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Olson, Diana L. 2000. Fire in Riparian Zones: A Comparison of Historical Fire Occurrence in Riparian and Upslope Forests in the Blue Mountains and southern Cascades of Oregon. Seattle: University of Washington. M.S. Thesis. 274 p.

Diana Olson [dlolson@fs.fed.us]
Abstract | Full text

Despite the ecological importance of fire in Pacific Northwest forests, its role in riparian forests is not well documented. This study reconstructed the historical occurrence of fire within riparian forests along different stream sizes within three different national forests in Oregon. Two study areas were located in mostly dry, low-severity fire regime forests in the Blue Mountains of northeastern Oregon (Dugout and Baker) and the third study area was located in more mesic, moderate-severity fire regime forests on the western slopes of the southern Oregon Cascades (Steamboat). Fire scar dates and tree establishment dates were determined from a total of 424 fire scarred tree wedges and 81 increment cores taken from 67 riparian and upslope plots. Based on the data from this study, fire was common historically in the riparian zones of all three study areas. Weibull median probability fire return intervals (WMPIs) for riparian forests in Dugout ranged between 13 and 14 years, and were only slightly longer than those for upslope forests (averaging one year longer). In Baker, differences between riparian and upslope forest WMPIs were greater, ranging between 13 and 36 years for riparian WMPIs, compared to 10 to 20 years for upslope WMPIs. However, further analyses suggested that forest type and slope aspect play a larger role than proximity to a stream when it came to differentiating fire regimes in this study area. For both Dugout and Baker it appeared that stream channels did not necessarily act as fire barriers during the more extensive fire years. Steamboat riparian WMPIs were somewhat longer (ranging from 35-39 years) than upslope WMPIs (ranging from 27-36), but these differences were not significant. Fires were probably more moderate in severity and likely patchy, considering the incidence of fires occurring only at a riparian plot or an upslope plot within a pair, but not at both. It is possible that fire return interval lengths were associated with aspect, but more sampling would need to be done to show this. Based on the results from this study, it is evident that: 1) restoring fire, or at least conducting fuel reduction treatments, will be necessary to protect riparian forests in comparable forest ecosystems, 2) forests should be managed according to forest type, not just by proximity to a stream, and 3) historical recruitment of large woody debris was likely small but continuous for low-severity fire regime riparian forests, with a relatively short residence time, and patchy and more pulsed for the more moderate-severity fire regime forests.

Full Text

Because the entire thesis is about 88.4 MB including scanned images, it has been divided into smaller portions. File sizes range from 1.2 MB to 5.5 MB and are in .pdf format. The first three files (the cover through 114) contain the body of the text and tables in the appendix, and the remaining pages (115-274) contain the fire maps.

Cover to page 24 (3.4MB)
Pages 25-50 (1.3MB)
pages 51-114 (435kb)
Pages 115-124 (5.3MB)
Pages 125-134 (5.1MB)
Pages 135-144 (5.1MB)
Pages 145-154 (5MB)
Pages 155-164 (5.3MB)
Pages 165-174 (5.1MB)
Pages 175-184 (5.2MB)
Pages 185-194 (5.4MB)
Pages 195-204 (5.3MB)
Pages 205-214 (5.4MB)
Pages 215-224 (5.5MB)
Pages 225-234 (5.3MB)
Pages 235-244 (4.7MB)
Pages 245-254 (5.1MB)
Pages 255-264 (5MB)
Pages 265-274 (5MB)

For further information, contact:
Dr. David L. Peterson, Team Leader
400 N 34th Street, Suite 201, Seattle, Washington 98103 USA
(206) 732-7812; (206)732-7801 fax

peterson @ fs.fed.us
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