High-resolution pollen as an indicator of fire severity during the Populus Period, 2000 - 4000 cal yr BP
Vachel Carter, Andrea Brunelle, Simon Brewer, Thomas Minckley
Department of Geography
Abstract
Previous Research
•  Carter et al., 2013 identified a unique vegetation transition period
from a logdepole pine dominated system to a lodgepole pine/
quaking aspen mixed forest between 3000-4000 cal yr BP.
They coined this period the ‘Populus period.’ (see figures below)
1. Quantify the changes in pollen abundance after 12 fire events that occurred between
2000-4000 cal yr BP to determine the severity of each fire event.
Quaternary Research 80 (2013) 406–416
•  Quantify the
ecological response
to determine low
severity vs. high
severity fire
•  Quantify the
changes from a
lodgepole pine
system to a quaking
aspen mixed forest
Contents lists available at ScienceDirect
Quaternary Research
journal homepage: www.elsevier.com/locate/yqres
Regionalization of fire regimes in the Central Rocky Mountains, USA
Vachel A. Carter a,⁎, Andrea Brunelle a, Thomas A. Minckley b, Philip E. Dennison c, Mitchell J. Power d
a
410
i n f o
Keywords:
Charcoal
Fire
Pollen
Vegetation
Climate
Climatic boundary
Lake sediments
Paleoecology
2. Determine the potential drivers of ecological change between 2000-4000 cal yr BP.
Climate Climate (2013) 406–416
a b s t r a c t
Fire is one of the most important natural disturbances in the coniferous forests of the US Rocky Mountains. The
Rocky Mountains are separated by a climatic boundary between 40° and 45° N, which we refer to as the central
Rocky Mountains (CRM). To determine whether the fire regime from the CRM was more similar to the northern
Rocky Mountains (NRM) or southern Rocky Mountains (SRM) during the Holocene, a 12,539-yr-old sediment
core from Long Lake, Wyoming, located in the CRM was analyzed for charcoal and pollen. These data were
then compared to charcoal records from the CRM, NRM and SRM. During the Younger Dryas chronozone, the
fire regime was characterized as frequent at Long Lake. The early and middle Holocene fire regime was characterized as infrequent. A brief interval from 4000 to 3000 cal yr BP, termed the Populus period, had a frequent
fire regime and remained frequent through the late Holocene at Long Lake. In comparison to sites from the
NRM and SRM, the fire regime at Long Lake was most similar to the SRM during the past 12,539 cal yr BP.
These results suggest the disturbance regime in the CRM has a greater affinity with those of the SRM.
© 2013 University of Washington. Published by Elsevier Inc. All rights reserved.
Introduction
Vegeta-on Vegeta-on Fire defined here as the geographical location also known as the Wyoming
Basin that separates the NRM and SRM (Baker, 2009) (Fig. 1). In this
Driven by factors such as temperature, precipitation, humidity, wind
context, the CRM can be viewed as the transition zone between the
and fuel availability (Westerling et al., 2003), fire is a dynamic force
Great Basin, the Great Plains, the NRM, and the SRM (Brunelle et al.,
shaping forest composition and is considered one of the most important
2013). The CRM is of particular interest because currently precipitation
natural disturbances in the coniferous forests of the western United
in the CRM and NRM is influenced from westerly storms originating
States (US). Understanding these variables is important for determining
from the northern Pacific Ocean in the winter, and both experience
how fire regimes may vary in response to climate change (Dale et al.,
summers that are relatively warm and dry (Mock, 1996; Shinker,
2001). One of the few ways we can learn about the interactions between
2010; Wise, 2010). However, it is unclear whether the CRM has been
fire and climate is to look at past fire regimes as a baseline against which
influenced by these same precipitation patterns through time or how
to measure modern changes. Fire histories obtained through the examdifferent precipitation patterns may influence fire regimes in the CRM.
ination and quantification of charcoal preserved in lake sediments are
The SRM typically experience precipitation patterns out of phase
particularly useful because of their long temporal span. Unlike tree
with the NRM; based on the observation that when the NRM are anomrings, which offer annual resolution but are generally age-limited to
alously wet, the SRM are anomalously dry (Dettinger et al., 1998; Wise,
the past few hundred years, charcoal records preserved in lake sedi2010). Within this dipole, the CRM historically has followed the moisments have the ability to reconstruct a fire history over millennia
ture patterns of the NRM (Mock, 1996; Baker, 2009; Shinker, 2010).
(Long et al., 1998). Charcoal records are also useful in that they can
The dipole fluctuation in precipitation between the NRM and SRM is asidentify long-term shifts in fire regimes during periods of major climate
sociated with El Nino–Southern Oscillation cycles (Wise, 2010), which
change (Brunelle and Whitlock, 2003). To understand the fire ecology
are known to influence wildfire occurrence and severity in particular
of a system, sediment-based fire reconstructions are compared to
regions in the United States (Westerling et al., 2003).
determine how fire regimes respond as climate changes through time
Past fire regimes in the NRM have been researched more heavily
(Minckley and Shriver, 2011; Minckley et al., 2012).
than those of the SRM, with even fewer fire reconstructions along the
The and
US macrofossil
Rocky Mountain
region is
normally
either
transition
between
two regions
et al., 2007,
2012;
Figure 4. Pollen percentage
data plotted
against
timedivided
for Longinto
Lake,
WY. Gray
shadingzone
indicates
5× the
exaggeration
of(Minckley
pollen percentage
data.
