350
Forest fire history of Desolation Peak, Washington
Jnnps K. Acn,E. Ma.nx FINNEy.I AND Ror-RNooE GouvEruarN2
Collegeof Forest Resources,University of Woshington,Seattle, WA 98195,U.S.A.
Received
April 17, 1989
Accepted September 26, 1989
A c ; e e , J . K . , F I t t N t v , M . , a n d o n G o u v u N a t N , R . 1 9 9 0 .F o r e s t f i r e h i s t o r y o f D e s o l a t i o nP e a k , W a s h i n g t o n .C a n .
J . F o r . R e s .2 0 : 3 5 0 - 3 5 6 .
Forestsin the vicinity of DesolationPeak, Washington,are of specialecologicalinterestbecauseof their transitional
nature betweencoastaland interior forest types. The area is west of the CascadeMountain crestbut in the rainshadow
ofmountains farther to the west. Fire return intervalswere hypothesizedto be shorter than typical for coastal forest
types, such as those dominated by western hemlock and Pacific silver fir, and longer than typical for interior forest
types,such as ponderosapine, owing to the closejuxtaposition of thesetypesat DesolationPeak. Sevenforest comntunity typeswere defined, and a 400-yearl'ire history was developedfor this 3500-haarea. The averagenatural fire rotation was 100 years;this varied by a factor of two by century and by topographic aspect.Foresttypes typical of coastal
regions,suchas Douglas-fir,- westernhemlock and mountain hemlock- Pacific silverfir, had mean fire return intervals
(108-137 years)much lower than in other westernWashington areas. The most interior forest type, ponderosapine
- Douglas-fir, had a higher mean fire return interval (52 years)than reported for similar forest typeseastof the Cascades.
Historically, fire has createdstructural and landscapediversity on DesolationPeak and may be an important process
in the maintenanceof such diversitv into the future.
A c E E , J . K . , F t t ' t N t v ,M . , e t D E C - i o u v e r n t N R
, . 1 9 9 0 .F o r e s tf i r e h i s t o r y o f D e s o l a t i o nP e a k , W a s h i n g t o n .C a n . J .
F o r . R e s .2 0 : 3 5 0 - 3 5 6 .
L,esior€ts de la r6gion de Desolation Peak, Washington, sont d'un inter€t ecologiqueparticulier de par leur nature
de transition entre les types forestiersde la cOteet ceux de I'int6rieur. Ce territoire se situe d I'ouest de la cr€te des
Cascadesmais est une rdgion sous le vent abritee de la pluie des montagnesplus a I'oucst. A causede I'etroite juxtaposition dcs types forestiersd Desolation Peak, on a 6mis I'hypothdseque les cyclesdes incendiesforestiersy sont
plus courts que la normale pour les types forestierstypiquesde la c6te comme ceux dominds par la Pruche de I'ouest
et le Sapin gracieux,et plus longs que la normale pour les types forestiersde I'int€rieur tels lespinddesd Pin ponderosa.
Sept communaut6sforestidresont 6tc identifieeset un historique des incendiesforestiersdes 400 dernidresanndesa
6te dressepour ce tcrritoire de 1500 ha. La pdriodemoyennede rotation des incendie-s
forestiersnaturelsest dc 100 ans,
v a l e u rv a r i a n t d ' u n f a c t L ' u d
r e d e u x s e l o nl c s i d c l ee t I ' e x p o s i t i o nd e l a p e n t e .L e s t y p e s f o r e s t i e r st y p i q u e sd e l a c 6 t e ,
comme les associationsSapin de Douglas - Pruchc de I'ouest et Pruche subalpine - Sapin gracieux, ont des cycles
desincendiesforesticrsbeaucoupplus courts(108-137ans)que ceuxdesautresregionsde I'ouestdu Washington.Le type
forestier le plus d I'int6rieur, I'associationPin ponderosa- Sapin de Douglas a un cycle des incendiesforestiersplus
long (52 ans) que celui rapporte pour des types forestierssemblablesd I'est des Cascades.Dans le pass6,les incendies
ont crde une diversitdde la structureet du paysageforestiersde DesolationPeak. lls pourraient constituerun el6ment
i m p o r t a n t d u m a i n t i e n d ' u n e t e l l e d i v e r s i t 6d a n s I ' a v e n i r .
