Comparison of seed bank composition over a gradient of pyrophilic vegetation

Seed bank compositions provide a record of past disturbances, the legacies of which may last thousands of years. Our goal was to determine if sites defined historically by fire-related (pyrophilic) tree species have seed bank compositions different from sites defined historically by pyrophobic tree species. We selected three 80+ year-old forested sites within the Monongahela National Forest, West Virginia, to represent three pyrophilic zones based on percent-pyrophilic-witness tree cover: Low (0-10%), Medium (40-50%), and High (80-90%). Soil plugs were collected to evaluate the seed bank and determine soil nutrients and charcoal abundance; cover of all understory plants was also estimated. The results, supported by the charcoal analyses, show significant differences between extant and seed bank vegetation, pyrophilic zones, and pyrophilic zones within each vegetation lifeform (extant vs. seed bank). The High zone seed bank had the greatest species richness, the most pyrophilic species, and differed the most from its extant vegetation, but was the least dense of all zones and a pyrophobic species ranked among its top five indicator species. These findings indicate mesophication and a depletion of pyrophilic species in the seed bank. The High site appears to be reaching a potential threshold where passive recovery to fire-adapted conditions may be unlikely.