THE HISTORICAL ROLE OF FIRE ON
THE BITTERROOT NATIONAL FOREST
STEPHEN F. ARNO i s an Associate Plant Ecologist on the Forest
Ecosystems research work unit at Missoula. He earned a
B. S. in forestry at Washington State University and a master's degree and a Ph. D. in forestry and plant science at the
University of Montanabefore joining the USDA Forest Service
in 1970. This study was supported by the Fire inMultiple Use
Management Rcscarch, Development, and Application Program headquartered at the Northern Forest Fire 1,aborator.y
in Missouln.
USDA Forest Service
Research Paper INT-187
December 1976
THE HISTORICAL ROLE OF FIRE ON THE
BITTERROOT NATIONAL FOREST
Stephen F. Arno
CONTENTS
Page
... ......... ... .. ... ..
METHODS.. . . . . . . . . . . . . . . . . . . . . . . . .
RESULTS AND DISCUSSION
... . . . . . . .. . . ..
Data B a s e . . . . . . . . . . . . . . . . . . . . . . .
F i r e Frequency. . . . . . . . . . . . . . . . . . . . .
C o r r e l a t i o n s Among Fire Years. . . . . . . . . . . .
Extent and Severity of Fires. .
. ...... ...
IMPLICATIONS FOR FIRE MANAGEMENT . . . . . . . .
Effects of F i r e Exclusion . . . . . . . . . . . . . . .
Means f o r Reducing F u e l s . . . . . . . . . . . . . . .
Extrapolating Fire History, . . . . . . . . . . . . . .
PUBLICATIONS CITED. . . . . . . . . . . . . . . . . . .
INTRODUCTION.
.I.
2
5
5
5
7
8
II
11
12
12
13
APPENDIX A--Fire F r e q u e n c i e s and Sample T r e e
,
Locations
15
APPENDIX B--Area Covered b y Individual F i r e s ,
Tolan C r e e k , 1900-1734
23
. . .. . . . .. .. . . . .... . .... .
.. ........ . ......
ABSTRACT
P r e s e n t s frequencies, intensities, and influences of f i r e on stand
s t r u c t u r e and composition on the B i t t e r r o o t National F o r e s t i n w e s t c e n t r a l Montana. T h r e e study a r e a s w e r e established, each having a
wide r a n g e of elevations and f o r e s t types. Findings a r e based upon
study of n e a r l y 900 individual f i r e s c a r s on living t r e e s , and on agec l a s s e s of shade-intolerant t r e e s attributable t o f i r e .
During the period f r o m 1600 to 1900 f i r e s w e r e frequent in m o s t
Biologists have long recognized that fire historically has had strong influence on
the ecology of Northern Rocky Mountain forests (Intermountain Fire Research Council
1970; Habeck and Mutch 1973). However, there is little data on frequency and severity
of fires in the various forest types before organized fire suppression evolved in the
early 1900's. Thus, questions and conjecture have arisen about the patterns and types
of fires that occurred: highly destructive crown fires at long intervals or creeping
ground fires at short intervals. Confounding this problem are great differences among
the types of forests found in this region (R. and J. Daubenmire 1968; Pfister and
others, in press) and probably among their respective "fire ecologies." A review of
the literature dealing with fire in the Northern Rocky Mountains is provided by Wellner
(1970) and is updated by Arno.
The present study was developed to provide detailed information on historical fire
in one small portion of the Northern Rockies. Specifically, the goal was to determine
historical frequencies, intensities, and influences of fire on stand structure and
composition in various forest types found on the Bitterroot National Forest in
west-central Montana. A knowledge of the workings and results of the historical fire
regime is an essential element in describing forest ecosystems, development of management alternatives, and planning subsequent programs and projects.
l~rno,Stephen F.
Investigation of fire history in the Bitterroot Range,
Montana. (In preparation)
1
Fire scars on trees were sampled intensively on three study areas in different
parts of the Bitterroot National Forest (fig. 1). Each of these areas includes similar
patterns of forest types extending over a broad elevational range (from about 4,000
to 8,000 feet) on a variety of exposures. The three study areas include terrain,
forest types, and presumably fire histories that are representative of the 1.2-millionacre Montana portion of the Bitterroot National Forest.
Sampling and analysis techniques were developed on the Onehorse Study Area, and
are explained in greater detail in Arno (footnote 1). (A "how-to-do-it" report for
determining Eire history based on these procedures is in preparation, by Arno and
K. Sneck.) The Tolan and West Fork Study Areas were selected to provide a broader
geographical basis for interpreting the role of fire in the Bitterroot National Forest
These latter sites were chosen in part because fuel-inventory studies were also being
conducted there as part of the Fire in Multiple Use Management Research, Development,
and Application Program (USDA Forest Service 1975). Each of the study areas was also
chosen to sample unlogged forest at all elevations on a variety of aspects, and to
record fire history in the form of fire scars on living trees and fire-initiated age
classes of shade-intolerant conifers.
NATIONAL
FOREST
) P{
HA
P
BUTTE
East Fork
Bitterroot River
TOLAN
West Fork
Bittmrroot River
SALMON
\%
;
i
fi
20 10
SCALE
0
40 m i l e s
ldd=ALl
Figure 1.--Location of the three study areas.
Initially, reconnaissance transects were made along roads, trails, and crosscountry routes into all major portions of each study area. An attempt was made to
visit representative aspects and elevations and not to over-sample narrow, ridgeline
ecotones where vegetative types and fire patterns converge. Three types of information
were gathered along each transect:
1. Habitat types, identified and mapped according to the Pfister and others
(in press) classification.
2. Sera1 stand types were described and periodically sampled, including increment boring 1 foot above ground level to identify all age classes of shade-intolerant
trees. (Corings were counted in the lab.)
3 . Fire-scarred sample trees, located and described in terms of number of
individual scars and tree soundness (lack.of decay).
I
After the initial reconnaissance, trees in each stand with the largest number of
relatively sound fire scars were chosen for sampling. A roller-tipped chain saw was
used on large trees to take a cross section of only the wood adjacent to the fire-scar
wound. This "partial cross section" resulted in removal of about 10 percent of the
basal area of a given large tree. Small or exceptionally rotten trees were felled.
Cross sections were sanded, and rings were counted and verified with a binocular
microscope (7 to 25 power) to determine the year of each fire scar.
Fire-scar sequences on individual trees were correlated with those from nearby
sample trees to obtain a master fire chronology for determining actual fire years.
Master chronology years should normally be within +1 year of the actual fire except
for records 250 or more years old, where accuracy diminishes. A sample of several
trees is necessary to document the entire sequence of fires in one location, because
individual fires often do not inflict a new wound on previously scarred trees (Arno,
footnote 1).
