COS 123-3 - High-intensity disturbances provide a critical window for seed bank replenishment

Abstract: Soil seed banks facilitate long-term survival and coexistence of plant species in ecosystems worldwide. However, forest seed banks, particularly those in temperate forests, are undervalued because of apparently low similarity between the seed bank and aboveground plant community. Additionally, ecological processes regulating soil seed banks in forests are understudied, with most papers focusing on single sites without any inclusion of possible dynamic drivers of seed bank replenishment and composition. Here, we:

A) experimentally evaluate the contribution of the seed bank to recovery from interacting natural and anthropogenic disturbance.

B) examine how disturbance and herbivory regulate seed bank replenishment.

We collected 1,352 samples (137,009 cm³) of soil from intact forest and paired salvage-logged and unsalvaged areas of four tornado blowdowns (top 1% sheer volume of soil ever collected in a seed bank study). To test the effects of deer herbivory on the seed bank, half of the disturbance plots where we collected soil were protected from deer browsing. We used bulk reduction and emergence methods to quantify the species richness and seed density of the seed bank within each treatment. Comparisons to the aboveground community were performed with data previously collected by Spicer et al. in 2017.

Using a space-for-time substitution, we observed that the undisturbed seed bank could have contributed >35% of the species present aboveground in the disturbance matrix. Seed bank composition overall was most similar to the post-salvaging plant community. However, a further 62% of the species aboveground are known seed banking species, suggesting they contributed to aboveground diversity here, but are either extremely rare in the seed bank or fluctuate seasonally. Additionally, the seed bank contained 22 species not found aboveground, including four species that were new to Powdermill Nature Reserve.

We expected that the natural and anthropogenic disturbances would facilitate seed bank replenishment, but that deer would reduce seed production and inhibit seed bank replenishment. While deer created small compositional changes, they did not reduce overall species richness or density of the seed bank. Salvage logging increased seed bank species richness (+5 species/plot) and density (+20 seeds/plot) relative to the intact forest. Surprisingly, wind disturbance alone reduced the seed bank density and richness, likely because seeds germinated from the seed bank but were quickly shaded out by advance regeneration and did not survive to reproduce. Thus, not only did the seed bank facilitate recovery from disturbance, but the higher-intensity anthropogenic disturbance facilitated seed bank replenishment.