[Traduitpar la revue]
Inlroduclion
The fire history of lorestson the westside ol the Cascade
M o u n t a i n s i n W a s h i n g t o n i s u s u a l l y c h a r a c t e r i z e db y
infrequent (200- to 500-yearinterval) fires that kill all the
trees in the stand (Morris 1934; Hemstrom and Franklin
1982). Fire has been an important disturbance process
in this maritime climate area for millennia (Sugita and
T s u k a d a 1 9 8 2 ;C w y n a r 1 9 8 7 ) .T r e e r e g e n e r a t i o na f t e r f i r e
is often prompt, but may extend in some instancesover
d e c a d e s( F r a n k l i n a n d H e m s t r o m 1 9 8l ) . A t h i g h e l e v a t i o n
(> 1500m), the tree re-establishmentprocessmay take a
century or more (Agee and Smith 1984). In the eastern
Cascadesof Washington,with an interior climaticinfluence,
the subalpine fire regime is similar to that of west side
forests,but the low-elevation( < 1000 m) fire regimeis one
of more frequent (10- to 50-yearinterval) fires (Agee 198l),
which may resultin forestswith multiple age-classes
(Larson
l98l).
lPresent
address:Department of Forestry and RangeManageme-nt,University of California, Berkeley, CA, U.S.A.
'Present
address:Bureau of Land Management,Palm Springs,
CA, U.S.A.
Pnnred in aanadi
lnrpnrnrl au ( anada
T h e N o r t h C a s c a d e isn W a s h i n g t o n( F i g . I ) i n c l u d el o w Iand forestson the moist westsideof the Cascades,
subalpine
forestsalong the crest, and interior forestson the dry east
side. A typical zonal forest-typesequenceup the coastalwest
side of the Cascadesis westernhemlock (Tsuga heterophylla
(Raf.) Sarg.), Pacific silver fir (Abies amabilis (Dougl.)
Forbes),and mountain hemlock (Tsuga mertensians(Bong.)
Carr). A typical zonal forest-typesequenccup the eastside
of the Cascadesis ponderosapine (PinusponderosaDougl.),
Douglas-fir (Pseudotsugamenziesii(Mirb.) Franco), often
rvith grand fir (Abies grandis(Dougl.) Forbes)or lodgepole
pine (Pinus contorta Dougl. var. latifolia Engelm.), and
subalpine fir (Abies lasioc'arpa(Hook.) Nutt.l (Agee and
Kertis 1987).
F o r e s t si n t h e v i c i n i t y o f t h e u p p e r S k a g i t R i v e r , R o s s
Lake area,are of a specialbotanicalinterestbecauseof therr
transitional nature betweenmoist coastal and dry interior
forests(Franklin and Dyrness1973).The area is westof thc
Cascadecrestbut is in the rainshadowof mountainsfarther
t o t h e w e s t , i n c l u d i n gM o u n t B a k e r , M o u n t S h u k s a n ,a n d
the Picket Range.The uniquenessof the arealiesin the close
juxtaposition of coastal and interior forest communities
rather than the presenceof unique community types (Agee
AGEE ET AL
351
for determinationof age; selectionwas basedon adequaterepresentation of speciesand sizecohorts in each stand. Wedge samples
were cut and removed from 50 trees in all locations where single
or multiple fire scarswere present(Arno and Sneck 1977),except
along trails. Multiple sampleswere taken in the same area only
when there was an obvious differencein the number of scarson
adjacent samples.
+-'). \,
ul
'or,'
Vegetation communit-v analysis
Two-way speciesindicatory analysis(TwtNSpAN)was used to
classifythe vegetationdata (Hilt 1979;Gauch 1982).Speciesimportance valuesusedas inputs to the programswere cover classesfor
shrubs and herbs and an averageof relative basal area and relative
cover (expressed
on the same 1-6 scale)for trees(Agee and Kertis
1987).
Fire history analysis
Incrementcoreswere mounted on boards, sanded,and counted
under a binocular microscope.Total tree age on a sarnplewas determined by adding to the ageof each core an estimatedage lor core
height. Correction factors were basedon unpublisheddata from
WASHINGTON
similar sitesthroughout the region (J.K. Agee, unpublisheddata).
