Modeling patch-scale expansion of arctic shrubs

对北极植被变化的研究通常是在地块一级或区域/生态系统尺度上进行的。与个体灌木斑块相关的中间尺度在很大程度上被忽视了。本研究将探讨斑块规模的动态北极灌木扩张的量化和建模灌木覆盖的变化，以前记录的重复摄影的科尔维尔河流域。将获得同一地点的其他历史航空照片，并绘制灌木地图，以更详细地确定20世纪后半叶发生的变化。这种方法依赖于扩张的空间特征，作为我们是否理解这一过程的关键指标。将开发细胞模型，依赖于一套简单的规则，以确定有多少灌木覆盖增加，如果模式匹配的模式显示在科尔维尔照片。一个类似的方法已经有效地模拟森林扩张在高山树线。操纵现有植被和新灌木的建立概率之间的反馈强度将被用来开发合理的假设，以指导未来的实验研究。虽然在这个版本的模型中，对建立和扩展的控制相对简单，而且没有明确地基于被认为是北极灌木生长关键控制因素的地球化学过程，一旦知道了斑块水平控制，这里产生的模型可以很容易地在将来修改，以更明确地包括这些过程。将要创建的模型是一个非常简单的随机细胞模型这是空间上明确的。该模型将使用逻辑增长模型，并将新灌木置于景观中，以测试不同类型繁殖的重要性和不同的反馈强度。该项目将显著扩展我们目前能够从重复照片对中学习的内容，并作为目前表征该主题研究的情节和生态系统尺度之间的关键联系。

Studies of Arctic vegetation change have typically been done at either the plot level or at regional/ecosystem scales. The intermediate scales associated with patches of individual shrubs have largely been ignored. This research will explore patch scale dynamics of arctic shrub expansion by quantifying and modeling the changes in shrub cover previously documented by repeat photography for the Colville River basin. Additional historic aerial photographs of the same sites will be acquired and the shrubs mapped to determine in more detail the changes that have occurred over the latter half of the 20th century. The approach relies on the spatial characteristics of the expansion as the critical indicator of whether we understand the process. Cellular models will be developed that rely on a set of simple rules to determine how much shrub cover increases and if the pattern matches those patterns shown in the Colville photos. A similar approach has been effective for modeling forest expansion at the alpine treeline. Manipulating the strength of feedbacks between existing vegetation and the establishment probabilities of new shrubs will be used to develop plausible hypotheses to guide future experimental research. Although the controls on establishment and expansion in this version of the model are relatively simple and not explicitly based on the biogeochemical processes that are thought to be the key controls on shrub growth in the Arctic, the model produced here can easily be modified in the future to include these processes more explicitly once the patch level controls are known.The model that will be created is a very simple stochastic cellular model that is spatially explicit. The model will use a logistic growth model and place the new shrubs on the landscape in ways that test the importance of different types of reproduction and with different feedback strengths. This project will expand significantly what we are currently able to learn from the repeat photo pairs and serve as a crucial link between the plot and ecosystem scales that currently characterize research on this topic.