Modeling Stand Vulnerability and Biological Impacts of the Hemlock Wooly Adelgid
	John Young, Dave Morton, Nissa Thomsen US Geological Survey, Biological Resources Division -- Leetown, WV Joe Clark, Frank van Manen US Geological Survey, Biological Resources Division -- Knoxville, TN Bob Ross, Randy Bennett US Geological Survey, Biological Resources Division -- Wellsboro, PA

Background: In the last two decades, substantial declines in eastern hemlock (Tsuga canadensis) have been observed throughout its range, resulting in widespread concern ( Hemlock defoliation has largely been attributed to the hemlock woolly adelgid (Adelges tsugae), an exotic aphid-like insect that is native to Japan. Resource managers expect the adelgid to continue to spread and consequently the entire hemlock forest community may be threatened. The impact of removal of this important climax forest species on the ecology of Appalachian forests is poorly understood, but has the potential for significant disturbance to biotic communities by changing energy inputs, micro-climatic environments, and physical habitat structure. The purpose of this research is to provide managers with an empirical model of stand vulnerability that can be used to assess the potential risk of hemlock decline due to hemlock wooly adelgid. Secondly, we are attempting to determine how avian and aquatic communities associated with hemlock stands are most likely to be impacted. This site describes research being conducted by component laboratories of the USGS Leetown Science Center on stand and community-level impacts of hemlock woolly adelgid. Stand Vulnerability Modeling (Phase I): In Shenandoah National Park (SHEN), hemlock defoliation and tree mortality have advanced at such a rapid pace that near complete mortality of some hemlock stands occurred within 3-4 years, while other stands have been less severely impacted. In other areas, such as Delaware Water Gap National Recreation Area (DEWA), the adelgid is present in large numbers but no significant mortality of hemlocks has been observed. The patchy nature of hemlock decline suggests that landscape-level processes may affect hemlock mortality either by regulating the dispersal potential of hemlock woolly adelgid, or by affecting the sensitivity of the trees themselves. For example, hemlock woolly adelgid can disperse by wind or by attaching to migrating animals including birds, deer, and man (McClure 1990). Consequently, prevailing winds, number of and distance to roads, proximity to migrating bird habitats, and stand composition, edge, and topography may contribute to hemlock woolly adelgid dispersal and ultimately to the extent of mortality. Likewise, sub-optimal habitat characteristics such as low soil moisture may be related to landscape variables such as aspect and elevation, which may act synergistically with hemlock woolly adelgid infestation to induce mortality. We are examining the relationship between hemlock stand mortality and landscape features. Our goal is to develop empirical models designed to predict stand vulnerability from landscape information. National Park managers could use this information to design pro-active strategies in areas where hemlock woolly adelgid has not spread such as Great Smoky Mountains National Park (GSMNP), or where infestation is recent and significant mortality has yet to be evidenced, such as at DEWA. The goal of phase 1 of this research is to construct an empirical model of hemlock stand vulnerability at site, landscape, and regional scales for SHEN (see study plan for more detail). Initial investigations will focus on this area due to the presence of HWA and the differential pattern of hemlock infestation and mortality observed in this park over the past 5-7 years. Results from this modeling effort will be integrated with phase 2 efforts in GSMNP, and DEWA, to predict potential impacts on biotic communities from loss of the eastern hemlock forest component. Potential Ecological Effects (Phase II): Hemlock stands may have co-evolved with other flora and fauna in stable, co-dependent associations. Preliminary data (Ross, unpublished), for example, show exclusive use of hemlock bench and ravine habitats (as opposed to equivalent hardwood sites) by 3 species of wood warbler and vireo (solitary vireo, black-throated green warbler, and blackburnian warbler), mixed use by 2 species (red-eyed vireo and ovenbird), and exclusive use of hardwood benches and ravines by 1 species (American redstart) of those surveyed. As stated, the loss of eastern hemlock has unknown consequences and may involve changes in energy inputs, microclimate, and physical habitat structure for several biotic communities. Hence, there is an urgent need to characterize the contribution of hemlock forests to avian biodiversity in large, forested landscapes. Following the initiation of the stand vulnerability modeling, we will characterize breeding bird populations in matched hardwood and hemlock stands of DEWA and, later, in GSMNP. Much of this data already exists and sampling schemes have already been developed for both areas. We will stratify and compare specific habitat types (bench, ravine, and mid-slope) within hardwood and hemlock stands for bird usage. From those data, models will be developed and coupled with stand vulnerability models to predict changes in avian communities at both areas. In addition to avian communities, loss of hemlock may have tremendous impacts on the aquatic ecosystems with which they are usually associated. Perhaps the most sensitive indicator of changes in aquatic environments are aquatic invertebrates. Invertebrate sampling currently is being conducted at both SHEN and GSMNP. We will supplement this monitoring effort with additional surveys in hemlock communities if necessary.

Hemlock Decline Research in Shenandoah National Park Introduction Study Plan GIS Atlas Selected Pubs In partnership with: See also: Hemlock Decline Research in Delaware Water Gap NRA Biological Resources Division Leetown Science Center Aquatic Ecology Laboratory