Potential of Tsuga spp. from western North America and Asia as replacements for eastern hemlock (Tsuga canadensis)

Abstract

Hemlock woolly adelgid (Adelges tsugae) has had a devastating impact on Tsuga canadensis and T. caroliniana in forests and managed landscapes in the eastern United States. Species of Tsuga from the western United States and Asia are reported to be tolerant or resistant to A. tsugae. We established plots containing T. canadensis, T. caroliniana, T. chinensis, T. diversifolia, T. heterophylla, T. mertensiana, and T. sieboldii in Katonah, New York, U.S., an area with high populations of A. tsugae, and monitored tree growth and infestation by adelgids over a 4-year period. Growth and survival of the hemlock species varied widely, the most vigorous species being T. canadensis and T. chinensis. Susceptibility to the adelgid also varied widely among species; some species (particularly T. canadensis) became readily infested, whereas others (e.g., T. chinensis) were apparently entirely resistant. Given the ability of T. chinensis to thrive in the climate of southeastern New York State and its apparent resistance to hemlock woolly adelgid, this species might be an appropriate replacement species, especially in managed landscapes. © 2009 International Society of Arboriculture.