Spatial Variability in Mountain Birch Population Dynamics Under Herbivory Pressure at Treeline in Northern Sweden

在接下来的一个世纪里，地球气候预计将变暖，降水模式预计将发生变化。全球各地的植被模式与气候条件有关，因此预计也会发生变化。由于气候和植被之间的联系，植被类型之间的边界被认为是确定气候变化影响的最佳监测地点。除了对气候变化的影响外，植被边界本身也是重要的生物地理特征。有可能成为敏感生物指示器的一条这样的边界是北纬的森林-冻土带交错带。它的存在是因为寒冷的温度限制了树在更高的海拔或纬度上的建立和生长。Fennoscandia的树线环境是气候变化的特别敏感的指标。它们特别令人感兴趣，因为它们发生在北极和高山条件的交汇处，以及形成林线的物种(山桦：毛白桦)。Czerepanovii)是落叶的，而大多数其他北半球的树线以针叶树为特征。这些树线的一个特别显著的特点是，它们受到驯鹿食草性的影响。事实上，驯鹿觅食可能会干扰桦树的上坡/向北迁移，从而限制树线应对气候变暖的能力。放牧驯鹿是当地土著人民(萨米人)文化的重要组成部分，因此，驯鹿与林线环境之间的互动在科学和实践上都具有重要意义。这项研究考察了物理环境特征，如坡向、地形位置和苔原植被与驯鹿施加的草食压力之间的相互作用，以评估在瑞典北部山区驯鹿牧区的树上带内建立山桦的可能性。树状年代学方法与驯鹿历史种群和区域气候数据相结合，将揭示这种环境中的形成时期。此外，描绘在最近温暖条件下建立的树苗密度的精细空间变化的地块水平数据将阐明地形、驯鹿食草性和来自苔原植被的竞争对桦树向上迁移能力的影响。这项研究将通过研究气候变化下草食性和树木建立之间的相互作用，为关于交错带(生态过渡带)的文献做出重要贡献。树线交错带被认为是各种环境中过渡带的模拟，因此结果应该是广泛适用的。用来分析交错带格局的程序可以在其他地方用于类似的情况。这项研究将有助于培养研究生和本科生，并将加强美国和瑞典科学家之间的联系。这项研究的结果将与萨米人分享。

During the coming century the Earth's climate is expected to warm and precipitation patterns are expected to change. Vegetation patterns across the globe are coupled to climatic conditions and are therefore also expected to change. Because of the linkages between climate and vegetation, the boundaries between vegetation types are thought to be excellent monitoring locations for identifying the effects of altered climate. In addition to their implications for climate change, vegetation boundaries are significant biogeographic features in their own right. One such boundary with the potential to be a sensitive bioindicator is the forest-tundra ecotone of northern latitudes. It exists because cold temperatures constrain tree establishment and growth at higher elevations or latitudes. The treeline environments of Fennoscandia are particularly sensitive indicators of climate change. They are of special interest because they occur at the intersection between both Arctic and alpine conditions, and the species that forms the treeline (mountain birch: Betula pubescens ssp. czerepanovii) is deciduous, while most other northern hemisphere treelines are characterized by coniferous trees. A particularly notable characteristic of these treelines is that they are impacted by reindeer herbivory. In fact, reindeer browsing may interfere with the upslope/northward migration of birch and thereby limit the ability of treeline to respond to climatic warming. Reindeer herding is an important part of the culture of the local indigenous people (Sami) and consequently the interaction between reindeer and the treeline environment is of interest both scientifically and practically. This research examines the interaction of physical environmental characteristics such as aspect, topographic position, and tundra vegetation with herbivory pressure exerted by reindeer to evaluate the establishment of mountain birch within the supra-treeline zone of a reindeer herding district in the mountains of northern Sweden. Dendrochronological methods combined with historic reindeer populations and regional climatic data will reveal periods of establishment within this environment. Additionally, plot-level data depicting fine-scale spatial variations in the density of tree seedlings that were established under recent warm conditions will elucidate the influences of topography, reindeer herbivory, and competition from tundra vegetation on the ability of birch to migrate upslopeThis research will make a vital contribution to the literature on ecotones (ecological transition zones) by investigating the interplay between herbivory and tree establishment under a changing climate. The treeline ecotone is considered an analog for transition zones in a wide variety of environments and therefore the results should be broadly applicable. The procedures used to analyze ecotone pattern can be used in similar situations elsewhere. This research will aid in the training of graduate and undergraduate students and will strengthen ties between scientists in the US and Sweden. Findings from this research will be shared with the Sami.