Impacts of Hemlock Decline and Ecological Considerations for Hemlock Stand Restoration Following Hemlock Woolly Adelgid Outbreaks

摘要

We present a synthesis of current knowledge and information of hemlock woolly adelgid (HWA, Adelges tsugae Annand) impact on hemlock forests and a conceptual framework of restoring damaged hemlock stands by HWA infestation. Native to Asia, HWA has been thriving in the eastern United States since the early 1950s and has become a serious pathological agent of both eastern hemlock (Tsuga canadensis (L.) Carriere) and Carolina hemlock (Tsuga caroliniana Engelm.) even since. By 2007, it was established inportions of 16 States from Maine to Georgia, where infestations covered about half of the range of hemlock and continuously spreading. The impacts of HWA induced hemlock mortality and decline on key ecosystem resource and processes are still not fully understood. Successful and effective restoration of the declined hemlock population is challenging and involves a complex process that commonly spans many years. Development of a management and restoration strategy that will establish priorities, standards, and practices could facilitate objective decisions and allocation of limited resources. In addition to encourage natural regeneration of hemlock in the damaged forest stands and both chemical and biological control, three strategies seem to stand outas possibilities: growing off-site stocks of hemlock seedlings for replant, creating hybrid hemlocks that are resistant to HWA, and replanting with the already resistant western hemlock or Chinese hemlock. Other ecological considerations in the context of restoring hemlock forests following HWA are also discussed.