Loss of biodiversity and its social cost in an agricultural landscape

Changes at the landscape level in a 100 ha area of southern Finland, have led to homogenization over the period 1954–1997, as measured by Shannon’s diversity index (SHDI) and Shannon’s evenness index (SHEI). Patch numbers (N), class areas (CA), and total edge lengths (TE) of ditch margins decreased markedly due to subsurface drainage. Woodland patches also decreased, as some of them were brought under cultivation, but increased in 1997 due to the demolishing of barns. An assessment of the social costs and benefits of subsurface drainage shows that it is not desirable to replace the few ditch margins that remain in the case area with subsurface drains. The management of field margins, buffer strips along waterways and woodland patches are included in the Finnish agri-environmental programme, but their importance for management of biodiversity in the agricultural landscape should be emphasized. The paper analyses landscape diversity loss at landscape and patch levels, and describes the roles of woodland patches and field margins in an agricultural landscape.