By: Jacqueline Loos, Ine Dorresteijn, Jan Hanspach, Pascal Fust, Laszlo Rakosy and Joern Fischer. Plos One 9(7): e103256.
European farmland biodiversity is declining due to land use changes, often involving agricultural intensification (mainly where the land is flat and easily accessible) or abandonment (mainly in rural areas rich in contours). Some Eastern European farming systems have sustained traditional forms of land use, resulting in high levels of biodiversity. However, under the influence of global markets and international policies, these systems are now subject to rapid and major changes. To effectively protect farmland biodiversity, it is important to understand which landscape features underpin species diversity.
In our recently published study, we focused on butterfly diversity patterns in response to landscape variables across a cultural-historic landscape in Southern Transylvania, Romania. In order to follow the notion of a natural experiment, we cross-stratified the landscape according to three categories, two of them representing gradients that are likely to change during a process of land use change- the amount of woody vegetation across the landscape and heterogeneity. We measured heterogeneity by the standard deviation of 2.5 m panchromatic SPOT satellite imagery, which we calculated within one hectare circles across the landscape. The third category represented the protection status, and in SCI, SPA and unprotected sites we made sure to cover an equal amount of study sites.We randomly selected 120 survey sites in farmland, 60 each in grassland and arable land. We applied standard butterfly transects to survey abundance and species richness, and repeated the surveys with a regular distance of three weeks at four occasions during summer 2012. We analysed species composition by Detrended Correspondence Analysis. We modelled total species richness, richness of functional groups, and the abundance of selected individual species in response to topography, woody vegetation cover and heterogeneity at three different spatial scales, using generalised linear mixed effects models. Another step in our survey was to predict distribution patterns of butterfly species richness across the agricultural areas of our study region.
In total, we counted 19,878 individuals of 112 species of butterflies. In a nutshell, we found that species richness was widely distributed throughout the entire landscape, which is formed by a mosaic of different land use patches. Surprisingly, we found a wide overlap in species composition in grassland and arable land. The main gradients along which composition changed were heterogeneity at the local and the context scale, woody vegetation cover at context and landscape scales. Furthermore, the species richness in arable land and grassland did not differ significantly. We found a positive effect of local heterogeneity on butterfly species richness in arable land, but a negative effect in grassland. Other variables that explained patterns of total species richness, richness of functional groups and individual species abundances included plant species richness, but also structural and topographic conditions at multiple scales.
Hence, our study revealed high conservation value of both grassland and arable land in extensive Eastern European farmland. Not only grassland, but also extensive, heterogeneous arable land provides important habitat for butterflies. While butterfly diversity in arable land benefits from the heterogeneity provided by small-scale structures, grasslands should be protected from fragmentation to provide sufficiently large areas for butterflies. Conservation management in extensive European farmland systems needs to consider entire landscapes, and implement appropriate measures at multiple spatial scales.