SEDIMENTARY ANALYSIS OF FIRE HISTORY AND PALEOHYDROLOGY, EAGLE LAKE, CALIFORNIA

This project used a high-resolution sedimentary technique to characterize the fire history and paleohydrology of Eagle Lake, California from present to 18 kyrs BP. To understand global fire history trends, and the influence of climatic and anthropogenic factors, continued mapping and analysis of fire history as an earth systems process is essential. Wigand et al. (1995) recommended a high resolution paleofire study be performed at Eagle Lake. Eagle Lake is in central Lassen County, California. Fire history and paleohydrology were analyzed using macro-charcoal, magnetic susceptibility, chemostratigraphy, radiochronology, and lithology from a 1 m sediment core. Fire history was characterized using CharAnalysis. Paleohydrology was characterized using lithostratigraphy and magnetic susceptibility. Chemostratigraphy was used to perform zonation analysis. Radiochronology was used to establish a geochronology. The fire history of the Eagle Lake can be divided into three periods: 18 to 10 kyrs BP, 10 to 2.8 kyrs BP, and 2.8 kyrs BP to present. Hydrologic activity during the first period was low, limiting fuel availability, and supporting small frequent fires. Hydrologic activity during the second period was initially low due to limited fuel availability, supporting small frequent fire. The beginning of the second period marks the end of the glacial period. After approximately 8 kyrs BP, hydrologic activity increased to moderate/high levels, and fuel availability increased, supporting larger moderately frequent fires until 4.2 kyrs BP. From 4.2 to 1.5 kyrs BP, fire frequency and magnitude were low due to neoglaciation. Hydrologic activity during the third period was moderate and decreased to present, allowing for low to moderately frequent fires with moderate magnitude. The climate of Eagle Lake prior to 15 kyrs BP was cold and moist, from 15 to 8.5 kyrs BP it was warm and dry, from 8.5 kyrs to 4 kyrs BP it was warm and wet, and from 4 kyrs BP to present it was cool and wet. Indigenous populations clearly influenced the fire history of Eagle Lake, moderated fire frequency over the Holocene, and set fires for forest understory management, wildlife management, manufacturing, and agricultural purposes. Despite evidence of indigenous occupation, it is difficult to distinguish anthropogenic influences from climatic trends.