Temporal dispersal in fragmented landscapes

Abstract

Despite a good understanding on how dispersal in space structures plant communities in fragmented landscapes, we know little about dispersal in time. Empirical evidence on temporal dispersal – the soil seed bank – is lacking, with only trait-based evidence on the seed banks’ importance for species persistence in fragmented landscapes. Therefore, seed banks of remnant grassland fragments were analyzed in how they changed compared to semi-natural grasslands following fragmentation. We studied the historical trajectories in time since fragmentation, fragment size and habitat quality of 134 grassland plots, linking these to their seed bank and plant community to understand how seed banks temporally connect grassland fragments, potentially conserving the flora of historically large semi-natural grasslands. Seed-banking grassland species were present in similar proportions in all remnant grassland fragments. The seed bank composition changed with time since fragmentation started, triggered by the deterministic loss of grassland species, generating nested subsets of the seed banks of semi-natural grasslands. The spatial heterogeneity in seed bank composition among grassland fragments limited the loss of grassland species at the landscape scale. The seed bank became an increasingly important constituent of total plant diversity with time since fragmentation started, as grassland species stored an increasingly larger proportion of their local diversity in the seed bank. Temporal dispersal enables the prolonged presence and persistence of numerous typical grassland species in fragmented landscapes. The seed banks’ storage effect of plant diversity is of considerable significance to efforts aimed at conserving and restoring plant diversity in fragmented landscapes.