New Harvard Forest Publication: Understory Vegetation in Old and Second Growth Hemlock Forests

Former REU (2000) and Ph.D. student (2007) Tony D'Amato along with HF ecologists David Orwig and David Foster recently compared the understory communities (herbs, shrubs, and tree seedlings and saplings) of old-growth and second-growth eastern hemlock forests (Tsuga canadensis) in western Massachusetts, USA. Second-growth hemlock forests originated following clearcut logging in the late 1800s and were 108 to 136 years old at the time of sampling. Old-growth hemlock forests contained total ground cover of herbaceous and shrub species that was approximately 4 times greater than in second growth forests (4.02 ± 0.41 versus 1.06 ± 0.47 %m2 ) and supported greater overall species richness and diversity. In addition, seedling and sapling densities were greater in old-growth stands compared to second-growth stands and the composition of these layers was positively correlated with overstory species composition (Mantel tests, r > 0.26, P < 0.05) highlighting the strong positive neighborhood effects in these systems. Ordination of study site understory species composition identified a strong gradient in community composition from second-growth to old-growth stands, related to differences in overstory tree density, nitrogen availability, and coarse woody debris characteristics among hemlock stands. These relationships suggests that differences in resource availability (e.g., light, moisture, and nutrients) and microhabitat heterogeneity between old-growth and second-growth stands were likely driving these compositional patterns. Interestingly, several common forest understory plants, including Aralia nudicaulis, Dryopteris intermedia, and Viburnum alnifolia, were significant indicator species for old-growth hemlock stands, highlighting the lasting legacy of past land use on the reestablishment and growth of these common species within second-growth areas.

D'Amato, A.W., D. A. Orwig, D. R. Foster. 2009. Understory vegetation in old-growth and second-growth Tsuga canadensis forests in western Massachusetts. Forest Ecology and Management 257: 1043–1052.