Plant species richness in midfield islets and road verges - The effect of landscape fragmentation

Small marginal habitats in the rural landscape may play an important role for plant species richness as refugias. Little is known how the surrounding landscape and landscape history influence these patterns. I analysed how plant species richness was affected by isolation, habitat area, past and present land use, and if landscape context matters. Plant species occurrence in two different types of small marginal habitats were analysed, road verges and midfield islets. The study was conducted in two different agricultural landscapes in Sweden; one open modern agricultural landscape and one traditional rural landscape, and the results compared. Present and past land use, and landscape change was analysed using aerial photographs and old maps. There was a large grassland reduction more than 50 years ago in the modern landscape, when there still were quite a lot of grasslands left in the traditional landscape. Area and connectivity were more important for plant incidence in small remnant habitats in the modern landscape, compared to the less fragmented, traditional rural landscape. On the other hand there were more grassland specialists, 23% in the traditional landscape compared to 16%. Species richness became higher on midfield islet if grazing was re-introduced. The legacy of surrounding landscape remains in the species pool for a long time, atleast 50 years, even in small grassland fragments. Although small grassland remnants are more sensitive to fragmentation effects compared to larger grasslands, they still encompass a substantial part of the grassland species pool and may be valuable for reconstructing grassland management at a landscape scale.