Authors: Cousins, Sara; Plue, Jan;

Ancient grasslands have some of the highest plant species richness in Europe. A long continuity of management and spatial connectivity is a prerequisite for the high species richness we can find there today. But at the same time, grasslands are threatened by habitat change and fragmentation. In three different research projects we analysed genetic diversity of Campanula rotundifolia or Galium verum to understand how habitat fragmentation have influenced the species, as indicators for community diversity. We used historical maps and aerial photographs from 36 landscapes in Europe, 48 in Sweden and several islands in the Stockholm archipelago to investigate grassland change over time. We found that grazing networks imprinted strong landscape-scale spatial patterning in pairwise population genetic differentiation and within-population genetic diversity of C. rotundifolia. In landscapes where ancient grasslands have disappeared landscape heterogeneity becomes more important to sustain large-scale populations and thus genetic diversity of C. rotundifolia. We found that the green infrastructure in the surrounding landscape were a genetic subset of the focal grassland populations of G. verum. Particularly a network of road verges supported gene flow from grasslands into the surrounding landscape. Our work highlights the importance of protecting ancient grasslands as they contain unique genetic diversity.