At 30 cm height, for example, the correction factor was as follows: Douglas-fir and grand fir, 3 years (mesic site) to 5 years
Ftr;. L Locationof DesolationPeak study area (shownin
(dry site); lodgepolepine, 3 years(low elevation)to 5 years(high
l e c r e a t i oAnr e a( N R A ) i n t h e
b l a c k )w i t h i nR o s sL a k eN a t i o n aR
elevation). Pacific silver fir and subalpine fir correction factors
N o r t h C a s c a d eosf W a s h i n e t o nB. r o k e nl i n e i s t h e c r e s to f t h e
were basedon height and the .spacingof the innernrosl rings on
CascadeMountains.
the sample:at 30 cm height, l0 rings/cm, the correctionfactor was
5 years,while at 30 cm height, 50 rings/cm, the correction factor
and Kertis 1987). Commonly, the west side zonal forest
was 20 years.
Fire dates were recorded from cores (Barrett and Arno 1988)
sequenceoccurs on mesic north and east aspects,whereas
and wedges.USDA Forest Serviceand the United StatesDepartthe east side zonal forest sequenceis found on drier south
ment of the Interior National Park Servicerecordswere reviewed
and westslopes.
for additional 20th century fire occurrences.Age-classinformaT h e o b j e c t i v eo f t h i s s t u d y w a s t o d e f i n e t h e f o r e s t f i r e
tion rvas also used to determinedisturbancedates. Distinct agej
u
s
l
h i s t o r yi n t h e v i c i n i t y o l ' D e s o l a t i o nP e a k
e a s to f R o s s
clas.sseparationsbetweengroups of treeson a plot were determined
Lake. It was hypothesizedthat the fire frequenciesfor east
from clustersof'tree agesfrom each plot. Each defined age-class
sideand westsideforestcommunitieswould reflectthe close
was representedby the oldest tree age in the cluster for plotting
proximity of thesequite different fire regimes:on the low
on the site map. Recruitment periodsafter disturbancein multiaged
end of the range for forest types common on the west side,
standswere usually lessthan 30 years. Age-classcoverageacross
and on the high end of the range for types common to the
the study area was mapped using I : 12 000 aerial photography
and the mapped age groups in the plots.
east side of the Cascades.To achievethis objective it was
Although fires weredated to specificyears(e.g., ca. 1648),there
necessaryto define the forest community types on Desolawas a lack of correspondence
betweendatesamong wedgesamples
t i o n P e a k a n d r e c o n s t r u ctth e d i s t u r b a n c eh i s t o r y o v e r t h e
(Arno
patterns
ring
owing
to
unusual
annual
in the vicinity of .scars
p
u
r
p
o
s
e
s
study area.For thc
of this study,a low severity
and Sneck 1977);otdesttreesin cohortsof age-class
werealso
data
fire is defined as one that kills primarily understory trees.
used to establishdatesof events.Accuracy of the pre-I 800 dates
A moderate severity fire kills most understory trees and
includesan approximate5-yearrange,while I 800 1900dateshave
leavesat leasta patchy overstory, with residualtreesoften
about a 2-year range and > 1900dates are accurateto the year.
scarred.A high severityfire kills most trees in the stand.
In ecosystemswith fire return intervals >20-30 years, dendrochronologicaltechniquesare lesscritical than in ecosystemswith
Methods
high fire frequency, where individual fire eventsare more easily
The Desolation
Peakstudyareais definedby RossLakeon the
confused (Madany et al. 1982). In areas with longer mean fire
west,LightningCreekon thesouthandeast,anda valleyand low
return intervals,where fires may often be of high severity,frequent
saddleto the north. Ross[,akeis a reservoircreatedin the 1940s fires may be uncommon, but if they do occur, their presenceis
in theSkagitRivervalley;manyfiresbeforethenburnedin areas likely to be missed if dendrochronologicaltechniquesare not
now inundated.A total of 97 plotsweresubjectively
established employed. Furthermore, fire event dates determined without
overthe 3500-ha
area,representing
dendrochronology, while suitable for calculating fire frequencies
the differentforesttypesand
apparentstandagesbasedon the sizeclassesrepresented
in medium to long fire return interval regimes,cannot be usedto
in the
stand.Fixed100-m'plotsweremostcommonlyused,because
in
associatefire with climate or other characteristicsof specificyears.
mostcasesplotsof this sizeencompassed
the rangeof treesizes
llistorical fire boundaries were mapped using the age-classmap
present
in the stand..lnwidelyspaced
stands225-or 400-m'plots and fire agesfrom wedgeand core information. Criteria for mapping were similar to those of Hemstrom and Franklin (1982):
wereoccasionally
employed.Aspect,slope,and elevationwere
measuredby compass,clinometer,and altimeter,respectively. (l) Uniformity. The nature of vegetationresponsesto fire has not
Diameterat breastheight, total tree height, and basalarea by
changed during the period of study.
