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A METHOD FOR DETERMINING
FIRE HISTORY IN CONIFEROUS FORESTS
OF THE MOUNTAIN WEST
STEPHEN F. ARNO and KATHY M. SNECK
USDA F o r e s t Service
G e n e r a l Technical Report INT-42
November 1977
A METHOD FOR DETERMINING
FIRE HISTORY IN
CONIFEROUS FORESTS OF
THE MOUNTAIN WEST
Stephen F. Arno and Kathy M. Sneck
INTERMOUNTAIN FOREST AND RANGE EXPERIMENT STATION
F o r e s t Service
U. S. Department of Agriculture
Ogden, Utah 84401
THE AUTHORS
STEPHEN F. ARNO is a Plant Ecologist on the F o r e s t Ecosystems
r e s e a r c h work unit at Missoula. He earned a B. S. in forestry
at Washington State University and a m a s t e r ' s degree and a
Ph. D. in f o r e s t r y and plant science at the University of Montana before joining the Forest Service in 1970. This study was
supported by the F i r e in Multiple Use Management Research,
Development, and Application P r o g r a m headquartered at the
Northern F o r e s t F i r e Laboratory in Missoula.
KATHY M. SNECK earned a B.S. in f o r e s t r y at the University of
Montana and worked 4 y e a r s a s a forest f i r e r e s e a r c h officer
for the Forest Research Institute, CSIRO, Australia. She is
now completing a m a s t e r ' s degree in f o r e s t r y at the University
of Montana--her thesis presents the f i r e history of Coram Experimental F o r e s t (east of Kalispell, Montana). She plans to
follow a c a r e e r in f i r e management and research.
RESEARCH SUMMARY
This General Technical Report describes a method for
investigating the history and ecological influences of wildf i r e in the inland coniferous forests of western North
America.
The method relies on the collection and analysis of
c r o s s sections of fire- scarred t r e e s and the identification,
from increment cores, of age classes of postfire t r e e
species. In logged a r e a s , fire- scar and age-class data can
be gathered from stumps.
and
tell
the
and
The Report covers selection and layout of study a r e a s ,
the collection and analysis of samples. The authors
how to interpret f i r e frequency, intensity, and size;
influence of fire on stand composition and structure;
the effects of modern f i r e suppression.
CONTENTS
Page
.........................
S E L E C T I O N OF A S T U DY A R E A . . . . . . . . . . . . . . . .
FIELD RECONNAISSANCE . . . . . . . . . . . . . . . . . . .
Laying Out T r a n s e c t s . . . . . . . . . . . . . . . . . . .
Gathering Data . . . . . . . . . . . . . . . . . . . . . . .
INTRODUCTION
..................
.....................
LABORATORY ANALYSIS . . . . . . . . . . . . . . . . . . .
P r e p a r i n g C r o s s Sections . . . . . . . . . . . . . . . . .
Counting Rings . . . . . . . . . . . . . . . . . . . . . . .
Cbrrelating Fire Chronologies . . . . . . . . . . . . . . .
Designating Stands . . . . . . . . . . . . . . . . . . . . .
Calculating Fire Frequency . . . . . . . . . . . . . . . .
Analyzing Age C l a s s e s . . . . . . . . . . . . . . . . . . .
Mapping Historic Fires . . . . . . . . . . . . . . . . . .
Selecting Sample T r e e s
Collecting Samples
1
2
3
3
4
11
11
15
15
15
17
20
22
23
25
INTERPRETATIONS
PUBLICATIONS CITED
.....................
27
INTRODUCTION
Throughout much of western North America, forest managers are making a transition
from a narrow policy of fire control to a broader approach called fire management
(Moore 1974). This change reflects their increasing interest in using fire in fuel
management, wildlife habitat management, silvicultural improvement, and natural area
management. Thus, managers want to evaluate the influence of fire on forest ecosystems.
But, to fully understand the role that fire has played, one should learn about the fire
history. The following questions should be investigated: what were the (I) average,
minimum, and maximum intervals between fires in various forest habitats? (2) sizes
and intensities of fires? (3) effects of past fire on forest vegetation, particularly
stand composition and age-class structure? (4) effects of modern fire suppression?
This paper outlines a method that a fire management specialist, land use planner,
or research forester can use to address these questions. Most of the individual
procedures were developed and used in various ways by other fire history investigators.
Detailed justification of this method and comparison with various alternatives are not
presented here; however, they are discussed by Arno (manuscript in preparation) and can
be evaluated by reading some of the most pertinent study reports, such as:
Alberta--MacKenzie 1973, Byrne 1968, Tande 1977
Arizona--Weaver 1951
British Columbia--Howe 1915
California--Wagener 1961, Kilgore 1973, McBride and Laven 1976
Colorado--Clagg 1975
Idaho--Burkhardt and Tisdale 1976, Marshall 1928
Minnesota--Frissell 1973, Heinselman 1973
Montana--Arno 1976, Gabriel 1976, Sneck 1977
New Hampshire--Henry and Swan 1974
New Mexico--Weaver 1951
Oregon--Weaver 1959, McNeil 1975, Soeriaatmadja 1966
Washington--Weaver 1961
Wyoming--Houston 1973, Loope and Gruel1 1973, Taylor 1974
The techniques employed are a relatively simple process of aging and correlating
dates from fire scars on trees as well as identifying fire-initiated age classes of
trees. The procedures were applied on three study areas in the Bitterroot National
Forest of western Montana where they provided a detailed analysis of the role of fire
since about the year 1600 (Arno 1976). Sneck (1977) recently field-tested the method
in an area on the Flathead National Forest that has been more heavily logged and has
had less frequent fires than the Bitterroot. As a result, improvements that she
suggested have been incorporated here. This method should be applicable to coniferous forests of the western United States andadjacent portions of Canada, inland
from the coastal forests.
Manpower and equipment f o r o b t a i n i n g f i r e h i s t o r y information a r e not e x t e n s i v e .
Once t h e study s i t e has been s e l e c t e d and i n i t i a l p r e p a r a t i o n made, estimated manpower
a l l o c a t i o n s a r e a s follows:
Type of Study Area
Manpower
Small (100 t o 300 a c r e s , 40 t o
120 h e c t a r e s ) , having one o r a few
closely r e l a t e d h a b i t a t types
P r i n c i p a l i n v e s t i g a t o r : 1 t o 2 weeks
( f i e l d i n v e s t i g a t i o n s and sampling, f i n a l
a n a l y s i s and writeup)
1.
Technician: 2 t o 3 weeks ( h e l p with
fieldwork, p r e p a r a t i o n and b a ~ i ca n a l y s i s
of f i e l d c o l l e c t i o n s )
2. Large (5,000 t o 10,000 a c r e s ,
2,000 t o 4,000 h e c t a r e s ) , having
d i v e r s e f o r e s t h a b i t a t t y p e s and
physiography
P r i n c i p a l i n v e s t i g a t o r : 6 t o 8 weeks
Technician: 10 weeks
About 70 p e r c e n t of t h e time i s s p e n t i n t h e o f f i c e (planning, a n a l y s i s , and
writeup) and can b e done d u r i n g any season.
SELECTION OF A STUDY AREA
Topography and f o r e s t t y p e s should be r e p r e s e n t a t i v e of a l a r g e r v i c i n i t y t o allow
f o r r e a s o n a b l e e x t r a p o l a t i o n o f t h e s t u d y r e s u l t s . I f r e s u l t s w i l l be applied t o a
s i z a b l e r e g i o n - - f o r example, 1,000,000 a c r e s (400,000 h a ) - - i t i s a d v i s a b l e t o s e t up
t h r e e o r more l a r g e study a r e a s i n d i f f e r e n t p a r t s o f t h e r e g i o n . A watershed o r o t h e r
l o g i c a l geographical u n i t should be s e l e c t e d a s a study a r e a and o u t l i n e d on a l a r g e s c a l e topographic map (7-1/2 minute s e r i e s o r , b e t t e r , 4 inches p e r m i l e ) . Areas with
s u b s t a n t i a l remnants of unlogged o r l i g h t l y s e l e c t i o n - c u t f o r e s t a r e most f a v o r a b l e f o r
study, although it i~ o f t e n h e l p f u l , e s p e c i a l l y i n moist f o r e s t t y p e s , t o i n c l u d e some
h e a v i l y logged a r e a s where stwnps can be analyzed f o r buried (healed over) f i r e s c a r s .
T h i s method can a l s o be used i n logged a r e a s where stumps a r e s t i l l r e l a t i v e l y sound
(stumps 30 o r 40 y e a r s o l d a r e o f t e n s a t i s f a c t o r y ) .
Road a c c e s s should be a v a i l a b l e a t l e a s t t o t h e periphery o f t h e s t u d y a r e a , and
i n a l a r g e s t u d y a r e a a network of t r a i l s and roads i s h e l p f u l .
FIELD RECONNAISSANCE
Laying Out Transects
A network of reconnaissance transects (not statistically based) should be laid out
on the topographic map of the study area. As illustrated in figure 1, this network
should lead through representative amounts of terrain on all aspects and elevations.
Such a network will normally provide a representative sample of the forest types.
Transect routes can be established to take maximum benefit of trailsand roads for access. Orienting the transects along topographic contours or perpendicularly up one
broad slope and down another is quite acceptable. Transects should not follow narrow
ridgetops or stream bottoms for miles, because these have vegetative and fire environments that may not be typical of most of the area. Instead, transects should generally
traverse broader slopes on all aspects from low to high elevations, and should be well
dispersed throughout the study area. Parallel transects can be made along longitudinal
or latitudinal lines; however, this approach requires more time for surveying the route
and is especially slow in rugged terrain.
(feet)
Figure 1 . --TopograpZc map o f a study area showing network o f t r a n s e c t s (WEc h u t i li zed
t r a i l and road a c c e s s ) and t r a n s e c t nwnbering scheme. Enlargement o f t r a n s e c t 3 shows
ha% t a t t y p e segments f3A, 3B, e t c . ), ecotones, sample p l o t s f *) .
