A novel approach using spatial analysis to assess impacts of biological control on hemlock woolly adelgid, Adelges tsugae, in Eastern forests

Six decades ago, hemlock woolly adelgid, Adelges tsugae, an invasive forest pest, was accidentally introduced from Japan into the United States, where it has greatly impacted hemlock health and survival. To combat this invasive pest, two predatory species were introduced and released on adelgid-infested eastern hemlock. Effects of these introduced predators on eastern hemlock are unclear. The objective of this study is to determine if spatial analysis is applicable to monitor the effectiveness of biological control on eastern hemlock. This study was conducted in the Great Smoky Mountains National Park, where composite infra-red imagery (3-band, 0.5 m resolution) was used to develop a spatial model using ArcMap 10. Eleven predator recovery sites and 11 non-recovery sites were selected; a buffer of 50, 100, 200 and 300 m was placed around each site. Based on visual interpretation of the spatial imagery, dead hemlocks within each buffered area were counted. Results indicated that spatial analysis could be an effective technique to monitor biological control efforts against hemlock woolly adelgid on eastern hemlock. This novel approach will enhance our understanding of biological control of hemlock woolly adelgid and enhance future efforts at management of this devastating invasive pest.