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ENVIRONMENTAL REVIEWS AND CASE STUDIES: Eastern Hemlock Conservation: A Collaborative Approach to Prioritization through a Diverse Partnership

  • Sarah Johnson (a1), Scott Bearer (a1), Andrea Hille (a2), Susan Stout (a3) and Rick Turcotte (a4)...


Eastern hemlock [Tsuga canadensis (L.) Carrière] is a valuable component of Allegheny Plateau forests in northwestern Pennsylvania and western New York. Since the 1950s, hemlock forests throughout the Central Appalachians have been under threat from a nonnative forest insect pest, the hemlock woolly adelgid (Adelges tsugae Annand). In 2012, to address this threat at the most meaningful scale, the United States Forest Service and The Nature Conservancy organized a diverse partnership to develop a strategy for landscape-level conservation of hemlock on the High Allegheny Unglaciated Plateau. The main goal of the partnership was to locate hemlock across the landscape regardless of land ownership and prioritize the hemlock for monitoring and protection from the adelgid. The priority Hemlock Conservation Areas that were identified by this partnership provide a guide for focusing limited financial and personnel resources, with the goal of protecting at least a portion of these areas from the impacts of the adelgid until more long-term management techniques are identified. To protect the important hemlock forests identified in this prioritization, a partnership of private and public land managers are forming a Cooperative Pest Management Area to continue this important collaboration, allocate scarce resources across the area, and allow private partners access to public funding for protection of priority hemlock on their lands.

Environmental Practice 18: 94–105 (2016)


Corresponding author

* Address correspondence to: S. Johnson, The Nature Conservancy, 2101 North Front St., Building 1, Suite 200, Harrisburg, PA 17110; (phone) 717-232-6001; (e-mail)