A ‘+’ symbol indicates the
northern
Rocky
Mountains
Range (NRM)
or southern
Rocky MounBrunelle et al., 2013). Based on climatic association, it is not understood
presence of pollen at the
trace
amounts.
Black
circles indicate
identified
macrofossils.
tains Range (SRM). The central Rocky Mountains Range (CRM) are
whether the CRM has a distinct fire regime, or whether its fire regime is
more similar to the NRM or SRM. Dettinger et al. (1998) proposed a
climatic boundary that separates the NRM and SRM between 40° and
⁎ Corresponding author.
E-mail address: vachel.carter@gmail.com (V.A. Carter).
N latitude,(4%)
but this
climatic
boundary was
stationary
percentages of Poaceae
(10%) and Amaranthaceae (~ 6.5%) pollen. 45°present
but
decreased
to likely
tracenotlevels
through the zone.
Fire Future Research
Preliminary Results
er
ac
ea
e
(I)
As
t
ea
e
(I)
(I )
Am
Po
ac
Po
pu
lu
s
ar
an
th
ia
(I)
(I)
(I)
To
ta
lP
in
e
Age (cal yr BP)
0033-5894/$
– see front matter
© 2013
Washington.
Published
by Elsevier Inc. All rights
reserved.
Cyperaceae pollen
percentages
were
lowUniversity
(3%).ofInitial
forest
constituCupressaceae
(3%) pollen percentages also decreased. Populus pollen
http://dx.doi.org/10.1016/j.yqres.2013.07.009
ents include Abies bifolia, P. contorta-type and P. flexilis-type based on
increased (1%) after 9000 cal yr BP. Artemisia pollen percentages (14%)
macrofossils.
along with Amaranthaceae (7%), Asteraceae (1%), Poaceae (2%) pollen
percentages were all lower than previous. Cyperaceae (1%) pollen percentages, as well as riparian species, including Salix (b 1%) and Alnus
Charcoal
(b 1%) increased. Short-term increases of Artemisia pollen percentages
Four fire episodes were identified with a mean fire return interval
and those of aquatic pollen types were notable in the 7-cm thick organic
(FRI) of 131 yr (Fig. 4). Peak magnitudes were variable between 0.1
layer (241–247 cm; 8600–8200 cal yr BP). Pinus flexilis-type increased
and 58.5 and averaged 18.0 particles/cm2/episode.
to 4% while Pinus contorta-type decreased to 2% during this shift. Abies
pollen increased to 5% and Picea pollen decreased to 3%. Around
LL-II: the early Holocene (depth 385–258 cm, 11,800–9400 cal yr BP)
9000 cal yr BP total Pinus pollen decreased to 36%, while Amaranthaceae
(14%), Asteraceae (3%), Poaceae (2%), and Cyperaceae (4%) all increased.
Pollen
Aquatic and riparian species, including Salix (2%), and Alnus (b 1%) also
Pollen percentages for subalpine species, Abies (5%) and Picea (7%)
increased.
increased during LL-II. Pinus pollen percentages also increased to 50%,
with Pinus flexilis-type and Pinus contorta-type pollen abundances averaging 5% and 10% respectively. Shrub and herbaceous pollen abunCharcoal
dances decreased in this zone with Artemisia pollen percentages
LL-III had 21 fire episodes with a mean FRI of 320 years, which
decreasing (18%), along with Cupressaceae (2%), Poaceae (4%), and
was the least frequent of the record (Fig. 3). Peak magnitudes
Asteraceae (2%). Cyperaceae pollen percentages increased to 4%. Abies
for the 21 events ranged between 0.1 and 871.0 and averaged
bifolia, Picea engelmannii and P. flexilis-type needles were present.
124.0 particles/cm2/episode. Two out of the 21 fires (5500 and
8230 cal yr BP) had peak magnitudes N500 particles/cm2/episode.
Charcoal
LL-II had 13 fire episodes with a mean FRI of 246 yr. Peak magnitudes
ranged between 0.3 and 144.0 and averaged 48.0 particles/cm2/episode.
LL-IV: the Populus period (depth 160–140 cm, 4000–3100 cal yr BP)
•  Charcoal results showing charcoal accumulation
and background (red line), 12 fire events (+ symbol),
fire return interval (FRI) and peak magnitude.
•  Pollen influx diagram showing the 6
most common pollen taxa and their responses
to each individual fire (the horizontal lines)
2000
2050
2100
2150
2200
2250
2300
2350
2400
2450
2500
2550
2600
2650
2700
2750
2800
2850
2900
2950
3000
3050
3100
3150
3200
3250
3300
3350
3400
3450
3500
3550
3600
3650
3700
3750
3800
3850
3900
3950
4000
4050
•  When aspen pollen
Influx increase, the FRI
increases and the
largest peak magnitude
event occurs.
