Fragmented grasslands on the Baltic Island of Öland. Plant community composition and land-use history

The relationships between properties of present landscapes and species diversity within fragmented grasslands have been the subject of many studies. However the potential roles of grassland history and past landscape structure as determinants of diversity have not been widely studied. We therefore focus on these roles with an overview of patterns of variation in plant community composition in grassland fragments, of known ages, within a 22 km2 site around the village of Jordtorp on the Baltic island of Öland. While the frequencies of individual vascular plant species in 328 50 cm × 50 cm quadrats showed trends related to grassland continuity and previous land use, the dominant gradients of plant community composition were interpreted in terms of gradients of soil moisture and eutrophication. Because relationships between grassland age and plant community composition are confounded by local grassland eutrophication, it is difficult to use the present grassland data set to draw conclusions about the extent to which the distributions of individual species reflect a long history of continuous grassland management or an absence of eutrophication. Our results suggest that studiesthat attempt to explore associations between grassland age and fine-scale species richness, or the occurrence of individual species, should be based on sampling rules that standardize the type of plant community that is to be compared between grassland fragments.