How long do tree seeds survive in soil seedbanks? A multi-species comparison in an old-growth deciduous temperate forest

We evaluated the performance of tree seeds in the soil seedbank of a temperate deciduous old-growth forest with respect to the total proportion of seeds that emerged as seedlings (PTOTAL) and the average time seeds were in the soil prior to emergence as seedlings (TAVERAGE). We analyzed 12 years of data on the seed dispersal and seedling emergence of 16 important tree species collected from more than 100 seed traps and quadrats. Using these estimates, we assessed whether seed banking is an effective regeneration strategy in forests compared to other life-history strategies. Persistence in the soil did not necessarily increase overall seed mortality. Phylogenetic constraints played a limited role in variations in PTOTAL and TAVERAGE among species, likely due to pronounced differences between closely related species. Estimated values of TAVERAGE were mostly less than 1.5 years. Some species had a PTOTAL greater than 0.20, despite having seeds with no known physical or chemical protection mechanisms. Seed size was not associated with seed performance. By contrast, greater per capita fecundity appeared to compensate for lower performance of banked seeds. Contrary to our expectations, species with longer TAVERAGE values exhibited higher seedling survivorship, implying an absence of trade-offs between seed banking and seedling banking, and even implying a synergy between these strategies. In old-growth forests, seeds stored in soil seedbanks likely provide a buffer during years with little or no seed production; however, seedbanks may not promote adequate regeneration following natural or artificial large-scale disturbances that remove parent trees.