John D. Stuarl, Departr.entof ForestryHumbodt StateUn versltyArcata,California
95521
ano
Lucy A. Salazar,Six RivefsNatona Forest T330BayshoreWay,EurekaCa fofnla95501
Fire Historyof White Fir Forestsin the CoastalMountainsof
NorthwesternGalifornia
Abstract
Fire inten'als are presentedfor !lhitc ilrfor.sts in the co.ls|lllmountainsofnofh$,estern California. Firc dateswere defiled ffom
fire scarsand trcc cstablish lcnt dateshom 28 logged samplingsitesspfeadacrossan arca approximrtely 125kln by 30 kn. Prc
suppressionmcdian firc inlcr!els nnged iioln 12 to l6l yeaf\. The medianfire intcrlal for thc pre suppressionpefiod (27 years)
$as significantl) \horlcr lhan ibr the suppressionperiod (7'1yeart. There \\'crc no significanrdilGrencesin medianfire inrerral\
among regelation scncs.Thcrc wcrc also no signiiicant regressionsofmedian llre inten'al wi!h dislancelioln the ocean.latitlrde.
or elevation. \,lost sampling !ilcs wcrc nuld aged and had experiencedmultiple surfacefircs. Somc sitcshad expefiencedstandreplacing fte\. Fife suppressionhas incrcascdstanddcnsil,"-.iicreased lhe densit] of shadetoleran! lrcc spccics.and decreased
the densit] of shadeintoleran!tree specic\.
Introduction
Fire history studiesof Califomia white 1lr (Ables
cr.lrcolor(Gordon& Glcnd.)Lindley lnr /orrcln
(Gordon) Andr. Murray) indicate that low elcvation sites have shortcr nrean fire intervals than
high elevationsites(McNeil andZobel 1980.Agee
1991).Low elevationsiteshave beenfound to
havc mcan fire intervalsbetween9 and 25 years
(Kilgore andTaylor 1979.McNcil andZobel 1980,
Bork l9tl5) andon high elevationsitesmeanfire
interr"alshavebeendeteminedto bc 40to 64 years
(McNeil andZobel 1980,Agee 1991,Taylorand
Halpern l99l). Thesedifferenccshave beenatt r i h u l e dl o l h e c o o l e r n d m o i \ t c re n \ i r o n r n c n t .
that are often presentat higher elevations(Agee
1993).Previousstudicsof white t'ir fire hisrory
have beenconductedin inland locations.Littlc is
known ofwhite fir firc historyin thecoastalmountains of northwesternCalifomia.
Pre-Europeansettlementfire ignitions were
thought to bc a result of both Native Amedcan
fircs and lightning(Agcc 1993).NativeAmericansburned regulally in the vicinity of whitc fir
forestson thcSix RiversNationalForestto naintain
plantsusedin basketryand lbr food and clothing
(Heffner198.1.
BlackbumandAnderson1993).
The objectives of this papcr arc to: 1) repofi
fire interyals fbr white fir forests in the coastal
mountainsofnorthwesternCalifomia andto compare then with othcr tirc history studiesof Cali280
N o r t h w e sSt c i c n c eV. d . 7 4 , N o . 4 , 2 0 0 0
r.tlOLUbr_rhc\!'rlir.rS.trJt,li.r\$ocixt.o
All.!hr.re,ened
fomia white fir. 2) comprLrelire intervals among
the different vegetationseriescontaining white
fir in the study area. 3) investigatewhcther elevation.latitude,ordislrncefrom thePacificOcean
are associatedwith medianfire inter.,'alsin these
stands.and,+)infer thc role fire and tire suppression havehad on speciescompositionand stand
structure.