Gathering Data
Recording Habi t a t Types
A continuous log of t h e f o r e s t h a b i t a t types should be kept along t h e t r a n s e c t
r o u t e , by means of t h e most c u r r e n t 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 (or s i m i l a r ,
e c o l o g i c a l l y based s t r a t i f i c a t i o n of f o r e s t environments) a p p l i c a b l e t o t h e a r e a . The
s t a t u s of t h e s e c l a s s i f i c a t i o n s i n t h e western United S t a t e s i s explained i n d e t a i l by
P f i s t e r (1976). In u n c l a s s i f i e d a r e a s , i t should be p o s s i b l e t o adapt a broader system
based on p o t e n t i a l climax t r e e s p e c i e s , s i m i l a r t o t ! ~ e s e r i e s l e v e l of a 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 . Vegetation should be c a r e f u l l y documented on h a b i t a t type- stand compos i t i o n p l o t s (described l a t e r u s i n g a f i e l d - f o r m c h e c k l i s t l i k e f i g u r e 2 ) . Logged a r e a s
can be h a b i t a t typed by e x t r a p o l a t i n g from s i m i l a r unlogged s i t e s nearby o r by u s i n g
o t h e r techniques described i n P f i s t e r and o t h e r s (1977).
As shown on f i g u r e 1, b o u ~ ~ q a r i e(ecotones)
s
between each h a b i t a t - t y p e segment
along t h e t r a n s e c t should be determined on t h e ground and drawn a c r o s s t h e t r a n s e c t on
t h e topographic map. The l o c a t i o n of each h a b i t a t - t y p e p l o t should a l s o be drawn on
t h e map. The completed h a b i t a t - t y p e t r a n s e c t s can provide a b a s i s f o r i d e n t i f y i n g t h e
topographic and e l e v a t i o n a l c h a r a c t e r i s t i c s a s s o c i a t e d with each h a b i t a t type (and,
o p t i o n a l l y , f o r p r e p a r i n g a h a b i t a t - t y p e map of t h e study a r e a ) . This w i l l allow f o r
a comparison o f t h e r o l e of f i r e by h a b i t a t type and w i l l a i d e x t r a p o l a t i o n of f i n d i n g s
t o a d j a c e n t a r e a s having s i m i l a r h a b i t a t t y p e s .
Obtaining Stand-Composi t i o n and Age-Class Data
Within each h a b i t a t - t y p e segment of t h e t r a n s e c t , t h e i n v e s t i g a t o r should s u b j e c t i v e l y s e l e c t a s i t e f o r a l / l 0 - a c r e (0.04-ha) p l o t having r e p r e s e n t a t i v e timber type
and s t a n d c o n d i t i o n s . He should then r e c o r d a l l t r e e s p e c i e s by 2-inch (5-cm) s i z e
c l a s s e s i n t h e p l o t . The h a b i t a t - t y p e f i e l d - f o r m ( f i g . 2) should be f i l l e d out here
also.
Next, increment c o r e s should be taken a t 1 f o o t ( 0 . 3 m) above ground l e v e l t o d e t e r mine t h e age c l a s s e s of s e r a l t r e e s p e c i e s i n t h e s t a n d . S i g n i f i c a n t q u a n t i t i e s of
s e r a l s p e c i e s ( f o r example, ponderosa p i n e i n a p o t e n t i a l Douglas- fir climax stand o r
lodgepole p i n e i n a p o t e n t i a l subalpine f i r climax) commonly r e g e n e r a t e a f t e r a f i r e .
Thus age c l a s s d a t a w i l l be e s s e n t i a l f o r i n t e r p r e t i n g t h e h i s t o r i c a l e f f e c t s of f i r e
on stand composition and s t r u c t u r e . Where s e r a l t r e e s a r e u n a v a i l a b l e , t h e climax
s p e c i e s can be used with t h e understanding t h a t they a r e l e s s l i k e l y t o have o r i g i n a t e d
after a fire.
A minimum of t h r e e t r e e s should be bored f o r each apparent a g e - s i z e c l a s s . Rings
should be c a r e f u l l y counted i n t h e f i e l d with a 10-power hand l e n s . I f t h e t h r e e t r e e s
r e p r e s e n t i n g one s i z e c l a s s d i f f e r by more than 10 y e a r s , a d d i t i o n a l t r e e s should be
bored u n t i l each age c l a s s i s r e p r e s e n t e d by a t l e a s t t h r e e ( p r e f e r a b l y s e r a l ) t r e e s .
F i e l d n o t e s should be taken t o d e s c r i b e stand composition ( t r e e s p e c i e s ) and
apparent age c l a s s e s along t h e t r a n s e c t s . This w i l l provide v a l u a b l e information,
augmented by t h e p l o t and f i r e - s c a r d a t a , f o r i n t e r p r e t i n g t h e e f f e c t s of h i s t o r i c a l
fire.
A l l c o r e s should be glued i n t o core-mounting boards ( f i g . 3) f o r l a b o r a t o r y
a n a l y s i s , and l a b e l e d with t h e l o c a t i o n , code number ( t r a n s e c t number, h a b i t a t - t y p e segment l e t t e r , and p l o t number), t r e e s p e c i e s , and diameter a t b r e a s t h e i g h t ( d . b . h . ) .
A c o r e board i s made by c u t t i n g grooves i n 1- by 8- inch (2.5- by 20-cm) lumber on a
t a b l e saw. A bead o f Elmers o r s i m i l a r "white glue" i s spread i n t h e bottom of a groove,
t h e c o r e i s then placed i n t h e groove, and a second c o r e board i s placed, smooth s i d e
.Doe
(CODE
I
OPOGRAPHY :
I-Ridge
'-Upper slope
3-Mid slope
4-Lower slope
5-Bench or flat
6-Stream bottom
DESCRIPTION)
HORIZONTAL
CONFIGURATION:
1-Convex (dry)
2-Straight
3-Concave (wet)
4-Undulating
CANOPY COVERAGE CLASS:
O=Absent
3-25 to 50%
T=Rare to 1% 4-50 to 75%
5.75 to 95%
1=1 to 5%
2=5 to 25"
6=95 to 100%
NOTE: Rate trees (>4" dbh
and regen (0-4" dbh) separately (e.g., 4/2)
'TREES Scientific Name
Abbrev
ABGR
1. Abies grandis
2. Abies lasiocarpa
ABLA
3. Larix lyallii
LALY
4. Larix occidental is
LAOC
PIEN
5. Picea engelmannii
6. Picea glauca
PIGL
7. Pinus albicaulis
PIAL
8. Pinus contorta
PIC0
9 . Pinus
10. Pinus monticola
PIMO
11. Pinus ponderosa
PIP0
12. Pseudotsuga menziesii
PSME
13. Thuja plicata
THPL
14. Tsuga heterophylla
TSHE
15. Tsuga mertensiana
TSME
~ H R U B SAND SUBSHRUBS
1. Alnus sinuata
ALSI
2. Arctostaphylos uva-ursi
ARUV
3. Berberis repens
BERE
4. Cornus canadensis
COCA
5. Holodiscus discolor
HOD1
6. Juniperus communis (+ horizontalis) JUCO
LEGL
7. Ledum glandulosum
LIB0
8. Linnaea borealis
9. Menziesia ferruginea
MEFE
10. Oplopanax horridum
OPHO
PWIA
11. Physocarpus malvaceus
PRVI
12. Prunus virginiana
13. Purshia tridentata
PUTR
RIM0
14. Ribes montigenum
15. Shepherdia canadensis
SHCA
16. Spiraea betulifolia
SPBE
17. Symphoricarpos albus
SYAL
18. Symphoricarpos oreophilus
SYOR
19. Vacciniu~llcaespitosum
VACA
20. Vaccinium globulare ( + membranaceum) VAGL
21. Vaccinium scoparium (+ myrtillus)
VASC
PERENNIAL GRAMINOIDS
AGSP
1. Agropyron spicatum
2. Andropogon spp.
AND
CACA
3. Calamagrostis canadensis
4. Calamagrostis rubescens
CARU
5. Carex geyeri
CAGE
6. Festuca idahoensis
FEID
7. Festuca scabrella
FESC
8. Luzula hitchcockii (= glabrata)
LUHI
PERENNIAL FORBS AND FERNS
ACRU
1. Actaea rubra
2. Antennaria racemosa
ANRA
ARNU
3. Aralia nudicaulis
ARC0
4. Arnica cordifolia
5. Athyrium filix-femina
ATFI
6. Balsamorhiza sagittata
BASA
7. Clematis pseudoalpina (+ tenuiloba) CLPS
8. Clintonia uniflora
CLUN
9. Equisetum arvense
EQAR
EQU
10. Equisetum spp.
GATR
11. Galium triflorum
12. Gymnocarpium dryopteris
GYDR
13. Senecio streptanthifolius
SEST
14. Senecio triangularis
SETR
15. Smilacina stellata
SMST
STAM
16. Streptopus amplexifolius
17. Thalictrum occidentale
THOC
18. Valeriana sitchensis
VASI
19. Viola orbiculata
VIOR
20. Xerophyllum tenax
XETE
Common Name
grand fir
subalpine fir
alpine larch
western larch
Engelmann spruce
white spruce
whitebark pine
lodgepole pine
limber ine
western white pine
ponderosa pine
Douglas-fir
western redcedar
western hemlock
mountain hemlock
1
Canopy Coverage Class
/ --T->
-
-2 - i - L
/
/
-----
-
I - _ I1/ - -A - - - 1-// 1 --
-/ - - - _ - -- I - - -- / L C - I --$-I
%-I---
/ --- -.- - - -L
--
/
/
------
/
4 - i -r- - - -1 -I-%
- - -3- 1 7 - --r-/----A-l-T
*-i--/
/
/
1
/ --- --/ -----------/
--------I---)--I--------- /
--
/- /
/
. . . . ./. . . . . . . . . ./ . . . . . . . . . /.
- - - - -/ - - - - - - - - I/ - P - - - - - - //
2- / /
Sitka alder
kinnikinnick
creeping Oregon grape
bunchberry dogwood
ocean spray
common ( + creeping) juniper
Labrador tea
twinflower
menziesia
devil's club
ninebark
chokecherry
bitterbrush
mountain gooseberry
buffaloberry
white spiraea
common snowberry
mountain snowberry
dwarf huchleberry
blue huckleberry
grouse whortleberry
-
.........................
------
----
------------------------.........................
.........................
.........................
.
-
- ----
---- -- - --
-~
-------
--------
1 - - 2 - - - I- - - -/-
,
-
-
-
1
bluebunch wheatgrass
bluestem
bluejoint
pinegrass
elk sedge
Idaho fescue
rough fescue
wood-rush
- - - - .---
-.
3-
baneberry
woods pussytoes
wild sarsaparilla
heartleaf arnica
lady fern
arrowleaf balsamroot
virgin's bower
queencup beadlily
common horsetail
horsetails & scouring rush
sweetscented bedstraw
oak fern
cleft-leaf groundsel
arrowleaf groundsel
starry Solomon's seal
twisted stalk
western meadowrue
sitka valerian
round-leaved violet
beargrass
-
------- -
-
4- - - - - - - --:
- - - -. - - -
-- - - - - - - - -
--
- - - - --
- - - -------------
-
--
.- - - -- - -
- .- - - - - - -
.- - - - - - -
- .- - - - - - - - - .- - - - - - - -
.- -
-
-
- - - - - - - - --
/
- - - - - - .- - - - - - - - - - - - - - - - ------
.- - - -
-
~
- -- - ---------
- - -- -- -.
