How important are small remnant habitats for biodiversity in the agricultural landscape?

Sammanfattning: The consequences of the agricultural intensification are many and include fragmentation of natural habitats, abandonment of small farms and traditional management, and increased inputs of pesticides and fertilizers. It has also lead to widespread declines in semi-natural grasslands and farmland biodiversity. Small remnant habitats such as midfield islets and road verges can harbour many species and hence be important in biodiversity conservation. This study investigated how plant species richness and richness of grassland specialists differ in three agricultural landscapes: one open landscape with crop fields, one with a lot of forest and one landscape with a mix of forests and fields. Field studies included plant inventories in the small remnant habitats. Species-area relationships, accumulated species curves and Jaccard similarity index were used to analyze the data, where total species richness and grassland specialists were analysed separately. It was found that the two landscapes with the most forest had higher species richness in midfield islets, but not in road verges, and that the intermediate landscape had the strongest species-area relationship. Species accumulation curves show the fastest species accumulation rate for midfield islets in the forest landscape and for road verges in the open landscape. The remnant habitats in the forest and intermediate landscapes were most similar to the semi-natural grassland in that landscape. The connectivity of the landscape, as well as the presence of semi-natural grasslands may help to explain the results. This study shows that small remnant habitats could be important for biodiversity conservation in agricultural landscapes and that managing the landscape in a way that preserves heterogeneity may be crucial for its continued species richness.