123Proceedings: Symposium on Sustainable Management of Hemlock Ecosystems in Eastern North America GTR-NE-267AbstractHemlock woolly adelgid (HWA) (Adelges tsugae), anintroduced aphid-like insect from Asia, is expanding acrossthe northeastern United States through the range of easternhemlock (Tsuga canadensis (L.) Carr.) and has the potentialto severely reduce or eliminate this important late-successional species. While infestation and unimpededmigration of HWA presents a tremendous managementproblem, it also has provided an unusual opportunity toexamine the impacts of an introduced pest as it spreads. Inorder to develop insights into these management issues, wehave developed a multi-faceted research effort thatexamines various forest responses to HWA outbreaks inConnecticut including stand and community reorganizationdynamics, landscape patterns of HWA infestation, damage,and hemlock mortality, microenvironmental changes andtheir impact on ecosystem processes, and the effect ofcutting infested forests on successional and ecosystemdynamics. This paper presents an overview of this research,conducted by Harvard Forest scientists.IntroductionHemlock woolly adelgid (HWA; Adelges tsugae Annand), anintroduced aphid-like insect from Asia, is expanding acrossthe northeastern United States through the range of easternhemlock and has the potential to severely reduce oreliminate this important late-successional species (McClure1995a; Orwig and Foster 1998). Despite the growingknowledge about the biology of HWA (McClure 1987,1989,1990,1991, 1995a; Salom et al. 1996; Young et al.1995) and increasing efforts to find, raise and releasenatural or exotic biological controls (Gouli et al. 1997;McClure 1995b; McClure and Cheah 1998; Sasaji andMcClure 1997; Others, this volume), we still know very littleabout how HWA infestation will affect forest and ecosystemprocesses. Therefore, this paper will present results frompast and current research by Harvard Forest scientists onthe various forest responses to HWA outbreaks in southernNew England.Research ApproachesStand-level DynamicsAs part of a large study investigating stand to landscapelevel forest dynamics resulting from HWA infestation, weexamined the initial community response of hemlock standsvarying in mortality levels in south-central Connecticut(Orwig and Foster 1998). Since 1995, mortality of overstoryand understory hemlock has risen to over 60% in half of thestands and continues to increase 5 to 15% per year. Thehealth and vigor of remaining trees has deteriorated in allstands, with the majority of trees containing less than 25%of their foliage. We have observed no sign of tree recoveryon these sites over the last 4 years and predict that allsampled trees will die within the next few years. A rapidrecolonization of these forests with seedlings of black birch(Betula lenta L.), red maple (Acer rubrum L.), and oak(Quercus) as well as opportunistic herbaceous species hascontinued to occur following additional hemlock mortality.Seedling densities have increased in moderately damagedsites and have thinned but increased in cover in heavilydamaged areas. We will continue to examine the ongoingdynamics in these forests to gain detailed information on themechanisms and rate of vegetation recovery.Landscape-level dynamicsData and observations from these original eight stands werelimited to southern Connecticut and we were interested inhow representative the results were compared to a muchbroader study region. To meet this objective we establisheda 5900 km2 transect surrounding the Connecticut RiverValley extending from Long Island Sound north to theMassachusetts border (Orwig et al. unpublished data).Within the transect we mapped hemlock stands from aerialphotographs and then visited and compiled information onstand composition and structure, presence of HWA, degreeof overstory and understory mortality, seedling densities,and site characteristics from 114 stands. HWA presence wasobserved in nearly 90% of all stands visited and hemlocksapling and overstory trees have experienced much higherrates of mortality (20 to 100%) in the southern part of thestate compared to rates in the northern part of the state (0 to15%). Hemlock mortality exceeded 20% on mosttopographic aspects, not just the drier southwest or westfacing slopes. The health of remaining trees exhibits apattern similar to mortality, with healthier trees located in thenorthern part of the transect. These data suggest that exceptlatitude, site factors play little, if any role in the susceptibilityof forests to adelgid, and that most stands will suffer heavyor complete mortality following infestation.Forest composition data from infested stands is useful inpredicting the species that will eventually replace hemlock.Currently, black birch, red oak (Quercus rubra L.), and redmaple are present in the overstory of most stands and arestarting to become established in the understory. We havefound that most forests contained few hemlock seedlingsbut modest to high densities of hemlock saplings (200 to800 ha-1). However, saplings are currently experiencing highlevels of adelgid infestation and mortality and seeds do notremain viable for more than a year or two. Therefore, wepredict a complete change in cover type from hemlock tohardwood-dominated forests across broad geographicalareas.Stand, Landscape, and Ecosystem Analyses of Hemlock Woolly AdelgidOutbreaks in Southern New England: An OverviewDavid A. Orwig and David R. Foster 11Harvard Forest, Harvard University, Petersham, MA 01366124Proceedings: Symposium on Sustainable Management of Hemlock Ecosystems in Eastern North America GTR-NE-267Ecosystem-level ImpactsResults from prior ecosystem-level research conducted onsites we have been following for several years (Jenkins et al.1999; Yorks et al. this volume) suggest that HWA infestationcan lead to dramatic changes in nitrogen cycling. Jenkins etal. (1999) found large increases in N mineralization andnitrification rates in infested versus healthy hemlock forests.However, we still do not know how rapidly these changesoccur, how long they persist, or to what degree changes insoil temperature or biotic uptake affect nutrient cycling. Inorder to answer these questions, we have initiated a studyexamining N availability, mineralization, and nitrification ratesin a subset of Connecticut sites that are infested with HWAbut have experienced little to no hemlock mortality (Orwig etal.