Structural and compositional change in an old-growth eastern hemlock Tsuga canadensis forest, 1965–2004

Eastern hemlock (Tsuga canadensis; hereafter hemlock) was once relatively common in the northeastern United States. However, recent disturbances – including exotic pests and white-tailed deer overpopulation – have exacerbated declines in hemlock forest in the 20th century. As a previously undisturbed stand, the Mianus River Gorge Preserve (MRGP) provided an ideal site to investigate the potential impact of these factors on the structure and composition of old-growth hemlock forests. The woody vegetation of this forest was first surveyed in 1965 and then again in 2004. The overstory tree community was similar between the two time periods with hemlock dominant in both samples. Conversely, seedlings, saplings, and transgressives exhibited sharp declines in most species, including hemlock, which resulted in dissimilar community composition and structure for these age classes between 1965 and 2004. Despite relative continuity in the dominance of mature hemlocks, low recruitment due to overbrowsing makes the long-term persistence of hemlock in the old-growth forest of MRGP tenuous.