-------------------------
-------------------------
-
--
-
--
- - .- - - - -
-
-
-
- -
--
-- - - -.
-SERIES
Figure 2.--Sample h a b i t a t type- stand composition f i e l d form ( P f i s t e r and o t h e r s 19771,
zl,ith ~ ~ e g e t a t i o n adata
l
from three p l o t s located in. figure I .
5
---
h3/i1j
kk
13"
(TOTAL LENGTH OF BOARD)
PAPER CARD
PAPER CARD
.....................................................................
. . . . . . . . .........-.
. . . . . . . . .....................................
...................................
..................................
...........................................
.......
...................................................................................................
...................
':.:.I .:':"'>:.:':':.:.: ....................................................................................
PRO IEC'rED
,,I,.H
I
' S
I
END VIEW
Figure 3 . --Increment core mounting board, s h o d ng increment cores, ri ng-counting
techniques, and labe l i n g system.
down, atop t h e f i r s t board. The two boards a r e then held t o g e t h e r with a p a i r o f heavy
rubber bands. Also, cores can be c a r r i e d i n labeled p l a s t i c drinking straws while i n
t h e f i e l d , then t r a n s f e r r e d t o c o r e boards.
Stand-composition and age- class information can be c o l l e c t e d i n s t a n d s t h a t have
been c l e a r c u t o r h e a v i l y logged i f stumps a r e not too r o t t e n o r too burnt t o age and i f
t h e year of logging can be determined. Species can be i d e n t i f i e d from t h e bark. Total
age can be. gathered by c r o s s s e c t i o n i n g sound stumps with a chain saw; r i n g counts
should be confirmed i n t h e l a b .
Docwnenti ng
re-Scarred Trees
The i n v e s t i g a t o r and t e c h n i c i a n should l o c a t e and record a l l f i r e - s c a r r e d t r e e s i n
a swath of f o r e s t along t h e t r a n s e c t r o u t e . By walking p a r a l l e l about 50 yards (45 m)
a p a r t , they can cover a swath about 100 yards (91 m) wide i n r e l a t i v e l y open f o r e s t s .
They should keep constant watch f o r t h e o l d e s t "catfaced" t r e e s a v a i l a b l e . (Catface i s
a term f o r an open s c a r r e s u l t i n g from one o r more f i r e s . ) On each c a t f a c e , t h e number
of e x t e r n a l f i r e s c a r s should be counted. Each individual f i r e s c a r has a s e p a r a t e f o l d
o r band of h e a l i n g t i s s u e , o f t e n appearing on both s i d e s of t h e c a t f a c e . Sometimes
t h e s e f o l d s a r e p a r t i a l l y o r wholly burned o f f by subsequent f i r e s , but u s u a l l y a
p o r t i o n of each f o l d remains a t l e a s t on one s i d e of t h e c a t f a c e a f o o t (0.3 m) o r more
above t h e ground. Figure 4 shows some examples of c a t f a c e s and corresponding c r o s s
s e c t i o n s o f t h e f i r e s c a r s . Catfaces a r e most prevalent on t h e upslope s i d e , e s p e c i a l l y
on old-growth t r e e s t h a t lean upslope.
Egure 4.--Examples of multiple f i r e scars on t r e e s and scar patterns i n cross sections.
Tolan no. 21
TREE DIED ( CAMBIUM) 1950
2nd FIRE SC
. AR
4-A. Lodgepole pine with three fire scars
Tolan no. 24
CAMBIUM 1915
FIRE 1785
3*
This tree probably germinated a b u t 1755 and apparently represents regeneration lrom the 1752 Fire shown i n part A
4-B. Nearby lodgepole pine with two fire scars
4-C. Old ponderosa pine stump with 13 externally visible scars
4-D. Ponderosa pine cross section with 21 fire scars
8
I n v e s t i g a t o r s must l e a r n t o d i f f e r e n t i a t e f i r e s c a r s from s c a r s caused by f a l l e n
t r e e s , f r o s t c r a c k s , r o o t r o t , and b e a r , r o d e n t , o r b e e t l e damage. (These a r e described
more f u l l y l a t e r . ) Also, they must recognize t h o s e healed-over f i r e s c a r s which a r e
i n d i c a t e d o n l y by a bark seam, g e n e r a l l y on t h e upslope s i d e . F i e l d experience w i l l
c l a r i f y t h e s c a r r i n g c h a r a c t e r i s t i c s of each t r e e s p e c i e s . Char on t h e o u t e r bark
confirms a t l e a s t one f i r e , probably within t h e l a s t 70 years. Char on t h e s u r f a c e of
any s c a r i n a c a t f a c e i s evidence t h a t a f i r e occurred after t h e year of t h a t s c a r .
A few t r e e s having t h e l a r g e s t number of r e l a t i v e l y sound f i r e s c a r s i n each stand
should be recorded and marked f o r r e v i s i t i n g . In s t a n d s having many old-growth t r e e s
with m u l t i p l e s c a r s , i t i s not necessary t o a l s o t a l l y a l l t h e younger t r e e s with only
one o r two s c a r s . The following d a t a should be recorded f o r each t r e e i n a "Log of
Fire- Scarred Trees":
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
t r a n s e c t number, habitat-type- segment l e t t e r , and s c a r r e d - t r e e Roman numeral
species
d.b.h.
maximum h e i g h t of c a t f a c e
number of e x t e r n a l l y v i s i b l e s c a r s
elevation
aspect
remarks such a s d e s c r i p t i v e l o c a t i o n and recommendation f o r sampling
This information ( t a b l e 1, p a r t A) w i l l provide t h e b a s i s f o r s e l e c t i n g sample t r e e s .
Each of t h e t r e e s i n t h e log should be p l o t t e d by numeralon t h e t r a n s e c t topographic
map.
F i r e - s c a r r e d t r e e s can a l s o be i d e n t i f i e d i n s t a n d s t h a t have been c l e a r c u t o r
h e a v i l y logged during t h e p a s t few decades by s y s t e m a t i c a l l y examining stumps. Because
f i r e s c a r s on low stumps a r e n o t r e a d i l y apparent a t a d i s t a n c e , c a r e f u l i n s p e c t i o n i s
necessary. F i r e s c a r s may have healed over and thus n o t be v i s i b l e on t h e o u t e r edge
of stump, but they can be seen i n t h e r i n g s (on t o p ) . F i r e- s c a r r e d stumps a r e recorded
similarly to fire-scarred trees.
Table 1
"Loq o f F i r e - c a r r e d T r e e s " examined i n t h e f i e l d reconnaissance ( p a r t A), and t h e l o g o f t r e e s a c t u a l l y sampled ( p a r a
i n s t u d y area
LOG OF FIRE-SCARRED TREES
PART A.
I r a n s e c t number,
h . t . segment
l e t t e r , and
scarred- tree
numeral
:
:
:
:
:
:
:
Species
:
d.b.h.
:
:
:
Maximum
h e i g h t of
cat- face
Inches
Feet
24
6
(Apparent)
number o f
external
scars
:
:
:
:
:
:
Elevation
:
Feet
7
4,650
Aspect :
Oegree
1A- I
PP
110
1A-I1
PP
29
7
13
5.050
90
IA-111
PP
32
7
11
4,750
100
Remarks
Across b r i d g e , 200 f t b e l m r o c k o u t c r o p s ,
good c r o s s s e c t i o n
Below l a r g e D o u g l a s - f i r snag, good c.s.
100 yds below r i d g e t o p , good c . s .
IA-IV
LPP
20
6
4
4.800
120
Flagged c l o s e t o IA-111, s l i g h t l y r o t t e n
10-1
PP
49
20
4
5,800
190
P o s s i b l y l i g h t n i n g s t r u c k . good c.s.
10-11
PP
31
16
2
5.500
170
I n dense stand of young PP, good c . s .
10-111
PP
22
10
4
5.600
200
Double t r u n k , 50 y d s e a s t o f t r a i l
10-1V
PP
20
8
1
5.500
180
1C-l
DF
24
10
2
5.400
80
Below r i d g e , f l a g g e d
I n dense s t a n d of young PP, n o t a good sample
1C-I1
DF
16
3
4
5.400
65
Below r i d g e
IC-111
PP
23
15
6
5.650
70
On r i d g e spur, good c.s.
PART B.
Sample
tree
number
:
: Reconnaissance :
:
code
: Species : d.b.h.
LOG OF SAMPLED TREES
: (Apparent) : ( A c t u a l )
: Maximum : number o f : number o f
: height o f : external : internal
: cat- face :
scars
:
scars
Inches
-
Feet
-
:
:
: Habitat :
: t y p e and : Photo :
: E l e v a t i o n : Aspect : phase
: number :
:
Feet
Remarks
Oegree
1
1A-I
PP
24
6
7
9
4.650
110
DFIAGSP
1
335O from b r i d g e , ZOO ft
below r o c k o u t c r o p s
2
1A-I1
PP
29
7
13
14
5.050
90
OFICARU
PIP0
2
315' f r o m b r i d g e , below
l a r g e DF snag
3
on&
PP
23
5
12
13
5.050
80
DFIAGSP
4
IA-I11
PP
32
7
11
13
4.750
100
DFIAGSP
4.5
5
10-1
PP
49
20
4
4
5.800
190
PPIFEID
13.14
6
~ond'
PP
19
3
4
4-5
5.200
200
PPIFEID
15
7
ond dl
PP
24
3
6
7
5,650
200
PPIFEID
FESC
16
8
16-111
PP
22
10
4
5
5,600
200
PPIFEID
FESC
17
Double t r u n k , 50 y d E of
trail
9
1C-I1
DF
16
3
4
5
5,400
65
DFIPHMA
PHMA
18
Below r i d g e 150 f e e t
10
1C-111
PP
23
15
6
6
5.650
70
DFIPHMA
19
On r i d g e spur
11 Not p r e v i o u s l y d i s c o v e r e d .
3
120 y d S o f t r e e no. 2
100 y d below r i d g e t o p
Lightning struck
100 y d N of road above
pullout
SAMPLING FIRESCARRED TREES
Selecting Sample Trees
After completing t h e f i e l d t r a n s e c t s , one can examine t h e Log of Fire- scarred
Trees and make preliminary s e l e c t i o n s f o r sampling. Generally, two o r t h r e e sample
t r e e s should be s e l e c t e d f o r each h a l f mile ( 0 . 8 km) of a given h a b i t a t - t y p e segment
on each t r a n s e c t . Some t r a n s e c t segments may not have f i r e - s c a r r e d t r e e s because few
t r e e s survived t h e most r e c e n t f i r e . In t h i s case, increment cores (age- class d a t a )
and t r a n s e c t f i e l d notes w i l l provide f i r e h i s t o r y information within t h a t segment.
