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Fire History in a Small
Ponderosa Pine Stand
Surrounded by Chaparral 1
J. H. Dieterich and A. R. Hibbert2
Located on the Prescott National
Forest, 20 miles south of Prescott,
Arizona, the Battle Flat pilot watershed was established in 1978 to
evaluate the various techniques
available for manipulating chaparral
cover to enhance water yield and
other resources. The predominantly
shrub cover is typical of thousands of
acres of chaparral in central Arizona.
A stand of ponderosa pine situated
in the lower reaches of the watershed
has been developing and maturing
over the past 100 years (fig. 1). Severely weathered stumps provided
evidence that this same general area
has been occupied by pine for at least
300 years. The pine stand, including
oak and juniper trees, was cutover in
the late 1800's to provide wood
products for the mining activity that
began in the 1860's. If prescribed
burning is to be used as a technique
for managing or manipulating chaparral, a general understanding of the
history of fire in the area would be
useful.
AI though no historical fire frequency data are available for Ari-
zona chaparral, fire suppression records indicate that fires have been
common. Lightning provides a moreor-less uniform fire risk, and results
in a relatively consistent source of
ignitions. Fires may have been set
intentionally by Native Americans,
although there is little reliable evidence to either confirm or refute this
theory. Prospecting and mining activity undoubtedly caused fires in the
area, but fires occurring before the
1860's could not logically be attributed to this cause.
Chaparral is well adapted to fire;
however, when chaparral burns, the
fire hazard is modified for many
years. Most chaparral shrubs are prolific crown and I or root sprou ters
that live to considerable age. Pond
(1971) found little change in species
composition after 47 years, with the
'Poster paper presented at the conference. Effects of Fire in Management of
Southwestern Natural Resources (Tucson.
AZ. November 14-17, 1988).
2
Former Research Forester and Former
Research Hydrologist. Rocky Mountain Forest and Range Experiment Station. Forestry
Sciences Laboratory. Arizona State University Campus. Tempe. AZ 85287-1304.
Figure 1.-Lower central Battle Flat watershed looking south. The oldest trees in the ponderosa pine stand, which are mostly visible here, were aged at approximately 100 years.
168
exception that there was an increase
in the amount of dead biomass
within the plants.
Fire behavior and fire spread in
chaparral are dependent upon a
number of weather-related factors
(Davis and Dieterich 1976). Total
amount of available fuel, and the ratio of living-to-dead fuel material are
also important. Although there is no
documented research on the subject,
those experienced in using fire and
suppressing fires in chaparral gener-
ally agree that if the chaparral stand
is less than 10 years old, fire spread
is unlikely (unless a grass cover has
invaded). Dead material begins to
accumulate in stands 10-15 years old,
and although in these stands fires
may spread upslope or with the
wind, sustained spread is not likely.
By about the 20th year, the dead-toliving fuel ratio has increased to a
level where continuous fire spread
may be expected. Stands older than
20 years can only become more flam-
mabie as the amount of dead material in the stand increases.
Documenting fire history for a
particular chaparral stand is difficult
because, for the most part, old firescarred material is not available that
can be accurately dated with standard techniques of dendrochronology. The Battle Flat area offers a
unique opportunity in that a reliable
record exists of historical fires burning in a ponderosa pine stand surrounded by chaparral. Fire history
information from this stand of ponderosa pine was used to determine
the fire regime in the ponderosa pine,
and assisted in formulating a theory
on the role that fire has played in development of the chaparral stand in
the area.
Stand Description and Data
Collection
The Battle Flat study watershed
and the area of the existing ponderosa pine stand are shown in figure 2.
At an elevation of 5,000 to 5,300 ft
and encompassing approximately
215 acres, the stand is best described
as uneven-aged with a scattered association of alligator juniper (juniperus deppeana) and Arizona white oak
(Quercus arizonica). The habitat type
is ponderosa pine/ Arizona white oak
(Pinus ponderosa/Quercus arizonica)
tIt
~
PONDEROSA PINE
(21Socr")
I
-•-
I
LOCATION OF
® FlR£ HISTORY
SPECIMENS
Figure 2. The Battle Flat study area is at an elevation of 5,000 to 6,000 feet along the crest of
the Bradshaw Mountains, 20 miles south of Prescott, Arizona.
169
(Muldavin et al. 1986). Canopy cover
of coniferous trees is about 45%.
There are few trees that might be described as fully mature (yellow pine),
but most of the large trees still fall in
the immature (blackjack) category.
Regeneration has been adequate and
there appears to be a good distribution of age classes (not measured).
The dominant vegetation on the periphery of the pine stand is shrub live
oak-mountainmahogany (Quercus
turbinella-Cercocarpus breviflorus) and
shrub live oak-mixed shrub plant
communi ties. Beyond the irregular
perimeter of the pine stand, scattered
young pine trees have become established in the chaparral; thus, it ap-
pears that the pine stand has been
slowly encroaching into the chaparral. The extent to which this can be
expected to continue is unknown.
