prairie-mycorrhizae

Washngton, of Bloogy WesternWashington Universty. Bellingham, R. K. Tveten and R. W Fondal, Depaftrnent 98225

Fire Effectson Prairiesand OakWoodlandson Fort Lewis,Washington Abstract Bciore 1800. iequent fifes naintrined ldaho lescuc prairics a.d Carry oak woodlands on Fon Le$is. Fire exclusion in thc | 900s.ho$'ever.has allox ed Scot's broom, Douglrs llr. and nunrerousherbaceousal iensto invadenativeprairiesard oak w ood lands. Since 1978, a managementprogran using prclcibcd iires on -15 yr rotationshas been used in an eftorl lo mainliin thc opcn communities. \Ve evxluatedthe role of fire on tescucprairics. oak rvoodlands.and broon thickels using prescribediires in lall I 99,t andspring | 995, and comprred pfeburn/postbumspecies lrcq ucncyro idcntity tire m aintainer,i.incfersen. anddecreasers.

Fall lires wcrc morc cffcctive than spring fifes. amdbesrpfomoted nativc spccicsand communities. Prescfibedfifes had no effect on Iduho lcscuc iicqucnc)'..rfiich maintxined donlinrnce ir the postlire prairic. olhcr native prairie graminoid\ and fotbs, .rnd hair! ca|s car. a pro inent alien, wefe mrintrined by fire. Prescribcdlirc! also maintainedopen Garl.l' oak w'()odlands.feduced Scot sbroo cover ir broom thickets,and killed snall Douglas lils. Thcsc iires. however,tendedto favof alien speciesinsteadof nalirc lpecies. A large praifie subjectedto >50 )r ol brcadcastburns ignited annually by afti]lery fire has been convened liom icscuc prairie to an open meador domin.rtedb) hairy ca|s car and aljen grasses.such as sweetvefnrl gnss. Ofthe three regiiles w c invcstigaled.fire i ntervalsshofteror longer th.rnthe I 5 yr irc rolation roll employed on Foft Le*,is rre detfimentalto tescue prairic rnd oak woodland. Exressn'eburning of life exclusion causcsloss ofprBirie and oak woodland.

lntroduction In regions whcrc recurring fire is an impofiant env onmeDtalfactor.manyplantspecieshavcfireandpersistdespiterepeated tolerantcharacteristics fires. Some plant comnunities are fire-dcpendent, persisting only vhere fires prevent n-Iore competitive,fi re-sensitivespeciesfrom displacing them. Fire stablecomnunities aremaintain(]d by lrequent. lou, intensity,low severity ground fires that exclude invasive.fire-avoiding specics (Andersonand Brown 1986,Agee 1993,Fonda et al. l998).Fire-stable conmunitiesincludcprairies(KuceraandEhrenreich1962,Anderson196,1, Ewing and Engle 1988.Wilson and Shay 1990), oakwoodlands(PlumbandMcDonald198I,White 1983,Guerin 1993),chaparral(Honon andltabel 1955.Vogl and Shon 1972.Conradet al. 1986). ponderosapine(Plrzirsptrarlerosrr) forests(Weaver 196,1,Covingtor et al. 1997),and longle;rfpinc (P. pulustis) tbrests (Greene 1931. Rebertuset al. 1989).

Most nativeprairicspeciesendurefue exbemely well (Anderson196:1,Old 1969,Heady 1972.

Antos et al. 1986,Ewing and Engle 1988,Wilson and Shay 1990). Firesmaintainprairiesby killing invadingtreesand shrubs(Thilenius 1964, Griffin 1977,Nimir and Payne 1978.Gruell et ' C o r r e s p o n d i ndgu l h o r : c m a i l i i b n d a ( 4 b i o l . w $ u . e d u

al. 1986).BothNimir andPayne( 1978.)andAntos et al. (1986) quantitledthe efl'ectsof fircs on s i t h . p e c i e es o m p o . i t i orni m i M r' r r r n r p r c i r i e $ lar to prairieson Fort Lewis, Washington,the 1<lcation of this study. Prescribedlires setin spring

by Nimir andPayne(1978)initially chrngedthe cover of someprairiespecies,but thoscdilference:tlecrclsedthroughuullhe fir.t grou ing 'ea. son. Antoset al. (1986)observedthat a summer wildfire initially rcduced ldaho fescue(-Feslu.a irla/rocnsis)cover and incrgasedtotal tbrb covcr. althoughthe communityretumedto prebumcover valueswithin threeyeaLrs.Neither ofthese studies provided dataon speciesticqucncy,howeveq which would havc clarified to what extent the speciesenduredfire.

The eftectsoffire on communitiesdominatcd by oaks have been studiedextensively(Boerner l 9 8 1 , W h i t e 1 9 8 3 ,M y e r s 1 9 8 5 .G u c r i n 1 9 9 3 . et al. 1995).especiallyin Califbrnia Glitzenstein (Heady1972.Green1979,PlumbandMcDonald 1981,Sugiharaand Reed 1987,Allen-Diu ancl Baftolome 1992). Some oaks are fire reslsters (Rowe 1983),protectedfiom lire damageby thick bark (Plumb 1979).but more commonly they are hre endurers(Rowe 1983),relying on postlire resproutingaftcr top-kil1(Boemer 1981,Plumb and McDonald 1981.White 1983,Myers 1985, A l l e n D i a z r n d B u n u l u r n el q q 2 . K e c l ( ) l q q l .

Guerin1993).PrescribcdfiresmaintainopenGanl' NorthwestScience, Vol. 73, No. 3, 1999 C 1 9 9 !b ! r h . \ o t h t r c n S . i e n r i i . A s s i f i d o n . A l l r l g r \ r e \ e n c d

l.+5

oak(Quertusgarrr,ara)woodlandsby reducing shrub cover. killing invading conit'ers,and topkilling oak sprouts(PlumbandMcDonald 1981.

White 1983). Sugiharaand Reed(1987)setfall fires in Califomia to mrintain Gary oak woodlands. Fires killed Douglas-fir (Pseudotsug.l ,??efi;leJii), but matureGarry oakswere not damaged. Fircs top-killedall oak stems<3 m tall. but all damagedstemsresproutedvigorously.

