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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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