Hemlock woolly adelgid in the southern Appalachians: Control strategies, ecological impacts, and potential management responses
Hemlock woolly adelgid (Adelges tsugae Annad; or HWA) is a non-native invasive pest that attacks and kills eastern hemlock (Tsuga canadensis (L.) Carrière) and Carolina hemlock (Tsuga caroliniana Engelm.). Hemlock is a ‘‘foundation species’’ due to its strong influence on ecosystem structure and function, especially in riparian areas. HWA management involves the integrated use of multiple approaches including chemical control, biological control, cultural treatments, host resistance, and host gene conservation. Despite extensive control efforts, large areas in the eastern US, but especially in the southern Appalachian region, have experienced extensive hemlock mortality. Most of the short-term impacts of HWA induced mortality on ecosystem structure and function are localized and small; however, long-term impacts such as large pulses of woody debris and changes in species composition that impact structure and function could be significant. Using a decision analysis framework, land managers should begin to strategically implement land management decisions to address observed short-term impacts and plan and manage for projected longer-term impacts. In order to maintain ecosystem services in response to long-term impacts, restoration efforts may require novel approaches, such as the introduction of non-native species, facilitated movement of native species to new habitats (e.g., white pine), and aggressive management of existing species (e.g., Rhododendron) with mechanical removal, fire, or chemicals.