Modeling patch-scale expansion of arctic shrubs

北极植被变化的研究通常是在地块一级或在区域/生态系统范围内进行的。与个别灌木斑块相关的中间鳞片在很大程度上被忽视了。这项研究将通过量化和模拟以前在科尔维尔河流域重复拍摄的灌木覆盖的变化来探索北极灌木扩展的斑块尺度动态。将获得相同遗址的更多历史航空照片，并绘制灌木地图，以更详细地确定20世纪下半叶发生的变化。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，依靠一套简单的规则来确定灌木覆盖率增加了多少，以及模式是否与科尔维尔照片中显示的模式匹配。一种类似的方法对高山林线上的森林扩张进行了有效的建模。控制现有植被和新灌木建立概率之间的反馈强度将被用来制定可信的假设，以指导未来的实验研究。尽管在这个版本的模型中，建立和扩展的控制相对简单，没有明确地基于被认为是北极灌木生长的关键控制的生物地球化学过程，但一旦斑块水平控制已知，这里产生的模型在未来很容易被修改，以更明确地包括这些过程。将创建的模型是一个非常简单的随机细胞模型，空间上是明确的。该模型将使用Logistic生长模型，并将新灌木放置在景观上，以测试不同类型繁殖的重要性和不同的反馈强度。这个项目将极大地扩展我们目前能够从重复照片对中学到的东西，并在情节和生态系统规模之间起到关键的联系作用，这是目前对这一主题的研究的特点。

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.