The seven fire history specimens
used for this analysis came from the
ponderosa pine stand located along
or near stream channels in the lower
portion of the watershed (fig. 2). All
samples were taken from dead material-mostly stumps that exhibited
fire scars on the base, or from pitchimpregnated wood fragments that
remained intact after decay had destroyed most of the stump. Despite a
careful search, no living trees were
found with fire scars, nor was there
any other recent evidence of fire in
the stand. Increment cores were also
taken from the largest and oldest appearing trees within the area to determine their age.
Analysis of Material
Seven specimens were collected
and prepared for analysis and dated
by dendrochronologists at the Laboratory of Tree-Ring Research, U niversi ty of Arizona, Tucson. The
specimens were very fragile and an
epoxy was used to stabilize them before cuts were made across the grain
to expose the ring pattern (fig. 3).
The cross sections were smoothed
with a sander to improve ring visibility and dating accuracy. Cross-dating, a standard ring-dating procedure used in dendrochronology
(Stokes and Smiley 1968), was used
to date all rings on the specimens.
Then, once the fire scars were identified, the dated ring in which each
scar occurred was determined (Dieterich and Swetnam 1984). The
original dating and fire scar identification done by one person was verified independently by a second dendrochonologist. Any disagreements
on scars or dates were rechecked and
differences resolved to arrive at the
final dates.
Because of the advanced stages of
decay in the wood surrounding the
fire scars, many of the specimens
lacked a pith, date (center of the tree
was not included), and/ or a cambium (the last ring produced prior to
cutting or death of the tree). However, cross-dating made it possible to
precisely date each ring even when
these years were unknown. The fire
dates were then plotted on a chart to
become the Master Fire Chronology
for the area.
Dating of the increment cores
failed to locate any trees older than
100 years.
History of the Area
A brief review of historical events
and activities in the area may help
explain some of the vegetative
changes that have occurred in the
past, and conditions as they exist today.
Gold was discovered in the Bradshaw Mountains in 1863 and placer
mining began soon after on streams
such as Turkey Creek. However, the
remoteness of the area and the hostility of the resident Apache Indians
caused mining developments to proceed slowly. The mining camps of
Good win, 5 miles north of Battle Flat
and Bradshaw City to the south, became active in the late 1860's and
early 1870's (Jaggar and Palache
1905). The discovery of silver deposits near Battle Flat spurred new mining activity in the 1870's.
The Peck Mine, 4 miles southwest
of Battle Flat, started in 1875 and
produced a million dollars or more
in the first 5 years. Other nearby
mines produced large quantities of
silver, but the rapid exhaustion of the
rich ore and the fall of the price of
silver brought this period to a close
by 1885.
The Tescumbia Mine and Mill appear to be the mining operations
closest to Battle Flat (fig. 2), although
the Peck Mine also may have utilized
timber products from the area. It
seems certain that the pine-oak-juniper stands found in Battle Flat were
heavily utilized for fuelwood, mine
timbers, and general construction. In
fact, it appears that the area was
largely cutover and most of the usable material removed by about 1880.
Results
The Master Fire Chronology (fig.
4) provides a summary of the length
of record for each specimen, the individual years in which fires were recorded on each specimen, gaps in the
record or periods when information
Figure 3.-Specimen 1 was collected in April 1979 and typifies the material used In the fire
history study. The fire-scarred portion of the cross section was preserved over the years by
heavy pitch; the remainder of the stem rotted away.
170
appears to be missing, and the total
number of fire years recorded by the
available cross sections.
6. Perhaps the most environmentally significant data
comes from the composite
record of fires for the 100year period (1770-1870). During this period all seven
specimens were contributing
about equally to the composite. Fires occurred somewhere within the 215-acre
area in 67 of the 100 years,
for an average fire interval of
1 fire every 1-2 years (1.5-yr
interval).
Detailed inspection of the Master
Fire Chronology (MFC) indicated the
following:
1. The MFC covers the period
1700-1874 (174 years).
2. The oldest dated ring was
1653.
3. The oldest fire scar was recorded in 1700.
7. If all the available data were
used, starting with the first
recorded fire in 1700 and
ending with the last fire in
1874, we find 92 fire-years in
the 174-year period for an
average fire interval of about
1 fire every 2 years (1.89 yr).
4. Specimen No. 4 recorded 25
fires during the 93-year period 1781-1874, for an average interval of 1 fire every
3.7 years. Specimen No.4
also recorded the longest period between fire scars, 45
years (1736-1781).
,g, The Master Fire Chronology
5. The longest continuous period of scarring was recorded on Specimen No. 6.
During the 149-year period
(1700-1849), 25 fires were recorded, for a mean fire interval of 6 years.
