The effects of litter accumulation through succession on seed bank formation for small- and large-seeded species

Questions How does litter accumulation through succession affect secondary seed dispersal and buried seed viability and consequently control seed bank formation for small- and large-seeded species? Location A post-mined peatland in northern Japan (45°06′ N, 141°42′ E) where the chronological sequence of plant community succession is known. Methods The movements of seeds after reaching the ground surface and the availability of viable seeds potentially contributing to seed bank formation at various depths were experimentally investigated for 1 yr in four species that produce different-sized seeds: Drosera rotundifolia (seed mass 0.01 mg), Lobelia sessilifolia (0.25 mg), Rhynchospora alba (0.87 mg) and Moliniopsis japonica (1.82 mg). The experiments were conducted in three successional stages with 0-, 4- and 9-cm thick litter layers. Results Seed emigration decreased and seed retention increased with an increase in litter thickness. Large seeds were retained within the litter throughout the experimental period, and fewer seeds were buried in peat compared to small seeds trapped by thick litter, which had shifted downward by the following early spring. Litter contributed to increasing the number of viable and ungerminated seeds. The number of viable seeds for all species was nearly zero on the bare peat surface. The numbers of viable seeds on and beneath the peat surface increased with increases in litter cover thickness. Conclusions The patterns of secondary seed dispersal and the availability of viable seeds were altered by litter accumulation through the progress of succession. Moreover, the effects of litter on seeds varied among species for which seed size differed. Overall, our results suggest that temporal changes in litter thickness through the progress of succession can play an important role in seed bank formation, which has potential impacts on the long-term dynamics of plant populations and the whole community.