Sincethe late 1800s.fire exclusionhasreduccd lirc incidencein many fire-stablecommunities, sothattire-dependent plantcommunitieshavebeen invadedby fire sensitivespecies(Cooperl961, Weaver 196,1.Myers 1985.Agee 1993). Fire exclusionalsopermitshigh fuel levelsto develop. which ultimately nay lead to high intensity,high severity fires that threatennormally llrc kterdnt comnunities (Gartner and Thompson 1972.

HabcckandMutch 1973,Griffin 1977.Gruellet al. 1982).

Prescribedfires. similar to those we used in this [esearch.arcdesignedto reducefuels,rcmove invasivespecies.and maintain lire-dependent comnrunities.Prescribed firescommonlyareset in prairies(Heady1972,1977;Nimir andPayne 1978;Arderson and Brown 1986:Gruell et al.

1986),oak woodhnds(Sugihara andReedI987). ponderosapine forests (Weaver 196,+,Ffolliott andGuertin1988).longleafpineforests(Guerin 1993), and giant sequoia (Sequoiadendron gigunteum)forests(Kilgore 1972,Parsonsand Nichols 198-5).

Douglas-fir is a commonly targetedspeciesof prescribedlire. becauseDouglas-1irbenelitsfrom lire exclusion on prairies and open woodlands throughout its range. Sincc the advent of fire e r c l u s i o n .D o u 3 l l ' - t i r h i r . i n r r d c d p r r r r i c r i n MontanaandWashington(Cooper1961,del Moral and Deardorff1976,Ageeand Dun* iddie I 98:1, Gluell et al. 1986).andoak woodlandsin Wash ington. Oregon,and Califbrnia (Spragueand Hanscn1946.Langl96l.Thilenius196;1, Franklin andDyrnessl973. Kerris1986,SugiharaandReed 1987). The cffectivenessof prescribedfirc at removing invadingDouglas-firtiom prairiesand oakwoodlandshasbeenstudiedin Montana(Gruell et al. 1986)and Califbrnia(Sugiharaand Reed 1987).but not in westernWashington.Grucll et al. (1986)notedthat spriDgand lall fires caused high mofiality among small Douglas firs. Fall fires burnsdmore thoroughly.and they tendedto kill largertrees. Sugiharaand Reed( 1987)con 1.16 Tvcten and Fonda

cluded that tall burning every 5 yr. coupledwith mechanicallemoval of occasionalDouglas-tir suNivors, maintainedGal.ryoak woodlands.

The studysite forthis researchwasFort Lewis, a 3,1.865ha nilitary installation-20 km sourhof Tacoma,Washington.Idahofescucprairies.Ganl oak woodlands,and Douglas-firforestsaredomi nant community types on Fort Lewis (Figure 1).

The prairies and oak woodlands of Fort Lewis exist on gravelly, glacial outwash plains deposited-14.000yr ago(UgoliniandSchlichte1973).

The soilsareclassifiedas Spanawaygravellysandy loam, a nearly level to undulating,somewhatexcessivelydrainedsoil (Zulauf 1979). The sur face layer is black gravclly sandy loam. with a dark grayish brown very gravclly sandy loam subsoil(Zulauf 1979).This soil type,with only a tew minor inclusions.forms the broad plain bct\'"'een LakewoodandRoy,on which Fofi Lcwis is located. Early explorersand settlersreported fiequent.late-seasonfires on the prairiesand oak woodlandsin this legion.suggesting that Native An'rericanssetfires to enhancethe growth of edible prairieplantsandto aid in hunting(Lang 196I, Norton 1979.Boyd 1986).

Fon Lewis is oneof severalprairieson outwash plains in wcsternWashington. The basic f1oristic compositionoftheseplairieshasbeenknown for years(Jones1936). The Mima Mound prairie. - 10 km southof Fon Lewis.was studiedby del Moral andDeardorf(1976).Thefloraofthis prairicis similarto the prairieon Fort Lewis,althoughit appearsrnoremodillcd than Foft Lewis prairies. Both prairies are dominatedby nativc Idaho t'escueand severalnative tbrbs. Camas (Camassiuquanuslt)is an indicatorspecies.Both prairiessuppofiprominentpopulations of aliens. especiallyhairy cats-ear(Hypot lneri s radicaxi) and Kentucky bluegrass(Poa prrrtensis). Hairy cats-earis note\\"ofihy.since it already was conspicuous and abundant in western Washington prairiesby the 1930s(Jones1936).

On Fon Lewis,fire exclusionhasallowed6,560 ha of thc original 16,800ha fescueprairie to be convertcdto tbrestsince 1870 (Figure2). Before 1870, fescueprairies were large and intcrconnected.Curently. only a fractionofthe original tescueprairic remainsas small,isolatedgrasslands (Figurcs 1, 2). Large areasof oak woodlandalsohavebeenlostto invadingDouglas-lirs. but past recordsdid nol distinguishoak woodlands tiom conifer forest.

Figure L The lescuc grasslandon Wier Prairje irr \,lay 1999. ln lirc left backgroundis a Carr! oak rvoodlandand cncroaching Douglas iir tbrest. In lion( ol lheserooded slards i\ a band ofScol s broonr. encroxchingon thc liscue grassland.

Fort Lewis Fire

141

is a resprouter,thus all control nethods must rccouDtfor broompelsistcnce aftertreatment.Broom \ p r o u l \ J r e l e r s t . u c c e s s l uilf t h e t r e : r t n t e ni 't applied during rnaximum growing seasonstress (Usseryand Krannitz1998).