(2) Aee continuity. Trees in stands with similar age cohorts,
species
wererecordedfor eachtree in the plot. Coverageof subwas determlnedby coverclass(1 : 0-590,
ordinatevegetatlon
separatecl
by younger standsbut not significantvegetationor
2 - 6-25V0, 3 : 26-50V0,4 : 5l-75V0, 5 : 76-95V0,and
topographic barriers, probably originated after the same fire
6 : 96-l00Vo).Roughly l0 treesper plot were incrementcored
episode.
3s2
CAN. J. FOR. RES. VOL. 20, I99O
TABLI l. Average basal area (BA; m2 ha r), cover (CV; 9o), and constancy (CON; 9o) of tree speciesin Desolation Peak forest
communlty [ypes
Pipo-Psnre
BA
Abam
Abgr
Abla
Chno
Pien
Pial
Pico
Pipo
Psme
Thpl
Tshe
Tsnre
CV
Pico-Psme
C]ON BA
CV
CON
Psme-Abgr
BA
CV
CON
Psme-Tshe
BA
CV
CON
tr
tr
ll
ll
Itr12trtr
Psme-Abam
BA
CV
Tsme-Abam
CON
BA
CV
CON
40
20
20
100
3tr
tr
tr
3tr
tr
4
14
tr
5
25
l4
'70
100
A
l
27
5
tr
35
26
1
96
40
l0
50
3tr40
31 50 100
Itr4035
tr
tr
16
29
35
13
l0
100
5-s
83
l5
t)
80
604
Pico-Abla
BA
CV
18
15
tr
6
tr
25
250
tr
CON
'75
25
7250
6n50
l o r a n a l y s i sw c r e A c m a , b i g l e a l n a p l c a n d P i m o , w c s t c r n w h i l c p i n e .
(3) T<tpographicc'onsistency.Disturbances other than fire, such
operateon steepgulliedslopes,
as avalanches,
characteristically
whereasmudflows and floods affect standsat valley bottoms.
Typically, thesedisturbances
do not havesurficialcharcoaland
can be distinguishedfrom fires.
(4) Conservativelimils. Reconstructedburns are often minimurn
reconstructions
of past
areasburncd and representconservative
fire events.
Two other assumptionsby Hemstrom and Franklin (1982)were
modified for this study:
(5) The rcgenerationspanassumptionwith early seraltree cohorts
spanning 75 years or more was not used in this study, even
though regenerationcan be very slow at elevations> 1500rn
has beenmore rapid in most
on DesolationPeak. Regeneration
locations becauseof the presenceof moderate severity fires
evidencedby substantialsurvivalof residualsafter many fires.
(6) Unlessspecilicfire evidencewas apparent, fires wereassumed
to burn uphill only until they reach a topographic barrier or
subalpineforest,sinceother studies(Schmidt 1960;J.K. Agee,
unpublisheddata) suggesta dampening of fire spreadand intensity when fires burn upslope into more moist fuels at higher
elevation.
Fire events,defined as either single fires or a seriesof simultaneous or closelyspacedfires, were reconstructedusing aerial photo
and topographic data along with, in priority order, (l) fire scars
from wedgesamples,(li ) coresspecificallyextractedto date a fire
scar, (lii ) coresexhibiting aberrant ring patterns,generallyassociated with datesdeterminedfrom i or ii, and (i v) age-classdata,
particularly where severefires had removed previous evidence.
Boundariesof past fires were estimatedby drawing lines equidistant
betweenpoints where fire scarsor age-classdata indicated a disarea
continuity in past disturbance.This techniqueunderestimates
coverageof fires becauselow severityfires may leavelittle or no
trace that is recognizabledecadesor centurieslater. Area coverage
of each fire was calculatedusing a dot-grid overlay on I : 24 000
scale maps, with 15.5 dots/cm.