The vertical bars in figure 2 show the number of sample trees scarred during each
fire year in each of the three study areas. It is evident from the dashed line that
sample size diminishes prior to the mid-1700's. This probably accounts for any
"apparent" decrease in the fires prior to 1750. In contrast, despite a large sample
size, fires diminished in the 1900's. Presumably, this decreasing fire occurrence partially reflects the role of organized fire suppression. Therefore, the interval 1735
to 1900 was considered to provide the best data base for analyzing fire frequencies in
the era prior to fire suppression (Arno, footnote 1).
TO correlate an adequate number of individual tree records for a given area, it
was necessary to calculate fire frequencies for stands of 200 to 800 acres. The
boundaries were drawn so that each stand represented only one category of habitat
types. The fire record for each stand was thus determined by correlating the individual
chronologies from the several sample trees within it. Consequently, the fire frequencies generated in this study (table 1) represent the average intervals between
fires detected in a given stand. On one hand it might be argued that these intervals
are actually shorter than would be expected for a given smaller stand because some of
the fires detected did not cover the entire 200- to 800-acre unit. However, this
effect is counterbalanced by the probability that many small or low-intensity fires
were not detected in a given stand by the scarred-tree sampling. All evidence
considered, these data should give a reasonable approximation of the incidence of
fire in a given stand. Frequencies were averaged for all stands in a given habitattype group in each study area. These habitat-type groups (table 1, columns 1 and 2)
serve as a basis for comparison of fire frequencies within as well as among the
study areas.
1590 1600 '20
I
L
70 60 50 40
30 20 10
'40
'80 1700 '20
'60
,
'40
I
I
2
e
Ln
1
w
pi
'60
'80 1900 '20 '40
I
I
I
rrc---------------
'60 1975
- --
I
70
60
- 50
- 40
- 30
- 20
- 10
'0
G
Onehorse
/ @ N d
/ /
A ye'
0
-
.
onn..
L1
1800 '20 '4Ll
'80
I
,--.a
-
'60
I
40
30 -
-
.
111~. I, 1. I
____-----Or
.III. 1 1
11.
11,1111
..
.I1
- - / /----------
Tolan
-
,I
I
.
- 40
- 30
- 20
-------,
---/--
'I
20
10 O ~ A -
- 10
1.11.
I
0
I
ce
-
W
m
Z
60
50 40
30 20 10
-
1-
West Fork
-
0
1590 1600 '20
- -j' .'
'60
'80
)---"----
-
/-0-
r---/--
_.----)'
1700 '20
-----'
/
.
'40
60
!50
40
- 30
- 20
- 10
'L 0
-.
'40
1
'60
.
,111
'80
1
I,, 1
a
1800 '20
I
'40 '60
1 . 1
n
'80
1
.I
I
1900 '20 '40
'60 1975
YEAR OF FI RE
Figure 2.--Forest fire chronoZogies for the three study areas on the Bitterroot N. F.,
Montana, shozowing the nwnber of sample trees scarred each fire-year. Dashed Zines
indicate the nwnber o f fire-susceptibte trees ( i . e . , trees aZready scarred a t Zeast
once) i n t & e sampZe.
Table 1 . - - F i r e frequencies f o r t h e p e r i o d 1735 t o 1900 on t h e t h r e e study areas i n t h e B i t t e r r o o t National Forest, Montana.
a l l f i r e years I d e n t i f i e d w i t h i n 200- t o RO0:acre h a b i t a t type u n i t s (stands).
Frequencies are based on
-1
-
H a b i t a t type grou s
{ p o t e n t h l ClimaX!
P f i s t e r and others.
i n press )
1. Pinus ponderosa/Festuca
ldahoensis
Pseudotsuga m e n z l e s i i /
Agropyron s p i catum
Pseudotsuga/Calamagrostls,
P. ponderosa phase
:
:
Oescriptive
location
: O m i n a n t trees:
Doninant
: w i t h continued:
overstory
: General : f i r e exclusion:
before 1900
:elevations:(most abundant: ( n o s t abundant
: (feet)
: tree f i r s t ) :
tree f i r s t )
V a l l e y edqe
Douglas-fir
ponderosa p i n e
:
:
Mean
:
: No. of
: stands : i n t e r v a l : stands
:(No. of : (min-max :(Wo. of
: trees) : i n t e r v a l ) : t r e e s )
: No. of : f i r e - f r e e
ponderosnpine
6 years
12-20)
:
:
:
:
:
Mezn
fire-free
interval
(win-max
interval)
:
Vest
:
: No. o f
: stands
:(No. o f
: trees)
Fork
v
: fire-free
11 years
(2-18)
: interval
: (min-max
: interval)
10 r e a r s
(2-18)
2. Pseudotsuga/Physocarpus
malvaceus
PseudotsugalCalamagrostlr
(except Cal. phase)
Montane slopes
PseudotsugalSymphori carpos
albus
PseudotsuoalVac. g l o b u l a r e
(except-Xerophyllum phase)
3. Abies grandis h a b i t a t
types
Moist canyon
4, PseudotsugalCalamagrostis,
Calamagrostis phase
Pseudotsuga/Vac. slobulare,
X e r o p h y l l m phase
L w e r subalpine
Abies lasiccarpa/
s 1opes
Xerophyl lum tenax
Abies lasiocarpa/Menziesia
ferruginea
Abies laslocarpa/Linnaea
borealis
5. Abies 1asiocarpalLuzula
h itchcockli
Abies lasiocarpa-Pinus
albicaulislVac.
scooarium
Upper subalpine
slopes
4200-6200
4300-4700
6000-7500
7500-8600
Oouqlas-fir
wand fir
subalpine f i r
Douolas-f i r
ponderosa p i n e
Douqlas-fir
lod?epole p i n e
western l a r c h
western l a r c h
lodpepole p i n e
Douolas-f l r
3
(46)
7 years
(2-28)
1
17 years
(71
(3-32)
1
17 years
(3-33)
lodoepole pine
Douglas-fir
('3)
subalpine f i r whitebark Dine
whitebark pine lodyepole pine
1
(3)
41 vears
(9-50)
(11)
16 years
(4-29)
4
(23)
--
.-
--
27 years
(5-62)
3
(13)
28 years
(16)
2
(14)
30 years
(4-78)
2
(141
33 yeays
12-66
3
3
19 years
(2-48)
--
(5-67)
Data Base
A t o t a l o f 889 i n d i v i d u a l f i r e s c a r s (from 171 t r e e s ) were documented i n t h e
3 s t u d y a r e a s ; 726 o f t h e s e occurred i n t h e 1735 t o 1900 p e r i o d . Ponderosa pine
(Pinus ponderosa), Douglas-fir (Pseudo+suga msnziesi-f), western l a r c h ( l t a ~ Z 3 :
o c c i d e n t a Z i s ) , lodgepole p i n e (Pinus contorts), and whitebark p i n e (Pinus aZbicauZZs)
a l l had m u l t i p l e f i r e s c a r s d a t i n g back a s f a r a s 250 t o 300 y e a r s , although i n most
a r e a s t h e lodgepole p i n e f i r e - s c a r r e c o r d s extended back o n l y 150 t o 200 y e a r s because
of s t a n d ages. Ponderosa p i n e provided t h e c l e a r e s t , most abundant, and o l d e s t r e c o r d s
i n a l l s t u d y a r e a s , with s c a r s a s o l d a s 400 y e a r s .
