The invasion of cheatgrass (Bromus tecto-
rum) throughout much of the Great Basin in
the early 1900s (Mack 1981) has changed the
fire regime within sagebrush- (Artemisia-)
dominated landscapes, resulting in more fre-
quent fires (Whisenant 1990). Total area burned
per year has also increased; over the last 5 years,
on average, >275,000 ha burned in Nevada
each year (Western Great Basin Coordination
Center 2004). Although it is evident that inva-
sion of cheatgrass has increased the frequency
and extent of fires in sagebrush environments,
we still have a poor understanding of sage-
brush fire history prior to 1900 A.D. Gruell
(1985) reviewed journal accounts for refer-
ences on fire made by early explorers and nat-
uralists and concluded that fire was a major
perturbation in the region before European
settlement. However, such observations are
widely scattered in time and space and pro-
vide no quantitative analysis of the frequency
of fire in a specific vegetation cover.
Reconstructing fire history within sagebrush
is problematic because fires are stand replac-
ing. In contrast, in forested environments, evi-
dence of past fires can be reconstructed from
fire scars found on surviving trees. Tree-ring
and fire-scar analysis allows us to identify and
date prehistoric fire events. This method has
been widely utilized throughout the West to
reconstruct forest fire histories extending back
hundreds of years (Swetnam 1993). In environ-
ments where fire-scarred trees grow within
or directly adjacent to sagebrush, this tech-
nique has been used to infer sagebrush fire
history (Houston 1973, Burkhardt and Tisdale
1976, Miller and Rose 1999). It is a question,
however, whether fire-return intervals calcu-
lated through this method are representative
of treeless valleys of the central Great Basin
dominated by sagebrush, primarily Artemisia
tridentata var. tridentata (Great Basin big sage-
brush) and A. tridentata var. wyomingensis
(Wyoming big sagebrush).
Western North American Naturalist 66(1), © 2006, pp. 64–77
LONG-TERM FIRE HISTORY IN GREAT BASIN SAGEBRUSH
RECONSTRUCTED FROM MACROSCOPIC CHARCOAL
IN SPRING SEDIMENTS, NEWARK VALLEY, NEVADA
Scott Mensing1, Stephanie Livingston2, and Pat Barker3
ABSTRACT.—We use macroscopic charcoal analysis to reconstruct fire history in sagebrush (Artemisia tridentata var.
wyomingensis and A. tridentata var. tridentata), in Newark Valley, Nevada. We analyzed charcoal at continuous 1-cm
intervals (~7–127 years), and pollen at 2- to 10-cm intervals (~70–263 years) in a core spanning the last 5500 cal yr BP
(calendar years before present). A charcoal peak in the historic period was associated with a >1400-ha fire dated to 1986
that burned in the watershed. We reconstructed the prehistoric fire history by inferring fires from similar charcoal peaks
that were significantly greater than the background charcoal accumulation. Our results suggest the fire regime is climate
and fuel driven. During periods of wetter climate, sagebrush increased and fires were more abundant, and during
extended dry periods when sagebrush decreased, fires were less frequent. Our method does not allow calculation of a
fire-return interval; however, our results support models that estimate a mean fire-return interval of up to a century in
Artemisia tridentata var. wyomingensis. The charcoal record indicates that fires have increased within the historic
period. This contrasts with pinyon/juniper studies that indicate an expansion of woodland associated with fewer fires in
the historic period. We suggest that in the central Great Basin, a regime of frequent fires in sagebrush that limits wood-
land expansion is true for the sagebrush-woodland ecotone, but in sagebrush-dominated valleys with lower fuel loads,
fires have always been less frequent. Protecting sagebrush-dominated valleys from frequent fire would appear to be
consistent with the prehistoric fire regime.
Key words: sagebrush, fire history, charcoal, Nevada, Great Basin, Artemisia tridentata var. wyomingensis.
1Department of Geography, 201 Mackay Science, University of Nevada, Reno, NV 89557.
23920 N.Westpoint Drive, Reno, NV 89509.
3State Archeologist, Bureau of Land Management, 1240 Financial Blvd., Reno, NV 89502.
64

The purpose of this paper is to test the use
of macroscopic charcoal recovered from sedi-
ments (Millspaugh and Whitlock 1995, Long
et al. 1998, Whitlock and Anderson 2003) as a
proxy for reconstructing fire history in sage-
brush. Our goal is to provide the first quanti-
tative charcoal analysis of fire history from a
sagebrush-dominated valley in central Nevada.