Natural fire rotations (NFR) (Heinselman 1973)were calculated
using the mapped fire areasfor various time periods and geographical units. A selectedtime interval divided by the proportion of
total area that is burned within that intervalyieldsthe NFR. Point
estimatesof fire frequency, using individual or clustered fire scar
samples, are more applicable in very frequent fire regimes where
trees are often scarred but rarely killed (Kilgore and Taylor 1979;
Dieterich 1980). Fire return interval methods that rely solely on
age-class
distribution and assumptionsabout randomnessof ignition (Johnsonand Van Wagner 1985)work best in areasof uniform
lires. A major disadvantage
terrainand stand-replacing
of the NFR
method is the needlo reconstructpast fire events,which can result
in conservativefire return intervals (Van Wagner 1978).
Mean fire rcturn intervalswere calculatedfor community types
defined by rwtNsnnN by dividing the averagenumber ol fires per
plot for a community type into the time period covered.A second
method of analyzingfire return intervalsfor vegetationwas used
to comparestandspeciescompositionand structurewith mean fire
return intervals(MFRls). On eachplot, the two speciesrepresenting the highest (primary dominant) and secondhighest (secondary dominant) tree densityin the combineddominant and codominant tree stratawere identified.The MFRI for a primary dominant
specieswas calculatedby pooling all plots where that specieswas
a primary dominant and dividing the mean number of fires per
plot into the time period covered. The same techniquewas used
for secortdarydominartt species.
Results
Foresl communities
Vegetation community types were identified through
rwrNSPANon the basis of floristic similarity. Sevenforest
community types were identified; vegetationcharacteristics
of the sitesare summarizedin Tables I and 2 and Fig. 2.
Comnrunitieswere named for two common conifer species;
the secondconifer in the name is the likely potential overstory dominant in the long-term absenceof disturbance
(plant series sensu Daubenmire 1968), whereas the first
named conifer is an associatedseral dominant.
Foresl fire events
Fires were detectedover a 400-yearperiod on Desolation
Peak. Major fires are discernibleover the entire period, but
the chanceof reconstructingsmall fire eventsdiminishesas
those eventsbecome older. A total of 29 fire eventswere
mapped (Figs. 3A-3L). The oldestfire (ca. 1573)was determined from fire wedge information and covered a southwest aspectthat has burned repeatedlysincethat time. The
ca. 1648fire was identified from widely scatteredage-classes
over the entire study area and probably burned a significant area adjacent to Desolation Peak. The ca. 1733 and
ca. 1782fires burned much of the same area covered by the
ca. 1573 fire. The ca. 178l fire burned south to southeast
aspects;a portion of the ca. 1782 fire was reburned.A fire
that probably started in an area that is now under RossLake
A G E E F , TA L .
353
T , A , s t - E2 . R e l a t i v e c o n s t a n c y ( 9 0 ) o f m a j o r s h r u b s i n D e s o l a t i o n P e a k f o r e s t c o m m u n i t y
types
Community type
PipoPsnre
Acer circinalurn
Amelonchier alnifolia
A rclostophylos Uva-ursi
Berberis nervosu
Ceanothus velulinus
Corylus cornuta
Holodiscus discolor
Lonicera hispidula
Pachistimo myrsiniles
R h odode nd ro n aI b ifl o ru m
Rosa gymnocarpo
Rubus parviflorus
Sallr spp.
Spiroea betuli.folia
Vaccinium spyt.
PicoPsme
+l
70
60
90
100
4l
22
59
60
52
26
52
PsnteAbgr
PsmeTshe
PsrneAbam
TsmeAbam
PicoAbla
)b
80
'76
80
10
88
40
100
72
24
24
36
48
l5
21
96
78
30
20
50
50
60
40
20
z)
50
60
100
100
N ( ) i l r : R e l a t i v ec o n s t a n c yi s t h e p e r c c n l a g co l p l o t s w i t h i n a c o r n n r u n i l yt y p e t h a r c o n l a i n s t h e s p c c i c s .S e eT a b l c I I o r
i l r c r n l : i l r J l i r , Io l \ n c ( i c \ u b h r e r i : r t i r r r r i .