Thrcc fire-managementregimesexist on Fon Lewis. The first. and nrost widespread,is fire exclusionon -28,000 ha. The secondregime conrprisesa prescribedlire program appliedpredoninantly in spring. Forr Lewis beganIighting presc bcd fires in the 1960s,andsince1978has prcscribedtire program manageda comprehensive on 3000 ha of prairies and oak woodlandswith 3-5 yr rotations. Most prescribedfires are set in February/March,but fires occasionallyare set in fall. Wier Prairie,in the southwestcomcr of Fort Lewis, is in this managcmentregime. The fes cue grasslandon Wier Pra;rie is presumedto be the closestapproximationto the original prairie conrmunity at Fort Lewis, although it contains alienspecies(Figure1). VaLrious oak woodlands associatedwith the prairiesareconsideredto representa fbrmer originalcomponentonFort Lewis.

The third fire regimc is a 3000 ha artillery impact area on the Ninety-first Division Prairie, where ftequentftaining fires within the prescriptionsof the fire managementplan are allowed to burn.

Bombingis concentrated in a central1000-1200 ha area.which we call Artillery Prairie. This site hasbeensubjectedto broadcastburns ignited by arlillery fire nearly annually lbr 50 yr Despite the heavy use of fire, no studieshave been pub lished on the ef'fcctsof tire on Fofi Lewis plairies and oak woodlands.

Figure 2. Land cover maps on Fol1 l,c$i\. lr|)ln datu prL) vided by TeresaHansenand Brandy Rlche of Forl I-cwis. B1,lckdcpicts the ertent offirested easl . o p i b a s c d o r1 8 5 3 1 8 1 8 w h i t er e p r e s e n p t sr a i r i c s T h n d f e c o f d s .B o t t o J n : b a i e od n 1 9 9 5 l a n ds u r ! c ] ! .

Scot s broom ( C,r'/1,!tr"!.rcoparil) hasbenefited lrom f-ueexclusion by invading many of the remainingprairiesandoak woodlandson Fon Lewis (Figure l). This alien shrubrapidly dcgradesprairies by fornringdense.l-3 m tall canopiesthat shadeplairiespecies.Maturcbroomstandsalso suppofihigh intensity.high sevedtyllres by gencratin-qlargeamountsofrvoodv luel. Scot'sbroom

148

Tvetenand Fonda

Fort Lewis is an excellentsiteto examinespecicsand communityresponses to prescribcdfi19 on prairies and oak wqrdlands. Fort Lewis has three widely divergent.documcntedfire regimes in a small area with unitirrm soils, it is the only site in westernWashingtonwith a long-standing program of consistcntprescribedburning, and it containsmany ofthe largest.highestquality les cue prairiesand oak woodlandsin westernWashington. This studywas designedto answerfour researchquestions: 1) what is the current com position of prairies and oak woodlandson Foft Leu,is? 2) will prescdbedfires nraintainthe status ofprairie and oak woodland species?3) do spccies irequency.cover, and recruitment v?ry be tween spring and fall prescribedburns'l 4) does prescribcdfire reducefiequency and density of

invadingDouglasfir, Scot s broom,andotheralien species?

prairie to ensurethat the site had been invaded fecenllh ) ) S c , ' t. b r r N m r n d t h r l p r a i r i ( : p c c i c . were still presentin the stand.

Methods

Fire ellectson woody speciesweredetermincd using l0 x 20 m macroplotsin oak woodlands and broom thickets. Garry oak and Scot'sbroom were surveyedtogetheron the samc44macroplots placedalong a kilonreterof prairie-oakwoodland for vascularspeciesfolecotone.Nomenclature krws Hitchcock and Cronquist (l973). Voucher specimens arehousedby theLandConditionTrend AnalysisProgramon Fort Lewis.

Cornmun ty Compos t on We set prescdbedtires in fescuegrasslandsand oak woodlands,currently managedunderthe 3 5 yr fire rcgime, and in broom thicketswhere praiin removingScot's rie lires hadpaftiallysuccceded broom. We used the annual broadcastbum at Artillery Prairie as the t'irc treatmentin the catseur merd,'u. Fire effectson herhacenu..pe,.ie. $,crcevaluatedon altematelx l m microplots arrangedalong transectsthat varied in length de pending on community type. The butler zones betweenthe 1 mr microplots were used to separatc the prescribedfire ffeatments. The distribution of burned microplots in each community is shownin Tablc l.

TABLE L Di\lribution of bufned pkxs fi)f understor) spc cies in eachcommunit) exposedto di1lcrcntburn tfeatnenrs. Thesc plors also contrlbuted to ihe d . r a o n p r c c x i s t i n gc o m p o s i t i o ni n T r b l e 3 .

Coinmunity

Fife regine

Ork !voodlund

351r 35yr

Bum drrc Aug 9'1 Scp 9.i N{ar95

ll 17 Broorn !hickel

t9 ll

l-5 vf 1 t7

8

5 13

Fescucgrasslandcomposition was surveyed using 90 micreplotson tbur,10-60m fansects. arrangedas two pairs of parallel transects. The 90 cats-earmeadowmicroplotswereplacedalong one randomlylocated180m transect,200 m insidethe artillery impact i]Llea, asdictatedby salct] reshictions. Microplots tbrsampling herbaceous speciesin oak woodlandsandbroomthicketswere within:14l0 x 20 m locatedon 3- l5 m transects macloplots(seebelow). Thesetansectswereshort All oakwood becausestandswerecliscontinuous. land macroplotswere locatedwithin 5 m of tree maximumcffcct trunkstoensurctheymeasuredthe of ffee cover on the understory. Al1 macroplots in broom thickctswerelocatedwithin 5 m ofopen

Data on preexistingcomposition were gathered May August 1994 on all microplots shown in Table I, andpostfire datawere gatheredon the samemicroplotsMry-July 1995. No 1995data wgre gatheredin the cats-carmeadow. The site hasbeensubjectedto annualbroadcastbulns for many years.and we presumedthat conposition has been unchanged lbr yeus. We estimated weighted cover, becauselire often reducesthe thickness of the foliage without changing the canopyspreadofthe plants. Cover(C'. ascanopy coverage)wasestimatedto thc ncarcstI %. Foli5%,. agedensity(D) wasestimaledto the Dearest expressedas a decimal. Weightedcover (C) was calculatedas C= C'* D. Cover,height,and diameterat breastheight were recordedtbr all oaks and Douglas firs. After the linal inventory,species were classilled as fire increasers,flre basedon changes maintainers.or tlre decreasers. gainedat least l0 in tiequency.Fire incrcasers pcrcentagepoints in fiequencyfrom preburnfre quency,fire naintainerswerc \\"ithintl0 percentagepoints of prcbum lrequencl', andfue decreasers pointsin trequencytiom lost atleastl0 percentage We chosel0 percentuge prebtrmlrequenc5. point. so that specieswith fiequenciesup to 90'lc had latitudeto increaseon thc site,and specieswith frequcnciesaslow as l0%,hadlatitudeto decrease. ln eithercase.maintainerswerc not automatically favorcd by this choice.