The d a t a b a s e i s d i s p l a y e d i n t a b l e s A-1, A-2, A-3, and accompanying f i g u r e s A-1,
A-2, A-3 (appendix A). Table A - 1 i s t h e master f i r e chronology f o r t h e Onehorse a r e a ,
showing t h e number o f sample t r e e s s c a r r e d d u r i n g each f i r e y e a r i n each s t a n d .
Figure A - l shows t h e l o c a t i o n s o f t h o s e s t a n d s and o f t h e sample t r e e s w i t h i n them.
S i m i l a r l y , t h e p a i r e d f i r e chronologies and maps p r e s e n t t h e d a t a f o r Tolan ( t a b l e A-2
and f i g . A-2) and West Fork ( t a b l e A-3 and f i g . A-3).
Fire Frequency
I t seems apparent from t a b l e s A-1, A-2, and A-3, and e s p e c i a l l y as t h e t o t a l
number o f f i r e s c a r s p e r s t u d y a r e a i s graphed i n comparison with sample s i z e i n f i g u r e
2, t h a t t h e E i r e f r e q u e n c i e s remained comparably high a s f a r back a s t h e r e c o r d s go-namely, t o t h e e a r l y 1600's a t Tolan and West Fork and t o about t h e y e a r 1500 a t Onehorse. Thus i t appears t h a t t h e f i r e f r e q u e n c i e s during t h e 1735 t o 1900 period r e p r e s e n t a p a t t e r n c o n t i n u i n g back a t l e a s t t o t h e y e a r 1600.
A l o g i c a l q u e s t i o n t h a t a r i s e s i s how f r e q u e n c i e s based on 200- t o 800-acre s t a n d s
compare w i t h t h o s e o b t a i n e d a t a s i n g l e p o i n t on t h e ground, a s i n g l e t r e e . A s an
example, f i g u r e 3 shows t h e s c a r r e d c r o s s s e c t i o n o f a ponderosa p i n e growing on t h e
"montane slopes'' ( t a b l e 1 , column 2) a t Onehorse. During t h e 1735 t o 1900 p e r i o d it
was s c a r r e d by 15 f i r e s a t an average i n t e r v a l o f every 11 y e a r s . T h i s compares w i t h
an average i n t e r v a l o f 7 y e a r s f o r s t a n d s i n t h a t c a t e g o r y ( t a b l e 1) a t Onehorse.
Trees growing o n l y a few dozen yards from t h e one i n f i g u r e 3 had s c a r s from a d d i t i o n a l
f i r e s . I t seems h i g h l y u n l i k e l y t h a t every f i r e could burn h o t enough a t t h e base o f
any given t r e e i n such a s t a n d t o i n f l i c t a new wound, e s p e c i a l l y when t h e y occurred s o
f r e q u e n t l y a s t o a l l o w o n l y l i g h t accumulations o f f u e l .
F i r e s occurred l e s s o f t e n i n t h e Tolan and West Fork a r e a s ( t a b l e 1 ) ; t h u s one
might expect i n d i v i d u a l t r e e s t h e r e t o be exposed t o more i n t e n s e f i r e s which a r e more
l i k e l y t o cause a s c a r . Average pre-1900 f i r e - f r e e i n t e r v a l s were c a l c u l a t e d f o r t h e
most f r e q u e n t l y s c a r r e d i n d i v i d u a l t r e e s i n each h a b i t a t - t y p e group. These i n t e r v a l s
proved t o be o n l y about 15 t o 20 p e r c e n t l o n g e r than t h o s e d e r i v e d f o r t h e e n t i r e 200t o 800-acre s t a n d s . Even t h e s e t r e e s might have missed being s c a r r e d i n one o r two
f i r e s , conf inning t h e stand-based e s t i m a t e s .
Figure 3. --Multiple fire-scar cross-sect-ion, showing 21 f i r e scars from 1659 through
1915. (Ponderosa pine sample t r e e #53, Onehorse stud2 area, B i t t e r r o o t National Forest)
These h i s t o r i c f i r e frequencies a r e compared i n t a b l e 1 by h a b i t a t - t y y e graups fox
each of t h e t h r e e study a r e a s . For i n s t a n c e , stands on t h e montane slopes (Pseudots-uga/
Physocarpus and o t h e r h a b i t a t types) had average i n t e ~ v a l sof 16 and 19 yeaTs between
f i r e s i n t h e Tolan and West Fork a r e a s , r e s p e c t i v e l y . The s h o r t e s t i n t e r v a l detected
between f i r e s i n any of t h e t h r e e stands i n t h i s category a t Tolan was 4 years. The
longest f i r e - f r e e i n t e r v a l t h e r e , during t h i s 1735 t o 1900 period, was 29 years. During
t h i s period t h e dominant o v e r s t o r y s p e c i e s was ponderosa p i n e ( t a b l e 1, column 5 ) ; wherea s Douglas-fir would dominate i n t h e absence of f i r e o r o t h e r disturbance (column 4 ) .
Comparable i n t e r p r e t a t i o n s can be made f o r o t h e r h a b i t a t types u s i n g t a b l e 1.
Inspection of t a b l e 1 r e v e a l s t h a t t h e r e l a t i v e f i r e frequencies by f o r e s t c a t e g o r i e s a r e n e a r l y i d e n t i c a l a t Tolan and West Fork. By c o n t r a s t , f i r e s occurred almost
twice a s f r e q u e n t l y throughout t h e Onehorse area--except f o r t h e upper subalpine slopes
where t h e sample s i z e was very small, and probably inadequate. One could argue t h a t t h e
Onehorse a r e a i s b a s i c a l l y d r i e r and t h e r e f o r e burns more f r e q u e n t l y , but t h i s reasoning
i s not borne out by f i e l d observations o r by t h e standardized h a b i t a t - t y p e c a t e g o r i e s .
A more p l a u s i b l e explanation i s t h a t f i r e s o r i g i n a t i n g on t h e lower s l o p e s a t Onehorse
spread more r e a d i l y upward throughout a l l t h e types because of t h e s t e e p topography.
However, t h e d a t a i n t a b l e 1 show t h a t f i r e frequencies decrease with i n c r e a s i n g
e l e v a t i o n a t Onehorse a t a r a t e comparable t o t h a t of t h e o t h e r a r e a s . Also, such an
explanation f a i l s t o account fox t h e high frequency of f i r e s on t h e lowermost u n i t s a t
Onehorse.
