New Harvard Forest Publication: Hemlock Seed Banks and Regeneration

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 the Hemlock Removal Experiment at the Simes Tract, Harvard Extension student Kelley Sullivan (M.L.S. 2005) and Harvard Senior Ecologist Aaron Ellison examined the seed bank composition of all eight 0.81 ha experimental plots. The seed bank samples from the hemlock-dominated plots contained 24 species (95% confidence interval = 20-28), significantly fewer than the 30 found in the hardwood-dominated plots. Seed banks from all plots were dominated by black birch, raspberry, and sedges 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.

Sullivan, K.A., and A.M. Ellison. 2006. The seed bank of hemlock forests: implications for forest regeneration following hemlock decline. Journal of the Torrey Botanical Society 133: 393-402.