F-ire Treatments We burned I m2 microplots in the grasslandson Wier andAnillery prairies,and l0 x 20 macroplots in the oak woodlandsand bloorn thickets.in September199.1and March 1995. The I m: microplotswere assignedrandomlyto thc firc trcalmcnls (Table l). Microplots not scheduled to be bumed were soakedwith water. Scratch Fort Lewis Fire

1,19

lines were placed around some of thc oak and broonl macroplotsbecauseofhigh luel loads. AII prescribedflres were set with l0 20'C ambient temperatures and20-507rrelativehunridity.Wind speedswere <5 km/h dudng all fires. exceptover the fescucgrasslandin March 1995when gusts reachedl0 km4r, causirr-Q fircs to escapeandburn 60 nicroplots, ratherthan the inlended30. Catsear meadownricroplotswere randomly placedin a single broadcastfife setby bombing in August 199.1.Fire weathcrtirr springfires waswell within the normal weatherpattemsfor prescribedfires.

Fall fires,hou,cver,weredelayedlaterthanplanned because sumner 199,1washot anddry for longer than normal. Prescriptionweatherandconditions werc nret a te\\"days atter light rain in early Sep tember.

All prairiernicroplotsbumedcompletely.Fires were patchy in the oak woodlands and broom thickets. Most ofthe unburnedareawas undcr a thick broom canopy,where grasscover was low andfuel moisturewashigh. Flameheightswere <l rn in prairie ard oak plots. <2 m in broom plots.

Tamn6rrr

rd< ^I Prd..'

ih6rl

of the platesreached246'to 343"(Table2). No platereached538'or 649o.

F u e lS a m p l i n g Samplesof the fucl lotrdswere collectedin May 1995fiom randomlyselectedunbumed andburned microplots createdfor the baselineconposition survey. Fuel sampleswere collectedfrom 12 nricroplots tbr each treatmentin each community. Becauseof the escapedfirc in the fescue grasslandin March 1995,however,unburnedprairie fuels were collectedtiom 12 microplots randomly placedin an adjacentunbumedarea. Fuels wele separatedinto live fine fuels (i.e., all live grassesandtbrbs).deadfine fuels.anddcadwood.

In the broom thickets. howevcr it u,as not feasible to separatedead fine fuels and dead wood becausebroom producedabundantbrittle twigs.

All fucl sampleswere oven-driedat l05oC for 48 hr in a tbrced-airoven,then weighed. Fuel loads are expresscdin kg,fta.

Experimental Desgn andStatistical Analysis The datafor preburn/postburn treatmentcompari sonsweregatheredin a riurdomizedcompleteblock ANOVA design;individualmicroplotsdefinedthe blocks. The data tbr fall/spring and unbumed/ burned treatmentcomparisonswere gatheredin a completely randonized design ANOVA. For all statisticalanalyses,the significancelevel was set at P = 0.05 befbre the researchbegan. Data reportedin the tablesas percentagcswere transformed by arcsinebetbre analysis.

tr 'ac

Peak firc temperatureswere measuredusing OMEGALAQ tempcrature-indicatingpaintsthat melt at 142",2,16",343",427', 538', and 649"C (Tablc 2). The rangeof paintswas stripedon 3 x l0cm alurninumplates.thentheplatcs$,ereplaced on thc ground in eachcommunityjust beforefires ucre \el. The rrnle ol lernperalure i . sc o n s i . tentuith low intensityfires. ln general.60-807r

TABLE 2. Percentol heai samplins pain!s bunrcd tl| dillereDl lire temperatLues b]' communit' type and llrc scason. Fire temperature\ nere measuredusing OMEGAI-AQ llrc scn\ilive paints on neral plrtes placed on the ground ir each co munilv bclint |he lires \rere set. No fifes reached518'C

Community

Season

Fe\cue grasshnd

PlJr('

1ll

)16

Spring Fall

t0 30

J

ll

Spring fall Spring Fall

,13 23 3'1 23 2/ l5 l0

ll

39

23 22 ll 33 t3

11 65 )9 6{J 11

'I -lns:4ur{ e 3,ll'

(L 121"

3 20

Ork woodland

Understort

Broom thicket

150

stnng Frll

TvetenandFonda

26 t6 30 l3 1 33

l0

538'

Results Preexistng Composit on The fcscuegrasslandon Wier Prairie was dominated by native prairie species,with thc excep tion ofhairy cats-ear,English plantain(P1dta.rso lanceolatd).and colonial bentgrass(Agl?-sll.! ie. li,rlhr doninanl\pe(ie\\\ cre lrrrrrrrr. Frequen. high on thc prairie. and total covcr was >807a l T a b l c3 r . U n . l e rt h cc u f f c n lJ - 5 1 r l i r e r , ' t r t i o n . the bunchgrassIdaho fescuc dominated. Hairy cats-earwas the mosl important prairie tbrb, but u i t h e u n . i J e r l b l sl e . sc o r e r . B , ' t hr p e c i c su e r e continuouslydistributedthroughoutthe sample area.Cryptogams,mtrinly the mossesRh4contitriutncancstett:an<lHlt trichumjrrttiptriturn. u c r c c o n l i n u o u . lt)l i : t r i b u l e di n t h e p r r r i r i ea-c countingfirr'-237ocover-.Oregonsunshine(r/io(Lt4tinuslepidus). ph,tLlumlutntum), prairiel]u.prne (Lirrl1.?..rrpcJlrs), k)ng-stoloned fi eldwood-rush sedge (Ccre-rpensylvanit:u),and English plan tain were nerrly continuouslydistributcdwith

frequenciesgrcaterthan807r,but allhad low covcr values (Table 3.). Hounds-tonguchawkweed (Hieraciun cynoglossoides)and westem witchgrass(Panicum octidenldl{, grew contrgiously.