Several t h r e a d s of evidence suggest another reason f o r t h e higher f i r e frequency
a t Onehorse. Anthropologists have long recognized t h a t Indians h i s t o r i c a l l y s e t f i r e s
i n t h e Rocky Mountains (Malouf 1969). Direct descendants of t h e f i r s t s e t t l e r s i n t h e
Sula Valley below Tolan study a r e a (Marvin and William Wetzsteon a t Sula, and M r . Lord
a t Moosehead Museum, n o r t h of Sula, 1975, personal communication.) s t a t e d t h a t when
t h e i r grandparents homesteaded t h e a r e a near t h e t u r n of t h e century, Indians p e r i o d i c a l l y
s e t f o r e s t f i r e s i n t h e nearby mountains, presumably t o improve forage production f o r
b i g game and horses. Indians occupied t h e B i t t e r r o o t Valley f o r a t l e a s t s e v e r a l cent u r i e s p r i o r t o white settlement i n t h e mid-1800's (Ward 1973). According t o D r . C.
Malouf, University of Montana, Missoula (personal communication), Indians p r e f e r r e d t h e
main B i t t e r r o o t Valley grasslands adjacent t o t h e Onehorse a r e a , t h e r e f o r e a b o r i g i n a l
burning probably would have been more common here than on t h e r a t h e r remote Tolan and
West Fork study a r e a s .
S t i l l another t e n t a t i v e suggestion of d e l i b e r a t e a b o r i g i n a l burning has a r i s e n
from Mehringer's (1976) a n a l y s i s of 12,000 years of p o l l e n and charcoal deposition a t
Lost T r a i l Pass Bog (located i n t h e "lower subalpine slopes" category, t a b l e 1) 7 miles
southwest of t h e Tolan study a r e a . Mehringer found t h a t a i r b o r n e charcoal has been dep o s i t e d c o n t i n u a l l y s i n c e t h e reestablishment of v e g e t a t i o n i n t h e a r e a a f t e r g l a c i a l
r e t r e a t 11,500 y e a r s ago. Presumably t h i s came from f i r e s burning i n a s i z a b l e , mostly
f o r e s t e d region upwind from Lost T r a i l Pass. However, t h e magnitude of charcoal dep o s i t i o n increased dramatically within t h e l a s t 2,000 years d e s p i t e no marked change i n
t h e f o r e s t type. To keep t h i s i d e a i n p e r s p e c t i v e , one must r e a l i z e t h a t t o hypothesize
an Indian-burning program from d e p o s i t i o n i n one bog i s a l a r g e e x t r a p o l a t i o n .
Correlations Among Fire Years
Comparison of t h e Onehorse d a t a with National Weather Service records between
1870 and 1920 revealed t h a t f i r e s were s t r o n g l y c o r r e l a t e d with drier-than-average
Table A - 4 (appendix A) d e p i c t s apparent c o r r e l a t i o n s
summers (Arno, footnote 1).
among t h e f i r e y e a r s on t h e t h r e e s t u d y a r e a s . E v i d e n t l y , r a t h e r e x t e n s i v e f i r e s
occurred simultaneously on a t l e a s t two of t h e a r e a s d u r i n g t h e f o l l o w i n g y e a r s :
Table A-4 a l s o shows t h a t t h e r e were a number of y e a r s when one a r e a was burned extens i v e l y , w h i l e t h e o t h e r s e v i d e n t l y experienced l i t t l e o r no f i r e .
Extent and Severity 0%Fires
I t i s much more d i f f i c u l t t o q u a n t i f y t h e i n t e n s i t i e s o f h i s t o r i c f i r e s t h a n it
i s t o simply document t h e i r o c c u r r e n c e and determine f i r e frequency. S t i l l , s e v e r a l
s o u r c e s of d a t a can b e i n t e r p r e t e d t o p r o v i d e an understanding of t h e h i s t o r i c r o l e
of f i r e .
Tmplicatione of Fire Frequency
The r e l a t i v e l y s h o r t i n t e r v a l s between f i r e s throughout t h e t h r e e s t u d y a r e a s
(t.able 1 ) suggest t h a t f i r e i n t e n s i t y was n o t u s u a l l y g r e a t because t h e r e was l i t t l e
time f o r heavy f u e l accumulation.
Age-c lass Findings
The r l s i n t a b l e A-2, f o r example, show t h a t many age c l a s s e s o f s h a d e - i n t o l e r a n t
c o n i f e r s were d e t e c t e d wherever a g e - c l a s s a n a l y s i s was conducted ( a l l s t a n d s except
A and I ) . (Some o f t h e r e g e n e r a t i o n d a t a i n t a b l e A-2 were provided by Ed Mathews,
Northern F o r e s t F i r e Laboratory, Missoula, Montana.) Less i n t e n s i v e a g e - c l a s s sampling
was done a t Onehorse and West Fork, b u t n e v e r t h e l e s s t h e r ' s i n t a b l e s A-1 and A-3 show
a s i m i l a r p a t t e r n o f mult.iple age c l a s s e s o f s h a d e - i n t o l e r a n t c o n i f e r s . Each age c l a s s
was r a t h e r easy t o r e l a t e t o a f i r e t h a t o c c u r r e d from 3 t o 10 y e a r s p r i o r t o e s t a b l i s h
ment o f t h e o l d e s t t r e e s i n t h a t c l a s s .
Some o f t h e age c l a s s e s d e t e c t e d i n a s t a n d a p p a r e n t l y r e s u l t e d from a f i r e t h a t
was n o t r e p r e s e n t e d a s a s c a r on sample t r e e s i n t h a t s t a n d . F i r e y e a r s 1811 and 1871
i n s t a n d F ( t a b l e A-2) a r e examples. When t h e a d j a c e n t s t a n d s ( E and G) had b o t h s c a r s
and r e g e n e r a t i o n , d a t i n g from t h o s e f i r e y e a r s , i t seems l i k e l y t h a t t h e f i r e had i n
f a c t v i s i t e d t h e stand i n question (stand F ) .
Evidence of Fires of Various Intensities
Both f i e l d o b s e r v a t i o n s and t a b l e A-2 ( s t a n d D , 1821 and 1871) s u g g e s t t h a t somq
f i r e s were o f such low i n t e n s i t y t h a t l i t t l e of t h e lodgepole p i n e o v e r s t o r y was k i l l e d
and t h e s t a n d was n o t opened s u f f i c i e n t l y t o a l l o w f o r e s t a b l i s h m e n t of a new age c l a s s .
T h i s i s evidence o f a l o w - i n t e n s i t y , c r e e p i n g ground f i r e i n lodgepole p i n e s t a n d s .