On l a r g e r study a r e a s having many miles of t r a n s e c t s , d i s t a n c e s between sample
groups can be increased. (Nevertheless, t h e i n v e s t i g a t o r should sample groups of two
o r t h r e e t r e e s i n c l o s e proximity i n o r d e r t o c o r r e l a t e f i r e - s c a r chronologies.) I f
t h i s i n t e n s i t y of sampling i s not f e a s i b l e , e s t a b l i s h a few small study areas with
r e p r e s e n t a t i v e t e r r a i n and vegetation, c o r r e l a t e t h e f i n d i n g s , then e x t r a p o l a t e r e s u l t s
t o t h e l a r g e r area. An example of t h i s approach i s provided by Arno (1976).
Trees with t h e g r e a t e s t number of e x t e r n a l l y v i s i b l e , i n d i v i d u a l f i r e s c a r s have
t h e highest p r i o r i t y f o r sampling. Avoid sampling t r e e s whose ring- count sequence may
be obscured by r o t .
Where candidate sample t r e e s have s i m i l a r numbers of s c a r s and soundness, o t h e r
f a c t o r s can be considered. For i n s t a n c e , t h e i n v e s t i g a t o r may choose t o sample a
ponderosa pine i n preference t o a Douglas- fir o r western l a r c h because t h e former
u s u a l l y has c l e a r e r s c a r r i n g s . A small, old-growth t r e e can be chosen i n preference
t o a l a r g e r dominant t r e e having a s i m i l a r s c a r sequence.
Final s e l e c t i o n s of sample t r e e s and stumps should be recorded on a f i e l d sheet
and on a map t h a t w i l l be used t o r e l o c a t e them f o r taking c r o s s s e c t i o n s .
Collecting Samples
Return t o t h e chosen sample t r e e s , watching f o r b e t t e r s c a r t r e e s t h a t may have
been overlooked. Inspect each chosen t r e e t o v e r i f y t h a t t h e d a t a supporting i t s
s e l e c t i o n were a c c u r a t e . Check e s p e c i a l l y t h e maximum number of f i r e s c a r s and d e t e r mine t h e b e s t p l a c e t o c r o s s s e c t i o n t h e trunk t o o b t a i n t h e f u l l sequence of s c a r s a s
well a s t h e p i t h and cambium. Photograph t h e c a t f a c e . Assign t h e t r e e a permanent
number and record i t i n t h e "Log of Sampled Trees" ( p a r t B o f t a b l e I), which includes
information l i s t e d i n t h e Log of F i r e - s c a r r e d Trees, p l u s t h e number of c r o s s - s e c t i o n a l
s c a r s , h a b i t a t type, and photograph number. Also, p l o t and l a b e l t h e sample t r e e ' s
l o c a t i o n on t h e topographic map.
Sectioning techniques suggested here provide p r i m a r i l y f o r study needs while seco n d a r i l y minimizing v i s u a l impact and s t r u c t u r a l damage t o t r e e s . In some a r e a s (Natt i o n a l Parks, wildernesses, p r i v a t e lands) i t may be necessary t o r e v e r s e t h e above
p r i o r i t i e s . In t h a t c a s e , t h i n wedge-shaped s e c t i o n s , not n e c e s s a r i l y p e n e t r a t i n g t o
t h e p i t h , can be taken (McBride and Laven 1976), with a handsaw i f necessary.
Small sample t r e e s - - t h o s e l e s s t h a n a f o o t ( 0 . 3 m) t h i c k a t stump h e i g h t - - s h o u l d
g e n e r a l l y be f e l l e d , c u t t i n g them o f f e i t h e r w e l l below o r w e l l above t h e p o i n t on t h e
t r u n k where t h e c l e a r e s t s c a r s a r e a p p a r e n t . A f t e r f e l l i n g , c u t t h e stump o r downed
t r e e t o o b t a i n t h e c l e a r e s t c r o s s s e c t i o n w i t h t h e maximum number of f i r e s c a r s .
Large, r e l a t i v e l y sound t r e e s a r e u s u a l l y b e s t sampled by t a k i n g a p a r t i a l c r o s s
s e c t i o n from one s i d e o f t h e c a t f a c e . As i l l u s t r a t e d i n f i g u r e 5, t h e p i t h , f i r e s c a r s ,
and cambium can u s u a l l y be o b t a i n e d by s e v e r i n g o n l y about 10 t o 15 p e r c e n t of t h e stem.
A r o l l e r o r s p r o c k e t - t i p p e d c h a i n saw (20- o r 24-inch bar) i s used t o make p a r a l l e l ,
h o r i z o n t a l c u t s 1- 1/2 t o 2 i n c h e s (4 t o 5 cm) a p a r t . These e x t e n d from t h e p i t h t o
t h e cambium a c r o s s t h e c l e a r e s t p o r t i o n o f t h e s c a r sequence, on o n l y one s i d e o f t h e
c a t f a c e . The c u t i s made j u s t d i e p enough t o i n s u r e t h a t it goes behind t h e d e e p e s t
p e n e t r a t i o n o f each s c a r s o t h e count c a n be made i n u n s c a r r e d t i s s u e .
(Normally t h i s
w i l l be 3 t o 4 i n c h e s deep.) Then t h e t i p of t h e saw i s pushed i n v e r t i c a l l y a l o n g
t h e back o f t h e p a r a l l e l c u t ; from cambium t o p i t h .
he- saw wound can be p a i n t e d
w i t h a n a s p h a l t - b a s e t r e e p a i l l t t 3 p r e v e n t e n t r a n c e o f i n s e c t s o r d i s e a s e (McBride and
Laven 1976) .
I n s p e c t t h e p a r t i a l c r o s s s e c t i o n t o i n s u r e t h a t it does e x t e n d behind each s c a r .
Draw arrows p e r p e n d i c u l a r l y a c r o s s any broken p a r t s t o a i d r e a s s e m b l y . (Glue t h e p a r t s
back t o g e t h e r i n t h e l a b . ) W r i t e t h e sample t r e e number ( t a b l e 1, p a r t B) i n b a l l p o i n t i n k on a l l p i e c e s i n two p l a c e s on t h e back o f t h e c r o s s s e c t i o n , where i t w i l l
n o t be sanded o f f . A l s o , w r i t e t h e sample number c o n s p i c u o u s l y on t h e t r e e o r stump
o r u s e a s m a l l metal t a g f o r t h i s p u r p o s e .
Compare t h e number of f i r e s c a r s on t h e c r o s s s e c t i o n w i t h s c a r s on t h e c a t f a c e .
Small s c a r s t h a t may r e p r e s e n t s c r a p e s o r r o d e n t damage when t h e t r e e was a s a p l i n g
s h o u l d b e d e n o t e d . S c r a p e s c a r s r e s u l t i n g from f a l l i n g t r e e s and s c a r s from mountain
p i n e b e e t l e a t t a c k s s h o u l d b e a n a l y z e d and d i s c o u n t e d i n t h e f i e l d a l s o . S c r a p e s c a r s
a r e g e n e r a l l y l o n g e r t h a n f i r e s c a r s , and t h e remains o f t h e f a l l e n t r e e c a u s i n g t h e
s c r a p e can u s u a l l y be found. S c a r s from b e e t l e a t t a c k s o f t e n r e s u l t from d i e b a c k o f
t h e cambium a t more t h a n one p l a c e a l o n g a given annual r i n g ; t h e s e s c a r s have an
i r r e g u l a r shape and may be c o r r e l a t e d t o a known epidemic y e a r .
Basal s c a r s may b e caused by r o o t r o t (ArmiZZaria meZZea), b u t t h e s e u s u a l l y ext e n d up b a s a l r o o t b u t t r e s s e s r a t h e r t h a n forming i n t h e hollows between b u t t r e s s e s
l i k e f i r e s c a r s . Also u n l i k e f i r e s c a r s , r o t s c a r s a r e n o t c o r r e l a t e d w i t h t h e u p s l o p e
s i d e of t r e e s . Various cankers o r animals a l s o cause s c a r s ; t h e s e a r e not u s u a l l y
b a s a l , b e a r l i t t l e resemblance t o f i r e s c a r s , and do n o t c h a r wood.
A f t e r c o u n t i n g t h e f i r e s c a r s on t h e sample t r e e ' s c r o s s s e c t i o n , e n t e r t h e t o t a l
i n t h e Log o f Sampled T r e e s ( p a r t B of t a b l e 1 ) . Examine each t r e e and c r o s s s e c t i o n
c a r e f u l l y i n t h e f i e l d because t h e c a t f a c e and a d d i t i o n a l c r o s s s e c t i o n s w i l l n o t be
a v a i l a b l e f o r checking i n t h e laboratory.
When sampling logged a r e a s , photograph t h e t o p of each stump ( v e r t i c a l l y ) , u s i n g
markers t o p i n p o i n t each f i r e s c a r and t h e p i t h . P r e l i m i n a r y r i n g c o u n t s c a n be made
i n t h e f i e l d , u s i n g a 10X hand l e n s i f n e c e s s a r y . Cross s e c t i o n s o f sound stumps can
be c u t and t a k e n t o t h e l a b f o r documentation and f o r r i n g c o u n t i n g w i t h a microscope.
I f t h e stump i s n o t sound enough t o s e c t i o n , o b t a i n t h e b e s t e s t i m a t e o f f i r e s c a r and
p i t h d a t e s , counting t h e r i n g s several times i f necessary.
To f a c i l i t a t e t r a n s p o r t i n g and h a n d l i n g , i t i s d e s i r a b l e t o minimize b o t h weight
and s i z e o f t h e c r o s s s e c t i o n s . F u l l c r o s s s e c t i o n s o f t e n need o n l y b e about an i n c h
t h i c k , and i f decay i s n o t e x t e n s i v e , t h e back 40 p e r c e n t of t h e c i r c l e , n o t i n c l u d i n g
p i t h o r s c a r s , can b e sawed o f f and l e f t i n t h e f i e l d . P a r t i a l c r o s s s e c t i o n s s h o u l d
n o t be made t h i c k e r o r d e e p e r t h a n n e c e s s a r y . The c h a i n saw and a few c r o s s s e c t i o n s ,
a l o n g w i t h an e x t r a q u a r t o f f u e l , can be c a r r i e d i n an e x t r a - l a r g e , aluminum-frame
backpack.
Figure 5 . - - Collecting a p a r t i a l cross s e c t i o n from a large t r e e .
ACROSS CATFACE.
FOUR F I R E S C A R S
2. M A K E VERTICAL C U T T O
INCLUDE P I T H .
BACK OF CROSS SECTION.
PARTIAL CROSS SECTION
4. CUTS MADE I N CROSS SECTION OF TREE.
a62)
A.
B.
*
D.
These sampling procedures may r e q u i r e some adjustment where f i r e s have destroyed
e x t e n s i v e s t a n d s . In such r e g i o n s , study a r e a s should be made l a r g e enough t o include
some of t h e boundaries of t h e b i g burns. The e x t e n t of such burns i s o f t e n d e t e c t a b l e
i n p a t t e r n s of f o r e s t development seen on a e r i a l photographs. F i r e s c a r and t o t a l age
information can be obtained from (1) s c a t t e r e d s u r v i v i n g t r e e s w i t h i n t h e burn, (2)
both young and o l d t r e e s (age c l a s s e s ) k i l l e d by t h e f i r e , (3) pockets of s u r v i v i n g
f o r e s t , and (4) t r e e s a t t h e p e r i m e t e r of t h e burn. Regeneration can be aged t o h e l p
d a t e t h e l a r g e burn i t s e l f . H i s t o r i c a l accounts a r e o f t e n a v a i l a b l e f o r d a t i n g l a r g e
and d e s t r u c t i v e f i r e s t h a t have occurred w i t h i n t h e l a s t 100 y e a r s o r more.
LABORATORY ANALYSIS
Preparing Cross Sections
A f t e r each day of sampling, c r o s s s e c t i o n s should be l a i d out f o r drying i n a
heated b u i l d i n g . Within a week o r two,surfaces should be d r y enough t o sand, so t h a t
r i n g s can be more a c c u r a t e l y counted and examined. A d i s k sander a t t a c h e d t o a l i g h t weight e l e c t r i c d r i l l , w i l l s u f f i c e .
Begin sanding with c o a r s e d i s k s (40 t o 50 g r i t ) having t h e h e a v i e s t paper backing
a v a i l a b l e . Then use f i n e and v e r y f i n e (125 g r i t ) sandpaper a s necessary t o b r i n g out
t h e r i n g s . I t i s not necessary t o sand t h e e n t i r e s u r f a c e , but only a moderately wide
band along and immediately behind t h e s c a r s t o allow f o r a complete r i n g count. Other
sanding t e c h n i q u e s , i n c l u d i n g hand sanding, a r e p r e f e r r e d by some i n v e s t i g a t o r s .
Counting Rings
A variable-power b i n o c u l a r microscope ( 7 X t o 25X) i s u s u a l l y e s s e n t i a l f o r a c c u r a t e
counting. (Sometimes t h i s can be borrowed o r r e n t e d . ) S e l e c t t h e c l e a r e s t s i d e of t h e
c r o s s s e c t i o n and count inward from t h e cambium. Count 1 year t o t h e o u t e r edge of t h e
outermost band of (darker) summerwood, and continue t o count from one band of summerwood t o t h e n e x t . Wetting t h e counting a r e a with water and o c c a s i o n a l l y s l i c i n g obscure
r i n g s with a r a z o r blade f a c i l i t a t e s counting. With a very sharp r e d p e n c i l , mark a
dash ( - ) along every 1 0 t h r i n g and a p l u s (+) on each f i r e - s c a r r i n g a s i l l u s t r a t e d i n
f i g u r e 6 . An a l t e r n a t i v e f o r wood with extremely f i n e r i n g s i s t o puncture t h e r i n g
with a f i n e d i s s e c t i n g needle. A f i n e red dot should a l s o be placed near such punctures
because t h e y may disappear i f t h e wood i s wetted.
I f t h e j u n c t i o n of t h e s c a r r i n g and undamaged t i s s u e i s obscured by p i t c h o r r o t ,
count p a s t t h e s c a r r i n g t o a c l e a r r i n g beyond t h e s c a r . Then follow t h e c l e a r r i n g
around p a s t t h e o b s t r u c t i o n and count back up t o t h e s c a r s u r f a c e .
Record t h e number of y e a r s back t o t h e most r e c e n t f i r e and between each previous
f i r e a s shown i n t a b l e 2. Rings should be counted c a r e f u l l y by one person and t h e n v e r i f i e d by another. On samples where some of t h e r i n g sequence i s u n c l e a r , t h e o p p o s i t e
s i d e of t h e c r o s s s e c t i o n ( o r t h e o p p o s i t e f a c e t of t h e c a t f a c e , i n t h e c a s e of a f u l l
c r o s s s e c t i o n ) should a l s o be counted.
Figure 6 . --How r i n g s are counted on a fire-scar cross section.
from the cambiwn i s marked "-";
scar rings are marked "+". )
(Every 10th year i n
Table 2.- - An example of r i n g - c o u n t t a b u l a t i o n s from seven t r e e s sampled i n one stand.
2
1
Cambium
Tree Number
4
3
5
F = fire; P = pith
6
7
1975
Cambium
1975
Cambium
1975
Cambium
1975
Cambium
1975
Cambium
1975
-84 r i n g s
1891F
-86 r i n g s
1889F
-86 r i n g s
1889F
-86 r i n g s
1889F
-86 r i n g s
1889F
-99 r i n g s
1876F
-108 r i n g s
1867F
- 30 r i n g s
1861F
-20 r i n g s
1869F
-38 r i n g s
1851F
-30 r i n g s
1859F
-87 r i n g s
1802F
-29 r i n g s
1847F
-
23 r i n g s
1844F
-15 r i n g s
1846F
-16 r i n g s
1853F
-49 r i n g s
1802F
-40 r i n g s
1819F
-38 r i n g s
1764P
-44 r i n g s
1803F
-103 r i n g s
1741P
-25 r i n g s
1821F
-24 r i n g s
1829F
-35 r i n g s
1767F
-17 r i n g s
1802F
-55 r i n g s
1748F
-34 r i n g s
1787F
-18 r i n g s 1811F
-11 r i n g s
1756F
-46 r i n g s
1741F
-
-17 r i n g s
1785F
9 rings
1802F
-29 r i n g s
1756F
-36 r i n g s
1766F
-17 r i n g s
1739F
-16 r i n g s
1750F
-14 r i n g s
1736P
Cambium
1975
Correlating Fire Chronologies
Ring c o u n t s from each i n d i v i d u a l t r e e may n o t be e n t i r e l y a c c u r a t e o r c o i n c i d e bec a u s e o f p o c k e t s o f obscured r i n g s o r r o t , o r due t o o c c a s i o n a l m i s s i n g r i n g s o r f a l s e
r i n g s . More a c c u r a t e e s t i m a t i o n s o f t h e a c t u a l f i r e y e a r s can be developed by combining
r e c o r d s from s e v e r a l t r e e s i n t o a " master f i r e chronology."
To c o r r e l a t e r e c o r d s from i n d i v i d u a l t r e e s , a r r a n g e them on a l a r g e s h e e t o f p a p e r
(such a s 10 l i n e / i n c h graph p a p e r ) . The chronology from each t r e e i s shown i n a v e r t i c a l column, and t h e t r e e s should be a r r a n g e d i n a l o g i c a l geographic o r d e r i n g s o t h a t
n e i g h b o r i n g t r e e s a p p e a r i n a d j a c e n t columns ( f i g . 7 ) . The t o p l i n e o f each column
r e p r e s e n t s t h e d a t e o f t h e cambial r i n g , u s u a l l y t h e y e a r t h e samples were c u t . Each
i n c h (10 s q u a r e s ) downward r e p r e s e n t s 10 y e a r s .
A f t e r t h e 10- year i n t e r v a l s a r e l a b e l e d on t h e edge o f t h e graph and a d j a c e n t
t r e e s a r e o r d e r e d , each i n d i v i d u a l t r e e chronology i s p l o t t e d . The c a m b i a l - r i n g y e a r
i s shown a s a d a s h and t h e p i t h y e a r a s "P."
I f t h e p i t h was n o t o b t a i n e d , t h e
e a r l i e s t r i n g on r e c o r d i s shown a s an "E."
Cross s e c t i o n s t h a t were e x c e p t i o n a l l y
c l e a r ( w i t h o u t p e r i o d s o f v e r y narrow r i n g s o r p a r t i a l l y obscured growth) a r e g i v e n
added w e i g h t : t h e i r s c a r y e a r s a r e marked w i t h an " X . "
On c r o s s s e c t i o n s where some
r i n g s a r e s l i g h t l y obscured and d a t e s a r e approximate, s c a r y e a r s a r e marked w i t h a
s o l i d d o t . On c r o s s s e c t i o n s e s p e c i a l l y d i f f i c u l t t o i n t e r p r e t , s c a r y e a r s a r e
marked w i t h an open d o t .
Next, t o t a l t h e number o f t r e e s s c a r r e d each y e a r on t h e r i g h t , a s shown i n f i g u r e
7. ( T o t a l i n g i s done f o r t h e e n t i r e s t u d y a r e a i f i t i s s m a l l , o r f o r each geographic
s u b d i v i s i o n o f a l a r g e r s t u d y a r e a . ) The p r o b a b l e f i r e y e a r s can now be determined by
i n s p e c t i n g t h e p l o t t e d c h r o n o l o g i e s , g i v i n g more weight t o t r e e r e c o r d s shown w i t h an
"X," and u s i n g t h e l a r g e s t t o t a l s o f i n d i v i d u a l s c a r s a s an i n d i c a t i o n o f t h e p r o b a b l e
f i r e y e a r . F i r e r e c o r d s ( i n c l u d i n g maps o f burned a r e a s ) and h i s t o r i c a l a c c o u n t s should
be examined; o f t e n t h e s e can be used t o v e r i f y t h e y e a r of f i r e s o c c u r r i n g w i t h i n t h e
past century.
I n s p e c t i o n o f t h i s c h a r t ( e x e m p l i f i e d by f i g . 7) may r e v e a l t h a t p a r t o f t h e r e c o r d
f o r a c e r t a i n t r e e i s c o n s i s t e n t l y a few y e a r s o u t o f sequence w i t h t h e e s t a b l i s h e d
p r o b a b l e y e a r s ( f o r example, t r e e number 1 i n f i g . 7 ) . Often such an i n d i v i d u a l chrono l o g y can be brought i n t o sequence by adding a few y e a r s a t one p o i n t i n t i m e , t h u s
moving i t s s c a r d a t e s back. T h i s phenomenon e v i d e n t l y r e s u l t s from m i s s i n g r i n g s and
u s u a l l y o c c u r s d u r i n g a p e r i o d when t h e t r e e grew a t an e x c e p t i o n a l l y slow r a t e . I t
p r o b a b l y r e p r e s e n t s a temporary c e s s a t i o n o f growth caused by d e f o l i a t i o n o r s e v e r e
f i r e i n j u r y . Craighead (1927) found t h a t some ponderosa p i n e s stopped forming annual
r i n g s f o r a s many a s 5 y e a r s a f t e r d e f o l i a t i o n and extreme f i r e i n j u r y , a l t h o u g h t h e y
remained a l i v e and u l t i m a t e l y resumed growth.
I n o t h e r c a s e s , i t may be p o s s i b l e t o s y n c h r o n i z e a n i n d i v i d u a l t r e e ' s f i r e chronology w i t h t h o s e o f i t s n e i g h b o r s by moving i t s s c a r d a t e s forward s l i g h t l y ( s u b t r a c t i n g a few y e a r s ) . T h i s may be an i n d i c a t i o n o f f a l s e r i n g s . These a r e r a t h e r f a i n t
and o f t e n d i s c o n t i n u o u s . I n t h e c a s e o f c r o s s s e c t i o n s t h a t cannot e a s i l y be c o r r e l a t e d w i t h t h e emerging m a s t e r f i r e chronology, i t i s i m p o r t a n t t o reexamine t h e r i n g
c o u n t s and t h e p r o b a b l e o r i g i n o f any q u e s t i o n a b l e s c a r s .
Unless a t r e e has d e f i n i t e s c a r s from two f i r e s w i t h i n 3 y e a r s o f each o t h e r , i t
i s b e s t n o t t o h y p o t h e s i z e s e p a r a t e f i r e s o c c u r r i n g on t h e same a r e a a t such s h o r t i n t e r v a l s . T h i s s u g g e s t i o n i s made because minor r i n g e r r o r s p r e s e n t i n most samples do
n o t a l l o w f o r p r e c i s e d e t e c t i o n o f such c l o s e - t o g e t h e r f i r e y e a r s without t h e c o n c l u s i v e
e v i d e n c e o f a d u a l s c a r . F i r e s o c c u r r i n g 4 o r more y e a r s a p a r t w i l l be d i s t i n g u i s h a b l e
on t h e chronology graph. Ring e r r o r s and d i m i n i s h i n g sample s i z e d e c r e a s e t h e a c c u r a c y
o f f i r e - s c a r r e c o r d s more t h a n 250 y e a r s o l d ; n e v e r t h e l e s s , f i r e frequency t r e n d s and
-
h
1
1m5
SPECIES PP LPP
TREE NO. I
2
PP
3
I
PP
4
DF
5
PP
6
PP
7
7
-
y
NO. OF TREES SCARRED THAT YEAR
--
--
.-
NO. OF FIRE- SUSCEPTIBLE TREES '
A TREE I S CONSIDERED FIRE- SUSCEPTIBLE
OV THE DATE OF THE FIRST SCAR AND THEREAFTER
SCAR DATES
X Clear r i n g s idate accurate1
8
Rings s l i g h l l y o b s c u r r e d (date approximatel
0 Rings d i f l l c u l t t o i n l e r p r e t
1 Dale adjusled to correlale c h r o n o l q y
P Plth
E Earliest r i n g o n cross seclion
-
Year of c a m b i u m
T n uLDEST
SCAR OR P lTH
Figure 7.--Graph o f the fire- scar chronologies from the seven t r e e s i n t a b l e 2 ,
showing adjustments t o ohtain a master f i r e chronology for the stand.
approximate f i r e y e a r s can b e determined by c o r r e l a t i n g f i r e r e c o r d s e x t e n d i n g back
300 y e a r s o r more on a few t r e e s .
When t h e p r e l i m i n a r y m a s t e r chronology i s completed, i n d i v i d u a l t r e e c h r o n o l o g i e s
should be a d j u s t e d t o d e f i n i t e f i r e y e a r s and r e c o r d e d i n a r e v i s e d master f i r e chronology f o r u s e i n f u r t h e r a n a l y s i s . The r e v i s e d chronology ( t a b l e 3) l i s t s f i r e y e a r s
by s t a n d ; i t i s e x p l a i n e d more f u l l y i n t h e n e x t s e c t i o n . A t t h i s p o i n t i t may be
p o s s i b l e t o i n t e g r a t e f i r e - s c a r sequences o b t a i n e d from stumps and dead s n a g s whose
c a m b i a l- r i n g y e a r i s unknown. The i n t e r v a l s between f i r e s c a r s on t h e dead samples
can be compared w i t h t h e i n t e r v a l s found on nearby l i v i n g t r e e s .
(The y e a r o f h i s t o r i c
l o g g i n g o p e r a t i o n s o r s e t t l e m e n t can be determined by c o r r e l a t i n g f i r e s c a r s found on
remaining stumps, o r a t t h e b u t t o f l o g s i n c a b i n s , w i t h t h e f i r e chronology.)
+
T a b l e 3.- - The m a s t e r f i r e c h r o n o l o g y f o r a l a r a e s t u d y a r e a , showing t h e number of sample t r e e s s c a r r e d
d u r i n each f i r e j e a r i n each s t a n d and i n d i c a t i n g f i r e s t h a t caused c o n i f e r r e q e n e r a t i o n
m o d ~ f i e das an example from A r n o 1976)
I
Fire
year
:
~
~ . 1 :
:
(4)*
B.I
5
:
:
8.2
4
:
:
8.3
(2)
STAND
: 0.1
(6)
number
:
:
0.2
[
:
0.3
4
:
--
1769
1766
1757
2
-.
--
1752
1750
1747
4
---
1743
1734
1730
--
--
1720
1710
1698
--
1
1
1686
1677
1670
---
1
---
1664
1658
1636
.
1587
1574
------
Total scars
50
1632
1611
1595
*
Number o f sample t r e e s .
F i r e s c a u s i n o c o n i f e r r e o e n e r a t i o n based on s t a n d a o e - c l a s s samples.
? Data weak.
E.I
5
: - T I - - ;o f s c a r s
)
-
Table 4 . - - F i r e f r e q u e n c i e s between 1735 and 1900 i n t h r e e study areas s t r a t i f i e d by h a b i t a t - t y p e qroups on the B i t t e r r o o t N a t i o n a l F o r e s t
( m o d i f i e d as an example from Arno 1976)
: Oomi nant t r e e s :
H a b i t a t - t y p e qroups
( p o t e n t i a l climax)
( P f i s t e r and o t h e r s
1977)
(1
:
:
Descriptive
location
(2)
A. Pinus ponderosa/Fes tuca
idahoensis
Pseudotsusa m e n z i e s l i /
V a l l e.y edqe
Agropyron spicatum
Pseudotsuga/Calamagros t i s ,
P. ponderosa phase
0.
Dominant
: w i t h continued:
overstorv
: f i r e e x c l u s i o n : b e f o r e 19Dn
: General : (most abundant :(most abundant
:elevations: tree f i r s t ) : tree f i r s t )
:
(3)
:
(5)
(4)
Feet
3800-5000
Douglas- fir
ponderosa p i n e
ponderosa p i n e
:
Onehorse
:
:
Mean
: No. o f : f i r e - f r e e
: stands : i n t e r v a l
:(No. o f : (min-max
: trees) : i n t e r v a l )
:
(7)
: 6
:
Tolan
:
Mean
: No. o f : f i r e - f r e e
: stands : i n t e r v a l
:(No. of : (min-max
: trees) : i n t e r v a l )
: 8
:
(9)
:
:
West Fork
:
: Mean
: No. o f : f i r e - f r e e
: stands : i n t e r v a l
:(No. o f
: trees)
:
(10)
1
:(min-max
:interval)
(11)
:
1
(11)
6 years
(2-20)
1
(4)
11 y e a r s
(2-18)
(4)
10 y e a r s
(2-18)
5
(46)
10 years
(3-31)
3
(11)
16 years
(4-29)
4
(19)
19 y e a r s
(2-48)
Pse~dots~ga/PhySocarp~S
malvaceus
Pseudotsuga/Calamagrostis
(except Cal. phase)
Montane slopes
PseudotsugalSymphori carpos
albus
Pseudotsuaa/Vac. g l o b u l a r e
(except-Xerophy 1lum phase)
C. Abies g r a n d i s h a b i t a t
types
N o l s t canyon
D. Pseudotsuga/Calamagrostis,
Calamagrostis phase
Pseudotsuga/Vac. o l o b u l a r e ,
Xerophyllum phase
Lower s u b a l p i n e
Abies l a s l o c a r o a /
slooes
Xerophyllum tenax
Abies l a s i o c a r p a / M e n z i e s i a
ferruglnea
Ables lasiocarpa/Linnaea
borealis
E . Ables l a s i o c a r p a / L u z u l a
hitchcockii
Abies lasiocarpa-Pinus
Upper s u b a l p i n e
albicaulis/Vac.
slopes
scoparl um
PInus a l b i c a u l i s - A b i e s
lasiocarpa
ponderosa p i n e
Douglas- fir
lodgepole p i n e
western l a r c h
4200-6200
Douqlas-fir
4300-4700
grand fir
western l a r c h
lodgepole p i n e
Douql as-f i r
1
(7)
17 y e a r s
(3-32)
--
6000-7500
subalpine fir
Douglas- fir
lodgepole pine
Douglas-fir
1
(9)
17 years
(3-33)
3
(16)
27 years
(5-62)
3
(13)
28 years
(5-67)
7500-8600
s u b a l p i n e fir
whi tebark p i n e
w h l t e b a r k p i n e lodgepole p i n e
1
(3)
41 years
(8-50)
2
(14)
30 years
(4-78)
2
(14)
33 years
(2- 68)
--
--
--
Designating Stands
On l a r g e study a r e a s , stands should be d e l i n e a t e d t o a i d a n a l y s i s of f i r e frequenc i e s , a s follows: L i s t a l l t h e h a b i t a t types encountered a t sample- tree s i t e s and
arrange them i n an ecological o r d e r ( f o r i n s t a n c e , by climax s e r i e s and from dry- tomoist o r warm-to-cold within each s e r i e s ) . Record t h e numbers of t h e t r e e s sampled i n
each h a b i t a t type. Group minor h a b i t a t types on t h e study a r e a with more p r e v a l e n t ones
t h a t a r e c l o s e l y r e l a t e d . L i s t t h e e l e v a t i o n , a s p e c t , and percent slope a t each sample
t r e e and summarize t h e s e f o r each major h a b i t a t type. Wherever s i t e parameters overlap
s u b s t a n t i a l l y , major h a b i t a t types can be combined. The goal i s t o e s t a b l i s h h a b i t a t type groups t h a t can be extrapolated t o adjacent a r e a s . Table 4 shows an example of
such groups used on a f i r e h i s t o r y study i n t h e B i t t e r r o o t National Forest.