StudyArea
This study was conductedwithin thc Mad River
and OrlcansRangerDistrictson the Six Rivcrs
NationalForcst.Studysitesu'erelocatedona serics
of mountain ridges that separatethe Six Rivcrs
National Forest fiom the Klamath and ShastaT r i n i l ) N r t i n r l F o r e s t sI n
. p a r t i c u l asr .i r e .u c r c
locatedonSouthFork Mountainon the Mad River
RangerDistrict and on ridges abovc Biuff Creek
on thc OrleansRangerDistrict(Figure1). Sampling sites were lbund on all aspectsand at elevations
liom 1.183nto 1,6,16
m. Themostsoutherly samplingsiteswere 127 kn fron thc nrost
norlhcrl)one.. .Ln,.l
lhe rno.t er.leriy \ile\ \\r.re
3l km tiom thc most westerlyones.The whitc
fir forestsoD the Six Rivcrs National Forest are
amongthe most westelly, occufiing from 26 km
to 81 km t'rom the Pacillc Ocean.
Annual precipitation varics frorn 175 cm on
SouthFork Mountainto 230cm on theridgesabove
Bluff Creek(Miles and Roath 1993).Ninety-fbul
N
*
0 5 1 0 1 5 2 0Miles
r
Figure L Location of samplirg sites on the Si.{ Rivcrs National Forest in north*estefn California. Bolded lines are the
national forest boundaries
White Fir Fire Hisroryin Calitbrnia 281
percentof thc prccipitationoccursduring the
nronthstrom October through May (Elford and
McDonough 1964).Temperatureand relative
hunidity are stronlily modemtedby the proximity of the Pacific Occan. For a given etevauon,
winter temperatLrres
are typically warmer and
\ u n t r n a rt ( n l p e r i l l u r ea\r e c o o l e rl h a n m o r c i n land forests.The avcrageJuly high tempemture
atWeitchpec,theclosest$,ealherstationwith sinilar weathcrto thestudysites.is 28.6'C.The sampling sites.beingat higherelevations.would be
5'to 8'coolcr (Eltirrd and McDonough196,1).
In mid-summer.
relativehumidityaverages
40 to
507c(EJtbrdandMcDonough1964).Eastwinds
can dr:imaticallyreducerelativehun.ridityand
rncrease
tefrperaturcs.
Duringa 3-yearpedodin
Eureka.windsblewfrom theeast57cof thetime.
fi'om the northeast67. of the time, and from the
soulhcasl177.of thetime (ElfordandMcDonough
196.1).Thunderstormsaccompaniedby lightning
occasionallyoccur.but lessoften than in the KlamathMountains,Cascades,
or the Siera Nevada
(AutomaledlightningdctectionsystemApdl 1985
November1997.).
Study sitesu'ere locatedin forestswith white
fir eithcroccuningas the don nantor co dominant species.Olhcr associated
conifersincluded
Douglas-lir (.Pseudotsuga
rzer;lesil (Milbel)
(Cdlocedrtrsdeturrens
Franco).inccnsc-ceLlar
(Tone)) Florin). Port Ortbrd-cedar(Chamaecy^paris lavsonianaA. Murra),),noble fir (ADies
p rrcc ru Rehder).ancl stgar pine (.PirtusLanrb
ert idr4 Douglas).We classifiedeachsamplingsite
r ' b e l o n r i n gI , \ t , n er ' l ( h r e ep o \ s i b l e\ e g e l J l i o r )
series:Whitc fir Douglas-fir.andIncense-cedar
(Salycr and Keeler-Wolf1995).
Fire suppressiou
lecordsdateto 1910on the
Six RiversNatiolal Forest.Aggressivefirc suppressionandprevemtion
of NativeAmedcanand
minerignitedfiresin rcmotcarcason theSix Rivers
NationalForest,however,did not beginuntjl the
end of Wolld War IL Othcr studiesfrom the KlanrathRegion found that tlre llcquency decreased
in the 1940's(Agee 1991.Wills andStuart1994.
Taylor and Skinner1998),presumablybecause
, ' l I n i ' r ee l l e c ( i \ e . u p p r ( . . i o cnf i o r l , .
