Standing vegetation as a coarse biotic filter for seed bank dynamics: Effects of gap creation on seed inputs and outputs in a native grassland

Questions Small-scale disturbances have been linked to the maintenance of plant diversity by promoting the coexistence of competitive and subdominant species. Many proposed mechanisms for this coexistence involve changes to the competitive dynamics or abiotic environment. However, another possible mechanism could be a change to seed bank dynamics, ultimately impacting the species available for re-establishment. Here, we test: (a) how gap creation alters seed bank composition, seed inputs (i.e. seed rain) and outputs (i.e. seedling establishment and predation); and (b) whether these changes are due to total vegetation removal or an indirect consequence of the removal of particularly influential species or traits. Location Rough fescue grassland in Alberta, Canada. Methods To test the impact of gap creation on seed bank dynamics, we experimentally removed or kept the standing vegetation intact in a paired-plot design. Within each pair, we combined field sampling with greenhouse emergence studies to measure seed bank composition throughout the growing season. To examine inputs, we added seed trays that collected seed rain, and to examine outputs, we measured germination in seed trays with or without seed predation. Results Seed bank composition within gaps was significantly different from the original standing vegetation before removal and the seed bank where standing vegetation was kept intact. Gap creation increased net seed rain and seedling establishment but had no impact on seed predation. These effects of gap creation on seed outputs seem to be reliant on the total removal of vegetation, while seed inputs are also dependent on the community and trait composition of the standing vegetation. Conclusions The creation of gaps through small-scale disturbances leading to a distinct seed bank community is another possible explanation for why we see increased beta-diversity with disturbance. Further, these gaps seem to be more important than standing vegetation compositional changes for preserving the local seed bank and promoting coexistence.