Wednesday, 19 November 2003: 1:30 PM
Holocene fire reconstructions from the northwestern U.S.: an examination at multiple time scalesPoster PDF (594.1 kB)
A network of fire history records in the northwestern U.S. provides an opportunity to examine the linkages among changes in fire, climate, and vegetation during the Holocene. The reconstructions are based on high-resolution charcoal and pollen data obtained from radiocarbon-dated lake-sediment records. Calibration of the records is provided by information on charcoal deposition following recent fires and the age of historical fires provided by dendrochronological studies. Throughout the Holocene, regional differences in fire activity are apparent: the Coast Range has been characterized by relatively few fires, the Klamath Mountains has experienced frequent fires, and fire regimes in the northern Rocky Mountains have been strongly governed by millennial and centennial climate variability. Within the northern Rocky Mountains, the fire history is spatially variable. High-elevation sites record lower fire frequencies than low-elevation sites. In addition, climate changes resulting from the amplification of the seasonal cycle of insolation in the early Holocene and its attenuation in the late Holocene are registered by vegetation and fire history data at the sub-regional scale. The summer insolation maximum in the early Holocene led to enhanced monsoonal circulation and wetter summers in parts of the northern Rocky Mountains causing fire frequencies to decrease. In other regions, a stronger-than-present Pacific subtropical high-pressure system promoted drier summers and increased fire frequencies. The juxtaposition of these strengthened circulation features in the early Holocene served to accentuate the sub-regional differences in precipitation, vegetation, and fire regimes evident today. In addition to the early Holocene period, heightened fire activity occurred at many sites ca. 1000 years ago during the so-called Medieval Warm Period. The association between episodes of intensified drought conditions, increased fire occurrence, and more xerophytic vegetation is observed on several time scales in the paleoecological record and suggests that modern fire regimes need to be evaluated in light of these long-term linkages to assess the effects of recent human actions and forest management practices.
Supplementary URL: http://http:\\geography.uoregon.edu\envchange