1 / 29

Of

A fire history reconstruction of the western San Juan Mountains using alluvial sediment and tree-ring methods. Of . Erica Bigio LTRR and Geosciences University of Arizona. L arge and severe wildfires of the past 10 – 20 years:.

anson
Télécharger la présentation

Of

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A fire history reconstruction of the western San Juan Mountains using alluvial sediment and tree-ring methods Of Erica Bigio LTRR and Geosciences University of Arizona

  2. Large and severe wildfires of the past 10 – 20 years: • Increasing trend in area burned across the western US over past 40 years • linked to earlier snowmelt, higher spring/summer temps • large areas of high-severity fire within burned areas Westerling et al., 2006

  3. Photo: Craig Allen Post-Fire Geomorphic Responses In mountainous areas, increased erosion on hillslopes and channel erosion in valleys Depending on the extent of high-severity burned area, runoff may lead to flooding and debris flow events at the watershed scale. Photo: John Moody

  4. In the Southwest, high-severity burned areas are larger when compared with historical conditions in ponderosa pine and mixed-conifer forests: Today 1500 – 1900 AD dense forest today Pre- 19th century open forest

  5. Fire history methods: Tree rings: Tree-Rings Alluvial fans: Lake sediments: 5,000 years 500 years 10,000 years

  6. Approach: Combine tree-ring and alluvial sediment methods Sediment exposure Fire-scarred tree Age-structure plot

  7. Study Area: Missionary Ridge Fire (2002); Durango, Colorado • Flooding and debris flows occurred throughout the burned area • created natural exposures of older sediment deposits in tributary stream • channels and alluvial fans Cannon and others, 2003

  8. Alluvial sediment accumulates in the valley bottoms and fans

  9. Central research question: • How have fire regimes have variedin ponderosa pine and mixed-conifer forests of the western San Juan Mountains over the past ~ 3,000 years, and how do fire regimes relate to climate variability over this time period? • Alluvial records may show broader range of fire regime changes than observed in the past 500 years • Specifically, the Medieval Climate Anomaly (AD 900 – 1300) • Evidence of crown fire activity during this time at alluvial fan fire history sites in the Northern Rockies and southwestern NM.

  10. N Sediment exposure Fire-scarred tree Age-structure plot Tree-ring and alluvial sediment methods combined within four study sites Additional sediment samples taken where available One study site published previously (Bigio et al., 2010)

  11. Locations sampled: Combined with tree-ring methods

  12. Upper Haflin Canyon

  13. Debris flow unit Burned soil surface

  14. Charcoal deposited with fine-grained sediments within clast-supported deposits

  15. Sediment characteristics (end members): Debris flow deposits are evidence of high-severity fires Fine-grained fluvial deposits indicates low-energy deposition and are used to infer low-severity fires

  16. Summary of Sediment Samples:

  17. All 14C dates from multiple locations within watersheds and fan surfaces • Increased fire-related sedimentation events from AD 900 – 1280 •  Medieval Climate Anomaly (AD 900 – 1300) • Increased fire-related sedimentation events from AD 1470 – 1650

  18. Medieval Warm Period Events (AD 900 – 1280):

  19. Locations of sedimentation events during the Medieval Period:

  20. Events from ~1400 - present:

  21. Locations of events from ~1400 - present:

  22. Example of recent charcoal deposit 263 +/-44

  23. Example of fine-grained sediment with abundant charcoal: 263 +/- 44 1485 – 1954 AD

  24. Fire-scarred trees Age-structure plots

  25. Haflin Canyon Fire Scar Chronology Widespread fire years defined by 25% of recording trees scarred by an event Most fire-scarred trees located on south-facing slopes

  26. Haflin Canyon North and South Facing Plot #3 North-facing plot South-facing plot

  27. Establishment Ages of all plots and fire scar data combined

  28. Conclusions: Increased fire activity during the Medieval Warm Period: Sediment characteristics indicate debris flow events (high- severity fire) and fine-grained deposition (low-severity fire) Multiple locations within a one watershed (Steven’s Creek), suggests a widespread fire event, including high-severity fire.  not observed throughout the study area High-severity burned area during the MWP may not have exceeded the extent of high-severity burned area observed during the Missionary Ridge Fire Localized fire activity observed in sediment record from 1470 – 1650 AD: Not as widespread as events observed in the MWP at the watershed scale  though synchronous throughout the study area

  29. Thanks to a great field and lab crew! Support from: • JFSP GRIN award PEO Scholar award LTRR/College of Science Awards • GSA graduate student award • NSF IGERT in Archaeological Sciences

More Related