Doctoral Dissertation Research: Mapping and Modeling Shrub Expansion in the Arctic National Wildlife Refuge

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Shrub expansion is a global phenomenon involving the transition from herbaceous to woody cover. This phenomenon is one of the most recognized components of terrestrial changes in the Arctic, but its precise characteristics in the latter half of the 20th century are largely unknown. This doctoral dissertation research project seeks to quantify the historic spatial characteristics of shrub expansion in the northern Alaska and investigate how landscape-scale environmental characteristics (topography, hydrology, shrub reproductive characteristics, and the existence, strength, and directionality of associated feedbacks) influence its development. The doctoral student's first objective will be accomplished by using historical (1950s-1980s) aerial imagery available from the United States Geological Survey (USGS) and high-resolution satellite imagery from the late 2000s. These imagery sets facilitate the mapping of shrub patches and their expansion over this time period. Pattern metric analysis then will be applied to these maps to determine how characteristics like patch density, patch size variability, and distance between patches have changed. The second objective will be accomplished through the development of a simple computer model that simulates shrub expansion over time in response to manipulations of shrub reproductive characteristics, topography and hydrology, and the existence, strength, and directionality of associated feedbacks. Statistical comparisons of the model output and maps of observed patterns of expansion will facilitate the generation of hypotheses regarding the landscape-level environmental controls on expansion. Because of variability in the cartographic scale of the USGS images, underestimations of shrub cover are likely. In order to assure its utility, the computer model to be refined will require fine-scale data regarding changes in shrub patches available from the U.S. Fish and Wildlife Service and the National Park Service. These new imagery sets will provide the detail needed for validation of the computer model.This research project will provide an improved understanding of the changing characteristics of shrub expansion in northern Alaska as well as a stronger foundation for the generation of hypotheses regarding its landscape-scale environmental controls. This will allow for future research avenues, such as field-based observations and/or experiments to test these hypotheses and the incorporation of nutrient-cycling characteristics (a dominant fine-scale environmental control on shrub expansion) into the simulation model. The project will provide an excellent education and training opportunity for an undergraduate student, and it will include a set of outreach efforts, including research presentations to students and members of the public in communities of primarily Alaskan Natives, such as Atqasuk, Barrow, Kaktovik, and Anaktuvuk Pass. Because shrub expansion is a process that affects the environment of native communities, the research should help communities address historic patterns and mechanisms. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.