Charcoal analysis is one of the few methods
available for reconstructing fire history within
treeless landscapes. Mensing et al. (1999) used
charcoal analysis to reconstruct fire history in
shrub-dominated chaparral environments in
California.
In central Nevada, pinyon-juniper wood-
lands containing Utah juniper ( Juniperus osteo-
sperma), western juniper ( J. occidentalis), and
single leaf pinyon (Pinus monophylla) typically
occupy slopes above sagebrush-dominated val-
leys. Reconstructing fire histories in these
woodlands is difficult because juniper are
thin-barked and susceptible to fire for at least
the first 50 years of growth (Miller and Rose
1999) and pinyons contain abundant resin and
typically burn completely when exposed to
flame (Robin Tausch personal communication).
Further, relict stands of pinyon and juniper with
scarred trees are typically confined to rocky
ridges (Burkhardt and Tisdale 1976) and are
not representative of soils that support sage-
brush. The few published fire history studies
of pinyon and juniper in east central Nevada
(Blackburn and Tueller 1970, Gruell et al. 1994)
and southwestern Utah (Tausch and West 1988)
give no explicit estimates of prehistoric fire-
return intervals in sagebrush-dominated envi-
ronments (Fig. 1).
Our knowledge of sagebrush fire history
comes almost entirely from fire-scar studies
on ponderosa pine (Pinus ponderosa), western
juniper, and Douglas-fir (Pseudotsuga mensezii),
growing in association with A. tridentata var.
vaseyana (mountain big sagebrush) from sites
in Oregon (Gruell 1999, Miller and Rose 1999),
Idaho (Burkhardt and Tisdale 1976), and Wyo-
ming (Houston 1973), respectively (Fig 1).
These studies suggest a fire-return interval of
15 to 25 years in A. tridentata var. vaseyana
(Miller and Tausch 2001), but the study sites
have more mesic climates than are found in
central Nevada, and fuel loads are likely far
greater. Annual precipitation at these sites
ranged from 300 mm to 500 mm as compared
with 185 mm at the central Nevada Field Lab
near Austin, Nevada, or 240 mm in Ely, Nevada.
We argue that a 15–25 year fire-return interval
is not representative for sagebrush-dominated
valleys in the central Great Basin where the
primary species are A. tridentata var. triden-
tata and A. tridentata var. wyomingensis.
Miller and Rose (1999) were able to collect
12 fire-scarred western juniper stumps and
logs in A. arbuscula (low sagebrush) in what
they considered a fuel-limited environment in
Oregon. They identified only 2 fires in the last
300 years with a period of 130 years between
these events. This is the only published study
that documents prehistoric fire history in
sagebrush habitat that is not dominated by A.
tridentata var. vaseyana.
Miller and Tausch (2001) presented a con-
ceptual model of fire-return intervals in forested
and sagebrush habitats dependent upon cli-
mate and fuel loads. For sagebrush, they sug-
gested that as climate becomes more arid, fuel
loads decrease and fire-return interval increases.
The shortest fire-return interval (15–25 years)
occurred in A. tridentata var. vaseyana, which
also occupied the wettest habitat and had the
highest fuel loads. Next in order they suggested
A. tridentata var. wyomingensis at 50–100
years, A. arbuscula at 100–200 years, and then
salt desert shrub (Atriplex spp.) at >500 years.
This conceptual framework is supported by 7
published studies of A. tridentata var. vaseyana
throughout the Intermountain West, and only
1 study of A. arbuscula (Miller and Tausch 2001).
The fire-return intervals for A. tridentata var.
wyomingensis and salt desert habitats are un-
documented estimates. Wright and Bailey (1982)
speculated that the natural fire return interval
in sagebrush may be 100 years, but this argu-
ment was based simply on the time needed for
sagebrush to succeed horsebrush (Tetradymia
canescens) following fires in southeastern Idaho.
Sagebrush in valleys in the central Great
Basin is dominated by A. tridentata var. wyo-
mingensis and A. tridentata var. tridentata.
Changes in fire regime in this habitat type due
to invasion of cheatgrass are leading to con-
version of sagebrush to annual grasses and
demise of species dependent upon sagebrush.
The increase of fine fuels in the interspaces
between native shrubs has created a situation
where some areas now burn every 3–5 years
(Whisenant 1990). The model presented by
Miller and Tausch (2001) suggests that the pre-
historic fire-return interval for A. tridentata
2006] SAGEBRUSH FIRE HISTORY FROM CHARCOAL 65