Understorycover was <30cl in the oak woodlands. and most was accountedfor by alien species(Table3). Underthccurent 3 5 yr fire rctation. rhizomatousgraminoidsdominatedtheunderstory (Table3). The tbur most prominentspecies,Kentucky bluegrass.long-stolonedsedge.colonial bcntgrass,andred tescue(Festucarubra), arc thtzomatous. Thesefour speciesplus sttcklingclover (Trifoliwn dubiurz)andEnglish plantain had greater cover in the oak woodlandsthan in the t'escuegrasslands(Table3). Idaho t-escue.hairy cats-ear.and Oregonsunshine.the dorninantf'escue grasslandspecies.werc greatly reducedundcroaks(Table3). Exceptfi)r long-stolonedsedge, frequenciesof the specicsnamedabovediffered noticeably betwccn fescue grasslandsand oak woodlands. Many other prairie species,such as hounds-tongue hawkweed.prairie lupine,pine

IABLE 3. Pcrccnt frequenc) (F) and mcan percent cover (C) of prccxisting composition of itscuc grassland.oak woodhnd. cats-eafmeldo$. and broom thicket species with at lcast I '/. colef rn one of lhc communitjes. N A = Nati\'e or Alier species.

Species Fetnkat illuhn? sir HVothdeis ralicatr

N A N N

Eriophtllnn lunurunt

; P Idtit! tgo I tx l t' t oI tt.t C u f tr t e n s r l t a I i c a

N

hlnic kLo(itu'rel.

IIi(ftk iun t \noelossoiLl(s

Fcscuc srusslano C F

100 39.9 100 7.8 9 8 + 9,t 1.7 l.,l 9: E

9

+

ll 66

1.0 2.0

ll [

+ 1.]

Oak woodland F C

8 5l

+ +

+i

r.o

92 51

5.2 3.7

98 .19

10.0 l.l

; I'unk unl scribtrcnilnun

N N

Cals-eaf meadow F C

8 100 98

2 58 6 ll 98 58

F

C

+ 19.1 r.3

0

; Ll + + 2.6 2.0

,13 .ll 7l

+ r.l -1.0

57 9.8

An I hox0 tt ht1,t d r ^ 1tu unt

Cr,,"plogams Toial numbef of species Tolal vasculaf eoler Total cr,vptogrn co!er

Broom thickcl

100

)).6 52 6t . l 22.6

15

+ 15.I

100

9.,1 1,1 39.0

66 t00 .13

2.8 61.6 1.9 31 12.2

Fort Lewis Fire

151

lupine (Lultirtu.tulbicaulisl, and westernwitchgrass.were absenl. Few woody speciesgrew in theoakwoodlands,andcryptogamswerea minimal componentof the understory(Table 3).

The annual training-causedfires on the calsearmcadowhaveresultedin <50%totalplturtcover.

Most of the cats-earmcadow cover consisted0f alienspecies,butmany nativespccicswerepresent assubordinatemembersofthe community. Hairy crts-ear and sweet vemal grass(Anthoxanthum drlJldlrlrr) donlinated,andboth werecontinuously distributedin the community(Table3). Swcct vcrnal grass is an alien annual,absentin the fes cuegrasslands anduncomnronanywhereon Fort Lewis exceptArtillery Prairie. Severalnativc,but subordinategrrminoids, including red fescue, Scribnerwitchgrass(Ponituntscribnerianurn),tnd lleld wood-rushwcrc t'avoredby annualburning, asindicatedby high liequencies.They were contagiouslyto continuouslydistributedin the prai rie. Frequencyof most prairiespecieswas signilicantly lower in the cats-earnleadow than the lescuegrassland. and manyspecieswele absent.

Idlhn fe.cue\\a\ Inefel) il mrnur(onrprncntin thc cats-carmeado\i'.

Scot'sbroom invasiondecimatesnativeprairie cover,becausecanopycoveris so high. Scot's broom wasthe only continuouslydistributedspe c i c r i n t h c r ct h i c l e t :r T r h l e. tt . \ l l n u t i \ e p r i l i r i e specieswere significantly reducedor absent in thebrc(nnthickets.Exceptfirr Iong-stoloned sedge, all other understory specieswere alien grasses andforbs (Table3). Colonirl bentgrass.

Kentucky

bluc-trass.andJong-stoloned sedgewerethedominant graminoids; wall bedstraw (Cali,nr parisiense), an alicn annual. \'"'asthe domlnant tirrb. All had inordinately low cover. Many bare areasexistedin thc thickets,becauseofthe dense broom canopy.

Prescribed Firein Fescue Grassland grassland (Table Six speciespromincntin thet'escue 3) were fire maintainers(Table4). Idaho f'escue. hairy cats-ea1and Oregon sunshine. the three most inrpoftantspecies,andthecrlptogamslraintainedhigh frequencyin bothtnll andspringbums.

Cryptogarncover increasedsignificantly in both burns,whercascover firr Idaho fescueand hairy catseardecreased significantly(Thble.1).Although both burn teatments significantly reduccdthe cover tl1 thc dominantfescue,no plantswere Lilled.

Conversely,hairy cats-earindividualswerekilled.

The hi-lh frequency tind cover values (Table 4) are accountedfor by densepostlire seedgennination and gro${h. Field wood-rushand prairie lupine were classificd as decreasersin response to the springfue only. Afterbolh Ieatments.cover for field wood-rushincreasedasaresrLltofa flush ofpost-firegrowth. Nearlyall prairielupineplants were killed by thc fires, so that the posttlre val ues shown in Tablc 4 were contrjbutedby recent germinants. Subordinatespeciesin the fescue grassland,but unlistcd in Tables3 or:1, were not afiected by fire. They maintaincd their preflre status,regardlcssof fire season.Canas, despite lo*' meancover,is in this category.

