Value of semi-natural areas as biodiversity indicators in agricultural landscapes

Semi-natural habitats are key elements between cultivated and natural areas. Ditch boundaries, buffer zones, barn areas and woodland patches were analyzed in Toholampi, Yläne, Nurmijärvi and Liperi localities in Finland over the period 1954–1998 by means of indicators for semi-natural areas, based on calculations of the sum of patch densities (PDsum) and the sum of patch areas (CAsum). There were only a few semi-natural habitats left by the late 1990s. The sharpest decrease in PDsum indicator values, by 90%, was found for Yläne, while the corresponding drops in the figures for Nurmijärvi, Toholampi and Liperi were 77, 65 and 59%, respectively. The CAsum indicator showed a similar trend. The indicators were tested by calculating the metapopulation capacity of the barn areas. The use of CAsum is suggested for semi-natural patches as a quick, cheap and robust monitoring tool and indicator of change in biodiversity value in agricultural landscapes. The indicator PDsum may be important to interpret landscape and habitat changes when attention needs to be paid to the mosaic of landscape elements.