Year of Award

2017

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Systems Ecology

Department or School/College

College of Forestry and Conservation

Committee Chair

Philip Higuera

Commitee Members

Ashley Ballantyne, Solomon Dobrowski, Ryan Kelly, Carl Seielstad

Keywords

fire, climate, boreal forest, arctic, Alaska, paleoecology

Subject Categories

Terrestrial and Aquatic Ecology

Abstract

Boreal forest and tundra ecosystems are globally important because the mobilization of large carbon stocks, and changes in energy balance could act as positive feedbacks to ongoing climate warming. In Alaska, wildfire is a key driver of ecosystem structure and function, and therefore fire strongly determines the feedbacks between high-latitude ecosystems and the larger Earth system. The paleoecological record from Alaska reveals the sensitivity of fire regimes to climatic and vegetation change over centennial to millennial time scales, highlighting increased burning with warming and/or increased landscape flammability associated with large-scale vegetation changes. This thesis focuses on two studies aimed at advancing our understanding of the history and spatiotemporal patterns of fire in Alaskan ecosystems over Holocene time scales (i.e., the past 10,000 years). In Chapter 1, I developed seven lake-sediment records of fire history spanning the past 465 years from CE 1550 to 2015. In Chapter 2 I synthesized 27 published sediment-charcoal records from four Alaskan ecoregions to evaluate variability and synchrony in fire activity over the past 10,000 years. In both chapters, fire history was inferred from interpretations of macroscopic charcoal records from lake sediments. Biomass burning varied over centennial and millennial time scales within each of the four Alaskan ecoregions. Both biomass burning and fire frequency increased significantly with the expansion of black spruce, c. 4-6 thousand years ago. Biomass burning also increased during the Medieval Climate Anomaly (MCA) in some regions, but results do not indicate prolonged periods of synchronous fire activity among regions. Upper limits to fire synchrony suggest fire-vegetation interaction may provide a negative feedbacks to increased burning. Increases in biomass burning with non-varying fire return intervals suggests an increase in fire severity during warm periods. Over the last century, our records also reveal significant increases in biomass burning. This research highlights the sensitivity of fire activity to broad-scale environmental change, including climate warming or major shifts in vegetation flammability. The lack of prolonged synchrony and apparent tradeoffs between tree recruitment and biomass burning indicate important vegetation feedbacks that may confer resilience of boreal forests to increased warming and fire activity.

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© Copyright 2017 Tyler J. Hoecker