Methods
Twenty-cightstimplingsitesu'erelocatedin logged
areasthat were dominatcd or co-dominatedby
white fir. Samplingsitesrangedin sizcfronr 1.2
282
Stuartand Salazar
to 10.9hr. with a meansizeof 4.2 ha (s.d.=2.,1
ha).The samplingsiteswere chosento be coincidcnt with logged areasto take advantageof
readilyavailablestunps.The sites.therefore.wcrc
not locatedwithout bias and may not ref'lectthe
variationfound throughoutthe rangeof white fir
in the broadly defined study area.We chosethis
samplingschemebecauseit was easierto llnd
fire scarson stunlpsthan on trces.Most trees in
our area,as well as in othcr similar vegetation
types in the Klamath Mountain fegion (Taylor
1993.Wills and Stuart 1994).have completely
healedover fire rvoundsdue to long fire-free intervals.Treesthatdid haveopenlire woundswcre
almost?Llways
rotten.Stumpsfrom recentlylogged
sites,in contrast,yieldedgood.soundwood.
Stem cross-sectionswere removed t'rom all
sound stumpshaving visiblc fire scarsand were
cut ascloseto thegroundaspossible,usuallywithin
30 cm. Cross-sections
werepreparedwith apower
sanderand sandedwith successivcly
finer grits
of sandpaperwhenever necessaryto render an
easilyreadablesurface.Onceprepared.the crossseclionswere agedusingahandlens.and in some
cases.a binocularmicroscope.Annualring counts
were madc on one or more radii, depcndingon
growth andeaseofinterpretability.Fire scardates
wcrc recordedas well as tree age at the tine of
l o g g i n pF
. i r e: ( r r \ $ e r e r e c o g n i u eudr i n g . r i t e ria described
by McBride( I 983).Sometreeshad
no fire scarsbut were aged as they presumably
represeDted
a cohofthavingbeenestablished
fbllowing fire. Three years werc addedto the ages
o [ t r e e .r t t h et i m . ', ' l ' l u g g i n gl o d e r i r er r c , . e . t blishment datesafter a reconnaissance
sample
dctcnninedthe meanageofstump-highseedlings.
Crossdatingof treerings(StokesandSmiiey 1968)
was not possiblewilh most specinens.presumably bccausecornpetitioninfluenccdradirl growth
more than climate. Othcr studieshavealso found
crossdating to be ditllcult in northwcsternCalilbrnia (Brown andSwctnan 1994.Wills andStuart
1994,Taylorand Skinner1998).
A master fire chronology fbr each sampling
sitewaspreparedbasedon fir'escardatesandveiLrs
of establishmentof cven-agedcohofis. Fire scar
dates that *,erg uncertainwere eithcr discarded
or adjustedusingthe techniquesdescribedbyAmo
and Sncck(1977).Only confirmedfirc datesnere
used to calculatefire interval statislics.The
Kruskall-WallisH-testwas selectedto be uscd
to detectsignitlcantdifferenccsin medianfile
interv;rlsbctweenvegetationsefiesand historic
periodsaftcr the datawere proven to be non-norwas usedto assess
mal. Simplclincarregression
whethermcdianfire intervalshad a statistically
latiwith elevation.
significantlincarrelationship
rude.or distancefrom the Pacific Ocean.
Succcssioninferencesfor white tir forestson
the Six Rivers National Forestwere derived using datafrornTalben(1996).Talben(1996)demonstratedstanddensityand specieschangesusirg datacollectedin 1961 1963on U.S. Forest
SeniceContinuousForestInvcnloryplotsandthen
rcmeasured
in 1993-1995.
He usedstanddensity
index as a standardizeddensity measure.Stand
densityindex is basedon thc numberof treesper
height
0.4ha for trees25 cm in diamctcraLbreast
andis independentofage andsitcquality(Reineke
Talbert'sdata
1933,StageI 968).We reanalyzcd
after selectingfbr tbrestscontaining white fir.
TABLE L Firc inicrlals for fie pre-suppressionperiod, the
supprcssionpcriod. a.d since the last fire. Data
arc nlcdian iirc intervalsfrom the samplingsites.
n = thc nunrberof sampling sites
Pre-suppression
Suppression
Yearssince
pedod
lasl lirc (datc
(161,1I94'1) ( 1 9 1 5 1 9 9 5 ) o f l a s t f i r c i 1 9 9 5 )
(n = 26)
(n = 18)
(n = 28)
Median
21
11
NIean
35
8l
Standard
deviati0n
Range
Mediantire intervalsfol all sanpledsitesrunged
from 12 to 16l years.Fire intervalswerehighly
variablcwithin samplingsiteswith coefTicients
of variationrangingfron 2l to ll,+7.. Pre-supp r e . \ i o nm e J i J nl ' i r ci n t c r rl l . t 2 7r e a r .' u e r e. i g nificantly shorterthan thc suppressionpedod (7.+
years)(P<0.001).Mcan fire intervals.hou'ever.
pedod
were longerfbr both thc pre-suppression
(83
years)
pefiod
and
the
suppression
135
)'ears).