TADLE'1. Percentfiequenc) .rndmeanlerce n! co|er of fescucgrasslandspccieswith rt le st 19.co\'erin o ne ol the trcatncnrs. in responseio irll lLnd sprine trescfibed burns. Speci!'\ co\cr \lrlucs $ilh unlike superscfiptsbe$'een prc and postbum. by itrtl or sprimgbum, are significantlt, different. Sjnrilarly. co\cr !alucs l.rckiDgsupefscfiptsare nor sig n i i i c a n t l yd i i l i r c n l . \ A = N r t i v e o r A l i e Ds p e c i e s .

Spccic\

N A

Frequ!!!!

Fallbum Sorinelburl Pre Po\i Pre Post

fall burn Prc Post

Srrllretulll Pre Post

Xlainfaincrs CDpt08.1lns r'?tnka kldlt).ttsis H,,t\\lnei\ nli( tltu Lrioph\llut la dtunj P a t t u u Dol t t i d . t n l i s H k' ru nl'n | |nosl o \ soidcs

100 r00 N 100 r00 A 100 100 \ 9 3 9 7 \ 7 3 6 1 \ 1 0 1 0 N N

l52

Tvctcnand Fonda

100 87

100 91

r00 100 100 9l 10 63

100 15.1. 37.5b .10.8. I l.7b r00 :1.5' r00 L9" 95 L8 1..1 65 0.9 0.6 5IJ 2.1 3.1 I)ecreasers in spring burn 98 80 0.6.

1.1' 95 78 1.3.

0..t

2r.5. 26.,{' 39..1" 1.1, t ./

9.1h 5.',71 t.2

1.0 Llt

o.rJ 2.0

0.'1, 1.5,

0.7b 0.3b

TABLE 5. Percentfiequ erc] and mern percentcover of oak \r oodland species$ ith trt least l7 cover in one of the rferLtme nts. in rc sponscb lllll and spring prc\cribcd bur. s. Spccic\ co\cr \alucs t!ilh unlikc supcr\cripl\ bclwccn prc mdposlburn treatnenls. by tall or spring burrr. are \ignificanrly differenr. Sinlilarlt, colef \.'alueshcking superscriptsare not s i g n i f i c r n t l !d i f i e r e n t .N A = N a t n e o r A l i e n s p e c i e s .

N A

Specics

Frcducncv Fallburn Springburn Prc Post P.e Post 9l

Httottu.ris

:ld

ftklittltd

Pldtttulgo lanceolLttd

N

Cdt(r pttt\\'lrankr

r00 58

l9 )1 )l

1) 21 l0

88

100 5ri

P r e s c r i b e dF i r e i n O a k W o o d a n d s Fivc ofthe six naintainersin oak woodlandsu,ere aliens(Table5). Two understolyspeciesin thc oak woodlandsrespondedappreciablyto fire, but only in telms of changesin frequency. Colonial bentgrasswasa decreascrin thc sprin-qbum treatm c n l .w h e r c a . l o n g . t n l o n c d. < d g eu r . u n i n crerserin the fallburn treatment(Tablc5). Kcntucky bluegrass.in the fall burn treatment.was the only specieswith a significantchange(decrease)in coverfbr eithertreatment.

Prescr bed Fire in Broom Thickets The trll ti re burnedsignificantlymoreofthe stand, causedsigniticantlygrertermoftality,andresulted of broom plants in signiticantlylessresproutin-e than the spring firc (Tablc 6). The fall fire resulted in significantly less density and cover of mature broom plants. had no signillcant eflect on seedlingdensity(Table6), and significantly rcducedpostfuecoverofsmall broornplants(Table 7). The patchyspringfire significantlyreduced postfireseedlingdensity,but had no other signiticant etl'ects(Tablc 6). Wc classificd Scot s broon in the understoryas a decreasel,although postfire frequency was merely tbur percentage pointslessthanprefireliequency(Table7). When all datatiom Tables6 and 7 irre viewecltogether, Scot'sbroom prominenceon the site decreased becauseof 1lre.

Fall bu Prc Post

\laintaincrs 90 9.7" 55 1.9 72 o.iJ 6l 66 0.5 38 15 0.9 38 0.1 Increaserin fall burn 100 6.,1 90 Dccftascrin springburn 76 59 3.1 r00 59

6.0" l.l

;;

Spriig burn Prc Post

ri.: r.2 0.ll u.8 l.,l 0..1

6.1 0.6 1.0 1.0 1.1 0.,1 1.1

1.9

9.0

1.1

TABLE 6. Efiects of Sep 9,1 and M.r 95 bums on Scot s broo r. Poslfirc dala $crc gathcredin Ma] 95 , ' f h , ' r hl . Un . . \ i , h i $ | | u | l l r \ e{ r t e f . , I t r ' (a b) arc signjicanlly dilicrcnt bcr\!ccn ilrll and sprins burns. Valueswith unlike subscfipts(c-d) r f e s i g n i f i c a n l l y r l i f f e f e n t b e t w e e np r e a n d pollburns. by fall orspring burns. Similarl!. vrl ucs lacking supcbcripts.rrerot signilicanll,r-dif-

Categor!

Fallburn Pre Po\t

Stem deNity per ln Co\cr (t; ) S e e d l i n gd e n s i t i ( p e rJ n r ) N4ortalrry(%) B a s r l s p r c u t i n g( t ; )

90.

52.9. 11..1, 5 8 . 1 2,1.8. 3.5" 1 3 . 8 E.r 5.9 6.-1.

87.0" 1.8"

Spn!]gbllL Pre Po\t

7li, 51.0 1:.0 3.0,, 30.8'

Cryptogamsalso were decreasers, losing 30 percentagepoints of prefire frequency. Exccpt tirr the maintainerKentuckybluegrass. all other unde$tory speciesin the broom thickcls wcre increaserswith fall lire (Table7). Five ofthe six increaserspecieswere aliens.and all occupied iueasthathadbeenbareundcrthc completebroonr canopybeforethe fire. Otherspeciesin the bloom thickets,unlistedinTablc7, maintaincdtheir status with the fill burn treatment.

