LONG-TERM FIRE HISTORY RECONSTRUCTION OF SUBALPINE FORESTS IN THE SIERRA NEVADA, CALIFORNIA, USA AND IMPLICATIONS FOR LATE HOLOCENE DROUGHT

HALLETT, D.J. AND ANDERSON, R.S.

Center for Environmental Sciences & Quaternary Sciences Program, Box 5694, Northern Arizona University, Flagstaff, AZ

Old growth subalpine forests in the Sierra Nevada burn infrequently compared to lower elevation forests and synchronous fire at these sites may be an indicator of anomalous regional drought. We present millennial-scale evidence of fire using lake sediment charcoal records from two subalpine sites, Gaylor Lake (3062 m) and Barrett Lake (2816 m), and compare these to other fire records based on historic fires, stand ages, fire scars as well as charcoal accumulation in lake sediments and meadow soils at lower elevation sites. Fire frequency changes inferred from charcoal records agree with other proxy climate records from the Sierra Nevada and help establish a connection between forest fires, fuel accumulation and drought events in the late Holocene.  Multi-proxy evidence suggests that widespread fire and frequent drought events occurred during the Medieval Warm Period (1000-700 cal years BP) and a less positive water balance during the late Holocene between 2400 to 1200 cal years BP may have limited fuel accumulation and fire activity at our higher elevation site.  Variations in background charcoal at both sites suggest a response to both fire activity and fuel loads.  Long-term climate variability has affected the frequency of forest fire at our sites and will most likely continue under a changing global climate.