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

灌木扩张是一个全球性的现象，涉及从草本覆盖到木本覆盖的转变。这一现象是北极陆地变化的最公认的组成部分之一，但其在20世纪下半叶的确切特征在很大程度上是未知的。本博士论文研究项目旨在量化阿拉斯加北部灌木扩张的历史空间特征，并研究景观尺度的环境特征（地形、水文、灌木繁殖特征以及相关反馈的存在、强度和方向性）如何影响其发展。博士生的第一个目标将通过使用美国地质调查局（USGS）提供的历史（20世纪50年代至80年代）航空图像和21世纪后期的高分辨率卫星图像来完成。这些图像集有助于绘制灌木斑块及其在这段时间内的扩展。然后将模式度量分析应用于这些地图，以确定斑块密度、斑块大小可变性和斑块之间的距离等特征是如何变化的。第二个目标将通过开发一个简单的计算机模型来实现，该模型模拟灌木随时间的扩张，以响应灌木繁殖特征、地形和水文的操纵，以及相关反馈的存在、强度和方向性。将模式输出和观测到的扩大格局的地图进行统计比较，将有助于产生关于景观一级对扩大的环境控制的假设。由于美国地质勘探局图像的地图比例尺的变化，可能会低估灌木覆盖。为了确保其效用，需要改进的计算机模型将需要美国鱼类和野生动物管理局和国家公园管理局提供的关于灌木斑块变化的精细数据。这些新的图像集将提供验证计算机模型所需的细节。该研究项目将提供对阿拉斯加北部灌木扩张变化特征的更好理解，并为关于其景观尺度环境控制的假设的产生提供更坚实的基础。这将允许未来的研究途径，如基于实地的观察和/或实验来测试这些假设，并将营养循环特征（灌木扩张的主要精细尺度环境控制）纳入模拟模型。该项目将为本科生提供良好的教育和培训机会，并将包括一系列推广工作，包括向主要是阿拉斯加原住民的社区（如Atqasuk、Barrow、Kaktovik和Anaktuvuk Pass）的学生和公众进行研究报告。由于灌木扩张是一个影响当地社区环境的过程，因此研究应该帮助社区解决历史模式和机制。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

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.