S i m i l a r evidence was a l s o observed i n many lodgepole f o r e s t s i n a l l b u t t h e northwestern
p a r t of Montana d u r i n g f i e l d s t u d i e s f o r t h e f o r e s t - h a b i t a t - t y p e c l a s s i f i c a t i o n system
( P f i s t e r and o t h e r s , i n p r e s s ) . I n northwestern Wyoming, Loope and Gruel1 (1973) found
evidence o f t h e h i s t o r i c r o l e o f c r e e p i n g ground f i r e s i n lodgepole p i n e f o r e s t s . Moreo v e r , t h e y s t a t e d t h a t even under high f u e l l o a d i n g s r e c e n t f i r e s have remained g e n e r a l l y
on t h e ground e x c e p t when e n c o u n t e r i n g s t r o n g winds o r extremely heavy l o a d i n g s . Modera t e upslope winds on s t e e p f o r e s t e d s l o p e s may produce t h e same e f f e c t a s s t r o n g winds
on more g e n t l e t e r r a i n .
I n g e n e r a l , t h e s e i n t e r p r e t a t i o n s f o r t h e Montana p o r t i o n o f t h e B i t t e r r o o t N a t i o n a l
F o r e s t d i f f e r from t h e view p r e s e n t e d by Wellner (1970) t h a t f i r e damage was " u s u a l l y
extreme" i n a l l major f o r e s t ecosystem t y p e s i n t h e Northern Rocky Mountains except
where ponderosa p i n e and sometimes where D o u g l a s - f i r i s t h e p o t e n t i a l climax. The
abundance o f t r e e s w i t h many f i r e s c a r s i n a d d i t i o n t o m u l t i p l e age c l a s s e s over most
o f t h e l a n d s c a p e i n t h e t h r e e s t u d y a r e a s s u g g e s t s t h a t u s u a l l y f i r e damage was n o t
extreme.
F o r e s t s i n t h e Montana p o r t i o n o f t h e B i t t e r r o o t National F o r e s t a r e g e n e r a l l y
l e s s p r o d u c t i v e and probably l e s s dense t h a n i n n o r t h e r n Idaho where W e l l n e r l s conclus i o n s seem most a p p l i c a b l e . T e r r a i n i s o,ften s t e e p , i n t h e B i t t e r r o o t e s p e c i a l l y on
t h e montane s l o p e s (Pseudo$suga h a b i t a t t y p e s , t a b l e 1 ) f a v o r i n g m o r e - i n t e n s e burning.
However, comparable exposures i n n o r t h e r n Idaho, c h a r a c t e r i s t i c a l l y have more d e n s e l y
f o r e s t e d western hemlock (Tsuga h e t e r o p h y l l a ) , western r e d c e d a r (Thuja p Z i c a t a ) , o r
grand f i r (Abies g r a n d i s ) h a b i t a t t y p e s ; t h a t a r e e v i d e n t l y more l i k e l y t o burn i n
s t a n d - d e s t r o y i n g f i r e s . Large h o l o c a u s t s (1910, 1919, P e t e King f i r e i n 1934, Sundance
and Trapper Peak f i r e s i n 1967) have o c c u r r e d i n n o r t h e r n Idaho i n t h i s c e n t u r y .
Most r e s e a r c h e r s a r e s t r o n g l y tempted t o g e n e r a l i z e about f i r e b e h a v i o r b u t p e r haps f i r e s i n t h e Northern Rockies a r e n o t b e s t d e s c r i b e d i n broad g e n e r a l i z a t i o n s .
D e t a i l e d s t u d i e s o f f i r e h i s t o r y a t v a r i o u s p l a c e s throughout o u r f o r e s t t y p e s should
u l t i m a t e l y r e s o l v e t h i s problem.
G a b r i e l (1976) r e c e n t l y completed a d e t a i l e d a n a l y s i s o f t h e f i r e h i s t o r y i n some
lodgepole pine-dominated f o r e s t s i n t h e Bob Marshall Wilderness o f n o r t h w e s t e r n Montana.
I n t h e s o u t h e r n h a l f o f h i s s t u d y a r e a , G a b r i e l documented t h e o c c u r r e n c e o f lowi n t e n s i t y s u r f a c e f i r e s a t 20- t o 40-year i n t e r v a l s i n each s t a n d . By c o n t r a s t , he
found t h a t l a r g e r , s t a n d - d e s t r o y i n g f i r e s had profoundly i n f l u e n c e d most o f t h e n o r t h e r n
h a l f o f h i s s t u d y a r e a . However, even h e r e he found about 20 l i v i n g lodgepole p i n e and
D o u g l a s - f i r t r e e s having two f i r e s c a r s each. T h i s s u g g e s t s a s p o r a d i c p a t t e r n o f s t a n d
d e s t r u c t i o n even d u r i n g r e l a t i v e l y h i g h i n t e n s i t y f i r e s .
A small p r o p o r t i o n o f t h e Onehorse and Tolan a r e a s and a s i z a b l e p a r t o f t h e w e s t e r n
u n i t o f t h e West Fork a r e a were a p p a r e n t l y burned i n h i g h - i n t e n s i t y f i r e s . A t Onehorsea f i r e - k i l l e d s t a n d e v i d e n t l y r e s u l t e d from a double burn i n 1889 and 1892 (Arno,
f o o t n o t e 1). A t West Fork a s i z a b l e s t a n d was k i l l e d i n 1889. A t Tolan a s t a n d was
k i l l e d a t t h e head o f t h e canyon bottom (between s t a n d s F, G , and H , f i g . A-2) i n 1785
on a s i t e t h a t was unique i n having no evidence o f f i r e having v i s i t e d i t s i n c e . I n
a l l s t u d y a r e a s , t h e h o l o c a u s t was r e s t r i c t e d t o a r e a s w i t h i n t h e lower s u b a l p i n e f o r e s t
dominated by lodgepole p i n e (Abies Zasiocarpa/XerophyZZm and Abies Zasiocmpa/Menziesia
h a b i t a t types) .
E x t e n t of F i r e s
Mapping e v e r y f i r e t h a t o c c u r r e d i n a given f o r e s t a r e a p r o v i d e s i n s i g h t i n t o t h e
e x t e n t and p a t t e r n s o f h i s t o r i c f i r e (Heinselman 1973). U n f o r t u n a t e l y , such mapping,
based on t h e f i r e s c a r and a g e - c l a s s d a t a , could n o t be done a t Onehorse because f i r e s
were t o o f r e q u e n t . A t West Fork, sampling was done i n s t a n d s t h a t were t o o d i s p e r s e d
over rugged topography t o a l l o w f o r mapping o f i n d i v i d u a l f i r e s . I n c o n t r a s t , t h e Tolan
d a t a was n o t hampered by t h o s e problems, and t h e a g e - c l a s s d a t a was ample, t h u s i t was
p o s s i b l e t o p l o t t h e e x t e n t o f each f i r e d e t e c t e d i n t h e Tolan d r a i n a g e between 1900
and 1734 (appendix B) .
