Modeling Landscape-Level Impacts of HWA in Shenandoah National Park
نویسندگان
چکیده
Eastern hemlock is in decline in many parts of its range in the eastern United States due primarily to infestation by the hemlock woolly adelgid (HWA). In Shenandoah National Park, HWA rapidly killed many hemlock stands after first appearing in 1989. While the severity of hemlock decline in Shenandoah National Park may preclude saving the hemlock forest component, an examination of the progression of decline across the landscape may provide insight into management potential for other areas under threat from HWA. We are exploring the potential to use satellite remote sensing and geospatial modeling as a tracking tool for HWA decline in the mountainous terrain of Shenandoah National Park. Pre(1984) and post(1997) infestation Landsat TM images were processed to remove atmospheric and topographic influences. Corrected pre-infestation images were used to classify hemlock stand areas and were used as a mask for subsequent analysis. Normalized difference vegetation indices (NDVI) were computed for both images, and assessed for rates of decline. Rates of decline from satellite imagery were compared to measures of hemlock decline from field plots, and to terrain characteristics through the use of regression tree statistical modeling techniques. Satellite image-based decline measures compare favorably to field estimates of decline, and show associations with landscape variables, especially elevation. However, variability in the post-infestation imagery shows only weak association with landscape variables, suggesting uniform decline by 1997, or the influence of unmeasured fineor coarse-scale parameters. Landscape analysis provides a useful tool for managers to track and assess the progression of eastern hemlock decline due to HWA, even in areas of high relief.
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