FireEtfects on Trees Fire drarnaticrlly affectedoak stems<l m tall or <2 cm dbh. The fall tires top-killedmore oaks Fo|t Leu is Fire

l-53

TABLE 7. Percent frequcnc) .rnd mean pcrccrt covef of hroom thickel specicswith |t leasr 1% cover. in responselo a Sep 9'1 prescnbcd bufn. Specic\ coler values rith unlike superscriplsbetween p r c a n d p o s t b u r na r c s i g n i f i c a n r l i d i l i c r e n t .

S r | .i a r l ) . . r , r . \ : , e . l J . l r . l r . r . f e 1 . r i p r . ( noi signilicaDdydifferent. N'-,{ = \lrive or Alien specte!.

Species

Freqlgllr Pre Post

N lA

\{aintainer ,11 2.0 Incrcasers i9 93 < 0 .t " 8| 1 0 0 1.8 5l 9l 1.2 ,t-1 56 2.1 l iI 93 t.l .1.1 6,+ 0.6 Decreascft 56 16 2.0 100 96 62.8' ,{,1

Tcesddlkt udi(u lis

(itre\ rn\\l., a in fl\pe ricLtn te tlorun! nt I'k"xaio ltl).eolukt

Cover Prc Post

N

CNptogams

L.1 1.5b 5.2 1.5 1.0 1.9

0.5

and fronr 21.3 to 10.6stems/hafor saplings<2 cm dlameter.No Douglas-firs>3 m tall or >5 cm dianrcterwere killed by fire.

Flre Effects on Fuels Comparedto the unburned condition. both fall and spring fires signilicantJyreducedtotal fuel loading(Table9). Fuel loadingswereloweslin f'escuegrasslandsand highcst in oak woodlands.

There was no significant ditlerencein luels after fall and spring fires il fescue grasslands. Fall and spring fires significantly reducedtotal fuels in the oak woodlands,rnainlyby reducingdead tine fuels. Fall tires in the broom thicketssignifi cantly reducedtotal fuels. but spring t-rresfailed to canJ throu-qhbroom thickets.

TABLE 9. Fire cllccts (m total iircl loading (kg/ha) in fescue grarsland.oakwoodland.ard broornrhicker.

Both fall and sping burns signiiic.rntl) reduccd r h et , . t r l U c .I . : , L l n t, r rr - . 1 . . n r . r r i t ) . . . , m paredto the unburnedcondjrion.

Llnburned

TABLE 8. I{cight and diamctcr classesof Carr! oaks topkllled b] i! 1and spri g prescribedfire\.

Fall Pfefirc Nunber density lop killecl

Splrg Prciire Numbcr densir)- top-killed

3,+

82.5 5.',7 3.9 1.1

S t e md i a c t e r ( c n )

<l 5 10

85.9 3..1 .{.1 5.6

11.1 t..1 0.7 tJ.l 0 '/6.) u,l 0

5,1.8 6.1 1.1 8.0 E.0

.1.1.5 1.6 0.2 0 0

60.n 1.1 3.8 5.,1

35.7 0.2 u 0

thiinthespringttresin thcseheighrdiamcterclasses (Table 8). Oak mortality tiom fire was Lrivial.

Of the pref-rledensitiesshown in Table 8, only three<l m tall sproutclunrps,with 5-10 stems each.andtu'o of the 5- l0 cm dbh trceswerekilled by fire. Otherwise.rll top killcd stemsresprouted.

Taller and larger diamcter ffees werc unalfected by fire.

Spring fire sigrificantly reducedDouglas-fir. liom 13.9to ,1.5stems/hafor saplings<l m tali.

154

t7[2 369.1 2ll0:1

t-) :3,15 1847

0 1929

Discussion

Srcrnheight(m) l-2 2 i

Fescuegrassl,lnd Oak woodland tsroon thicket

Sprine

Tretcn andFonda

A11tlres in this study favorcd prairies and oak u'oodlandsby killing invading Scot's broon and Dou-qlas-trr(Tablcs4-7). Prairie speciesare fire endurers,so that prescribedlires did not damage the lescuegrassland,regardlessof fire season (Tables3. ,1). The presentspeciescomposition in the fcscuegrasslandhas beenmaintainedusing prescribedfires for 20 yr Prescribedfires temporarily reducedIdaho fescuecover,had no signitlcant effect on frequency,and did not rem o r e l J a h ul e . c u ea s t h ed o m i n a npr r a i r i e. p c cies.Prescribedfires causedno significantchanges to most native or alien subordinates.nor to com munity cornposition.Furthennorc,prescdbedfi res maintainedopen Garry oak standsby k)p-killing Gary oak saplingsandseedlings,rcducingScot s broom cover.and killing youngDouglas-firs.

Fire regimesshorteror longer than the 3-5 vr o n F o r rL e u i s h a i c h e e n. h o u n i t , lirer.,trrr,'n be deleteriousto prafies andoakwoodlands(Table 3). Excessive burninghalmsmostnativcprairie

bumrng specics.Fifty yearsof annualbroadcast changed1000-1200ha ofArtillery Prairie tiom a communitydominatedby pcrcnnialbunchgrasses to onedonrinatedbyalienforbsandannualgrasses (1hble3). Comparedto thefcscuegrassland, native plantcoverwassi-tnificantly lower.andcommunity compositionwas dramaticallyaltercd. The displacenentof Idaho tescueas the dominant 'pecie' unJ Ihe frc\en(e of nnnl rlien .pecie: indicatedthatthenativeprairiccommunityis not adaptedto prolongedannualburning. Annual burning,however.hasmaintaincdgraminoid and forb dominanceb1'climinating Scot s broom and

by Douglas-fir. restdctinginvasion/establishInent Comparedto excessiveburning,hou'evcr,fire exclusionaffectsamuchgreaterarcaon Forl Lewis.

