OJFOpen Journal of Forestry2163-0429Scientific Research Publishing10.4236/ojf.2014.42014OJF-42889ArticlesEarth&Environmental Sciences Evaluating Southern Appalachian Forest Dynamics without Eastern Hemlock: Consequences of Herbivory by the Hemlock Woolly Adelgid ndrewG. Birt1*YuZeng1MariaD. Tchakerian1RobertN. Coulson1CharlesW. Lafon2DavidM. Cairns2JohnWaldron3WeiminXi4Szu-HungChen1DouglasA. Street5Southern Research Station, US Forest Service, Alexandria Forestry Center, Pineville, USADepartment of Geography, Texas A&M University, College Station, USADepartment of Biological and Health Sciences, Texas A&M University-Kingsville, Kingsville, USADepartment of Environmental Studies, University of West Florida, Pensacola, USAKnowledge Engineering Laboratory, Department of Entomology, Texas A&M University, College Station, USA* E-mail:abirt@tamu.edu(NGB);1402201404029199November 21st, 2013January 3rd, 2014 January 21st, 2014© Copyright 2014 by authors and Scientific Research Publishing Inc. 2014This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

Eastern hemlock (Tsuga canadensis Carriére) and the Carolina hemlock (Tsuga caroliniana Engelmann) are ecologically important tree species in eastern North America forests that are currently threatened by the hemlock woolly adelgid (HWA, Adelges tsugae Annand, Hemiptera: Adelgidae). HWA has spread rapidly from its original introduction site into new areas. Once present, HWA kills its hosts over a period of 4 to 10 years leading to a phenomenon that is known scientifically and colloquially as hemlock decline. To date, quarantine, chemical management, and biocontrol efforts have failed to curb the spread of the HWA. As such, forest management efforts are now being redirected towards developing an understanding of the effects of hemlock removal on vegetation dynamics, changes in forest composition, and changes in ecosystem function. In this study, we parameterize a spatially explicit landscape simulation model LANDIS II for a specific forested region of the southern Appalachians. Parameterization involves defining the life-history attributes of 37 tree species occupying 11 ecological zones and is based on knowledge of: current vegetation composition data, recent historic management and fire regimes, and life-history traits of each species. The parameterized model is used to explore a simple scenario of catastrophic hemlock mortality likely to occur as a result of HWA herbivory. Our results emphasize that hemlock is an important foundation species. When hemlock is removed from the system, forest composition changes considerably with a greater presence of shade intolerant pine and oak species. Additionally, hemlock removal leads to a period of transient, relatively unstable vegetation dynamics as the forest communities restructure.

Hemlock; Forest Dynamics; LANDIS II; Hemlock Woolly Adelgid; Southern AppalachianReferencesBirt, A. G., Xi, W., & Coulson, R. N. (2009). LANDISVIEW: A visualization tool for landscape modeling. Environmental Modelling & Software, 24, 1339-1341.http://dx.doi.org/10.1016/j.envsoft.2009.04.007Botkin, D. B. (1993). Forest dynamics: An ecological model. Oxford: Oxford University Press.Burns, R. M., & Honkala, B. H. (1990). Silvics of North America: Vol. 1: Conifers & Vol. 2: Hardwoods. Washington DC: US Forest Service.http://www.na.fs.fed.us/spfo/pubs/silvics_manual/Volume_1/vol1_Table_of_contents.htmCairns, D. M., Lafon, C. W., Birt, A. G., Waldron, J. D., Tchakerian, M. D., Coulson, R. N., Xi, W., & Klepzig, K. D. (2008). Simulation modeling as a tool for