C o mm u n i t y T y p e s
P t P o P 1 ; 1 yRnle P)n)r) Psrne Tsnrt: Ptco
Psrne Psnte A b g r 1 5 5 s A b a r n A L x i r | A f ; l : r
tr
h
O
;
E'p9lei"ol
lltl
I II
I
lP'"i h'"d
_5
++l
Pll
a
J,_r_
O
|
LttH
| lpicol
E
,9
4ttt
lPieol
I
-Y
l=c| |cI
I ll*-d
F.j l I
a
ctt
A
r-------1 |
-T-
II
|
--r-
.\r]-.'
t|l
e E I ll I
ce
1i
l*.4
1"".{I
-=
r
I
ll
u/
r-
a)
|
tt
I
l_ l
l___i
within eachcommunity
Ftc. 2. Percentdensityof treespecies
type by forestlayer:0-3 m height,3-10 m height,and >10 m
lessthan l09o of relativedensityare
height.Species
constituting
category(shadedblack).
lumpedin a miscellaneous
burned up two sides of a major west-facing drainage in
ca. 1806.An area on the eastside of Desolation Peak, which
had not been burned by a major fire for 165 years,burned
i n c a . 1 8 1 5 .I n c a . l 8 l 9 a n d c a . 1 8 3 2 ,s m a l l f i r e s b u r n e d
lower portions of the southwest-facingslopes.
The fire of ca. l85l coveredmost of the mountain. Some
areasshown as unburned islandswere not mapped as burned
owing to lack of evidence for reconstruction of the fire,
although it is possiblethey did burn. A similar area was
mapped by Ayres (1899) as an old burn that had not
restocked.In ca. 1865. another small fire burned on the
w
n7
@ W' !) %--)
Br---r-\
\/
)\
ffitstz
ffiroae
're
S tzes
l)tez
,C:N
vlA
rT T-
!rasz
ffitast
fraosffirszzffiiaeo
ffiros
ffiiaea
IN <;7
Y<-,/
\-/
$rars
lrsrs
'(-i)
t.\
/i\
\\
lluffitaoa
ffiraoo
J,o---4
)I
(..
\) <)
$%
\
\-_./
ltwffiiaea ffitass[rooa Irsrs
ffires+firos ffieosltst+
\2/
'n
lil
km
-F---l
o 2 4
6
ffiisza
Irgqs eo
810
Irrc. 3. Individualfire eventssinceca. 15"73
at DesolationPeak.
Multiplefireyearson a singlemaparedenotedby differentshading.
lower elevationsouth slopes.In ca. 1868and ca. 1872,the
northeastern portion of the mountain was burned. The
ca. 1872 fire, which showed an age-classslightly younger
than the lower elevationca. 1868fire, might have beeninterpreted as a singleevent, but fire scar data indicated a separa-
CAN. J. FOR. RES. VOL.20, I99O
354
Te,sr-E 3. Natural fire rotations for
Desolation Peak
Time period
Mean fire return
interval (years)
Natural fire
rotation (years)
r600- l 699
t'700-1799
r 800-l 899
I 900-I 985
100
208
60
103
I 5 7 3 *r 9 8 5
100
TABr-Fr4. Natural fire rotation by
a s p e c to v e r t h e 1 5 7 3 - 1 9 8 5p e r i o d
Natural fire
rotation (years)
North
East
South
Southwcst
West
TaeLE 5. Mean fire return intervals for forest communitv tvoes
on Desolation Peak
Ponderosapine - Douglas-iir
Lodgeple pine - Douglas-fir
Douglas-fir - grand fir
Douglas-fir - western hemlock
Douglas-fir - Pacific silver fir
Mountain hemlock - Pacific silver fir
Lodgepole pine - subalpine fir
Tneln 6. Mean fire return intervalsfor major
species where they are either primary or
r e c o n d a r yd o n r i n a n t s
Mean fire return
interval (years)
t82
107
9'7
65
t20
t i o n o f 4 y e a r s .I n c a . 1 8 8 0 ,m u c h o f t h e w e s t s l o p eo f t h e
mountain burned, and over the next 4 decadessmall fires
occurredin scattcredlocationsaround the mountain. Other
small fires may haveoccurredearlierin the record,but could
not be identified on the landscape.
T h e a r e ao f t h e l 9 l 9 f i r e w a s r e b u r n e db y t h e l a r g e r f i r e
o f 1 9 2 6 .T h e 1 9 1 9f i r e w a s r o m a n t i c i z e di n J a c k K e r o u a c ' s
(1958, 1960) novels The Dharma Bums and Desolation
Angels, although he assumedthe burned area was a singlc
large fire in 1919.The first fire apparentlyburned primarily
in subalpineforests(Fig. 3K), whereasthe secondwas part
of the 20 000-ha Big Beaver fire that started near what is
t o d a y t h e s o u t he n d o f R o s sL a k e , j u m p e d t h e S k a g i tR i v e r ,
and endednorth of DesolationPeak (Fig. 3L). Sincethe big
1926fire, only scatteredareashave burned in a period whcn
a fire suppressionpolicy has been in effect.
