Professor University of Minnesota, Minnesota, United States
Understory fires, canopy gaps, and low deer populations were historically important disturbances that co-maintained forest plant communities throughout the eastern United States. Over the last century plant diversity in these forests has changed, as fires were suppressed, large canopy gaps became less prevalent, and deer populations exploded. However, soil seed banks may be a key reservoir to restore historic forest biodiversity, as this layer of the forest can hold viable seeds for hundreds of years and could allow for lost species to re-establish with the reintroduction of historic disturbances. We investigated whether seed banks respond to the restoration of multiple, historic disturbances using a long-term experiment in central West Virginia that factorially manipulates low-intensity fire, canopy gaps, and deer browsing. Thirteen years after the initiation of the fire/deer/gap experiment, we collected soil from each disturbance treatment combination, germinated the soil’s seeds during a greenhouse emergence trial, and identified germinants to species.
Over 3,600 seedlings representing 57 different taxa were counted in our emergence trials. We found that understory fire increased mean seed species richness by 20% (p < 0.05) and mean seed abundance by 91% in comparison to unburned plots (p < 0.05). Canopy gaps also increased seed abundance by 53% in comparison to closed canopy treatments (p < 0.01), but did not influence species richness or Shannon diversity. Excluding deer decreased mean seed Shannon diversity (p < 0.05). In comparison to untreated controls, combined fire and canopy gap treatments increased mean species richness by 28% (p < 0.05) and synergistically increased seed abundance by 162% (p < 0.01). Combined fencing and canopy gaps also increased seed abundance by 81% (p < 0.001). Only the combination of fire and deer presence lead to a slight increase in Shannon diversity (p = 0.09). Our results confirm that disturbances can interactively change a seed bank’s long-term diversity and density, and that the response of the seed bank is contingent on specific combinations of disturbances. Our findings may be an important consideration for managers who are employing multiple historic disturbances to restore biodiversity and are depending on seed banks to meet their goals.