Hemlock Woolly Adelgid Research in the Southern Appalachians
The Problem
Hemlock woolly adelgid (HWA) is a non-native invasive pest that impacts eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana). HWA was first reported in the 1950’s in the northeastern U.S. , and has now spread to the southern Appalachian region of northern Georgia , western North Carolina , and southern Virginia . Without control, hemlocks typically die within 5 to 7 years after infestation. Unfortunately, neither natural predators nor host resistance have been able to stop the spread of HWA. Hemlock trees serve important ecological roles in the southern Appalachians . They are a keystone species in near-stream areas, providing critical habitat for birds and other animals, and shading streams to maintain cool water temperatures required by trout and other aquatic organisms. Hemlocks are also prized for their visual beauty in both forest and urban settings.
A comprehensive research program is underway to address four key elements of the HWA problem:
- Evaluating control strategies to reduce or eliminate the spread of HWA,
- Understanding the impacts of hemlock mortality on ecosystem resources,
- developing monitoring techniques that determine and predict HWA spread, and
- Developing and evaluating restoration techniques to mitigate the impacts of hemlock mortality on ecosystem resources.
The research is being led by the USDA Forest Service’s Southern Research Station and is being coordinated with the Northeastern Research Station, university cooperators throughout the Eastern U.S., and USDA Forest Service, State and Private Forestry’s Forest Health Protection through participation in the HWA Research Coordinating Committee and the HWA Steering Committee. Most of the work will be centered at the Coweeta Hydrologic Laboratory in western North Carolina . The 5400 acre watershed has conducted watershed ecosystem research for 70 years and has strong supporting information on climate, soils, vegetation, and water quality.
Research Activities
Evaluating Control Strategies
Biological control offers the best hope for long-term management of HWA in forests where chemical control is impractical. Thus far, three beetle predators of HWA have been brought into the Eastern U. S. and released, but evaluating their effectiveness has proven difficult in northern regions because harsh winters and declining host trees affect both the predators and their HWA prey. We plan to release and study these predators in or near the Coweeta Hydrologic Laboratory to evaluate their impact on HWA populations. These studies will provide insight into how the predators respond to low density populations at the leading edge of the infestation and how the milder winters in the South affect their ability to control HWA. A fundamental problem in evaluating predator impacts is how to sample HWA and the predators to effectively characterize their abundance over time. Research on HWA biology and sampling protocols will address these problems.
Partners
University of Georgia, Virginia Tech, SRS-4505 (Athens)
Understanding Impacts
Research has been initiated to determine the impacts of HWA mortality on key ecosystem resources. In 2003, twenty study plots were located in areas with and without evidence of HWA infestation. These plots are being used to establish baseline measurements of nutrient, carbon, and water pools and cycling rates. Measures include: nitrogen mineralization, soil CO 2 flux, litterfall and coarse wood debris inputs, forest floor mass and decomposition, microenvironmental changes, overstory and understory species composition, and stream habitat and water quality. In FY04, HWA-related changes in microenvironment and transpiration will also be quantified. As the HWA infestation progresses, continuous monitoring of both terrestrial and aquatic ecosystems will quantify the impacts of hemlock mortality on ecosystem resources such as terrestrial and aquatic wildlife habitat, biodiversity, and water quality.
In addition, experimental plots have been located to simulate the impacts of hemlock loss on ecosystem processes. On a sub-set of these plots, all hemlock trees within the plots will be girdled to simulate HWA induced mortality. Detailed process-based measurements of carbon, water, and nutrient cycling will be used to predict potential impacts of actual HWA mortality.
Partners
University of Georgia, Virginia Tech, SRS-4505 (Athens)
Monitoring HWA Spread
In 2004, a network of monitoring plots will be established to determine rates and patterns of HWA spread. This network will utilize the approximately 800 long-term vegetation plots that were established at Coweeta in the 1930’s. The long-term plots span gradients in soil, climate, slope, aspect and elevation comparable to those observed across the southern Appalachian region. A subset of plots will be surveyed on an annual basis to determine HWA infestation dynamics. These data will be combined with aerial photography, satellite imagery, and other remote sensing tools to examine the predictive ability of remote sensing tools for detecting HWA infestation. In addition, infestation patterns will be correlated with topographic, edaphic, and biological variables to determine controls on HWA infestation.
Partners
Restoration
The final phase of the HWA research program will be to develop techniques and strategies for restoring areas that have been impacted by HWA. This research component will not be initiated until further information is gained about the success of control strategies in the southern Appalachian region and the effects on HWA mortality on ecosystem resources.
![[Printer]](/coweeta/local_resources/images/printers/print.gif){kind=small}