Collaborative Research: Hydrologic and Permafrost Changes Due to Tree Expansion into Tundra

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The Arctic has been warming at an accelerating rate over the last several decades, and at the same time, trees and shrubs have been invading into tundra across the polar regions of Alaska, Canada, and Russia. These shifts in vegetation may, in turn, have the potential to influence regional hydrology and climate. The goal of this collaborative project is to combine approaches to study water, energy, and carbon cycling to understand inteactions between forest and tundra, including permafrost. The investigators will examine the effects of tree expansion, or encroachment, on movement of water between earth and air in an understudied forest-tundra boundary in the Siberian Arctic. The methods will include collection and analysis of field data, use of remote sensing, and modeling. The investigators will collaborate with scientists and students in Russia, and U.S. graduate students will be exposed to interdisciplinary research, perform field work in Russia, and have the opportunity to develop international collaborations. Various outreach activities will inform the public about results of this research and more generally, about the role of the Arctic in global environmental change. These activities include development of museum exhibits at the Museum of Natural History (MI), Orton Geological Museum (OH), Museum of Prairiefire (KS); public research seminars engaging indigenous people of Yamal (Russia); and documentaries showcasing this study in social and news media.The objective of this project is to study changes in hydrology and permafrost associated with tree expansion into tundra areas at the scales of both the field observational program and the regional Western Siberian Plain. The underlying hypotheses are that the tree encroachment process 1) alters the seasonality of heat exchange between the land and the atmosphere, 2) increases surface evapotranspiration, and 3) leads to warming of the subsurface with a progressive increase of thickness of soil seasonal thaw depth. The research builds on fifty years of observations in the areas with documented larch and spruce encroachment in the Polar Urals and southern Yamal Peninsula of Russia. The investigators will use a novel theory combined with comprehensive field observational data and remote sensing analyses to reveal the differences in heat exchange between the tundra and forest land covers. Pairs of field monitoring plots will be identified, with expansion of larch and spruce in one plot and no encroachment in the second of the pair. Field observations will include measurements of: micrometeorology, snow conditions, and radiative fluxes; tree-scale sap flows; snow water equivalent; soil temperature, moisture, and heat fluxes; active layer thickness; and soil composition. Field data will inform a model to derive surface energy budgets and heat fluxes. Remote sensing data from 1980s to present will connect local trends inferred from these field observations with regional characertistics of the Western Siberian Plain. Observed and modeled heat fluxes will be used in a comprehensive physical model to study the impact of vegetation encroachment on permafrost dynamics at both local and regional scales, and analysis of uncertainty will assess the reliability of the project findings.