The mcdianandmeannunber of yearssincethe
and 78 years.respectively
last fire was 74 _v-cars
(Table l). There u,erc no significant differences
i n m e d i . r nl i r e i n t e r r a l .h c l $ c c nr c g c l r l i o n\ e
ries (P=0.284)(Table2). Thcrc were also no sig
nificantregressions
ofmedian llrc inten'alasfunc
tionsofdistanceliom the PacificOcean0J=0.001,
P=0.86),latitude(f=0.0,14,P=0.29).or elevation
(rr=0.052.P=0.25).
3:l
31,163
3l)
1 2 -1 6 l
39
1 81 6 3
TAULE l. Fire interlals (years)oflegetation seriescontain
ing whiie fir. Data.rre nedian iire inter!als from
rhe srmpling sites. r = the numbcr C)1sampling
sireswidin a \cgculion scrles.
whiic iir l)ouglas llr Incense-cedar
(n=16)
(n=9)
(n=3)
Resultsand Discussion
A total of 126tire-scarredstumpswas found in
thc sampling areas.The number of tlre-scared
stumpsper samplingsite varied t'rom0 Lo11with
a meanof:1.5.Thesestumpsproducedan aggregatcof 238 agedfire scarsand an averagcof 8.5
agedflre scarsper samplingsite.Treeestablishment dateswere Llsedas surrogatesfor fire dates
on samplingsitesrvithoutflre-scarredstumpsand
on siteswith evident cohortsof $,hite fir. A total
of I 12 llees was usedto rcpresentcohortsacross
all sanpling sites.
11
l8
'1u
,ll
26
3l
lE
12 82
1 61 6 1
\{ern
Standarddeliition
Range
51
1 5 . 5l 0 , l
The median and mean prc-suppressionfire
intervals (27 and 35 years, respectively)on our
samplingsiteswerebctwcenfirc interr'alsrepofied
for inland low elevation and high elevation fbryears,respectively)
ests(9 25 yearsand,10-6:1
(McNeil andZobel 1980.Agee 1991Taylorand
H r l p e mr I 9 aI r .O u ru i t h i na n Jh e t u e e n . i lrer n F c
in fire intervalsare similarto thosetbund in Douglas fir dominatedlbrestsin the Klamath Mountains (Wills and Stuart 199,1.Taylor and Skinncr
1998).in Douglas-fir lorestsin the Cascades
(Morrison and Swanson1990).and in red fir 1br(Taylor1993).The
estsin the southemCascades
somewhatlongel fire inten'alsdeterminedlbrour
relativelylow elevationsitesareundoubtedlydue
to lower fire dangercaused.in part, by the moist,
cool climate of the Pacillc Ocean.The summertime domeof cool, moistmarineair usuallyextends b the first sct of high ridges east of the
occan. East of these ridges, there are typically
sharp summefiime gladients of increasinghigh
temperalureand decleasinglow relative humidity (Elford andMcDonough1964).Thunderstorms
White Fir Fire History in Califbrnia
283
and lightning arc lcss ticqucnt closc to the cotrst
thanon inlandsites(Elfbrd andMcDonough196.1,
Automatedlighming detectionsystenApdl 1985
Novenber 1997).Many fires. therefore.werc
probablyignited by Netive Americansburning
to culture baskeffy matedals,food, and clothing
(Heflher 1984,BlackburnandAnderson1993).
