PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Structural changes in an old growth eastern hemlock-northern hardwood stand in south-central Pennsylvania following invasion by the hemlock woolly adelgid.

Cage, Leonard¹, Shumway, Durland^*,1, Lewis, Mark^*,1, ¹ Frostburg State University, Frostburg, Maryland

ABSTRACT- Tsuga canadensis (L.) Carr. (eastern hemlock), the dominant tree species in many old growth eastern hemlock-northern hardwood forests of the northeastern United States, has been slowly disappearing as a result of the activities of the exotic hemlock woolly adelgid (HWA), Adelges tsugae Annand. Feeding on xylem ray parenchyma cells by this pernicious invader results in the defoliation of T. canadensis, leading to hemlock death within 4 years. An old growth eastern hemlock-northern hardwood stand in the Sweet Root Natural Area located within Buchanan State Forest in south-central Pennsylvania, USA was evaluated for changes in forest structure over a 6-year period, beginning at the onset of HWA invasion in 1998. Tree ring analysis revealed a significant increase (P<0.05) in growth response by Betula lenta L. and B. alleghaniensis Britton while suggesting a decrease in growth response of surviving T. canadensis in the understory. Analysis of tree data showed a significant decrease (P<0.05) in basal area, relative basal area, relative density, and importance value of T. canadensis and a significant increase (P<0.05) in relative basal area, relative density, and importance value of B. alleghaniensis. The decrease in canopy cover and resultant increase in light at the subcanopy level due to hemlock death are thought to account for the release of suppressed hardwoods such as B. lenta and B. alleghaniensis. Analysis of coarse woody debris (CWD) data indicated an increase in total volume from 1998 to 2004 and allowed for description of the stand with regard to CWD decay class. The increase in CWD as hemlocks die can affect abiotic factors such as nutrient cycling and stream flow. This continuing study contributes to a growing body of information on how HWA infection and the consequential loss of hemlocks affect understory species and stand structure in old growth eastern hemlock-northern hardwood forests.

Key words: Tsuga canadensis, Adelges tsugae, Betula spp., Sweet Root Natural Area