthworms) that waders use for food.
Management agreements do have a positive effect on the reproductive success of meadow birds, but this does not result selecting their nesting habitat in these fields. Only the starling, an extremely common bird of all lowland habitats including major cities, preferred to forage on fields with management agreements. Species richness of hover flies is also higher on fields with management agreements, especially in the month May. Bees also benefit of agri-ecological schemes, although the bee fauna in Dutch agricultural landscapes remains poor (3 species: the honeybee and two bumblebees).
The results point out that the current management prescriptions are not very effective. Farmers’ motivation and expertise may play a crucial role. Nature conservation will be of secondary importance, and most farmers lack the knowledge in what way economically inevitable measures (e.g. grass silaging, lowering of ground water table) may interfere with nature conservation measures. Kleijn and Berendse advice European countries to make sure agri-environmental schemes are accompanied by scientifically sound evaluation plans.