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Eastern Hemlock (Tsuga canadensis) Forests of the Hocking Hills Prior to Hemlock Woolly Adelgid (Adelges tsugae) Infestation

Knisley, Jordan K.
http://orcid.org/0000-0001-9247-1309
http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1617969072642887

Abstract Details

2021, Bachelor of Arts (BA), Ohio University, Environmental Studies.
Eastern hemlock (Tsuga canadensis) is an important foundation species, altering its environment and supporting a variety of organisms not generally found in deciduous forests. The hemlock forests of the Hocking Hills region in southeast Ohio are particularly unique, occurring in isolated pockets in ravines and on steep slopes on the western edge of the range of the species. However, this unique ecosystem is under threat from hemlock woolly adelgid (HWA, Adelges tsugae), an invasive insect pest which entered the state in 2012. The goal of this study is to characterize the hemlock stands of the Hocking Hills just prior to HWA infestation and describe how these forests have changed in the past decade in terms of growth and mortality. An additional goal is to record non-hemlock species growing alongside these hemlock stands which could become dominant following HWA-induced mortality, as well as any invasive plants present which could pose a threat to native diversity following such a disturbance. In order to accomplish these goals, thirty 20 x 40 m plots established roughly a decade ago were resampled. Within these plots, the diameter of tagged trees was measured and their health and canopy position assessed, and saplings counted as well. Transects measuring 10 x 50 m were established on the upper slopes or ridges above each plot to record non-hemlock species that have the potential to seed into the hemlock stands below. The existence of any invasive plants was also recorded in both plots and transects. It was found that hemlock, for the most part not yet impacted by HWA, was still the dominant species in all plots, with an average importance value of 47.78. Storm damage and competitive thinning rather than HWA infestation appeared to account for the majority of mortality. Growth and mortality rates among hemlocks (on average, 1.18% annual growth and 13.24% total mortality) were both comparable to those seen in deciduous species on the plots. A mixture of hardwood species such as tulip poplar (Liriodendron tulipifera), chestnut oak (Quercus montana), white oak (Quercus alba), sweet birch (Betula lenta) and red maple (Acer rubrum) were common components of hemlock stands. Therefore, these trees can be expected to be among the first species to dominate the canopy following future hemlock mortality. Chestnut oak dominates the deciduous stands above the hemlock plots, with red maple, white oak, and red oak (Quercus rubra) also commonly recorded. Each of these species could contribute to the composition of post-HWA forests by dispersing to the slopes and valleys below. Invasive plant species were found at one-third of sampling sites, with Japanese stiltgrass (Microstegium vimineum) being by far the most numerous. This is worrying, as the expansion of invasive species following hemlock mortality could potentially inhibit the regeneration of native species. In short, a variety of deciduous species appear poised to take advantage of increased resource availability in the absence of hemlock, but unfortunately the same can also be said for invasive plants. The results of this study can inform forest management and conservation efforts in the isolated and unique hemlock stands of southeast Ohio.
James Dyer (Advisor)
68 p.
Environmental Studies
Eastern Hemlock; Hemlock Woolly Adelgid; HWA; Hocking Hills

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Citations

  • Knisley, J. K. (2021). Eastern Hemlock (Tsuga canadensis) Forests of the Hocking Hills Prior to Hemlock Woolly Adelgid (Adelges tsugae) Infestation [Undergraduate thesis, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1617969072642887

    APA Style (7th edition)

  • Knisley, Jordan. Eastern Hemlock (Tsuga canadensis) Forests of the Hocking Hills Prior to Hemlock Woolly Adelgid (Adelges tsugae) Infestation. 2021. Ohio University, Undergraduate thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1617969072642887.

    MLA Style (8th edition)

  • Knisley, Jordan. "Eastern Hemlock (Tsuga canadensis) Forests of the Hocking Hills Prior to Hemlock Woolly Adelgid (Adelges tsugae) Infestation." Undergraduate thesis, Ohio University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1617969072642887

    Chicago Manual of Style (17th edition)

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