Sincethe early 1960s,und presumablysince
hre suppressionbegan.forestswith white firhave
become denser.Standdensity indexesincrcascd
fbr all treespeciescombined.increased
for tolerant ffee species.and decreasedfor intolerantffee
species(Table3). Tolerantspecieswere white fir,
Douglas-fir', incense-cedar,and chinquapin
( Ch r.vsolep is ch rysopftt'l1a(Hook.) Hielmq). Intolerant speciesincluded California black oak
(Quertus kelloggii Ncwb.), madronc(Arbalas
nenziesii Pursh),ponderosaptne (Pinus ponderzsa Laws.). and sugarpine.
Changesin the proportional standdensity in
dexcontributedby speciesoverthe samplingperiod revealed that white fir and chinquapin increased,incense-cedarcontributed the same
proportional amount to the overall standdensity
index:andDouglasfir, ponderosapine.
sugarpine,
Pacific rnadrone,and Calitbrniablack oak decreased(Table 3).
Most of the sampling sites were multi-aged
andhadexperienced
nrultiplesurlacetires.In most
cases.there were more fire scar dateson a sam
pling site than there were cohorts of established
trees.Most fires, presumably,llere not severe
enough to createsufficient growing spaceto
reinitiatea cohoft. Occasionallythough,a surface fire was seveleenoughto allow tree re-esin gaps.On a tew samplingsitesthere
tablishment
u'ere dominant even aged cohorts that presum
ably had become establishedlbllowing a stand
replacingfire or wind event.Thesepatternsare
similar to those found in Douglas fir/hardwood
fbrestson the KlamathNationalForest(Wills and
Stuart1994.TaylorandSkinner1998).in mixed
$'hiteflrforestsin southernOregon(Agee1991),
and in Douglas-fir forestsfrom the central westem Cascades
of Oregon(MorrisonandSwanson
1990).Fire has beenthe predonrinant
standreplacing disturbancein theseforestsover the past
severalcenturiesand was presumablysimilarly
p r e d o m i n a no t\ c r t h ep a s rl e u m i l l e n n i a .
284
Stuart and Salazar
TABLE 3. Thify-two years of changein stand density in
dexesof major tree speciesoccurring in $hitc 1lr
fofests.Data are from Talbert ( 1996).
1961,1963
1 9 9 3 1- 9 9 5
Proponional
Pfoportiooal
Stand
stand
Stand stand
densitl'. density
density densit\
index
index
index indcx
371.'1 L000
121.1 1.000
rhile iir
162.8 0.138
207.9 0..t90
Douglas lil
1 3 1 . 9 0.355
l'10.5 0.311
0.0.10
16.8 0.0:10
chinquapin
Calilbnia black oak
Pxcific nadfone
2.3
0.006
11.5
0.031
2.9
0.007
1.6
0.020
5.5
0.013
11.1 0.02'7
8.,t
0.023
7.0
0.017
susarpine
13.3
0.036
9.2
0.022
other species
i8.7
ponderosapnre
tr.5
0.05-5
Continuedfire suppressionin white fir forests
on the Six RiversNationalForestshouldleadto
fufiher increasesin total standdensity,increascs
in standdensityoftolerant species,anddecreases
in standdensity of intolerantspecies.In particuIar, white fir shouldcontinueto increasein density andextendinto previouslyunoccupiedstands.
The relative importanca of Douglas fil should
continueto decreaserelativeto white tlr in stands
u herethel arecodominant.
pine.sugar
Ponderora
pine, and Califbrniablack oak shouldcontinue
to decrease
in densityand will eventuallybe extilpated ftom nlore stands.Thesesfuctural changes
will increaselive fuel loading and vertical fuel
continuity.
Acknowledgements
We thank Bob Garcia, and Stan Pfister lbr their
help in designingand implementingthis study.
David CussinsandZan MendonEawere invaluable field assistants.Jenl' Allen supplied stand
density index data from Brian Talbert's thesis.
Thanks to Carl Skinner and John Innes fbr their
reviews.Funding for this study was provided by
the Six RiversNationalForest,the Depanment
of Forestryat HumboldtStateUniversity,and a
Mclntire-Stennisgrant.
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Receit'ed11 Januan 2000
Accepted8 Jull- 2000
White Fir Fire History in Calitbrnia
285