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

在未来的一个世纪里，地球的气候预计会变暖，降水模式预计会发生变化。全球的植被模式与气候条件有关，因此预计也会发生变化。由于气候与植被之间的联系，植被类型之间的边界被认为是识别气候变化影响的极好监测地点。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。其中一个可能成为敏感生物指标的边界是北纬地区的森林-苔原过渡带。它的存在是因为寒冷的温度限制了树木在高海拔或高纬度地区的生长和生长。芬诺斯坎迪亚的林木线环境是气候变化的特别敏感的指标。它们是特别有趣的，因为它们发生在北极和高山条件的交汇处，并且形成树线的物种（山桦树：桦树）。Czerepanovii)是落叶树，而大多数其他北半球树木线的特点是针叶树。这些树线的一个特别显著的特征是它们受到驯鹿食草性的影响。事实上，驯鹿的觅食可能会干扰桦树的上坡/北移，从而限制了树线对气候变暖的反应能力。驯鹿放牧是当地土著人民（萨米人）文化的重要组成部分，因此驯鹿与树线环境之间的相互作用在科学和实践上都很有趣。本研究考察了物理环境特征（如地形、地形位置和苔原植被）与驯鹿施加的草食压力的相互作用，以评估瑞典北部山区驯鹿牧区超树线区内山地桦树的建立。树木年代学方法结合历史上的驯鹿种群和区域气候数据将揭示在这种环境下建立的时期。此外，在最近的温暖条件下建立的描绘树木幼苗密度精细尺度空间变化的标样数据将阐明地形、驯鹿食草性、通过研究气候变化下草木和树木的相互作用，本研究将对过渡带（生态过渡带）的研究做出重要贡献。树线交错带被认为是各种环境中过渡带的类比，因此结果应该广泛适用。用于分析过渡带格局的程序可用于其他地方的类似情况。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.