Patterns of fire frequency
Natural fire rotations were calculatedfor the entire area
o v e r t h e t i m e p e r i o d 1 5 7 3 - 1 9 8 5a n d f o r e a c h c e n t u r y
(Table 3). The NFRs were also calculated by aspect
(Table 4). The average NFR for the area was 100 years,
interpretedto mean that in the courseof a century an area
equal in sizeto the study areawould burn; someareaswould
burn twice and others not at all. Wide temporal and spatial
variations are evident during the time period covered by
the study. The post-1900period has a NFR equal to the
averageover the whole study period, whereasthe period
1800-1899has a low NFR. The l'100-1799period has a high
NFR, whereasthe large fire in ca. 1648resultsin an average NFR (100 years)for the 1600-1699period. lnfrequent
fire eventsof wide extent markedly affect the calculations,
and the probable occurrenceof additional but unidentified
fires in the 1600-1700period may make this NFR conservative. Southwestaspectsburned most frequently whereas
north aspectsburned least frequently.
Mean fire return intervals for community types (Table 5)
showed a range of 52-137 years. The ponderosa pine Douglas-fir type has the shortest MFRI; it is most common
52
76
93
l3'1
108
t3'7
109
Ponderosapine
Lodgepolc pine
Douglas-fir
Weslern red cedar
W e s t e r nh e r n l o c k
Pacific silver fir
S u b a l p i n ef i r
Mountain hemlock
Primary
dominant
Secondary
dominant
44
69
94
> 4l I
169
192
154
137
56
82
84
204
t26
r08
89
I z-t
on the southwesa
t s p e c t st h a t h a v e b u r n e d r e p e a t e d l yw i t h
low severity fires. The lodgepole pine - Douglas-fir comm u n i t y , w i t h t h e n e x t l o w e s tM F R I , i s f o u n d o n m o s t o t h e r
aspectsat low elevation.The Douglas-fir - grand fir community is found in protected lorv-elevationdraws, which
o c c a s i o n a l l yh a v e n o t b u r n e d , s o i t s M F R I i s h i g h e r . T h e
Douglas-fir - westernhemlock community has burned the
leastof the low-elevationcommunities.It is found primarily
on north aspectsthat are floristicallyand climaticallysimilar
to moist lowland forestsfarther to the west. The remaining
community typestend to be subalpineforest typesand have
m o r e s i m i l a r M F R I s t h a n t h e m o n t a n ef o r e s t s .T h i s i s d u e
to the widespreadnature of past high-elevationfires and
limited geographicseparationbetweenthe subalpinetypes.
Fire frequency variation was also assessedfor species
wherethey were primary or secondarydominants(Table 6).
Ponderosa pine and lodgepole pine were the only species
to have shorterMFRIs wherethey wereprimary dominants.
These are the only two major speciesat Desolation Peak
that are restrictedto early seralstatus;all of the other species
or potentialvegetationdominants(sensu
are late successional
Daubenmire 1968)in some locations. As their dominance
dependson seral community maintenancethrough disturbance, the early seral speciesshould be more dominant
where disturbanceis more frequent and the MFRI is lower.
Speciesthat are later successionalor relatively fire sensitive,
including subalpine fir, mountain hemlock, and Pacific
silver fir, have longer MFRIs where they are primary
dominants and tend to be secondarydominants wheredisturbance by fire is more frequent. Douglas-fir is both a major
seral speciesin middle- to high-elevation communities and
AGEE ET AL
a major potential vegetation dominant in the drier lowland
communities. Over the study area, it has roughly equal
MFRIs whether it is a primary or secondarydominant.
Discussion
The spatial arrangementof the forest communities on
DesolationPeak is influencedby temperatureand moisture
gradients,which were also found to be important in other
Pacific Northwest forests(Zobel et al. 1976;del Moral and
Watson 1978)and in the North Cascades(Agee and Kertis
l 987).
Variable fire environmentson DesolationPeak are illustrated by the spectrumof fire return intervals in the forest
community types. The communitiesin drier, warmer environments have the shortestMFRIs, whereasthe communities in cooler, wetter environmentshave the longestMFRIs.
Thesefire fiequenciesalso reflect the landscapeheterogeneity
within which they occur.
At DesolationPeak, the interspersionof west side and east
side types has a significant influence on fire frequencywithin
a forestcommunity. The ponderosapine - Douglas-fircommunity has an MFRI of 52 years, far higher than fire
intervals for the type elsewherein the Pacific Northwest
where environmental gradients are more gradual and a
homogeneous
contiguousforestis present(Wischnofskeand
A n d e r s o n1 9 8 3 ;F i n c h 1 9 8 4 ;J . K . A g e e ,u n p u b l i s h e dd a t a ) .
The lodgepolepine - Douglas-fir community has an average MFRI higherthan typically found in similar forest types
of westernMontana (Arno 1980).The Douglas-fir- western
hemlockcommunity fire intervalsare below thosecalculated
for either Douglas-fir (230 years) or western hemlock
(598 years)for westernWashington (Fahnestockand Agee
1983),but are closeto thoseof 100 yearsfrom Means(1982)
and Morrison and Swanson (1990) for dry Douglas-fir
forests of the Oregon Cascades.The Douglas-fir - grand
f i r c o m m u n i t yh a sa n M F R I w i t h i n t h e w i d e r a n g eo f A r n o
(1980)from the northernRocky Mountainsand Wischnolske
and Anderson (1983) from the WenatcheeValley of
W a s h i n g t o n .T h c m o s t c o o l a n d m o i s t f o r e s t e o m m u n i t y ,
t h e m o u n t a i n h e m l o c k- P a c i f i c s i l v e rf i r c o m m u n i t y , h a s
a n M F R I f a r b e l o w t h e 4 3 4 y e a r sf o r s i m i l a r f o r e s t t y p e s
a t M o u n t R a i n i e r( H e m s t r o ma n d F r a n k l i n 1 9 8 2 ) .T h c f i r e
return intervals of Desolation Peak forest communities
appearto reflect the juxtaposition of forest types not commonly found together,lengtheningfire return intervals for
communities with typically frequent fire regimes and
shorteningthem for communities with typically infequent
fire regimes.
Although forest environmentand interspersionof forest
typesare important influenceson fire return intervals,patterns of lightning and aboriginal ignitions are also important. Indiansinhabitedthe Skagit River valley in the vicinity
of DesolationPeak, and a preliminary analysisof fire scars
on stumps now underwater most of the year about 5 km
north of the study area suggestsa l0- to l5-year fire return
interval on the vallby floor (Taylor 1977).Such closelyplaced
fires are generally absent from the record on Desolation
Peak, suggestingmore frequent burning in the vicinity of
the Indian village (e.g., Barrett and Arno 1982).Although
mining era fires were common in the Cascades(Mack 1988)
during the last half of the l9th century, the settler influence
found elsewhere in the North Cascades (Ayres 1899;
J))
Hemstrom and Franklin 1982) is not locally apparent at
Desolation Peak.
The short NFR for the lTth century and the long NFR
for the l8th century would not be notable if Desolation Peak
were the only area in the Pacific Northwest to show such
a record. However, a similar pattern is reported for the
forests at Mount Rainier (Hemstrom and Franklin 1982),
the southern Olympic Mountains (Henderson and Peter
l98l), and the west-centralCascadesof Oregon (Morrison
and Swanson 1990).This apparent regional pattern is not
explained by any of the separatestudies, but may reflect
climatic changessuch as the Little Ice Age (Hendersonand
Brubaker 1986)and associatedchangesin biomass flammability, dry summer winds, or lightning storm frequency.
The forests of Desolation Peak have been significantly
influencedby fire over the past half millennia and no doubt
for millennia before. The preservationof the structuraland
landscapediversity of thesenatural ecosystemswill require
maintenanceof thesedisturbancepatterns into the future.
Over the last 4 centuriesa fire has burned on Desolation
Peak about every 15 years.Although it is unlikely the major
seral dominants ponderosapine and lodgepolepine would
disappearwith completefire exclusion,the spatialextentof
thesecommunitieswould shrink over time. Forest communities dominated by these speciesare unusual west of the
Cascadecrest,and future activemanagementof disturbance
by fire will help maintain this unique landscapediversity.
Acknowledgment
This researchwas supported by cooperalive agreement
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