Fire History and Dendrochronology
Photo by Daniel Heffernan
Agenda: Last class of 2013 
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Notes on 4/26
Fire history lecture
Break
Lab
Done!
Credits- Debra Kennard,
Laboratory of Tree Ring
Research, H. D. Grissino’s
Ultimate Tree Ring website
The Importance of Fire history
Fire history is the study of the chronology of fire
events over time, providing detailed information
about a forest’s historical fire regime
• Provides a benchmark by which we can measure
change (e.g. estimating the effects of past fire
exclusion helps us predict the future)
• Can serve as a guide for determining appropriate
burn intervals for management plans
• Informs designation of desired future conditions,
or references for restoration
Restoration- to what?
Why?
How do we
know what
the “natural”
or historical
fire regime
is for a
given
ecosystem?
Fire Regime Attributes
Frequency
Severity
Area
Type
Intensity
Severity
Synergy
Distribution of ecosystems in S. Florida
From Fire Effects on Flora (Brown and Smith 2000).
How do we
determine
the attributes
of a historical
fire regime?
Gleaning Fire History Information
Depends on what is available:
Paleoecological: Analysis of stratified lake or bog/soil sediments
for charcoal; pollen analysis
Gleaning Fire History Information
• Historical records or folklore (natives, explorers, settlers)
• Vegetation or stand age class distributions
• Photographs, remote sensing: Chronosequence (e.g. LANDSAT)
Dendrochronology
• dendro: tree.
• chronology: study of time
• “Dendrochronology examines
events through time that are
recorded in the tree‐ring
structure or can be dated by
tree rings.”
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Speer, J. 2010. Fundamentals of Tree‐Ring Research. The
University of Arizona Press
Applications of Dendrochronology
• Ecology: insect outbreaks, forest
demographics and growth patterns
• Climatology: past droughts or cold periods
• Geology: past earthquakes, volcanic
eruptions
• Anthropology: past construction, habitation,
and abandonment of societies
• Fire history!
Dendrochonology for Fire History =
Dendropyrochronology
• Fires that damage
cambium leave a scar
• Fire occurrence is
determined by estimating
the year of fires based on
tree rings and location fire
scars.
• Can also be used to
determine fire intensity, fire
seasonality, extent, and
associated climatic
• Takes advantage of variability in
patterns.
annual growth rings (complacent
vs. sensitive species)
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A close-up 
photograph of an
individual tree ring
showing the
earlywood (larger
cells) and latewood
(smaller cells), as
well as a resin duct
(growth is from
bottom to top)
(photo © LTRR).
A diagram showing the tree rings of a
"ring porous" tree species, such as oak
(Quercus spp.) and elm (Ulmus spp.)
(growth is to the right) (photo © LTRR).
Close-up photographs of conifer tree
rings showing different types and
rates of tree growth (photo © LTRR).
What does
dendropyrochronology tell you?
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Frequency
Season
Areal extent?
Severity?
Years of fires?
Synergy with
climate, other
disturbances
Terms
• Fire Return
Interval: length of
time between one
fire and the
next/previous fire
• Mean FRI: avg. of
above
Example application of fire history
studies: climate relationships
• PIPO Fire history reconstructions show that fires
correlated with climate oscillations—wet/dry
Niño3 SST (ENSO)
A. SW
Annual
Precip.
Superposed Epoch
Analysis
(SEA) of fire years
at Archuleta Mesa
SOI (ENSO)
B. Four
Corners
Drought
Index
(PDSI)
(Brown and Wu 2005)
Years of fires: Depends on knowing a date!
Or does it?
Increment cores taken from Douglas-fir (Pseudotsuga menziesii) trees growing on Mt.
Graham in southeastern Arizona (photo © H.D. Grissino-Mayer).
Cross-Dating
• Matching of ring width patterns between specimens used to
identify the exact year in which a ring was formed
• Useful when no known date is available; ring width patterns in
a dead wood sample can be “overlapped” on (live) samples
with known dates
• Accounts for tree ring anomalies
• Extends fire histories back into the past, much further than
even the oldest living tree
But trees grow at different rates,
even in the same stand!
• Skeleton Plotting: accounts for the fact “trees in a
homogenous stand or forest usually exhibit the same
relative pattern of growth variation through time, BUT
• Often have absolute growth rates that differ substantially
due to living in different microsites” (Laboratory of Tree Ring
Research, T. Veblen, AZ)
Skeleton Plotting
General Procedures
• Mark relatively narrow rings on graph paper– the
narrower the ring, the taller the line
• Match these patterns between samples
• Account for missing or false rings
• Date your sample
• Identify fire years
• Create Master Fire Chronology
Group 1
Group 2
Example of Master Fire Chronology for ponderosa/Doug-fir forests of Boulder, CO
Limitations of tree-ring analysis
for fire history
• Cannot be used in areas
without trees, or where trees
are killed by fire (Pinyonjuniper woodlands, sand pine
scrub)- it will only provide date
of last fire
• Conservative estimate: Fire
scars may be healed-over,
some trees might not record a
given fire
• A large number of samples is
required for cross-dating
• Sampling is destructive
Set of fire scars shown in a section taken from a sugar
pine (Pinus lambertiana) growing in California (photo ©
A.C. Caprio).
Limitations, challenges, cont.
• The record gets worse the further back in
time you go
Percent of Trees Scarred
(%)
Number of Trees
120
100
80
60
40
20
0
1813
1865
1913
1946
% Trees scarred
No. of trees
1986
• And the larger the area sampled, the greater
number of scars you’ll find (for a while)
Results depend on the factors that
influence fire behavior– where & how you
sample matters!
Fire and Lightning Scars Across Topography
80
70
60
50
40
30
Fire Scars
Lightning Scars
20
10
0
Ravine
Hilltop
Knoll
Lower
Slope
Mid Slope
Upper
Slope
Ridgetop
• …and does that mean that fires occurred there more
frequently, or scarred trees there more often?
Some trees scar more easily than others…
60
No. Scars
50
40
PSME
30
PIPO
20
10
0
N
E
S
W
…and evidence may be better
preserved in certain microenvironments
Despite these limitations,
fire history data is widely used to
characterize fire regimes, and provides
the basis for many management
frameworks.
Class
Challenge:
Use what you
know (fire
behavior,
fuels, plant
ecology) to
infer the fire
regime of this
forest
What you will do
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Lab Exercise in pairs
Hand-in by end of class
Have a look at the samples
Extra Credit-- Go to:
http://www.ltrr.arizona.edu/skeletonplot/Sk
eletonPlot19.htm (review the tutorial)
• Do the Crossdating: Skeleton Plot for
Yourself exercise