Grouped Taxa
•  Examine grouped taxa
Canopy vs. Understory
responses to thresholds
& Conifers, successional, using an LDA approach.
deciduous, herbs, and shrubs
•  Analyze pre-fire and
post-fire pollen taxa
to examine the ecological
responses after
each fire event to
determine the mechanism
that altered the FRI. This
will be done using a SEA
approach.
LL-III: the middle Holocene (depth 258–160 cm, 9400–4000 cal yr BP)
Pollen
Total Pinus pollen was the dominant pollen type during LL-III, averaging 68%. Abies pollen percentages averaged a peak of 4% around
9000 cal yr BP. Pinus flexilis-type (1%) and Pinus contorta-type (6%) pollen percentages decreased in this zone. Picea pollen was initially
10000
50000
100000
1000 2000 3000
500 1000 1500
200 400 600 800
250
Pollen
From 4000 to 3100 cal yr BP, Populus pollen percentages increased
from 1% to 31% and remained high for ~900 years. The increase in
Populus pollen abundance was anomalous in western North America
pollen diagrams, so these counts were verified by Carter, Brunelle and
Minckley. All relative pollen abundances were lowered by the inclusion
of Populus pollen percentages in the terrestrial sum. Pinus pollen
500
•  LDA results indicating a threshold of 100 particles/cm2/episode using the 6 most common
pollen taxa. Figures show pre fire samples and post fire samples (called the response). Group 0 indicates
the 100 particles threshold. Group 1 indicates the 200 particles threshold.
Methods
Acknowledgements
•
•
Charcoal
c
Article history:
Received 24 January 2013
Available online 5 September 2013
Site Location
Long Lake, Wyoming
Pollen
RED Lab, Department of Geography, University of Utah, Salt Lake City, UT 84112, USA
Department of Geography and Program in Ecology, University of Wyoming, Laramie, WY 82071, USA
URSA Lab, Department of Geography, University of Utah, Salt Lake City, UT 84112, USA
V.A. Carter et al. / Quaternary Research 80
d
Utah Museum of Natural History, Department of Geography, University of Utah, Salt Lake City, UT 84112, USA
b
a r t i c l e
Ar
te
m
is
This study attempts to analyze fire severity using lake sediments from
southeastern Wyoming, during a unique period of time coined the ‘Populus
period’ (Carter et al., 2013). The Populus period (3800-2800 cal yr BP) was a time
when vegetation composition and fire regimes changed from a Lodgepole pine
dominated ecosystem to Lodgepole pine/Quaking Aspen mixed ecosystem. This
study investigates fire events between 2000-4000 cal yr BP to determine the
ecological response associated with fire events and to identify top-down or bottom-up
drivers. In order to determine fire severity, this study compares high-resolution
charcoal and pollen data to peak magnitude, which is an output from a statistical
treatment program called CharAnalysis. Linear discriminant analysis (LDA) was
used to set a threshold by which individual pollen taxa and grouped pollen taxa are
either associated with low or high severity fires. Based on the LDA results, the
severity threshold for individual pollen taxa are fire events with peak magnitudes
greater than 100 particles/cm2/episode. The LDA results indicate severity thresholds
of grouped pollen taxa ranging between 100-200 particles/cm2/episode. Superposed
epoch analysis (SEA) is used to model pollen behavior both pre and post fire events
to determine the ecological response associated with each of the fire events.
Statistical analysis using LDA and SEA can potentially be used in combination to
determine fire severity, which will be beneficial to land managers and policy makers
in the 21st century.
Research Objectives
Funding was made possible by Rockies Express Pipeline LLC, Great Basin Earth
Science, Global Change and Sustainability Center, the Don Currey Scholarship, the
David C. Williams Scholarship and the U.S. Forest Service.
•
•
•  Blarquez and
Carcaillet.(2010) &
Shriver and Minckley
(2013) both successfully
used the SEA approach to
examine pre-and-post fire
responses. This study
examines the ecological
response at a much higher
resolution than previously
used.
Citations
Blarquez, O., and Carcaillet, C., 2010. Fire, fuel composition and resilience threshold in subalpine ecosystem. PLoS ONE
5(8), e12480
Carter, V.A., Brunelle, A., Minckley, T.A., Dennison,P.E., Power, M.J., 2013. Regionalization of fire regimes in the Central
Rocky Mountains, USA. Quaternary Research 80, 406-416.
Minckley, T.A., and Shriver, R.K., 2011. Vegetation responses to changing fire regimes in a Rocky Mountain forest. Fire
Ecology 7(2), 66-80.
Shriver, R.K., and Minckley, T.A., 2013. Late-Holocene response of limber pine (Pinus flexilis) forests to fire disturbance in
the Pine Forest Range, Nevada, USA. Quaternary Research 78, 465-473.
.