Hemlock Woolly Adelgid
Currently the hemlock woolly adelgid (HWA) is threatening eastern hemlock with elimination across its range. While infestation and unimpeded migration of HWA presents a tremendous management problem, it also has provided an unusual opportunity to examine the impacts of an introduced pest as it spreads. In order to develop insights into these management issues, we have developed a multi-faceted research effort that examines various forest responses to HWA outbreaks in southern New England including:
- stand and community reorganization dynamics
- landscape patterns of HWA infestation, damage, and hemlock mortality
- microenvironmental and ecosystem function changes
- response of avian and other wildlife communities
- changes in stream chemistry, physical habitat, vertebrate and invertebrate community composition, and trophic structure
A web page has been devised as a central depot for researchers studying Hemlock Woolly Adelgid. These pages include contact information, areas of interest and preliminary data.
In many stands, we have observed high hemlock mortality rates (50 - 100%), no sign of tree recovery, and the health and vigor of remaining trees continues to deteriorate. Forests have been transformed by a rapid recolonization of black birch (Betula lenta L.), red maple (Acer rubrum L.), and oak (Quercus) seedlings, as well as opportunistic herbaceous species. We have observed a geographical trend in reduced HWA infestation intensity and tree mortality and enhanced hemlock crown vigor occurs from south to north, coincident with the temporal colonization pattern of HWA.
Harvard Forest researchers have initiated several studies to examine the various ecosystem function changes associated with chronic HWA outbreaks including changes in nitrogen (N) availability, mineralization, and nitrification rates, decomposition, and throughfall chemistry.
In addition, we are investigating the response of various wildlife species and stream communities associated with the decline and loss of eastern hemlock and their replacement by hardwoods.
Selected Publications:
Stadler, B. T. Müller, D. Orwig, and R. Cobb. 2005. Hemlock woolly adelgid in New England forests: canopy impacts transforming ecosystem processes and landscapes. Ecosystems. In press.
Tingley, M., D. A. Orwig, R. Field, and G. Motzkin. 2002. Avian response to removal of a forest dominant: consequences of hemlock woolly adelgid infestations. Journal of Biogeography 29: 1505-1516
Orwig, D. A. and M. L. Kizlinski. 2002. Vegetation response following hemlock woolly adelgid infestation, hemlock decline, and hemlock salvage logging. In: Symposium on the Hemlock woolly Adelgid in eastern North America proceedings. New Jersey Agricultural Experiement Station, New Brunswick, NJ
Orwig, D. A., D. R. Foster, and D. L. Mausel. 2002. Landscape patterns of hemlock decline in New England due to the introduced hemlock woolly adelgid. Journal of Biogeography 29: 1475-1487
Orwig, D. A. 2002. Stand dynamics associated with chronic hemlock woolly adelgid infestations in southern new England. In: Symposium on the Hemlock Woolly Adelgid in Eastern North America Proceedings. New Jersey Agricultural Experiment Station, New Brunswick, New Jersey
Kizlinski, M., D. A. Orwig, R. Cobb, and D. Foster. 2002. Direct and indirect ecosystem consequences of an invasive pest on forests dominated by eastern hemlock. Journal of Biogeography 29: 1489-1503
Kizlinski, M. 2002. Vegetation and ecosystem response to eastern hemlock decline and logging: direct and indirect consequences of the hemlock woolly adelgid. MFS Thesis, Harvard University
Cobb, R. C. and D. A. Orwig. 2002. Impact of hemlock woolly adelgid on decomposition: an overview. In: Symposium on the Hemlock Woolly Adelgid in Eastern North America Proceedings. New Jersey Agricultural Experiment Station, New Jersey
Orwig, D. A., C. V. Cogbill, D. R. Foster, and J. F. O'Keefe. 2001. Variations in old-growth structure and definitions: forest dynamics on Wachusett Mountain, Massachusetts. Ecological Applications 11: 437-452
Yorks, T. E., J. C. Jenkins, D. J. Leopold, D. J. Raynal, and D. A. Orwig. 2000. Influences of eastern hemlock mortality on nutrient cycling. In . In K. A. McManus, K. S. Shields, and D. R. Souto (Eds.), Sustainable Management of Hemlock Ecosystems in Eastern North America. Symposium Proceedings.
Weiskittel, A. *. 2000. Stand response to hemlock woolly adelgid infestation in Connecticut. Proceedings, Ohio Academy of Science
Orwig, D. A. and D. R. Foster. 2000. Stand, landscape and ecosystem analyses of hemlock woolly adelgid outbreaks in southern New England: an overview. Pp. 123-125 In K. A. McManus, K. S. Shields, and D. R. Souto (Eds.), Sustainable Management of Hemlock Ecosystems in Eastern North America. USDA
Orwig, D. A., R. C. Cobb, M. L. Kizlinski, S. J. Currie, and D. R. Foster. 2000. Ecosystem response to hemlock decline from hemlock woolly adelgid in southern New England. In: ESA
Foster, D. R. 2000. Hemlock's future in the context of its history: an ecological perspective. In: Sustainable Management of Hemlock Ecosystems in Eastern North America. USDA GRT-NE, Symposium Proceedings
Jenkins, J., J. Aber, and C. Canham. 1999. Hemlock woolly adelgid impacts on community structure and N cycling rates in eastern hemlock forest. Canadian Journal of Forest Research 29: 630-645
Orwig, D. A. and D. R. Foster. 1998. Forest response to the introduced hemlock woolly adelgid in southern New England, USA. Journal of the Torrey Botanical Society 125: 59-72
Orwig, D. A. and D. R. Foster. 1998. Ecosystem response to an imported pathogen: the hemlock woolly adelgid. Arnoldia 58: 41-44