The Baltic Sea region is home to the most species rich plant community in the world: semi-natural grasslands. This imposes a global responsibility on Baltic Sea countries to conserve semi-natural grasslands and their diversity for future generations. However, semi-natural grasslands in the Baltic Sea region are severely fragmented. In fragmented landscapes, species diversity relies upon remnant grassland patches, which harbour remnant grassland species populations. These populations are ever more extinction prone due to local environmental, demographic and genetic bottlenecks, magnified by the loss of spatial seed and gene flow caused by fragmentation.
Seed banks may help plant species survive in fragmented landscapes as they locally disperse species, individuals and genes in time. By including seed banks in conservation and restoration targeting remnant communities, their success can be maximized as seed banks may buffer demographic decline and erosion of genetic diversity in remnant populations, or help re-establish plant species gone locally extinct.
Using the Stockholm (Sweden) and Åbo (Finland) archipelagos as perfectly fragmented systems, we study how seed banks could assure demographic and genetic continuity in remnant populations. Campanula rotundifolia and Hypericum perforatum will serve as model organisms. Both have similar plant traits but differ in a seeds’ ability to remain viable, i.e. seed longevity. This allows extrapolation of the study outcome across species.
We select 4 island landscapes, 2 with and 2 without rotational grazing management between islands. Per landscape, we select 5 islands. Per island we select 1 small and 1 large population per species. This design allows us to investigate whether seed banks are more important to genetic and demographic continuity: 1) in small compared to large populations and 2) when spatial seed and gene flow are impaired. Genetic diversity will be quantified in all above- and belowground populations. A disturbance field experiment will activate the seed bank to see how many individuals, species and genes seed banks infuse into remnant populations and communities. Finally, we investigate the success of grassland restoration in terms of the recovery of genetic diversity in restored grasslands in Sweden, Finland, Estonia and northern Germany. We expect that plant species with higher seed longevity see a swifter seed bank driven recovery of genetic diversity.