B11N-05
WHO IS IN THE DRIVER’S SEAT? MILLENNIAL-SCALE RECORDS OF WILDFIRE IN THE WESTERN USA REVEAL A COMPLEX INTERPLAY OF CLIMATE, FIRE, AND VEGETATION
Monday, 14 December 2015: 09:00
2010 (Moscone West)
Jennifer L Pierce1, Grant A Meyer2, Erica Bigio3, Nathan Nelson4, Michael J Poulos1, Sara Jenkins5, Kerry Elizabeth Riley6, Kerrie Weppner7, Lar Svenson8, Erin P Fitch9 and Jed Frechette2, (1)Boise State University, Boise, ID, United States, (2)University of New Mexico Main Campus, Albuquerque, NM, United States, (3)University of Arizona, Laboratory of Tree Ring Research, Tucson, AZ, United States, (4)USDA Forest Service Rocky Mountain Research Station, Rocky Mountain Research Station, Boise, ID, United States, (5)University of British Columbia, Mineral Deposit Research Unit, Vancouver, BC, Canada, (6)Utah State University, Geology Department, Logan, UT, United States, (7)Boise State University, Department of Geosciences, Boise, ID, United States, (8)USGS Idaho Water Science Center, Biophysical Ecology of the Intermountain West, Boise, ID, United States, (9)Hawai'i Institute of Geophysics and Planetology, Honolulu, HI, United States
Abstract:
A new synthesis of 10 study areas and >480 14C dates of Holocene fire and erosional response are recorded in alluvial fan sediments of the interior western US. Chronologies are from high elevation mixed conifer forests in the N. Rockies, ponderosa and Douglas-fir forests in the N. Rockies and SW, and low elevation sagebrush steppe and piñon-juniper woodlands near the Snake River Plain. Results are as follows: 1) Late Holocene arrivals of ponderosa, lodgepole and piñon pine at Northern Rockies sites correspond with increased fire severity, linking vegetation and fire regime changes. 2) Deposit types vary with environment; sheetfloods are more common in sparsely vegetated sites and in drier Holocene periods with open forests, whereas dense forests and infrequent severe fires often produce debris flows. 3) Climate variability drives ponderosa pine and Douglas-fir forests in both the SW and N. Rockies to burn ‘at both ends of the spectrum’, where frequent low-severity fires are typical, but higher-severity fires burn during severe droughts following fuel buildup over wet decades. 4) Fires in dry sage steppe are generally fuel-limited, but burn during prolonged wet and variable climates; grazing, land-use, and invasive species, particularly influence modern fires. 5) At moist high-elevation lodgepole and mixed conifer sites in Yellowstone and central Idaho, episodic large debris flows indicate high severity burns, often during severe multidecadal droughts. 6) Regionally coherent peaks exist ca. 200, 500, 900, 1700 and 2600 cal yr BP, but fire activity is not generally synchronous among sites. Differences in climate among sites likely account for some asynchroneity. 7) Recent severe fires have burned in 8 of 10 sites described; erosional response appears particularly anomalous in the SW, where impacts of fire suppression and land use are greatest. Widespread and severe modern fires may herald the arrival of a no-analog era of fire in the western US.
