Influences of Herbivory on Treeline Under Changing Climate

在世界各地的北极和高山地区都存在树线，许多树线被证明在短时间和长时间跨度内都对气候变化做出反应。到目前为止，大多数树线研究都集中在树线位置的气候控制上。然而，一些树线环境除了气候外，还可能受到食草动物的控制。这个研究项目的重点是Fennoscandian树线，这些树线受到驯鹿食草性和零星的秋蛾侵扰的影响。放牧驯鹿是当地土著人民(萨米人)文化的重要组成部分。这项研究的目的是发现草食如何与气候变化相互作用，影响林线上树木的建立和生长，从而促进主要交错带(植被边界)的迁移潜力。这项研究将使用树状年代学方法结合瑞典北部气候、驯鹿种群和秋季飞蛾暴发的长期高质量数据集来完成。主要的假设是，大型食草动物种群的存在对树木的建立和生长产生了负面影响。这一假设将通过相关分析、方差分析和协方差分析进行检验。预计林线以上地带的大量植树时期与驯鹿种群较少和没有飞蛾暴发的时期相对应。同样，当控制气候变化时，当食草动物数量较少时，树木生长会很快。植被边界的动态引起了广泛的兴趣，因为它们与气候变异性有关。尤其是树线交错带，受到了对气候变化影响感兴趣的科学家的极大关注。这项研究将通过研究食草动物的影响，为树线动力学的科学做出重要贡献。了解食草动物和气候的综合影响对于解释树线植被的变化至关重要。树线交错带是对各种环境下交错带的模拟，因此其结果应该具有广泛的适用性。此外，通过揭示驯鹿觅食对植被的影响，这项研究将为可持续驯鹿放牧实践的实施提供信息。该项目将为研究生和本科生提供研究和教育机会。

Treelines exist world-wide in both Arctic and alpine locations, and many have been shown to respond to changes in climate over both short and long time spans. Most treeline research to date has focused on climatic controls of treeline location. Some treeline environments, however, are potentially controlled by herbivory in addition to climate. This research project focuses on Fennoscandian treelines, which are affected by reindeer herbivory and sporadic infestations of autumnal moths. Reindeer herding is an important part of the culture of the local indigenous people (Sami). The objective of this research is to discover how herbivory interacts with climatic variability to influence the establishment and growth of trees at treeline, and thereby contributes to the migration potential of a major ecotone (vegetation boundary). The research will be accomplished using dendrochronological methods combined with long-term high-quality datasets of climate, reindeer populations, and autumnal moth outbreaks in northern Sweden. The primary hypothesis is that establishment and tree growth are negatively affected by the presence of large herbivore populations. The hypothesis will be tested using correlation analysis, analysis of variance and analysis of covariance. It is expected that periods of abundant tree establishment in the supra-treeline zone correspond to periods with low reindeer populations and no moth outbreaks. Similarly, when controlled for varying climate, tree growth will be high when herbivore populations are low.The dynamics of vegetation boundaries are of broad interest because of their link to climatic variability. The treeline ecotone, in particular, has received much attention from scientists interested in the effects of climate change. This research will make a vital contribution to the science of treeline dynamics by investigating the influence of herbivory. Understanding the combined influences of both herbivory and climate are critical for interpreting changes in treeline vegetation. The treeline ecotone is an analog for ecotones in a wide variety of environments, and therefore the results should be broadly applicable. Moreover, by revealing the influence of reindeer browsing on vegetation, the research will inform the implementation of sustainable reindeer herding practices. The project will provide research and educational opportunities for graduate and undergraduate students.