Fire exclusionhas allowed Scot's broom and Douglas fir to invadeprairicsand oak woodlands (Figure 1). Closedstandsof Scot'sbroom and D , ' u g l l . - f i rc l i m i n u t en e r r l l r l l n l t r r e p r r i r i e species:closedcanopieswithin Douglas-firfbrestseliminateboth prairie andoak woodlandspecies.

Mo.l pre'Crihedliru prt'Brctn.stri\( to promote grasslandand savannahstructuresby limiting the stemdensityof woody species.In general,prairiefircs initially reducegraminoidcover (Nimir andPayne1978.Antoset al. 1986)or bio mass (Ewing and Engle 1988).promoterapid herbaceouspostfire growth (Antos et al. 1986). and have positive effects (rr no efl'ect) on frequency of thc native prairie species(Anderson and Bailey 1980.Whitc 1983.wilson and Shay l990). The prairieson Fort Lewis respondcd exactlyin this nanner to prescribedfires.

Prescribedfir'eson Fofi Lewis resultedin top kill and tdggeredresproutingfor small Gary oak individuals.but causedDodamageto maturetrccs.

Theseresponses to flre irc colnmonin manyoaks.

Someof the well known oak speciesthat endure fire by resprouting are blue oak (QuercLts tlouglasii).scruboak (Q. dtonout).and interior live oak (Q. l.'is1i:r:rii) in Califbrnia (Allcn-Diaz rnd Bartolome1992.Keeley1992):Gambeloak (Q. gcnrbelii) in Arlzona(Harrington1985);mynlc oak(Q. wrtifoliu), sandJivcoak (Q. gemindte). turkey oak (8. laeris). blueiack oak (Q. incana\, and sand post tt'tk (Q. nurgarettu) in Florida (Guerin1993,Glitzcnsteinet al. 1995);.jack oak (Q. ellipsoidalis)and bur oak (Q. moc:rocarpa\ in Minresota(white l9ll3); and white oak (Q.

a/ba).blrck ork (Q. wlutina)- and chestnutoak (Q. prizris)in New Jersey(Boernerl98l ).

Sornefire efl'cctson Fot Lewis differed from resultsobservedelsewhere.Fires were followed by higher tbrb covcr in Califomia prairies and oak woodlands(Heady 1972,Sugiharaand Reed 1987),Montanaprairies(Antoset al. 1986).and (Whitc 1983),but not Minnesotaoak savannas in corrcspondingcommunitieson Fort Lewis.

Likewise. cryptogam cover was lower after fire compared in Montanaprairies(Antoset rl. 19136), to higher cryptogam cover after fires in fescue grassland.

Our researchindicatesthat fire is essentialin rnaintainingprairie and oak woodland conrmunitiesin westernWashingbn. Early explorersand . c l l l c r \n o t c da h i g hi n c i d e n coel l l r e , ' nf r r r i r i e .

(Lang 1961,Norton1979,Boyd 1986),andprairie coveredmore areain the mid- 1lJ00sthan currently (Figure 2). Excluding fires sincethe early 1900shasallowed Douglas fir to invadeprairies trndoakwoodlands,suggesting thatfireoncehelpcd maintainthe more opencommunities(Figures l, 2). The situationat Fofi Lewis is identicalto thc Mima Mound prairie.r,here Douglas fir invasion haschangedprairie speciesadaptedto xeric, lo$' fefiility soils to fbrest specicsadaptedto mesic, moref'er-tilesoils (del Moral andDeardorff 1976).

At lca.t oneoI the contributor\to bellernulrienl inventoryis Scot'sbrrxrm.aknown nitrogen fixer (Usseryand ltannitz l998).

On Fort Lewis, only tiequently burned arcas havecontinuedto suppofilargepraides and open oak woodlands (Tables3-5). The current prescribed burning program. howevcr. must be expandedto reverseprairielossto Scot'sbrcom and Douglas-lir. This study has shown that tall tires killed more Scot s broom and Douglas-fir than spring fires, but fall lires had nearly the samc beneficialeffects(e.g..reducingfuels. maintain ing spccies)as spring lires on prairies and oak woodlands. A program basedon fall fircs could help remove Scot'sbroonl and Douglas fir from heavilyinvadcdsites.The exacttiming of firein broom thickets determineshow successfullythe program will work. Although Scot's broom resprouts,stemsof all diametersresproutless successfullyaf'tcr mid-summer cutting (Ussery and Krannitz 1998). On thc other hand. broom seedsmaturein rnid-summer(Usseryand Krannilz l g q R r .* ' r h J lp o s l l i r cg e r m i n a l i o inn r e s p u n . e

Fofi Lewis Fire

155

to a late summel or early-fall fire could repopulatethe sitewith broom seedlings.Using a model fbrest,van of hre il Calitbrnia mixed-conit-er Wagtendonk( 1983)showedthat morethan one prescribedlire cycle is likely to be required to restorethe balanccd firc rcgimc. We anticipate thatmultiple fires will be necessary on Fon Lewis.

Already.secondfiresareneededto kill densebroom leproduction betbre seedcrops can be produced in the secondpostfire growing season. A strat egy ofaggrcssivcmcchanicalor chemicalremoval of Scot'sbroom, Douglas-fir.and other promincnt invadcrsshouldsupplementprescribedbum ing to help restorepraifies and oak woodlandsto theopcn.historicalcondition.Giventhenumber ofalien specieson the prairies(Tables3 6). many of which havc bccn aroundfor decades(Jones

1936),snpplemental seedingandplantingofnative speciesmay be needed. Once the balancedcondition ofnative prairie specieshasbeenachieved, both f'all and spring prescribcdfircs should ef'tectivelymaintainthesecommunities.

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156

Tveten and Fonda

Acknowledgements It is a pleasureto thank Fort Lewis lbr funding this research(WAFO 081094). We are indebted to Joe Reasoner.John McGuire. Charlie Askins, Lori Bclangcr, andIngcrSchmidtforhclpingwith various aspectsof the prescribed fires. Teresa HansenandBrandy Riche providedthe basicfigures t'rom which Figure 2 was constructed by JeannieGilben. David L. Petersonand an anony mous reviewerprovideduseful criticism that inprovedthe manuscript.

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