The Seed Bank of Hemlock Forests: Implications for Forest Regeneration following Hemlock Decline

Soil seed banks are especially important for forest regeneration in stands with few understory species and individuals. The understory of hemlock (Tsuga canadensis)-dominated stands in New England primarily consists of hemlock seedlings and saplings, but all size classes of hemlock are attacked by the hemlock woolly adelgid (Adelges tsugae). Prior to the initiation of a large-scale manipulative experiment designed to examine the impact of the adelgid on hemlock forest ecology, we documented the seed bank composition of eight large (0.81 ha) experimental hemlock-dominated and young hardwood-dominated plots. The seed bank samples from the hemlock-dominated plots contained significantly fewer species (rarefied species richness = 24; 95% confidence interval = 20-28) than those from the hardwood-dominated plots (species richness = 30). Seed banks from all plots were dominated by Betula lenta, Rubus spp., and Carex pensylvanica. Among plots, there was little compositional relationship between the forest overstory and its understory on the one hand, and its seed bank on the other hand. Because seeds of hemlock and birch persist for only a few years in the seed bank, and because hemlock seedlings are readily attacked and killed by the adelgid, damaged hemlock stands are more likely to be replaced by stands of black birch and other hardwoods than by hemlock.