Beautiful Days in the Neighborhood: Modeling Self-Perpetuated Climate and Forest Expansion during the Mid-Holocene

Thesis (Master's)--University of Washington, 2021At the end of glacial periods, warmer temperatures induce ice sheet retreat, exposing the land surface for forest establishment. The emergence of forest transforms the area from high to low albedo. Lowering land surface albedo can lead to additional local warming and the potential for this feedback-driven warming to further influence nearby climate, and these changes could be enough to accelerate forest expansion beyond what is orbitally driven alone.Pollen records show rapid expansion of needleleaf evergreen forest in Alaska during the mid-Holocene. Using this period as a case study, we explore the possible role of plant- atmosphere feedbacks in accelerating forest expansion in a two-step experimental set-up. By examining these feedbacks, we seek to gain a more comprehensive understanding of past and potential land-atmosphere interactions. Using a simplified reconstruction of this period, we simulated the climate response to initial forest establishment (in a coupled CLM-CAM experiment) and applied the modified climate to nearby vegetation (in an offline CLM experiment) to determine if the initial forest expansion could have led to more favorable growing conditions in the region. We isolated the effect of a forest’s presence on nearby climate, examined consequent local productivity changes for plants relevant to boreal forest succession, and explored the mechanisms at play