Influences of Herbivory on Treeline Under Changing Climate

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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.