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Georgia Journal of Science

Article Title

REMOTE SENSING ANALYSIS OF EASTERN HEMLOCK IN RESPONSE TO THE HEMLOCK WOOLY ADELGID AND BIOLOGICAL CONTROL IN THREE NORTH GEORGIA RELEASE SITES

Abstract

Introduction of the invasive insect, Adelgis tsugae (Hemlock Wooly Adelgid or HWA) has devastated the health of Tsuga canadensis (Eastern Hemlock) stands. To control this damage and facilitate the recovery of T. canadensis, biological control organisms in the form of the predatory Coleopterans, Sasajiscymnus tsugae and Laricobius nigrinus, have been released in specified Hemlock Conservation Areas (HCAs) in the north Georgia mountains. The purpose of this study was to see if we can determine, through remote sensing techniques using satellite images, if biopredatory release has had positive benefits in the hemlock health in these areas. To understand the scope of T. canadensis recovery we chose to survey three biological control release sites, located at Davidson Creek (Habersham County), Boggs Creek (Lumpkin County) and Wolfpen Gap (Union County) using modified and simple remote sensing techniques through Google Earth satellite imagery and QGIS for a nine-year period. T. canadensis identifications were confirmed initially by field survey. Computational measurements of canopy cover for three randomly selected trees at each site were acquired by hand-drawing polygons around the visible perimeter in satellite imagery and extracting associated values. Within a nine-year period, nonparametric repeated measures analysis found that canopy area of selected trees did not change significantly. Canopy area and cumulative release of biological controls were found to have strong positive correlations (p = <0.001, r2 = 0.88). This study provides evidence of the likelihood that T. canadensis has reached levels of competitive plateau in forest systems and may attest to the efficacy of biological control releases on the mitigation of invasive pests. Future studies may focus on increasing sample size and comparing results with areas that have no biological control treatments.

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