Holocene fire occurrence and alluvial responses at the leading edge of pinyon–juniper migration in the Northern Great Basin, USA

Abstract

Fire and vegetation records at the City of Rocks National Reserve (CIRO), south-central Idaho, display the interaction of changing climate, fire and vegetation along the migrating front of single-leaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma). Radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response, and fossil woodrat (Neotoma) middens revealed pinyon and juniper arrivals. Fire peaks occurred ~ 10,700–9500, 7200–6700, 2400–2000, 850–700, and 550–400 cal yr BP, whereas ~ 9500–7200, 6700–4700 and ~ 1500–1000 cal yr BP are fire-free. Wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late Holocene, whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid-Holocene. Increased fires during the wetter and more variable late Holocene suggest variable climate and adequate fuels augment fires at CIRO. Utah juniper and single-leaf pinyon colonized CIRO by 3800 and 2800 cal yr BP, respectively, though pinyon did not expand broadly until ~ 700 cal yr BP. Increased fire-related deposition coincided with regional droughts and pinyon infilling ~ 850–700 and 550–400 cal yr BP. Early and late Holocene vegetation change probably played a major role in accelerated fire activity, which may be sustained into the future due to pinyon–juniper densification and cheatgrass invasion.

The predominance of post‐wildfire erosion in the long‐term denudation of the Valles Caldera, New Mexico

“…Previous studies that have quantified the relative importance of wildfire‐affected erosion in the long‐term denudation of landscapes have generally attributed a lower percentage, i.e., between 30 to 77%, to wildfire‐affected conditions [ Meyer et al ., ; Pierce et al ., ; Fitch and Meyer , ; Weppner et al ., ; Riley et al ., ]. As noted in section 1, however, actual estimates could be higher or lower than these values.…”

OSL chronology of middle to late Holocene aeolian activity in the St. Anthony dune field, southeastern Idaho, USA

“…For example, reduced fire frequency between 6700 and 4700 cal BP in semi-arid south-central Idaho, is interpreted to be due to drought-induced reduction of vegetation (Weppner et al, 2013). Charcoal-based fire reconstructions from northern Idaho suggest high fire frequency~6000e3500 cal BP, interpreted to be due to decreased summer precipitation (Brunelle and Whitlock, 2003).…”

“…Numbers represent locations of proxy records. 1-Sand Creek dunes, ID Gaylord et al, 2000), 2-Blackfoot dunes, ID (Pearce and Rittenour, 2009;Rittenour and Pearce, 2011), 3-Clearwater Range, ID (Brunelle and Whitlock, 2003), 4-City of Rocks, ID (Weppner et al, 2013), 5-Juniper Canyon dunes, WA (Sweeney et al, 2004), 6-Smith Canyon dunes, WA (Schatz, 1996), 7-Hanford dunes, WA (Smith, 1992), 8-Great Basin, CA (Li et al, 2001), 9-Rocky Mountain lake, WY (Mensing et al, 2013), 10-Bear Lake, UT/ID (Moser and Kimball, 2009 Sediment analysis indicate that the potential source material for the St. Anthony dune field was deposits of glacial Lake Terreton, a large shallow lake that existed in northeastern Idaho during the Pleistocene (Coughlin and Gaylord, 1999;Coleman, 2002). Nearby Mud Lake is a vestige of Lake Terreton whose now-exposed lacustrine sediments have been eroded and redeposited by the wind (Forman and Pierson, 2003).…”

Vegetative and climatic controls on Holocene wildfire and erosion recorded in alluvial fans of the Middle Fork Salmon River, Idaho

“…This was likely a stronger control prior to the arrival and spread of cheatgrass (Bromus tectorum) into the region in the late 1800s (Peek, 2000), a species that creates a more continuous ground cover than native sagebrush and bunchgrass communities, but is much more prone to severe fire (Stewart and Hull, 1949). Modern sheetflood deposits also have a stronger association with rangeland environments than forests in central Idaho (Meyer et al, 2001;Nelson and Pierce, 2010;Weppner et al, 2013).…”

“…Nonetheless, substantial fire-related debris-flow activity occurred in the MFSR in both upper and lower basins 570-320 and 260-0 cal yr BP. A clear regional peak in fire activity in alluvial charcoal records is seen at about 550 cal yr BP, especially across drier, lower-elevation environments of the lower South Fork Payette River (Pierce et al, 2004), Wood Creek (Nelson andPierce, 2010), and City of Rocks, Idaho (Weppner et al, 2013). The prominence of this peak is in part due to better preservation and exposure of young alluvial sediments, but it also corresponds to a period of relative warmth and drought ca.…”