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

在即将到来的世纪，地球的气候预计将变暖，降水模式预计将发生变化。 地球仪的植被格局与气候条件相关联，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地理特征。有可能成为敏感生物指示器的一个边界是北方纬度的森林-冻原交错带。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建立和生长。芬诺斯堪的亚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，并且形成树线的物种（山桦：Betula pubescens ssp. czerepanovii）是落叶的，而大多数其他北方的树木都是针叶树。 这些树木线的一个特别显著的特点是，它们受到驯鹿食草动物的影响。 事实上，驯鹿吃草可能会干扰桦树向上/向北迁移，从而限制林木线应对气候变暖的能力。驯鹿放牧是当地土著人民（萨米人）文化的一个重要组成部分，因此驯鹿与林木线环境之间的相互作用在科学和实践上都很有意义。本研究探讨了物理环境特征，如方面，地形位置，苔原植被与驯鹿施加的食草动物压力的相互作用，以评估建立山区桦树内的驯鹿放牧区在北方瑞典山区的超树线区。树木年代学方法与历史驯鹿种群和区域气候数据相结合，将揭示在这一环境中定居的时期。此外，描绘在最近温暖条件下建立的树苗密度的小尺度空间变化的样地一级数据将阐明地形、驯鹿食草动物、这一研究将对生态交错带的研究做出重要贡献（生态过渡区）通过调查气候变化下草食动物和树木建立之间的相互作用。林线交错带被认为是一个模拟的过渡区在各种各样的环境，因此，结果应该是广泛适用的。分析生态交错带格局的方法可用于其他类似的情况。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.