A 9000-year fire history from the Oregon Coast Range, based on a high-resolution charcoal study

Abstract

High-resolution analysis of macroscopic charcoal in sediment cores from Little Lake was used to reconstruct the fire history of the last 9000 years. Variations in sediment magnetism were examined to detect changes in allochthonous sedimentation associated with past fire occurrence. Fire intervals from ca. 9000 to 6850 calendar years BP averaged 110 ± 20 years, when the climate was warmer and drier than today and xerophytic vegetation dominated. From ca. 6850 to 2750 calendar years BP the mean fire interval lengthened to 160 ± 20 years in conjunction with the onset of cool humid conditions. Fire-sensitive species, such as Thuja plicata Donn ex D. Don, Tsuga heterophylla (Raf.) Sarg., and Picea sitchensis (Bong.) Carr., increased in abundance. At ca. 4000 calendar years BP, increases in allochthonous sedimentation increased the delivery of secondary charcoal to the site. From ca. 2750 calendar years BP to present, the mean fire interval increased to 230 ± 30 years as cool humid conditions and mesophytic taxa prevailed. The Little Lake record suggests that fire frequency has varied continuously on millennial time scales as a result of climate change and the present-day fire regime has been present for no more than 1000 years.

Assessing Paleo-Biodiversity Using Low Proxy Influx

“…Consequently, to solve the problem of low-influxes, our approach involving the calculation of influxes at regular intervals while maintaining the dependency through the original samples (based on count and volume interpolation, [29]) allows the use of rarefaction on the macroremain record. Our results indicate that, at the study site, floristic richness increased gradually between 10,000 and 7,000 cal BP.…”

“…Finally, the interpolated counts were transformed to concentrations (numbers.cm −3 ) that were in turn converted to influxes (numbers.cm −2 .yr −1 ) by multiplying concentrations by sediment accumulation rate (cm.yr −1 ) for each sample, resulting in a regularly spaced time series of pollen or macroremains. This procedure uses the pretreatment method of charcoal records for reconstruction of fires as proposed by Long et al [29] and was adapted for the pollen and macroremain records by modifying the interpolation procedure from the freely available CharAnalysis software {https://sites.google.com/site/charanalysis/Higuera, 2009 #308}.…”

Recognizing Women Leaders in Fire Science

“…Dr. Johnston's research focuses on assessing environmental factors on poor health such as the epidemiology of smoke pollution, as well as health impacts of airborne allergens and heatwaves. Her notable works include human impacts of wildfires, such as public health costs and projected mortality rates from smoke exposure [38,[164][165][166]. Her recent works continue to build on research to quantify the health and economic impacts on the public from wildfire smoke [167], as well as other studies aimed at better informing the public of the air quality risk [168].…”

“…Dr. Whitlock's research focuses on quaternary climate change and the role of humans and climate change in forming fire regimes. Her notable works include assessing the climate controls of fire occurrence and large-scale patterns in the Holocene [37] and reconstructing multi-thousand-year-old fire histories [38,39]. Her recent works have included contributions to a synthesis calling for more adaptation to wildfires in western North American forests [14] and further research on late-glacial and Holocene fire activity [40,41].…”

Filling a Geographical Gap: New Paleoecological Reconstructions From the Desert Southwest, USA

“…Sample volume was adjusted to maintain a significant number of charcoal particles, but to reduce excessive counts (>1,000 particles). Methods and rationale follow Clark (1988) and Long et al (1998). While taphonomic studies of large particle deposition on fluvial wetland surfaces have not been conducted, isotopic analysis of ciénega sediments indicates pooling and stagnation of surface waters (Minckley et al, 2009), suggesting sedimentation of charcoal fragments would be similar to those of lake and bog surfaces.…”