Although many o f t h e s e f i r e s were n o t o f high i n t e n s i t y , t h e y were n o t confined
t o small a r e a s . I n c o n t r a s t , i n r e c e n t t i m e s , f i r e s o f low-to-medium i n t e n s i t y a r e
suppressed b e f o r e they cover l a r g e a r e a s , whereas h i g h - i n t e n s i t y crown f i r e s may cover
l a r g e a r e a s . Observations (Kilgore 1975; Mutch 1974) from a r e a s where n a t u r a l f i r e s
have r e c e n t l y been allowed t o run t h e i r c o u r s e (White Cap Area, B i t t e r r o o t National
F o r e s t ; Grand Teton and Sequoia-Kings Canyon National P a r k s ) , show t h a t low- t o mediumi n t e n s i t y f i r e s may cover l a r g e a r e a s by advancing s p o r a d i c a l l y , o f t e n slowly, u n t i l
heavy f a l l and w i n t e r p r e c i p i t a t i o n f i n a l l y e x t i n g u i s h e s them.
Interpretations
The general p a t t e r n of f i r e s and age c l a s s e s i n each s t a n d ( t a b l e s A - 1 ,
A-2,
and
A - 3 i s c l e a r l y one o f f r e q u e n t f i r e s l e a v i n g s u b s t a n t i a l remnants o f e a r l i e r age c l a s s e s .
Most pre-1900 f i r e s on t h e B i t t e r r o o t study a r e a s a p p a r e n t l y burned l i g h t l y on d r i e r
s l o p e s a t lower e l e v a t i o n s , p e r p e t u a t i n g ponderosa p i n e a s t h e dominant s p e c i e s i n open
s t a n d s . These f i r e s k i l l e d much o f t h e ponderosa p i n e r e g e n e r a t i o n and most o f t h e
invading Douglas- f i r . F i r e s tended t o burn with g r e a t e r i n t e n s i t y on n o r t h - f a c i n g
s l o p e s , where dense, young growth o f D o u g l a s - f i r p r e s e n t e d more o p p o r t u n i t y f o r c a r r y i n g
a f i r e above t h e ground. Even h e r e , 'however, much o f t h e old-growth ponderosa p i n e ,
D o u g l a s - f i r , western l a r c h , and even sgme lodgepole p i n e s u r v i v e d . I n t h e lower suba l p i n e f o r e s t , dominated by lodgepole p i n e , f i r e s o f t e n were o f low o r medium i n t e n s i t y ,
s p r e a d i n g mostly on t h e f o r e s t f l o o r . There were o c c a s i o n a l h o t s p o t s where a s t a n d
was l a r g e l y k i l l e d through b o l e h e a t i n g o r a "run" through t h e o v e r s t o r y .
Holocausts have a l s o c l e a r l y been a p a r t of t h e spectrum o f f i r e s (Sleeping C h i l d ,
Saddle Mountain, and Corn Creek f i r e s i n 1960 and 1961) o c c u r r i n g on lower s u b a l p i n e
s l o p e s i n t h e B i t t e r r o o t . They a r e unusually i n t e n s e f i r e s t h a t had a dramatic e f f e c t
on thousands of a c r e s of f o r e s t .
S t i l l h i g h e r , i n t h e upper s u b a l p i n e f o r e s t , f i r e s were l e a s t f r e q u e n t and a l s o
l e s s i n t e n s e , probably because of m o i s t e r and s p a r s e r f u e l s . Some o f t h e s e l a t t e r
f i r e s undoubtedly s p r e a d upslope from more f a v o r a b l e burning c o n d i t i o n s a t lower
e l e v a t i o n s and then burned l e s s i n t e n s e l y a s f u e l s thinned o u t and m o i s t u r e i n c r e a s e d .
1MPLICATIONS FOR FIRE
MANAGEMENT
Effects of Fire Exclusion
Data from all study areas (tables A-1, A-2, A-3) show a marked decrease in fire
since about 1920. Modern, airborne fire-suppression techniques theoretically can
result in very effective control of potentially low-to-medium intensity fires. Thus
a major ecological force has been largely excluded for half a century, and the years
since the last burn on most of the forested land now exceed the longest fire-free
intervals recorded between 1735 and 1900 (table 1). In some forest types, this has
allowed fuels to accumulate. In many stands were Douglas-fir is the potential climax
tree, dense understories of this species have developed, making a ladder of fuels that
now endangers even the fire-resistant, old-growth overstory of ponderosa pine, Douglasfir, and western larch. Throughout the subalpine forest on the Bitterroot, additional
heavy fuels have been generated as a result of massive overstory kills of lodgepole
and whitebark pines by the mountain pine beetle (Dendroctonus ponderosae) in the 1920's
and 1930's.
Also, severe infestations of d w a ~ fmistletoe (Arceuthobiwn spp.) in Douglas-fir,
western larch, and lodgepole pine at various locations on the Bitterroot have contributed
to stand stagnation and loss of vigor, Presumably, the effect of dwarf mistletoe adds
to the fuel generation rates and thus increases vulnerability of the forest to severe
fire damage. This situation is partially a result of fire exclusion. Alexander and
Hawksworth (1975) have analyzed current knowledge of the interrelationships between
natural fire and dwarf mistletoe infestations, and have commented on possible applications of prescribed fire for control of the parasite. Other possible relationships of
continued fire exclusion to insect damage, such as to western budworm in Douglas-fir
and mountain pine beetle in overly dense ponderosa pine stands on the Bitterroot, also
warrant concern.
Continued fire suppression without fuel management apparently promotes accumulation of fuels as well as greater continuity of fuels over the landscape; this probably
favors the development of high-intensity fires.
Means for Reducing Fuels
High fuel loadings eventually will be reduced by decay, fire (wildfire or prescribed
fire), or removal. Decay is relatively slow in these cool, dry forests and thus seems
inadequate unless augmented by various types of prescribed fire or logging, or a combination. Where resource managers do not establish a fuel reduction program, nature may
eventually do so by means of a large, uncontrollable wildfire. Mankind does not
generally find this alternative safe or otherwise acceptable. Logging and slash disposal
can reduce fuels in many areas. However, in some areas, this may be either uneconomical
or unacceptable because of other management goals.
In the latter situation, the prescribed use of fire should be seriously considered
for fuel reduction and stand management. Prescribed burning in dense stands on
Pseudotsuga habitat types has recently been demonstrated on the Lubrecht Experimental
Forest in western Montana (Norurn 1976). Also, information from the following sources
can supply much of the framework necessary for using fire in such stands:
1. Findings of natural fire studies in national parks (Kilgore 1975) and wilderness (Habeck and Mutch 1973; Mutch and Habeck 1975);
2. Techniques developed for managing fire in wilderness (Aldrich 1973);
3 . Other current research of the Fire in Multiple Use Management Research, Development, and Application Program (USDA Forest Service 1975).
Fire could be applied when burning conditions are moderate, and are forecast to remain
stable, especially in early autumn.
