HR: 1330h
AN: GC12A-0144    [PDF]
TI: Disturbance Frequency Changes in Western North and South America During the Holocene
AU: * Whitlock, C
EM: whitlock@oregon.uoregon.edu
AF: University of Oregon, Department of Geography, Eugene, OR 97403 United States
AU: Bartlein, P
EM: bartlein@uoregon.edu
AF: University of Oregon, Department of Geography, Eugene, OR 97403 United States
AU: Bianchi, M M
EM: mariam@bariloche.com.ar
AF: CONICET-CRUB, Universidad Nacional del Comahue, S.C. de Bariloche, 8400 Argentina
AU: Briles, C
EM: cbriles@darkwing.uoregon.edu
AF: University of Oregon, Department of Geography, Eugene, OR 97403 United States
AU: Brunelle, A
EM: andrea.brunelle@geog.utah.edu
AF: University of Utah, Department of Geography, Salt Lake City, UT 84112 United States
AU: Long, C
EM: clong@oregon.uoregon.edu
AF: University of Oregon, Department of Geography, Eugene, OR 97403 United States
AU: Markgraf, V
EM: markgraf@spot.colorado.edu
AF: University of Colorado, INSTAAR, Boulder, CO 80309 United States
AU: Marlon, J
EM: jmarlon@oregon.uoregon.edu
AF: University of Oregon, Department of Geography, Eugene, OR 97403 United States
AU: Meeker, C
EM: jmarlon@oregon.uoregon.edu
AF: University of Northern Arizona, Quaternary Studies Program, Flagstaff, AZ 86011 United States
AU: Power, M
EM: mpower@darkwing
AF: Indiana State University, Dept of Geography, Geology and Anthropology, Terre Haute, IN 47809 United States
AU: Walsh, M
EM: mwalsh2@darkwing.uoregon.edu
AF: University of Oregon, Department of Geography, Eugene, OR 97403 United States
AB: Fire is the dominant form of natural disturbance in temperate forested ecosystems, and as such, it serves as a process that links climate change to biosphere response. High-resolution charcoal records from the western temperate forests of North and South America provide an opportunity to compare current and recent (pre-settlement) changes in disturbance frequency with those during the Holocene. Charcoal data describe past fire activity under different climate and vegetation settings and offer information on changing levels of biomass as well as variations in fire frequency. An assessment of North American sites indicates gradually increasing levels of charcoal from the late-glacial to 2 ka, which is consistent with increasing fuel production during the Holocene. Fire-frequency data from both hemispheres indicate that the spatial heterogeneity evident in modern fire regimes has existed throughout the Holocene despite changes in the large-scale controls of climate. The heterogeneity is a result of spatial variations in the seasonal distribution of precipitation and their influence on fire climate and weather. Summer-dry areas (i.e., low summer:annual precipitation) registered higher-than-present fire activity in the early Holocene from ca. 13 to 7 ka. In North America, fire activity was apparently controlled by the early-Holocene strengthening of the northeast Pacific subtropical high during the summer insolation maximum. In Patagonia, high fire activity may have caused by the carry-over effects of low winter soil moisture during the winter insolation maximum. A decline in fire activity in summer-dry regions in the late Holocene suggests seasonally wetter conditions as a result of the onset of ENSO, less seasonality in precipitation, and/or the development of more closed forests. Summer-wet regions show the influence of stronger monsoonal circulation in the early Holocene, which caused a reduction in fire activity. In these regions, the late Holocene featured steadily increasing disturbance frequency until the fire suppression era. Fire anomalies (past conditions relative to the last 3000 years) at different sites suggest that the timing of the establishment of modern fire regimes is highly variable.
DE: 0400 Biogeosciences
DE: 1620 Climate dynamics (3309)
DE: 3309 Climatology (1620)
DE: 3344 Paleoclimatology
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting