Date of Award

Spring 2025

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Russell G Congalton

Second Advisor

Benjamin T Fraser

Third Advisor

Jeffrey Garnas

Abstract

Eastern hemlock (Tsuga canadensis) is an ecologically-important tree species in the forests of eastern North America. This species is currently declining throughout much of its range due to the invasive insect species hemlock woolly adelgid (Adelges tsugae) and elongate hemlock scale (Fiorinia externa). The introduction of these insects in the region, in addition to drought, development, and native insect species, threatens the persistence of eastern hemlock on the eastern landscape. This study endeavored to use satellite remote sensing to assess eastern hemlock decline in New Hampshire currently and over time from 2000 to 2022. Several classifications were performed in order to evaluate our ability to detect eastern hemlock-dominated forests in southern New Hampshire generally, and to evaluate our ability to detect levels of decline in hemlock woolly adelgid-infested eastern hemlock-dominated stands in southern New Hampshire. Landsat and Sentinel imagery, various classification algorithms, and object- and pixel-based methods were experimented with to determine the methodology for producing the classifications with the highest overall accuracies. A series of classifications of Landsat imagery at a regular time-step over the study period using the Random Forest algorithm was also performed in order to map decline over time in these stands. Lastly, a time series analysis was completed using the LandTrendr algorithm to assess vegetation indices that may be useful in detecting decline over time in hemlock woolly adelgid-infested eastern hemlock-dominated stands. This study found methodology that was highly accurate at detecting eastern hemlock-dominated forests in southern New Hampshire, and methodology that was moderately accurate at detecting levels of decline in hemlock woolly adelgid-infested eastern hemlock-dominated stands. This study also found that the series of classifications of Landsat imagery over a regular time-step was effective at mapping decline over time in these stands. Lastly, this study found vegetation indices that may capture decline over time in pest-infested eastern hemlock-dominated stands in southern New Hampshire.

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