A burning program would require carefully developed fire prescriptions designed to
accomplish management objectives, while minimizing unwanted fires (Barrows 1974). After
the initial fuel reduction, maintenance of desirable fuel and stand conditions should
become less difficult. A fuel management plan might incorporate both prescribed fire
and naturally caused fires burning under certain conditions in specified areas. Natural
fires not burning as desired would be suppressed.
ExtrapolatingFire History
Resource managers should be able to approximate pre-1900 fire frequencies in various
parts of the Montana portion of the Bitterroot National Forest by extrapolating from
table 1. Most areas of the Forest probably had frequencies comparable to those found
at Tolan and West Fork, except that slopes of the Bitterroot and perhaps the Sapphire
Range immediately adjacent to the main Bitterroot Valley may have had rates more like
those at Onehorse.
The Forest habitat-type map and recent topographic maps will provide the basic information for assigning the appropriate habitat types in table 1 to the land in question.
Analysis of the latest timber-inventory data and timber-type maps will be important for
obtaining a knowledge of fuels and stand conditions necessary for developing fire management programs.
PUBLICATIONS CITED
Aldrich, D. F.
1973. Wilderness fire management: planning guidelines and inventory procedures.
USDA For. Serv. North. Reg., Missoula, Mont. 36 p.
Alexander, M. E., and F. G. Hawksworth.
1975. Wildland fires and dwarf mistletoes: a literature review of ecology and prescribed burning. USDA For. Serv. Gen. Tech. Rep. RM-14, 12 p. Rocky Mt. For. and
Range Exp. Stn., Fort Collins, Colo.
Barrows, J. S.
1974. The challenges of forest fire management. West. Wildlands 1(3):3-5.
Daubenmire, R., and J. B. Daubenmire.
1968. Forest vegetation of eastern Washington and northern Idaho. USDA For. Serv.
Tech. Bull. 60, 104 p., Wash. Agric. Exp. Stn., Pullman, Wash.
Gabriel, H. W.
1976. Wilderness ecology: the Danaher Creek drainage, Bob Marshall Wilderness,
Montana. Ph.D. diss., Univ. Mont., Missoula. 224 p.
Habeck, J. R., and R. Mutch.
1973. Fire-dependent forests in the northern Rocky Mountains. Quaternary Res,
3(J) :408-424.
Heinselman, M. L.
1973. Fire in the virgin forests of the Boundary Waters Canoe Area, Minnesota.
Quaternary Res. 3(3):329-382.
Intermountain Fire Research Council.
1970. The role of fire in the Intermountain West. Symp. Proc. School For., Univ.
Mont., Missoula.
Kilgore, B. M.
1975. Restoring fire to national park wilderness. Am. For. 81(3]:16-19, 57-59.
Loope, L. L., and G. E. Gruell.
1973. The ecological role of fire in the Jackson Hole area, northwestern Wyoming.
Quaternary Res. 3 (3) 3425-443.
Malouf, C.
1969. The coniferous forests and their uses in the Northern Rocky Mountains through
9,000 years of prehistory. In: Coniferous forests of the Northern Rocky Mountains,
Proc., p. 271-290. Univ. Mont., Center Nat. Res., Missoula.
Mehringer, P. J., Jr.
1976. Postglacial history of Lost Trail Pass Bog, Bitterroot Mountains, Montana.
Co-op. Agreement Rep., Wash. State Univ.-USDA For. Serv. Submitted to Fire Manage.
RDEA Program, Intermt. For. and Range Exp. Stn., Missoula, Mont. 48 p.
Mutch, R. W.
1974. I thought forest fires were black! West. Wildlands 1(3):16-22.
Mutch, R. W., and J. R. Habeck.
1975. Forest and forestry; forest fire control. p. 209-212. McGraw-Hill Yearb.
Sci. and Tech., New York.
Norwn, R. A.
1976. Fire intensity-fuel reduction relationships associated with understory burning
in larch/Douglas-fir stands. In: Annu. Tall Timbers Fire Ecol. Conf. Proc. 14.
Pfister, R., B. Kovalchik, S. Arno, and R. Presby.
Forest habitat types of Montana. USDA For. Serv. Gen. Tech. Rep. Intermt. For. and
Range Exp. Stn., Ogden, Utah. (In press)
U.S. Department of Agriculture, Forest Service.
1975. Fire in multiple use management--applying research results. USDA For. Serv.,
Intermt. For. and Range Exp. Stn., Ogden, Utah.
Ward, L. C.
1973. Prehistory of the Bitterroot Valley. Master's Thesis, Univ. Mont., Missoula,
129 p .
Wellner, C. A.
1970. Fire history in the northern Rocky Mountains. In: The role of fire in the
Xntermt. West., Proc., p. 42-64. Sch. For., Univ. Mont, Missoula.
APPENDIX A
Fire Frequencies and
Sample Tree Locations
Table 9-1.--Apparent f f r e years and the n w b e r s o f trees scarred i n each stand (200- t o $00-acre h a b l t a t type u n t t l l
of t h e Onehorsc study area, B i t t e r r o o t N a t i o n a l Forest, Pontana.
--
:1.flley
:
F i r e :e a r :
Total
SCPPS
-
edre
-:-.
(ll)*
93
:
:
!
2. ~.U*gnlanelo
;
: c
1
.,
133
1
:
84
Number of sample t r e e s .
" nay I n c l u d e
1856 f i r e ( s ) .
Fires causinq c o n i f e r r e g e n e r a t i o n
es
I ' a b i t a t type Qroops/stands
:4. L o r e r s u b a l ~ i n e : 5 , llpper s u b a l o l n c ' : T o t a l
. 3. M o i s t c a n y g ~ : ~slooes
,
:
slope5
-- : number
!
: of scars
:
(7)
:
(3)
:
(76)-
?%rip
1
136
31
24
7
508
'ON
I
N
SCALE
0
1
-
I
I
0
2
1 mile
I
1' kilometer
Figure A-1.--Topographic map of the Onehorse study area showing *ha geograph.i.cu n i t s and
sample-tree Zocations.
Table A-2.--Apparent f i r e years and t h e numbers o f t r e e s scarred i n each stand (200- t o 800-acre h a b i t a t
t y p e u n i t s ) o f t h e Tolan study area, B i t t e r r o o t N a t l o n a l Forest, Montana.
:
F i r e I -1
year :
T o t a l scars
*
r
1.
Valley
edae
(4)*
50
H a b i t a t type qroups/stands
: 4. Lower subalpine
:
s l o es
2. Montane s l o es
:
F
: D'
:
C : I : D
B
: (5)
: (4) : ( 2 ) : (6) : (6) : ( 4 )
:
29
18
15
28
19
: 5 . Upper sub-:
Total
: a1 i n e s l o es :
number
:
:
: o f scars
(45)
:
( 8 ) : (6) :
13
Number o f sample t r e e s .
F i r e s causing c o n i f e r r e g e n e r a t i o n based on stand aqe-class samples.
