Disjunct eastern hemlock (Tsuga canadensis) stands at its southern range boundary1

Abstract

Hart, J. L. and D. Shankman (Department of Geography, University of Alabama, Box 870322, Tuscaloosa, AL 35487). Disjunct eastern hemlock (Tsuga canadensis) stands at its southern range boundary. J. Torrey Bot. Soc. 132: 602–612. 2005.—Eastern hemlock (Tsuga canadensis) occurs throughout much of the Appalachian Mountains, extending from southern Quebec and Ontario southward to Georgia and along the Appalachian Plateau to Alabama. Eastern hemlock is one of the most dominant trees in Appalachian forests. Near its southern boundary in central Alabama, eastern hemlock occurs in small, isolated populations restricted to cool, moist slopes with north to east aspects and low and middle slope positions. Ten stands of eastern hemlock, believed to be the southernmost populations, were studied in order to determine reproductive viability and habitat characteristics. In each of the stands, eastern hemlock dominates the canopy and is present in a wide range of size and age classes. Eastern hemlock is most abundant in seedling size classes and the number of individuals generally decreases with increasing size. Population size, age, and vertical structure indicate that eastern hemlock stands at the species' southernmost boundary contain viable populations that are regenerating, even if highly localized. During the late Pleistocene and early Holocene, eastern hemlock likely had a broader distribution in the southern Appalachian Mountains. The remnants of this larger distribution are now restricted to steep slopes where a combination of sandstone outcrops, seepage, and springs maintain adequate microclimatic conditions needed for regeneration of the species.