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Abrams, M.D., Copenheaver, C.A., Black, B.A., and van de Gevel, S.. 2001. Dendroecology and climatic impacts for a relict old-growth, bog forest in the Ridge and Valley Province of central Pennsylvania, U.S.A. Canadian Journal of Botany 79(1):5869.
Abrams, M.D., and Orwig, D.A.. 1996. A 300-year history of disturbance and canopy recruitment for co-occurring white pine and hemlock on the Allegheny Plateau, USA. Journal of Ecology 84(3):353363.
Allen, M.C., Sheehan, J. Jr., Master, T.L., and Mulvihill, R.S.. 2009. Responses of Acadian flycatchers (Empidonax virescens) to hemlock woolly adelgid (Adelges tsugae) infestation in Appalachian riparian forests. The Auk 126(3):543553.
Bjorkbom, J.C., and Larson, R.G.. 1977. The Tionesta Scenic and Research Natural Areas. USDA Forest Service General Technical Report NE-31. USDA Forest Service, Upper Darby, PA, 23 pp.
Brantley, S., Ford, C.R., and Vose, J.M.. 2013. Future species composition will affect forest water use after loss of eastern hemlock from southern Appalachian forests. Ecological Applications 23(4):777790.
Burns, R.M., and Honkala, B.H., technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654. USDA Forest Service, Washington, D.C., 877 pp.
Butchkoski, E., and Turner, G.. 2010. Northern Flying Squirrel: Glaucomys sabrinus macrotis. Pennsylvania Game Commission, Harrisburg, PA, 3 pp.
Cessna, J., and Nielsen, C.. 2012. Influences of hemlock woolly adelgid induced stand level mortality on nitrogen cycling and stream water nitrogen concentrations in southern Pennsylvania. Castanea 77(2):127135.
Ellenwood, J., and Krist, F.. 2007. Building a nationwide 30-meter forest parameter dataset for forest health risk assessments. Forests and remote sensing: methods and operational tools. Proceedings of ForestSat, November 5–7, 2007. Montpellier, France, 5 pp.
Ellenwood, J., Krist, F., and Sapio, F.. 2009. Continuing developments in building a nationwide 30-meter forest parameter dataset for forest health risk assessments. USDA Forest Service, Forest Health Technology Enterprise Team, Fort Collins, CO, 4 pp.
Ellison, A.M., Bank, M.S., Clinton, B.D., Colburn, E.A., Elliott, K., Ford, C.R., Foster, D.R., Kloeppel, B.D., Knoepp, J.D., Lovett, G.M., Mohan, J., Orwig, D.A., Rodenhouse, N.L., Sobczak, W.V., Stinson, K.A., Stone, J.K., Swan, C.M., Thompson, J., Von Holle, B., and Webster, J.R.. 2005. Loss of foundation species: Consequences for the structure and dynamics of forested ecosystems. Frontiers in Ecology and the Environment 3(9):479486.
Eschtruth, A.K., Cleavitt, N.L., Battles, J.J., Evans, R.A., and Fahey, T.J.. 2006. Vegetation dynamics in declining eastern hemlock stands: 9 years of forest response to hemlock woolly adelgid infestation. Canadian Journal of Forest Research 36:14351450.
Eschtruth, A.K., Evans, R., and Battles, J.J.. 2013. Patterns and predictors of survival in Tsuga canadensis populations infested by the exotic pest Adelges tsugae: 20 years of monitoring. Forest Ecology and Management 305:195203.
ESRI. 2012. ArcGIS Desktop: Release 10.1. Redlands, California. Environmental Systems Research Institute.
Evans, R. 2002. An ecosystem unraveling. In Proceedings: Symposium on the hemlock woolly adelgid in eastern North America, B.R. Onken, R. Reardon, and J. Lashomb, editors. East Brunswick, NJ, February 5–7, 2002. USDA Forest Service, NJ Agricultural Experiment Station, and Rutgers, New Brunswick, NJ, 2333.
Evans, A.M., and Gregoire, T.G.. 2007. A geographically variable model of hemlock woolly adelgid spread. Biological Invasions 9:369382.
Ford, C.R., and Vose, J.M.. 2007. Tsuga canadensis (L.) Carr. mortality will impact hydrologic processes in southern Appalachian forest ecosystems. Ecological Applications 17(4):11561167.
Fry, J., Xian, G., Jin, S., Dewitz, J., Homer, C., Yang, L., Barnes, C., Herold, N., and Wickham, J.. 2011. Completion of the 2006 National Land Cover Database for the conterminous United States. Photogrammetric Engineering and Remote Sensing 77(9):858864.
Havill, N.P., Montgomery, M.E., Yu, G., Shigehiko, S., and Caccone, A.. 2006. Mitochondrial DNA from hemlock woolly adelgid (Hemiptera: Adelgidae) suggests cryptic speciation and pinpoints the source of the introduction to eastern North America. Annals of the Entomological Society of America 99(2):195203.
Jenkins, J.C., Aber, J.D., and Canham, C.D.. 1999. Hemlock woolly adelgid impacts on community structure and N cycling rates in eastern hemlock forests. Canadian Journal of Forest Research 29:630645.