understanding the landscape ecology of southern pine beetle infestations in southern Appalachian forests. Geography Compass, 2, 580-599.http://dx.doi.org/10.1111/j.1749-8198.2008.00098.xCairns, D. M., Lafon, C. W., Waldron, J. D., Tchakerian, M. D., Coulson, R. N., Klepzig, K. D., Birt, A. G., & Xi, W. (2008). Simulating the reciprocal interaction of forest landscape structure and southern pine beetle herbivory using LANDIS. Landscape Ecology, 23, 403-415. http://dx.doi.org/10.1007/s10980-008-9198-7Clark, J. T., Fei, F., Liang, L., & Rieske, L. K. (2012). Mapping eastern hemlock: Comparing classification techniques to evaluate susceptibility of a fragmented and value resource to an exotic invader, the hemlock woolly adelgid. Forest Ecology and Management, 266, 216-222. http://dx.doi.org/10.1016/j.foreco.2011.11.030Cobb, R. C., Orwig, D. A., & Currie, S. (2006). Decomposition of green foliage in eastern hemlock forests of southern New England impacted by hemlock woolly adelgid infestations. Canadian Journal of Forest Research, 36, 1331-1341.http://dx.doi.org/10.1139/x06-012Day, F. P., & Monk, C. D. (1974). Vegetation patterns on a southern Appalachian watershed. Ecology, 55, 1064-1074.http://dx.doi.org/10.2307/1940356Ellison, 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., & Webster, J. R. (2005). Loss of foundation species: Consequences for the structure and dynamics of forested ecosystems. Frontiers in Ecology and the Environment, 9, 479-486.http://dx.doi.org/10.1890/1540-9295(2005)003[0479:LOFSCF]2.0.CO;2Flatley, W. T., Lafon, C. W., & Grissino-Mayer, H. G. (2011). Climatic and topographic controls on patterns of fire in the southern and Central Appalachian mountains, USA. Landscape Ecology, 26, 195-209. http://dx.doi.org/10.1007/s10980-010-9553-3He, H. S., & Mladenoff, D. J. (1999). Spatially explicit and stochastic simulation of forest landscape fire disturbance and succession. Ecology, 80, 81-99.http://dx.doi.org/10.1890/0012-9658(1999)080[0081:SEASSO]2.0.CO;2Heard, M. J., & Valente, M. J. (2009). Fossil pollen records forecast response of forests to hemlock woolly adelgid invasion. Ecography, 32, 881-887. http://dx.doi.org/10.1111/j.1600-0587.2009.05838.xLafon, C. W., & Grissino-Mayer, H. D. (2007). Spatial patterns of fire occurrence in the central Appalachian Mountains. Physical Geography, 28, 1-20. http://dx.doi.org/10.2747/0272-3646.28.1.1Lafon, C. W., Waldron, J. D., Cairns, D. M., Tchakerian, M. D., Coulson, R. N., & Klepzig, K. D. (2007). Modeling the effects of fire on the long-term dynamics and restoration of yellow pine and oak forests in the southern Appalachian Mountains. Restoration Ecology, 15, 400-411. http://dx.doi.org/10.1111/j.1526-100X.2007.00236.xMcClure M. S. ,et al. (1991). Density-dependent feedback and population cycles in Adelges tsugae (Homoptera: Adelgidae) on Tsuga canadensis Environmental Entomology 20, 258-264.Mladenoff, D. J., & He, H. S. (1999). Design, behavior and applications of LANDIS, an object-oriented model of forest landscape disturbance and succession. In: D. J. Mladenoff, & W. L. Baker (Eds.), Advances in spatial modeling of forest landscape change: Approaches and applications (pp. 125-162). Cambrige: Cambridge University Press.Nuckolls, A. E., Wurzburger, N., Ford, C. R., Hendrick, R. L., Vose, J. M., & Kloeppel, B. D. (2009). Hemlock declines rapidly with hemlock wooly adelgid infestation: Impacts on the carbon cycle of southern Appalachian forests. Ecosystems, 12, 179-190.http://dx.doi.org/10.1007/s10021-008-9215-3Orwig, D. A., & Foster, D. R. (1998). Forest