Diversity of butterflies in the agricultural landscape: the role of farming system and landscape heterogeneity

To examine the importance of management practices and landscape structure on diversity of butterflies 16 farms with organic or conventional management were censused during 1997 and 1998. On each farm a transect route was walked during July and the beginning of August, six times in 1997 and five times in 1998. The farms were located in the central part of Sweden in two adjacent regions with the same pool of species. The organic and conventional Farms were paired with help of the Bray-Curtis dissimilarity index according to land use to control for landscape structure on the farm level. On each Farm calculations were made of large- and small-scale landscape heterogeneity with the help of GIS. A grid with a mesh size of 400 m was placed over each farm and the small-scale heterogeneity was calculated as the mean habitat diversity of four squares. The large-scale landscape heterogeneity described the landscape in which the farms were imbedded, and covered an area of 5 x 5 km. No differences in butterfly diversity, number of species or number of observations were noted between organic and conventional farms. Butterfly diversity was positively correlated with small-scale landscape heterogeneity while butterfly abundance was positively correlated with large-scale heterogeneity. Both large-scale and small-scale heterogeneity were important For the composition of species. The landscape structure seemed to be more important for butterfly diversity and species composition than the farming system in itself.