Document Type

Thesis

Date of Degree Completion

Summer 2016

Degree Name

Master of Science (MS)

Department

Resource Management

Committee Chair

Megan K. Walsh, PhD.

Second Committee Member

Craig Revels, PhD.

Third Committee Member

Jennifer Lipton, PhD.

Abstract

High-resolution charcoal and pollen analyses were used to reconstruct a 16,000-year-long fire and vegetation history of the Blair Lake watershed in the Willamette National Forest of Oregon. The record shows that during the late glacial period, overall fire frequency was relatively low. Pinus and Abies were the dominant vegetation, along with Pseudotsuga and Alnus, suggesting that an open-canopy conifer forest developed soon after the area was glacier free. Fire frequency increased during the early Holocene. Warmer and drier conditions are reflected in the herbaceous vegetation, Artemisia, Poaceae, and Cyperaceae, suggesting that meadows or other openings were part of the forest environment at this time. Fire frequency decreased at the beginning of the middle Holocene and was relatively stable until it began increasing at ca. 6,000 cal yr BP, and the highest fire frequency for Blair Lake occurred at ca. 5,500 cal yr BP. Increases in Tsuga heterophylla and Tsuga menziesii during the middle Holocene indicate that conditions were wetter, and decreases in Pseudotsuga and Alnus suggest that the forest was more closed than earlier. Fire frequency decreased at the beginning of the late Holocene and was especially low at ca. 3,000 cal yr BP. It then increased until ca. 900 cal yr BP, before decreasing toward present. Decreases in Pinus and Artemisia, combined with increases in Tsuga heterophylla, Tsuga mertensiana, and Cupressaceae, indicate cold, wet conditions prevailed during the late Holocene. Herbaceous pollen was higher during the late Holocene than at any other time in the record, suggesting that meadows may have been an important part of montane forest environments. Archaeological and historical data were combined with the paleoenvironmental reconstructions at Blair Lake in order to better understand the role that humans may have played in the creation and/or use of montane forests and whether human activity or climate was the major influence on past fire and vegetation history. Climate seems to have been the major driver past fire and vegetation history, but it is likely that humans contributed to the fire activity at Blair Lake, particularly during the middle and late Holocene.

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