After some of t h e s e h a b i t a t - t y p e groups have been t e n t a t i v e l y e s t a b l i s h e d , p l o t a l l
sample t r e e s on a topographic map of t h e study a r e a and w r i t e i n t h e h a b i t a t - t y p e group
found a t each of t h e s e p o i n t s . Inspect t h e map t o s e e i f it shows s e v e r a l (4 t o 10)
sample t r e e s on t h e same h a b i t a t - t y p e group within a r e a s o f a few hundred a c r e s . I f
sample t r e e s i n a given h a b i t a t - t y p e group a r e more dispersed than t h i s , enlarge o r
r e d e f i n e t h e h a b i t a t - t y p e groups so t h a t s e v e r a l sample t r e e s from each h a b i t a t - t y p e
group occur within a r e a s of a few hundred a c r e s .
These assemblages o f sample t r e e s (on s i m i l a r h a b i t a t types) should be o u t l i n e d
Figure 8 shows an example of such
on t h e map, and w i l l now be r e f e r r e d t o a s "stands."
s t a n d s o u t l i n e d on a topographic map. The f i n a l h a b i t a t - t y p e groups should be assigned
a l e t t e r code (A, B , e t c . ) , and each stand a number; t h u s "B.3" i s t h e code designating
t h e t h i r d stand i n h a b i t a t - t y p e group B . Stands should be shown by t h e i r l e t t e r number code on t h e map.
WEST F O R K STUDY A R E A
PART A
cmw1 I"lW,
Figure 8 . --Topographic maps
o f two study areas showi n g sample t r e e s (nwnbers)
and stands by habitat- type
groups (Letter-nwnber
code). Compare part A
with t a b l e 4 , c o l m 10.
Compare part B w i t h
t a b l e 4, colwim 6 .
U ,/LI
mile
Calculating Fhe Frequency
The s t a n d s and h a b i t a t - t y p e groups can now be used f o r c a l c u l a t i n g f i r e f r e q u e n c i e s
( f i r e - f r e e i n t e r v a l s ) on an a r e a b a s i s . F i r s t , however, l o g i c a l t i m e p e r i o d s must a l s o
be e s t a b l i s h e d f o r c a l c u l a t i n g f i r e f r e q u e n c i e s . For i n s t a n c e , t h e most r e c e n t p e r i o d
(of p e r h a p s 40 t o 60 y e a r s , depending upon t h e a r e a ) can be a s s i g n e d a s t h e " f i r e
s u p p r e s s i o n " p e r i o d , r e f l e c t i n g t h e t i m e p e r i o d when o r g a n i z e d s u p p r e s s i o n was w e l l
e s t a b l i s h e d and e f f e c t i v e .
By c o n t r a s t , s u p p r e s s i o n a c t i v i t i e s were g e n e r a l l y minimal i n f o r e s t e d a r e a s o f t h e
Mountain West p r i o r t o 1900; t h u s t h a t y e a r might be chosen a s t h e end o f t h e " h i s t o r i c
f i r e " p e r i o d , r e f l e c t i n g t h e t i m e when f o r e s t f i r e s were caused p r i m a r i l y by l i g h t n i n g
and n a t i v e I n d i a n s . I n some a r e a s m i n e r s o r s e t t l e r s may have s e t many f o r e s t f i r e s
i n t h e l a t e 18001s,necessitating t h e delineation of s t i l l another f i r e period ( f o r
example, " s e t t l e m e n t - e r a f i r e p e r i o d " 1860-1910).
The b e g i n n i n g d a t e chosen f o r a n a l y s i s o f t h e " h i s t o r i c f i r e " p e r i o d w i l l depend
upon how f a r back t h e f i r e - s c a r r e c o r d s e x t e n d . I t can be chosen a r b i t r a r i l y b u t
i n d e p e n d e n t l y o f a c t u a l f i r e - s c a r y e a r s . For i n s t a n c e , i n one s t u d y (Arno 1976) t h e
y e a r 1735 was s e l e c t e d because i t was t h e e a r l i e s t d a t e when a t l e a s t f i v e sample t r e e s
were a l i v e i n each s t a n d , and t h u s c o u l d have r e c o r d e d a f i r e . L a t e r , two a d d i t i o n a l
a r e a s were s t u d i e d i n t h e same N a t i o n a l F o r e s t , and i t was determined t h a t each had
a d e q u a t e f i r e - s c a r r e c o r d s e x t e n d i n g back a t l e a s t t o 1735. Consequently, 1735 t o 1900
was t h e n used a s a s t a n d a r d i z e d p e r i o d e n a b l i n g d i r e c t comparison o f r e l a t i v e frequenc i e s among a l l t h e s t u d y a r e a s .
Before d e c i d i n g upon f i r e frequency p e r i o d s , graph 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 and t h e t o t a l number o f " f i r e - s u s c e p t i b l e t r e e s " ( t r e e s
a l r e a d y h a v i n g been s c a r r e d a t l e a s t once) i n t h e sample, a s i l l u s t r a t e d i n f i g u r e 9 .
Note t h a t sample s i z e d i m i n i s h e s markedly toward e a r l y y e a r s o f t h e r e c o r d , and t a k e
t h i s i n t o account when e v a l u a t i n g f i r e f r e q u e n c i e s t h r o u g h t t h e r e c o r d . I d e n t i f y and
c o n s i d e r any obvious changes i n h i s t o r i c f i r e f r e q u e n c i e s d u r i n g t h e p e r i o d o f r e c o r d
when e s t a b l i s h i n g f r e q u e n c y p e r i o d s .
WEST FORK STUDY AREA
60
W
ct
I-
%
ct
W
m
50
40
60
-
F I RE-SUSCEPTI BLE TREES
30:
20
10 -
---/--
50
.-r'
L- - - -4I RE- SCARRED TREE'\
S
/
:
/-----)/
- 40
- 30
- 20
- 10
0
1590 1600 '20
'40
'60
'80
1700 '20
'40
'60
'80
1800 '20
'40
'60
'80
1900 '20 '40
'60 1975
YEAR OF FIRE
Figure 9.--Nwnber of scmrple t r e e s scarred each f i r e year and the t o t a l nwnber of f i r e s u s c e ~ t i b l et r e e s i n the s m p l e (data from Arno 1976). A t r e e i s considered f i r e
susceptible on the date of the f i r s t scar and thereafter.
T a b l e 5.--An example o f f i r e frequency c a l c u l a t i o n s f o r d i f f e r e n t stands w i t h i n a
s i n g l e s t u d y area (Arno 1976). Stand l o c a t i o n s a r e shown i n f i q u r e 8B,
Onehorse Stud.y Area
:
Stand
A. 1
B. 1
B. 2
B.3
B. 4
B.5
C.l
D.l
:
:
No.of
sample
trees
11
10
9
10
9
8
9
9
:
: No. y e a r s
: i n period
165
165
165
165
165
165
165
165
Time p e r i o d 1735 t o 1900
Total
Fire
: Minimum and maximum
i no. f i r e s = frequency
: fire- free interval
Years
Years
s
t
i
s
+
t
s
s
29
24
18
15
24
12
10
10
=
=
=
=
=
=
=
=
5.7
6.9
9.2
11.0
6.9
13.8
16.5
16.5
2
3
3
3
3
3
3
3
&
P1
&
&
&
&
&
&
20
21
28
31
15
31
32
33
After the "historic fire frequency" period has been established, see how far back
in time comparable frequencies were recorded. For example, in figure 9 the analysis
period was 1735 to 1900, but it was reasoned that comparable frequencies extended back
to about 1630 (see also table 3). Thus, rates established on the basis of a 165-year
interval were apparently representative for a period of about 270 years (1630 to 1900).
It may be desirable also to calculate fire frequencies for the transition period
(for example, 1900 to 1925) between the "historic" and "suppression" periods.
An example of fire frequency calculations for such periods is shown in table 5.
The mean, minimum, and maximum fire-free intervals are shown for each stand. Mean
intervals can be averaged for all stands in a habitat-type group. For example, the
five stands in habitat type group B, table 5, have a mean fire-free interval of
10 years--this mean is shown in column 7 of table 4. This facilitates comparison of
fire frequencies from one study area to another in similar habitat types, as shown in
table 4. Also, comparing values from the "historicw and "suppression" periods will
indicate the effect of suppression on fire frequency.
Analyzing Age Classes
The first major step in age-class analysis is to count annual rings on the increment cores gathered in field transects. Counts should be made using a variable-power
binocular microscope, with the cores wetted, shaved, and sanded as necessary. Counts
begin at the cambium and progress to the pith as was done in cross-section analysis.
Every 10th ring (outer edge of summerwood band) should be marked with a fine red line
(or a dissecting-needle puncture) and every fifth ring with a dot. Counts are made to
the innermost ring or the pith and written on the core board next to the field data for
that tree, as shown in figure 3.
Where an increment core missed the pith, the number of additional rings to the pith
is estimated by considering the curvature and thickness of the innermost rings. As
illustrated in figure 3, it is helpful to draw the circles represented by the arc of
the inner rings, using a compass, and then extrapolate a similar ring width to the pith.
The estimated number of additional years to the pith is then written next to the ring
count with a plus sign (for example, "86 + 4").
After the counts are completed and verified, they should be tabulated by plot.
Total ages of trees from each plot are listed in chronological order as shown in figure
10. To obtain the total age, add an estimate of the number of years for establishment
23
STAND D. 3
I
I PLOT
NO. 1
TREE AGES
I N 1415
PLOT
NO. 2
PLOT I
NO. 3
60
80
---*
.
APPARENT
FIRE AND YEAR
CAUSING REGENERATION
-------- ] 1892
200
--- = YEAR OF FIRE
Figure 10. --Age-class designations based upon increment bom'ngs of seral t r e e s taken z'n
stand D.3 shown i n table 3. Each dot represents t o t a l t r e e age, based on an increment
core plus 5 years t o reach boring height (1 foot).
and growth t o boring height (1 f o o t , 30 cm). Such f a c t o r s can be worked out by c u t t i n g
and aging l a r g e numbers of seedlings of various s p e c i e s on various s i t e s . However,
considering a l l t h e v a r i a b l e s , it may be necessary t o use a general f a c t o r - - f o r example,
5 years f o r t r e e s bored a t 1 f o o t on t h e B i t t e r r o o t National Forest (Arno 1976). The
increment-boring d a t a can be augmented by including t h e t o t a l age of cross- sectioned,
f i r e - s c a r r e d t r e e s with t h e sample from t h e n e a r e s t appropriate p l o t ; only s e r a l species
should be used, however.