18
R
22
8
202
WATERSHED BOUNDARY
STANDS BY HABITAT TYPE GROLIPS :
1. - - A
( Compare with table 1
2.
B. C, I
4.
D, E, F
5.G,H
-
-
Scale.
-
0
12
lrnile
\
/
\
0
--..--/#
Figure A-2. --To'opogmtph<cmap of XoZan Creek study area (800-ft contour interval)
showing smpZe tree Zocations.
Table A-3.--Apparent f i r e years and t h e numbers o f t r e e s scarred in each stand (200- t o 800-acre h a b i t a t type
u n i t s ) o f t h e West Fork study area, B i t t e r r o o t National Forest, Montana.
:
1.
ffre- :
year :
Total scars
*
**
Valley
edqe
A*
( 7 ) ~
36
:
:
:
A
: (7)
36
H a b i t a t type groups/stands
:
4. Lower subalpine
2. Montane slopes
slopes
*
D :
B : C :
F :
E :
G
: (4) : ( 5 :
( 7 ) : (4) : ( 6 : ( 7
34
15
38
9
10
12
5. Upper sub: a l p l n e slopes
:
H : I
:
( 7 ) : (3)
:
11
:
: T o t a l nwnber
:
:
ofscars
(50)
14
Stand A represented b o t h h a b i t a t type groups b u t I s n o t repeated i n c a l c u l a t i n g the t o t a l column.
Number o f sample t r e e s .
F i r e s causing c o n i f e r regeneration.
179
Figure A-3. --Topographic map of West Fork study area, RavaZ Zi County, Mon$ana, shodng
s w Z e tree Locations.
T a b l e A-4.--Number o f sample t r e e s s c a r r e d by y e a r f o r each o f t h r e e study areas on t h e B i t t e r r o o t N a t i o n a l F o r e s t ,
Montana. F i r e - y e a r c o r r e l a t i o n s among t h e study areas a r e u n d e r l i n e d . ( n = number o f sample t r e e s )
Fireyear
1838
1837
1835
1834
1831
1829
1328
1825
: Onehorse
:
n=78
Tolan
n=45
: West
a
Fork
n=59
..
:
'
Fireyear
: Onehorse : Tolan : West Fork
n=78
:n=45 . n=59
Fireyear
1
8
4
3
1725
1722
1720
1717
2
Totals
9
5
2
1
10
3
7
34
5
1715
1712
1710
7
2
2
3
: Onehorse
:
n=78
ToIan
n=45
516
202
:
West
Fork
n=59
198
APPENDIX B
Area Covered by Individual Fires,
Tolan Creek, 1900-1734
Dots show sample
s = s c a r on t h a t
r = regeneration
detected i n
t r e e locations.
tree t h a t year.
from t h a t f i r e
t h e stand.
-
TO SULA 5 MILES
1871 FIRE
-_
---
5 MILES
',
,,: J
\
I
[.+)
#
1842 FIRE
'.
\
q*
;
'
I-
\
\
I
6-
: *&+
,, +
,
\
$
1794 FlRE
1"
...,, .
5 MILES
\
L
>
,
.
*
I
I
?"a-
1785 FlRE
1752 FlRE
1757 F l R E
4"
C
C
TU SULA--
5 MILES
*
U 5 GOVERNMENT PRINTING OFFICE 1976-777-023.7 REG 8
C
I
I
I
't
I
1
1
4
I
!
I
Arno, Stephen F.
1976. The historical role of f i r e on the Bitterroot National
Forest. USDA For. Serv. Res. Pap. INT-187, 29 p. Intermountain F o r e s t and Range Experiment Station, Ogden,
Utah &1401.
1
I
I
1
I
Presents frequencies, intensities, and influences of f i r e on
stand structure and composition on the Bitterroot National F o r e s t
in west-central Montana. Three study a r e a s were established,
eachhaving a wide range of elevations and forest types. Findings
a r e based upon study of nearly 900 individual fire s c a r s on living
trees, and on age-classes of shade-intolerant t r e e s attributable
to fire.
Presents frequencies, intensities, and influences of f i r e on
stand structure and composition on the Bitterroot National Forest
in west-central Montana. Three study a r e a s were established,
eachhaving a wide range ofelevations and forest types. Findings
a r e based upon study of nearly 900 individual f i r e s c a r s on living
t r e e s , and on age-classes of shade-intolerant t r e e s attributable
to fire.
KEYWORDS: f i r e ecology, fire frequency, f o r e s t succession,
habitat types.
Arno, Stephen F.
1976. The historical role of fire on the Bitterroot National
Forest. USDA For. Serv. Res. Pap. MT-187, 29 p. Intermountain Forest and Range Experiment Station, Ogden,
Utah 84401.
I
I
8
1
KEYWORDS: f i r e ecology, f i r e frequency, forest succession,
habitat types.
I
Arno, Stephen F.
1976. The historical role of f i r e on the Bitterroot National
Forest. USDA For. Serv. Res. Pap. MT-187, 29 p. Intermountain F o r e s t and Range Experiment Station, Ogden,
Utah 84401.
A r o , Stephen F.
1976. The historical r o l e of f i r e on the Bitterroot National
Forest. USDA For. Serv. Res. Pap. IPIT-187, 29 p. Intermountain F o r e s t and Range Experiment Station, a d e n ,
Utah 84401.
I
Presents frequencies, intensities, and influences of f i r e on
stand structure and composition on the Bitterroot National Forest
i n west-central Montana. Three study a r e a s were established,
eachhaving a wide range of elevations and f o r e s t types. Findings
a r e based upon study of nearly 900 individual f i r e s c a r s on living
trees, and on age-classes of shade-intolerant t r e e s attributable
t o fire.
1
I
I
!
KEYWORDS: f i r e ecology, f i r e frequency, f o r e s t succession,
habitat types.
1
1
I
B
I
I
1
I
1
I
I
I
I
I
I
tI
Presents frequencies, intensities, and influences of f i r e on
stand structure and composition on the Bitterroot National Forest
in west-central Montana. T h r e e study a r e a s were established,
eachhaving a wide range of elevations and forest types. Findings
a r e based upon study of nearly 900 individual fire s c a r s on living
t r e e s , and on age-classes of shade-intolerant t r e e s attributable
to fire.
I
KEYWORDS: f i r e ecology, f i r e frequency, forest succession,
habitat types.
I
I
t
I
Headquarters for the Intermountain Forest and
Range Experiment Station a r e in Ogden, Utah.
Field programs and research work units a r e
maintained in:
Billings, Montana
Boise, Idaho
Bozeman, Montana (in cooperation with
Montana State University)
Logan, Utah (in cooperation with Utah State
University)
Missoula, Montana (in cooperation with
University of Montana)
Moscow, Idaho (in cooperation with the
University of Idaho)
Provo, Utah (in cooperation with Brigham
Young University)
Reno, Nevada (in cooperation with the
University of Nevada)