5. CHARCOAL AS A FIRE PROXY
CATHY WHITLOCK (whitlock@oregon.uoregon.edu)
Department of Geography
University of Oregon
Eugene
OR 97403-1251 USA
CHRIS LARSEN
Department of Geography
University of Buffalo, SUNY
Buffalo
NY 14261-0023 USA
Keywords: charcoal analysis, fire history, lake-sediment records
Introduction
Charcoal analysis of lake sediments is used to reconstruct long-term variations in fire occur-
rence that can complement and extend reconstructions provided by dendrochronological
and historical records. In the last 15 years, several papers have reviewed the methods for
charcoal analysis of lake-sediment cores and its use as a tool for studying fire history (e.g.,
Tolonen, 1986; Patterson et al., 1987; MacDonald et al., 1991; Clark, 1988a; Clark et al.,
1998; Long et al., 1998; Whitlock & Anderson, in press). In most cases, pollen and charcoal
data from the same cores are used to examine the linkages among climate, vegetation, fire,
and sometimes anthropogenic activities in the past. The growing use of charcoal analysis
reflects a heightened interest within the paleoecological community to consider fire as an
ecosystem process operating on long and short time scales, as well as an increasing need
on the part of forest managers to understand prehistoric fire regimes. In this chapter, we
discuss issues of site selection, chronology, and methodology in charcoal analysis, based
on recent advances in the discipline. We also review the theoretical and empirical basis for
charcoal analysis, including assumptions about the charcoal source area and the processes
that transport and deposit charcoal into lakes.
Fire reconstructions based on lake-sediment records are derived from three primary
data sources: particulate charcoal that provides direct evidence of burning; pollen evidence
of fluctuations in vegetation that can be tied to disturbance; and lithologic evidence of
watershed adjustments to fire, such as erosion or the formation of fire-altered minerals.
Charcoal analysis quantifies the accumulation of charred particles in sediments during
and following a fire event. Stratigraphic levels with abundant charcoal (so-called charcoal
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J. P. Smol, H. J. B. Birks & W. M. Last (eds.), 2001. Tracking Environmental Change Using Lake Sediments.
Volume 3: Terrestrial, Algal, and Siliceous Indicators. Kluwer Academic Publishers, Dordrecht, The Netherlands.

76 CATHY WHITLOCK & CHRIS LARSEN
peaks) are inferred to be evidence of past fires. Pollen analysis is used to detect past fires
on the assumption that fire and post-fire succession will alter somewhat the local plant
community and its pollen representation in the sediments. Lithologic analyses supplement
charcoal data by detecting changes in the input of allochthonous sediment and evidence of
soil mineral alteration due to heating. The lithologic record has been used to deduce the
location of a fire within a watershed and also fire intensity.
Charcoal production, transport, and deposition
Charcoal is produced when a fire incompletely combusts organic matter. The rate at which
charcoal accumulates in a lake depends on the characteristics of the fire (e.g., how much
charcoal is produced) and the processes that transport and deliver charcoal to the lake
(Fig. 1). Primary charcoal refers to the material introduced during or shortly after a
fire event. Secondary charcoal is introduced during non-fire years, as a result of surface
run-off and lake-sediment mixing. The relationships between fire characteristics and the
accumulation of primary charcoal and between taphonomic processes and the deposition
of secondary charcoal are discussed separately, but it is important to remember that both
sources comprise the sedimentary charcoal record.
Fire size, intensity, and severity all affect charcoal production and aerial transport,
although little information is known about these relationships. Because charcoal particles
can be carried aloft to great heights and transported great distances (Radtke et al., 1991;
Andreae, 1991), the source of the charcoal may be from regional (distant) fires, extralocal
(nearby but not within the watershed)fires, or local (within the watershed) fires. The distance
that charcoal is carried during a fire has been discussed in several papers, including Swain
(1978), Tolonen (1986), Patterson et al. (1987), Clark (1988a), Whitlock & Millspaugh
(1996); Clark & Royall (1995, 1996), Clark et al. (1998), and Gardner & Whitlock (2001).
Simple Gaussian plume models suggest that particles diameter are released
relatively close to the ground and deposited near a fire (Clark & Patterson, 1997). These
models predict that particles in size travel well beyond 100 m, and very small
particles are lofted to great heights and travel long distances. Theoretical models also
suggest a “skip distance” between the base of the convective column and the site of
deposition. In principle, few charcoal particles smaller than in diameter should
be deposited within 6 km of the convection column (Fig. 2).
Four studies following modern fires confirm model predictions by showing a decrease
in charcoal abundance away from the source. In one study, charcoal accumulation in small
lakes following the 1988 fires in Yellowstone National Park indicated that charcoal particles
diameter were abundant in sites <7 km from the fire (Whitlock & Millspaugh,
1996); beyond that distance the accumulation of such particles declined sharply. A more
comprehensive study of the upper sediment of 35 lakes followed a 1996 fire in the Cascade
Range of Oregon (Gardner & Whitlock, 2001). Levels of charcoal were
compared for the upper two core samples (0–2 cm and 2–4 cm depth) in burned sites and
sites located within few kilometers upwind and downwind of the fire. Cores from the
burned sites had statistically greater charcoal abundance in the top sample than those from
unburned sites, and the peaks (i.e., difference between the top and second sample) were
better defined than in unburned sites. Sites downwind of the fires had more charcoal in