Wading Birds Rarer in Conserved Areas
Dutch conservation agreements pay farmers for adopting agricultural practices intended to benefit nature, but a new analysis suggests that they are not working. The agreements are not helping and in some cases may even harm their target species — the diversity of plants and meadow birds has failed to increase, and the numbers of wading birds has actually decreased in fields with conservation agreements.
“It is clear that the scientific basis for the Dutch management agreements is largely missing,” say David Kleijn and Ruben Smit of Wageningen University, The Netherlands, and five coauthors in the June 2004 issue of Conservation Biology.
As agriculture has intensified, biodiversity has declined dramatically in western Europe. Accordingly, European Union countries spent about US$29 billion on conservation agreements between 1992 and 2003. But no one knows whether they really work.
The researchers tested the effectiveness of two kinds of Dutch conservation agreements (botanical agreements and meadow bird agreements) that prohibit changes in drainage and limit fertilizer and herbicide use. Meadow bird agreements also prohibit disturbing fields during the breeding season. The researchers compared plant diversity in 22 pairs of fields with and without botanical management agreements, and they compared bird diversity in 23 pairs of fields with and without meadow bird agreements.
The results showed that these two kinds of conservation agreements failed to increase biodiversity. For example, fields with botanical agreements did not have more plant species than those without agreements. And fields with meadow bird agreements did not have more of the target species than those without agreements.
Worse, fields with meadow bird agreements had about 40 percent fewer wading birds than those without agreements. The researchers suspect that waders may avoid fields with conservation agreements because they receive less fertilizer and so have fewer earthworms to eat. “Our results reveal an important weakness of management agreements aimed at promoting waders,” say the researchers.
This could help explain why threatened wading birds are still declining in The Netherlands. For example, the black-tailed godwit population keeps dropping, even though conservation agreements cover much of its best remaining habitat. About half of Europe’s black-tailed godwits (Limosa limosa) breed in The Netherlands, which historically has a great diversity of meadow birds and grassland plants.
The problem may be that the conservation agreements are not addressing the underlying reason for biodi-versity loss, say the researchers. Meadow bird and grassland diversity depend largely on the country’s historically high groundwater levels. However, groundwater levels are now kept low so that farmers can use their fields early in the spring. Although this gives them a longer growing season, it also makes the soil dry out faster and so decreases the population of worms and other soil-dwelling prey available to wading birds. “Conservation measures that require little adaptation of the farming system… are not likely to yield positive effects in intensively used agricultural landscapes,” say the researchers.
Kleijn, D. et al. 2004. Ecological effectiveness of agri-environment schemes in different agricultural landscapes in The Netherlands. Conservation Biology 18(3):775-786.
Photo: Black-tailed godwit (Limosa limosa) ©Richard Ford digitalwildlife.co.uk