The effect of land use diversity and spatial heterogeneity on farmland birds in Norway
The decline in farmland bird populations observed throughout Europe during the last decades has attracted much attention. These trends are often related to agricultural intensification or land abandonment. Several countries have established agri-environmental schemes (AES) to stimulate farmers to implement measures to counter the observed negative trends among farmland birds. In recent years, however, it has been questioned whether these measures and subsidies functions as intended. We argue that before devising management plans that are efficient to conserve farmland birds there is need for a detailed land use assessment. In this study we investigated the relationship between land use spatial heterogeneity, land use diversity and species richness and abundance of farmland birds. Monitoring the distribution and abundance of birds is part of the Norwegian monitoring program for the agricultural landscape. The monitoring program is based on maps of 1 x 1 km squares distributed across the agricultural landscape where the land use classification is the result of detailed interpretation of aerial photographs. The data were used to calculate measures of diversity and spatial heterogeneity of land use. Within 120 monitoring squares permanent observation points were established for recordings of breeding birds.
There was a clear and positive relationship between species richness and abundance of farmland birds and the amount of agricultural area. However, land use spatial heterogeneity was significant for both farmland birds as well as non-farmland birds, suggesting that heterogeneity is important for bird species in general. We also found a negative relationship between land use diversity and bird species richness and abundance. The effect of landscape characteristics such as unmanaged grassland or uncropped land and field size had no detectable effect on species richness of farmland birds. Our findings highlight the importance of a complex landscape for species richness and abundance of farmland birds. However, we also show that potential management effects of landscape elements depend on the landscape context. Our results suggest that there is a need for landscape analyses before proper management strategies are implemented. In order to develop effective management plans the requirements for acceptable measures as part of AES-programs cannot be to general but adapted to regional and local landscape conditions.