Title page for ETD etd-04252012-112350


Type of Document Master's Thesis
Author Walker, David Matthew
URN etd-04252012-112350
Title Radial growth response of eastern hemlock to infestation of hemlock woolly adelgid
Degree Master of Science
Department Forestry
Advisory Committee
Advisor Name Title
Copenheaver, Carolyn A. Committee Chair
Salom, Scott M. Committee Member
Zink-Sharp, Audrey G. Committee Member
Keywords
  • dendroclimatology
  • dendroentomology
  • dendrochronology
  • Adelges tsugae
  • Tsuga canadensis
Date of Defense 2012-04-13
Availability unrestricted
Abstract
Hemlock woolly adelgid (Adelges tsugae Annand) is causing defoliation and mortality of eastern hemlock (Tsuga canadensis (L.) Carrière) in the eastern United States. The objectives of this study were to quantify changes in tree-ring width and wood anatomy for trees that survived adelgid infestation, and to contrast dendroclimatic relationships across a latitudinal gradient. Six sites spanning the current range of hemlock woolly adelgid (HWA) infestation were selected. At each site, 23 infested eastern hemlocks were cored and two trees were felled at the Virginia site

and thin-sectioned using a sliding microtome for analysis of wood anatomy. Tree cores were cross-dated and ring widths were measured. For each site, t-tests were used to determine if there

was a difference in radial growth pre- and post-HWA arrival. To compare differences in pre- and post-HWA cell properties, t-tests were used. For dendroclimatic analysis, Pearson correlation

coefficients were calculated between radial growth and monthly climate variables. Three sites showed significant suppression in radial growth after HWA arrival and latewood produced post-

HWA arrival had significantly smaller cells with reduced cell-wall thickness than latewood produced before HWA arrival. This indicates that HWA can reduce a tree’s photosynthate production. The relationship between hemlock growth and climate also varied with latitude and site, with trees growing further south or on shallower soils being more sensitive to moisture levels. This sensitivity to drought can also partially explain the variation in hemlock response to adelgid feeding, as trees affected by moisture stress tend to be more sensitive to insect attack.

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