2
ffi 4
Ill
provides a record of several
periods when fires occurred
somewhere within the pine
stand in consecutive years.
For example, fires were recorded to have burned somewhere within the stand in 9
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Figure 4. Master Fire Chronology for 7 specimens collected In Battle Flat. The lower line contains tne composite record of fire scars for all specimens.
171
consecutive years (17821790); 5 consecutive years
(1848-1852); and 4 consecutive years (1812-1815, 18171820, and 1822-1825).
No fire scars were discovered on
living trees (all living trees were less
than 100 years old), and there is no
evidence of recent fires in the area. A
logical question might be, ''Why, after such an extended period of fire
activity in the area, should there be
another extended period when there
were no fires?" The absence of recent
fires in the area agrees with the results of two fire history studies in
Arizona on the Coconino National
Forest adjacent to the Prescott National Forest. At Chimney Spring on
the Ft. Valley Experimental Forest,
north of Flagstaff, Arizona, the last
recorded fire was in 1876 (Dieterich
1980a). At Limestone Flats, at an elevation of 6,900 ft but only 65 air
miles to the east of the Battle Flat
area, the frequency of fire essentially
terminated at the tum of the century,
with the last general fire on the area
in 1898 (Dieterich 1980b, Dieterich
and Swetnam 1984). Probable explanations for this decrease in fire incidence include the reduction in use of
the area by Native Americans, more
intensive fire protection, change in
characteristics or condition of the
pine stand and/or the surrounding
stands of chaparral, and a change in
occurrence of lightning-caused fires.
Lightning occurrence probably has
not changed much over the years;
but the characteristics of the pine and
chaparral stands have changed and,
at least in the pine stand, this may
have contributed to the change in fire
incidence. The stand of ponderosa
pine that was present before 1863
when the mining began was in
marked contrast to the present stand.
The pre-1863 stand would have included a range of size and age
classes, including many old-growth
trees. In fact, Specimen No. 6 was at
least 300 years old when it was cut in
1863. There would have been an
abundance of standing snags and,
although surface fires were frequent,
there would have been a sufficient
amount of dead and rotten material
available in which lightning fires
could propagate. Some large down
and dead material would have been
present, the ground fuels would have
been predominantly needles, grasses,
and forbs; these light fuels would
have been present in sufficient quantities to support the spread of fire.
The current stand represents the
early stages of development in ponderosa pine succession. Few snags
are present and heavy ground fuels
are absent, reducing the chances for
lightning to start fires in rotten logs.
Pine needles are the predominant
ground cover; grasses and forbs are
sparse, are continually grazed, and
cannot compete with the heavy mat
of needles that continues to build.
Management Implications and
Conclusions
Fire history information from the
ponderosa pine stand in the Battle
Flat area provides direct evidence of
the influence that fire has had in the
pine stand, and indirect evidence of
the role that fire has played in the
development of the area's chaparral
stands.
Because of land-use changes that
were occurring around the turn of
the century, it is helpful to look at the
fire history during three separate periods (pre-mining, mining, post-mining) and determine some of the implications for present and future
management of the area.
been a source of ignitions, and Native Americans, in the area at the
time, probably contributed to fire
starts.
With fires burning on an average
of 2-year intervals, a fairly open
stand of pine would result with a
ground covering of grasses and
forbs. Fuels needed to sustain ignition and spread of fire would come
from this herbaceous rna terial and
from the annual needle-fall from the
pine overstory. Short fire intervals
would result in fires of very low intensity whose behavior would range
from a very rapid spread in dry,
windy conditions, to a very slow
patchy spread during less favorable
burning conditions.
We can infer that many of the fires
starting in the ponderosa pine probably reached the perimeter of the
stand where pine trees mixed with
the shrubs. If the chaparral stand was
less than 10 years old and the grasses
had not come in, fire spread would
be stopped. If the chaparral had gone
15-20 years without a fire and/or if
there was a grass cover, the fire
might continue to spread into the
chaparral. The chaparral stands that
existed during the pre-mining period
could logically be characterized as
being a "mosaic" in which brush
stands of all ages (up to about 20-25
years) would have been represented.
With this type of mosaic, large fires
like the Battle Fire in 1972 that
started on the edge of Battle Flat and
burned more than 28,000 acres
would have been a rare occurrence.
The fire history in the Battle Flat
area during the pre-mining period
was characterized by fires burning at
very short intervals in the pine, and
fires burning in the chaparral at
intervals of not less than 15-20 years.
Pre-mining Fire History (Before
1863)
The fire history data show that
fires occurred frequently in the Battle
Flat pine stand before 1863 when the
first mining began in the Bradshaw
Mountains. Lightning has always
Active Mining Period Fire History
(1863-1885)
Fire history material is unavailable
for the period beginning soon after
the start of placer mining in the Brad172
shaw Mountains (1863), and only
Specimen No.4 recorded fires after
1871 (1873 and 1874), the year when
the major silver mining activity began.
