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 upslope
This 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.
