Modeling patch-scale expansion of arctic shrubs

北极植被变化的研究通常是在样地水平或区域/生态系统尺度上进行的。与单个灌木斑块相关的中间鳞片在很大程度上被忽略了。本研究将通过对科尔维尔河流域重复摄影记录的灌木覆盖变化进行量化和建模，探索北极灌木扩张的斑块尺度动态。将获取同一地点的其他历史航空照片，并绘制灌木图，以更详细地确定20世纪下半叶发生的变化。该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。细胞模型将被开发出来，它依赖于一套简单的规则来确定灌木丛覆盖面积增加了多少，以及这种模式是否与科尔维尔照片中显示的模式相符。类似的方法在模拟高山林木线的森林扩张方面是有效的。操纵现有植被与新灌木建立概率之间的反馈强度将用于提出合理的假设，以指导未来的实验研究。虽然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生物地球化学过程，而生物地球化学过程被认为是北极灌木生长的关键控制因素，但一旦知道了斑块水平的控制，这里产生的模型可以很容易地在未来进行修改，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，它在空间上是明确的。该模型将使用逻辑增长模型，并将新灌木放置在景观中，以测试不同类型繁殖的重要性和不同的反馈强度。该项目将大大扩展我们目前能够从重复照片对中学到的东西，并作为目前该主题研究特征的地块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.