\
L i s t t h e t o t a l ages of individual t r e e s by p l o t , i n s p e c t them, and d e s i g n a t e p o s s i b l e age c l a s s e s a s i n f i g u r e 10. A t l e a s t two s i m i l a r ages a r e necessary f o r designati n g an age c l a s s . Because of f i e l d sampling procedures, most age c l a s s e s w i l l be
i d e n t i f i e d by t h r e e o r more t r e e s .
Once t h e t e n t a t i v e age c l a s s e s have been assigned, based on t h e o l d e s t t r e e i n
each c l a s s , t h e next s t e p i s t o t e s t f o r c o r r e l a t i o n s between age c l a s s e s and t h e f i r e s c a r chronology. Consult t h e study a r e a map and f i n d t h e stand number ( f i g . 8) t h a t
a p p l i e s t o each a g e - c l a s s p l o t . P l o t s i s o l a t e d from designated stands should be
analyzed s e p a r a t e l y , afterwards.
The next s t e p i s t o examine apparent c o r r e l a t i o n s between each t e n t a t i v e age c l a s s
and t h e f i r e years i d e n t i f i e d on t h a t stand. For example, i f an age c l a s s i s 115 years
( t o t a l age of t h e o l d e s t t r e e s i n t h e c l a s s ) i n 1975, one would expect it t o have r e s u l t e d from a f i r e occurring only one o r a few years before 1860. We can check t h e
master f i r e chronology ( t a b l e 3) t o s e e i f a f i r e was detected ( v i a s c a r s ) i n t h a t
stand a few years p r i o r t o 1860. Ten o r twelve years might be considered t o be a
reasonable maximum i n t e r v a l f o r i n i t i a l establishment a f t e r f i r e on most s i t e s .
Longer i n t e r v a l s a r e reasonable a f t e r very l a r g e stand- destroying f i r e s .
I f t h e r e i s no f i r e - s c a r evidence during t h e preceding years and t h e age c l a s s
seems r a t h e r d e f i n i t e , i n s p e c t f i r e - s c a r records from neighboring s t a n d s . I f they show
a d e f i n i t e f i r e , one can assume t h a t it a c t u a l l y spread i n t o t h i s stand although it
d i d not s c a r t h e sample t r e e s . Another p o s s i b i l i t y i s t h a t very few t r e e s i n t h e
e n t i r e a r e a survived t h a t f i r e . I f t h i s i s t h e case, age- class d a t a from o t h e r p l o t s
and t r a n s e c t n o t e s w i l l confirm i t . Age c l a s s e s not a s c r i b a b l e t o any of t h e above
s i t u a t i o n s apparently a r e not r e l a t e d t o f i r e .
Considerable i n s i g h t regarding t h e h i s t o r i c r o l e of f i r e i n age- class s t r u c t u r e
of f o r e s t s can be obtained by incorporating t h e age- class d a t a i n t o t h e f i r e chronolo g i e s f o r each stand a s shown i n t a b l e 3. I f t h e s e d a t a show t h a t age c l a s s e s of s e r a 1
s p e c i e s were apparently e s t a b l i s h e d without f i r e , t h i s suggests t h a t o t h e r agents such
a s epidemics of n a t i v e i n s e c t s o r d i s e a s e s o r massive blowdowns were responsible. I f
t h e s e d a t a ( t a b l e 3) show t h a t c e r t a i n f i r e s were not followed by pronounced regenerat i o n , regeneration may have been destroyed by subsequent f i r e before t h e t r e e s had
grown l a r g e enough t o withstand f i r e . (The f i r e records should be checked f o r t h i s
p o s s i b i l i t y . ) Another p o s s i b i l i t y i s t h a t creeping ground f i r e s d i d not k i l l enough of
t h e stand t o allow f o r a new age c l a s s .
Mapp,ingHistoric Fires
The s i z e and perhaps t h e configuration of h i s t o r i c f i r e s can be found by p l o t t i n g
f i r e evidence on a small map o f t h e study a r e a ( f i g . 1 1 ) . Map each f i r e year (from t h e
master chronology) s e p a r a t e l y . I n d i c a t e l o c a t i o n s of t r e e s scarred t h a t year by placing
an lfs'f next t o t h e dot r e p r e s e n t i n g t h a t t r e e . I n d i c a t e regeneration a t t r i b u t e d t o
t h a t f i r e year by drawing an "r" i n t h e c o r r e c t p l o t l o c a t i o n . Using t h i s evidence of
t h e f i r e , one can now roughly o u t l i n e t h e a r e a covered. Aerial photos and f i r e suppression records may a l s o be u s e f u l . Heinselman (1973) and Tande (1977) have made
d e t a i l e d maps showing areas covered by many i n d i v i d u a l f i r e s during t h e course o f
two c e n t u r i e s .
Figure 11. --Maps showing the apparent e x t e n t of fi4res by year on a study area.
= sample t r e e s , s = scar-on t h a t t r e e t h a t year, r = regeneration from t h a t f i r e
detected i n t h a t stand.
INTERPRETATIONS
By i n s p e c t i n g t h e r e s u l t s of t h e s e v a r i o u s a n a l y s e s , t h e i n v e s t i g a t o r can summari z e f i r e f r e q u e n c i e s f o r both t h e " h i s t o r i c " and " s u p p r e ~ s i o nperiods
~~
by h a b i t a t t y p e s .
He can document e f f e c t s of n a t u r a l f i r e on f o r e s t composition and s t a n d s t r u c t u r e by
h a b i t a t type (columns 4 and 5, t a b l e 4 ) . Using c u r r e n t timber type (timber inventory)
and h a b i t a t - t y p e information, he can e s t i m a t e t h e probable e f f e c t s of c u r r e n t f i r e
management on f o r e s t composition, s t a n d s t r u c t u r e and, p o s s i b l y , f u e l accumulations.
Considering f i r e f r e q u e n c i e s and r e l a t i n g t h e maps of h i s t o r i c f i r e s t o t h e s u r v i v i n g
t r e e growth a s well a s t o a g e - c l a s s information i n g e n e r a l , he can i n t e r p r e t r e l a t i v e
f i r e i n t e n s i t i e s experienced i n t h e v a r i o u s s t a n d s and h a b i t a t t y p e s . Stand- destroying
f i r e s , f o r i n s t a n c e , w i l l be obvious from a g e - c l a s s d a t a , s i n c e no s u r v i v i n g t r e e s a r e
t o be found except f o r widely s c a t t e r e d v e t e r a n s t h a t g e n e r a l l y have a s c a r d a t i n g t o
t h a t f i r e . Maximum h i s t o r i c i n t e r v a l s between n a t u r a l f i r e s can be compared with
i n t e r v a l s during t h e suppression p e r i o d t o judge e c o l o g i c a l i m p l i c a t i o n s .
This information on f i r e h i s t o r y and v e g e t a t i o n can be c o r r e l a t e d with f u e l invent o r i e s , i n s e c t and d i s e a s e information, w i l d l i f e - h a b i t a t t r e n d s , e t c . , t o e s t i m a t e
t h e e f f e c t s of v a r i o u s types of f i r e management p r a c t i c e s . Thus, t h e s e f i n d i n g s should
a l s o h e l p i n s e l e c t i o n of reasonable goals and methods f o r f i r e and f u e l management.
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ir U.S. GOVERNMENT PRINTING OFFICE:1978-777095 1 21
28
A r n o , Stcphcn F. , and I<ath\. ICI. Snecl;
1 9 7 7 . il neth hod l o r d e t e r m i n i n g f i r ? h i s t o r \ - in c o n i f e r o u s
f o r e s l s in tile Mountain LVcst. USDA F o r . SPY\. Gen. 'l'ech.
I n t e r ~ n o u n t a i n F o r r u t nncl Range
IXep. IN'!'- 3,2s p.
' : ~ i ) ~ r i ~ : Station,
t , ~ ~ t Ogden, lltah 34401.
I l t ~ s ~ r i b ea smelhocl i'or determining h i s t o r i c f i r e frecluenel-, i n t e n s i t \ - , ;ind s i z e f r o m c r o s s s c c t i o n s collcctecl f ~ . o m
f i r e - s c a r r r t i t r e e s and t r e e age classes determinecl t l i r u ~ q 1 1
i ncr(2n:i.l;' h o r i u g s . T e l l s how Lo i n t e r p r e t t h e influence o f
i'iri 1.2 ;l,;n:i cornpn!iition ni2d s t ~ u c t u r eand how t o iclcntil:\
c l f e r l s of m o d e r n f i r < $s u p p r e s s i o n ,
I<EY\YORI_>S:fire ecologj,, f i r e h i s t o r b . j o r e s t e c o l o g ~ i'orest
,
lire.
A r n o , Stephen F . , and I<athv hI. Snecl,
1 9 7 7 . A method t o r c l e t e r l n ~ n ~ nf gi r e hl s t o r c In c o n ~ f c r o u s
t o r e s t s In the Mountalu Wc'st. LISDA F o r . S e r v . Gen. T e c h .
I n t e r m o u n t a n F o r e s t and Range
Rep. INT- 4 2 , 2 b p.
Experiment StatLon, Ogclcn, Utah 84401.
D e s c r i b e s :I mcthod f o r determining h i s t o r i c f i r c frequenc\-, i n t e n s i t y , and s i z e f r o m c r o s s s e c t i o n s collected f r o m
f i r e - s c a r r e d t r e e s and t r e c age c l a s s e s d e t e r m i n e d through
i n c r e m e n t b o r i n g s . T e l l s how t o i n t e r p r e t the influence of
f i r e in s t a n d conlposition and s t r u c t u r e and how t o idcntify
e f f e c t s of m o d e r n f i r e s u p p r e s s i o n .
I<EYWORDS: f i r e ecologv, f i r e h i s t o r y , f o r e s t e c o l o g ~ ,l o r c s t
fire.
H e a d q u a r t e r s f o r the Intermountain F o r e s t and
Range E x p e r i m e n t Station a r e i n Ogden, Utah.
Field p r o g r a m s and r e s e a r c h w o r k 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
U n i v e r s i t v of Idaho)
Provo, Utah (in cooperation with B r i g h a m
Young University)
lieno, Nevada (in cooperation with the
U n i v e r s i t y of Nevada)