Lutz, H.J. 1930. Original forest composition in northwestern Pennsylvania as indicated by early land survey notes. Journal of Forestry 28:10981103.
Mathewson, B. 2009. The relative abundance of eastern red-backed salamanders in eastern hemlock-dominated and mixed deciduous forests at Harvard Forest. Northeastern Naturalist 16(1):112.
McClure, M.S. 1990. Role of wind, birds, deer, and humans in the dispersal of hemlock woolly adelgid (Homoptera: Adelgidae). Environmental Entomology 19(1):3643.
Midwest Invasive Plant Network. 2011. CWMA Cookbook: A Recipe for Success, second edition. Midwest Invasive Plant Network, funded by USDA Forest Service, Northeastern Area State and Private Forestry, 23 pp.
Mladenoff, D.J. 1987. Dynamics of nitrogen mineralization and nitrification in hemlock and hardwood treefall gaps. Ecology 68(5):11711180.
Nowacki, G.J., and Abrams, M.D.. 1994. Forest composition, structure, and disturbance history of the Alan Seeger Natural Area, Huntington County, Pennsylvania. Bulletin of the Torrey Botanical Club 121(3):277291.
Onken, B., and Reardon, R.., technical coordinators. 2011. Implementation and status of biological control of the hemlock woolly adelgid. USDA Forest Service Forest Health Technology Enterprise Team, FHTET-2011-04, Morgantown, WV, 230 pp.
Orwig, D.A., and Foster, D.R.. 1998. Forest response to the introduced hemlock woolly adelgid in southern New England. Journal of the Torrey Botanical Society 125(1):6073.
Ouellette, D. 2002. Responding to the artificial introduction of hemlock woolly adelgid (Adelges tsugae Annand) on landscape nursery stock in Maine. In Proceedings: Symposium on the hemlock woolly adelgid in eastern North America, B.R. Onken, R. Reardon, J. and Lashomb, editors. East Brunswick, NJ, February 5–7, 2002. USDA Forest Service, NJ Agricultural Experiment Station, and Rutgers, New Brunswick, NJ, 276279.
Paradis, A., Elkinton, J., Hayhoe, K., and Buonaccorsi, J.. 2008. Role of winter temperature and climate change on the survival and future range expansion of the hemlock woolly adelgid (Adelges tsugae) in eastern North America. Mitigation and Adaptation Strategies for Global Change 13(5–6):541554.
Poland, T.M., and McCullough, D.G.. 2006. Emerald ash borer: Invasion of the urban forest and the threat to North America’s ash resource. Journal of Forestry 104:118124.
Quimby, J.W. 1996. Value and importance of hemlock ecosystems in the eastern United States. In Proceedings of the First Hemlock Woolly Adelgid Review, S.M. Salome, T.C. Tigner, and R.C. Reardon, editors. Charlottesville, VA, October 12, 1995. USDA Forest Service, Morgantown, WV, 18.
Ross, R.M., Redell, L.A., Bennett, R.M., and Young, J.A.. 2004. Mesohabitat use of threatened hemlock forests by breeding birds of the Delaware River basin in northeastern United States. Natural Areas Journal 24(4):307315.
SAS Institute Inc. 2011. Base SAS 9.3 Procedures Guide. SAS Institute Inc., Cary, North Carolina.
Smitley, D., Davis, T., and Rebek, E.. 2008. Progression of ash canopy thinning and dieback outward from the initial infestation of emerald ash borer (Coleoptera: Buprestidae) in southeastern Michigan. Journal of Economic Entomology 101(5):16431650.
Tingley, M.W., Orwig, D.A., Field, R., and Motzkin, G.. 2002. Avian response to removal of a forest dominant: Consequences of hemlock woolly adelgid infestations. Journal of Biogeography 29(10/11):15051516.
Trotter, R.T. III, and Shields, K.S.. 2009. Variation in winter survival of the invasive hemlock woolly adelgid (Hemiptera: Adelgidae) across the eastern United States. Environmental Entomology 38(3):577587.
Turcotte, R.M. 2008. Arthropods associated with eastern hemlock. In Fourth Symposium on Hemlock Woolly Adelgid in the Eastern United States, B. Onken, and R. Reardon, editors. Hartford, CT, February 12–14, 2008. USDA Forest Service, Morgantown, WV, 61.
USDA Forest Service. 2005. Pest Alert: Hemlock Woolly Adelgid. USDA Forest Service Northeastern Area State and Private Forestry, NA-PR-09-05, Newtown Square, PA, 2 pp.
Whitney, G.G. 1990. The history and status of the hemlock-hardwood forests of the Allegheny Plateau. Journal of Ecology 78(2):443458.
Whitney, G.G., and DeCant, J.P.. 2003. Physical and historical determinants of the pre-and post settlement forests of northwestern Pennsylvania. Canadian Journal of Forest Research 33(9):16831697.


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