Since most of the stands had been
cut by 1874, we can only speculate on
what the fire occurrence was like
during this period. Lightning strikes
remained a normal occurrence, and
there may have been land-clearing
fires designed to open up the country
to improve access and movement.
Thus, the burned mosaics in the
chaparral stands were possibly still
maintained because of the increased
settlement in the area and the fact
that there was probably little effort to
control fires except when they threatened mines or improvements. Grazing may have also begun to interupt
the fire cycle.
Post-mining Period Fire History
( 1885 to Present)
There was only scattered mining
activity in the area after the turn of
the century. However, grazing continued and, with the advent of fire
protection, aided by the existing
natural mosaic pattern, and by the
fact that frequent fires in the late
1800's had prevented accumulations
of fuel, early fire protection efforts
would have been largely successful
in preventing large fires.
Improved protection (in the absence of prescribed burning) resulted
in a progressive increase in areas of
mature and overmature stands of
chaparral. By 1920, most of the effects from the natural mosaic burning common until the 1860's had disappeared and large continuous areas
of chaparral were developing that
were at least 20 years old, with many
much older.
Today, thousands of acres of chaparral have long since passed the mature stage and exist in an overmature
condition. The Battle Fire that started
along the western edge of Battle Flat
(but did not burn the watershed)
started in brush cover that had
probably been growing without
interruption since around the turn of
the century. Although an aggressive
fire protection program has been
largely successful in extinguishing
chaparral fires when they are small,
the fire hazard in the chaparral
stands is actually increasing. Fuels
are present in sufficient quantities
and over such large continuous areas
that large fires in the future are inevitable.
In conclusion, land managers responsible for protecting and managing these areas must recognize that
(1) large fires will continue to occur
at indeterminant intervals, and under
conditions that are dictated largely
by weather, ignition sources, and
available suppression forces; (2) although prescribed burning is a useful, environmentally acceptable tool,
it is unlikely that it can be practiced
on a scale sufficient to restore the
natural mosaic patterns present in
the chaparral stands at the turn of
the century; and (3) because of (1)
and (2) above, the manager must
carefully select the areas to be treated
with prescribed fire, basing decisions
on the resource needs and on the
strategic location of the area in relation to regions of high fire risk requiring special protection measures.
Acknowledgement
A special thanks to Marvin Stokes,
Thomas Swetnam, and Tom Harlan
of the Laboratory of Tree-Ring Research. University of Arizona,
Tucson, for their assistance in collecting the material, preparing it for
analysis, completing the cross-dating,
and preparing the Master Fire Chronology.
field workbook. Gen. Tech. Rep.
RM-24. Fort Collins, CO: U.S. Department of Agriculture, Forest
Service, Rocky Mountain Forest
and Range Experiment Station.
8 p.
Dieterich, J. H. 1980a. Chimney
Spring, forest fire history. Res.
Pap. RM-220. Fort Collins, CO:
U.S. Department of Agriculture,
Forest Service, Rocky Mountain
Forest and Range Experiment Station,8 p.
Dieterich, J. H. 1980b. The composite
fire interval-a tool for more accurate interpretation of fire history.
In: Proceedings of the Fire History
Workshop; 1980 October; Tucson,
AZ. Gen. Tech. Rep. RM-81. Rocky
Mountain Forest and Range Experiment Station: 8-14.
Dieterich, John H.; Swetnam, Thomas W. 1984. Dendrochronology
, of a fire-scarred ponderosa pine.
Forest Science. 30:238-247.
Jaggar, T. A., Jr.; Palache, Charles.
1905. Bradshaw Mountains Arizona. Geologic Atlas of the United
States, Folio 126. Washington, DC:
U.S. Geological Survey. 11 p.
Muldavin, Estaban; DeVelice, Robert
L; Dick.:.Peddie, William A. 1986.
Forest habitat types of the
Prescott, Tonto, and western
Coronado National Forests, Arizona. Final Rep. Coop. Agreement
28-2K-307, Fort Collins, CO: U.S.
Department of Agriculture, Rocky
Mountain Forest and Range Experiment Station. 74 p.
Pond, Floyd W. 1971. Chaparral: 47
years later. Res. Note RM-69. Fort
Collins, CO: U.S. Department of
Agriculture, Rocky Mountain Forest and Range Experiment Station.
11 p.
Stokes, M.A.; Smiley, T. L. 1968. Introduction to tree-ring dating. Chicago, IL: University of Chicago
Press.
Literature Cited
Davis, James R.; Dieterich, John N.
1976. Predicting rate of fire spread
(ROS) in Arizona oak chaparral:
173