response to the introduced hemlock woolly adelgid in southern New England, USA. The Journal of the Torrey Botanical Society, 125, 60-73.http://dx.doi.org/10.2307/2997232Orwig, D. A., Foster, D. R., & Mausel, D .L. (2002). Landscape patterns of hemlock decline in New England due to the introduced hemlock woolly adelgid. Journal of Biogeography, 29, 1475-1487.http://dx.doi.org/10.1046/j.1365-2699.2002.00765.xPeet R. K., Wentworth T. R., & White P. S. ,et al. (1998). A flexible, multipurpose method for recording vegetation composition and structure Castanea 63, 262-274.Preston, R. J., & Braham, R. R. (2002). North American trees (5th ed.) Ames, IA: Iowa State Press.Ross, R. M., Bennett, R. M., Snyder, C. D., Young, J. A., Smith, D. R., & Lemarie, D. P. (2003). Influence of eastern hemlock (Tsuga candensis L.) on fish community structure and function in headwater streams of the Delaware River basin. Ecology of Freshwater Fish, 12, 60-65. http://dx.doi.org/10.1034/j.1600-0633.2003.00006.xScheller, R. M., Domingo, J. B., Sturtevant, B. R., Williams, J. S., Rudy, A., Gustafson, E. J., & Mladenoff, D. J. (2007). Design, development, and application of LANDIS-II, a spatial landscape simulation model with flexible temporal and spatial resolution. Ecological Modelling, 201, 409-419.http://dx.doi.org/10.1016/j.ecolmodel.2006.10.009Shifley, S. R., Thompson, F. R., Larsen, D. R., Mladenoff, D. J., & Gustafson, E. J. (2000). Utilizing inventory to calibrate a landscape simulation model. In: M. Hansen, & T. Burk (Eds.), Integrating tools for natural resource inventories in the 21st century, proceedings of IUFRO conference (pp. 549-561). Boise, ID: North Central Research Station, USDA Forest Service.Shugart, H. H. (1984). A theory of forest dyanamics: The ecological implications of forest succesion models. New York: Springer-Verlag. http://dx.doi.org/10.1007/978-1-4419-8748-8Simon, S. A., Collins, T. K., Kauffman, G. L., McNab, W. H., & Ulrey, C. J. (2005). Ecological zones in the southern Appalachians: First approximation. Asheville, NC: Southern Research Station, USDA Forest Service.Small, M. J., Small, C. J., & Dreyer, G. D. (2005). Changes in a hemlock-dominated forest following woolly adelgid infestation in southern New England. The Journal of the Torrey Botanical Society, 132, 458-470. http://dx.doi.org/10.3159/1095-5674(2005)132[458:CIAHFF]2.0.CO;2Snyder, C. D., Young, J. A., Lemarie, D. P., & Smith, D. R. (2002). Influence of eastern hemlock (Tsuga Canadensis) forests on aquatic invertebrate assemblages in headwater streams. Canadian Journal of Fisheries and Aquatic Sciences, 59, 262-275.http://dx.doi.org/10.1139/f02-003Tredici P. D., & Kitajima A. ,et al. (2004). Introduction and cultivation of Chinese hemlock (Tsuga chinesnsis) and its persistence to hemlock woolly adelgid (Adelges tsugae) Journal of Arboriculture 30, 282-286.USDA (2010). Counties with established HWA populations 2010.http://na.fs.fed.us/fhp/hwa/maps/2010.pdfWaldron, J. D., Lafon, C. W., Coulson, R. N., Cairns, D. M., Tchakerian, M. D., Birt, A. G., & Klepzig, K. D. (2007). Simulating the impacts of southern pine beetle and fire on pine dynamics on xeric southern Appalachian landscapes. Applied Vegetation Science, 10, 53-64. http://dx.doi.org/10.1111/j.1654-109X.2007.tb00503.xXi, W., Waldron, J. D., Lafon, C. W., Cairns, D. M., Birt, A. G., Tchakerian, M. D., Coulson, R. N., & Klepzig, K. D. (2009). Modeling long-term effects of altered fire regimes following southern pine beetle outbreaks. Ecological Restoration, 27, 24-26.http://dx.doi.org/10.3368/er.27.1.24