International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire
RESEARCH ARTICLE

Late Holocene fire–climate relationships of the western San Juan Mountains, Colorado

Erica R. Bigio A C , Thomas W. Swetnam A and Philip A. Pearthree B
+ Author Affiliations
- Author Affiliations

A Laboratory of Tree-Ring Research, 1215 E. Lowell St., University of Arizona, Tucson, AZ 85721, USA.

B Arizona Geological Survey, 1955 E. Sixth Street, PO Box 210184, Tucson, AZ 85721, USA.

C Corresponding author. Email: ebigio@email.arizona.edu

International Journal of Wildland Fire 26(11) 944-962 https://doi.org/10.1071/WF16204
Submitted: 9 November 2016  Accepted: 6 August 2017   Published: 27 October 2017

Abstract

In recent decades, warming temperatures and severe drought have contributed to large and severe wildfires in the south-western United States. To put current wildfires in a long-term context, we reconstructed fire events with alluvial stratigraphy methods in south-western Colorado, and compared with paleoclimate records over the late Holocene. The chronology of 32 fire-related sedimentation events from six tributary basins was established using 48 radiocarbon dates. Based on deposit characteristics, we found episodes of increased high-severity fire for 2750–2350 cal yr BP (800–400 BCE); 1400–1175 cal yr BP (550–775 CE); 1050–700 cal yr BP (900–1250 CE); and 525–250 cal yr BP (1425–1700 CE). There were peaks in low-severity fires in 2350–2000 cal yr BP (400–50 BCE) and 300–70 cal yr BP (1650–1880 CE). Two of the four episodes of high-severity fire corresponded with multi-decadal droughts, including clusters of extreme drought years. The most recent fire episode was preceded by wetter conditions and decreased frequency of extreme drought years, which facilitated the build-up of fuel loads. However, previous high-severity episodes were not consistently preceded by wetter conditions. Steep slopes and overall rugged terrain were also likely contributing factors to fuel accumulation and high-severity fires. A recent wildfire followed a fire-free interval of greater than 120 years and likely contained more extensive areas of high-severity burned area than fire events over the late Holocene.

Additional keywords: alluvial sediments, fire history, fire-related debris flow, mixed conifer, ponderosa pine.


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