v75 p219 Thysell and Carey

ResearchStatof, U.S ForestService,3625
DavidR.Thyselland Andrew8. Carey,iPacf c Northwest
93rdAvenue
S.W O ymp a Washngton985129193
QuercusgarryanaCommunitiesin the PugetTrough,Washington
Abstract
Among thc legacics of the Vashon Glaciation are Oregon white oak (Quercus gijn\dnd). prairie, wetland. and Douglas-fir
(P\eulo^ugu n.tl.iesii) comnNnities rrayed in a mosaic in the Puget Sound ,Area(PSA). N1uchof this mosaic has been destroyed.The largestremaining portion is on FoIt Lewis Military Reser\ation.\\'e examined oak communities on FoIt Lewis to
assessencroachmentb! exotic plantsand b) Douglas-fir. to determineamountsof fegenerationof oak and othef tree species.and
1()comparcoak communiit diversit,v!lifi that ofnearb) Douglas-fir forestsand glacialtillpmides. For the 221aryestcommunitics. $c dclcrmincd dcnsiticsoftrees. djstribuiiorrsoftree diametersand heights.amountsof regenefationfor each tree species.
e\idcncc of ciogcnou\ di\turbanccs.and covers of \ascular understo4 species.For siudy sites.we calculatedbasalareasoftree
\pccics. richncssand dilcrsity of \ascular plants.and percentagesof speciesthal \\ ere eriotic.$'e consnxcted specie\accumula!ion curvesforoak comrrun ities. llougla\-fir forests.and pfairies.\\t peI{ormedBfa)-Cunis and weighteda!efaging ordinations
for 176sampling plots from lhe 22 sites.Oak communilies were tlpically nore diversethan eitherDouglas fir lbr€stsor prairies
and $ere transitionalin speciesconposition belween them.Holrever, oak conmunities containednunerous exotics.particularly
Scot's broom (a)liflrr r.o/drirr) and colonial bentgrass(Asr.,r/ir ..rpillrir"i.1).}losl oak conxnunilies conuincd large diameter
Douglas-firs and other tfee speciesand appearedro be trunsfbrmirg to coniier or coniier/mixed hardwood loresls.With succes
sion, exotic specie\ becomelessprevaleni,butthe exlent and abundanceofoaks is diminished.Nlairlenrnce ofoak communities,
in oak stands,removal ofDouglas-iir, developmentofreplaceand the PSA naturalmoiaic. ma,vrequiretree-densit)manageDrent
nrcnt oak sites.prescribedburning. and mechanicalsuppressionofexoiics before burning.
lntroduction
Thc PugetSoundArea(PSA) of Washingtoncon
tains much of the human population of the state
as well as land fomrs and plant associationsnot
found in adjrcent fbrestedregions(Franklin and
Dymess1973.l(uckeberg l99l). The nearsealevelelevationof thePugetTrough,PugetSound
itsclf, and the sunoundingmountainrangesprovide PSAwith a wam andrelatively dry climate.
The VashonGlaciationshapedthc soilsandphysiogrrphl of PSA.Ketllelake5andpond..morajnes.
gravellyout$ash plainsand tcrraccs,and welldruinedsoilsrangingtrom cobblesto sandyloams.
r l o n s u i t h r i r e r : o r i g i n a t i n gi n t h e m o u n t a i n s .
provided a diversity of habitatswithin the landscape(Leighton19J8,Kruckcberg1991).
The PSA haslong bcen inhabitedby people.
lndigenous people shapedvegetationby setting
tlres to maintain grasslandsdominatedby ldaho
f e . c t t er l r - . i r . rt , i J a h o t n i \ t J n d( u n l u i n i n gu \ e Corcspo.dcncc to: Andre\\, B. Carey. Pacific Nofth\\'est
RcscarchStation. LJSDAForestSen ice..1625- 93rd A\enue
S . W . O l y m p i a ,\ \ l A 9 8 5 i ] - 9 1 9 3 ; T e l . : 3 d 1 7 5 3 ' 1 6 8 8 :F a x :
3 6 0 - 9 5 6 - 1 3 ' 1 6arc a r e v @. f\ . f e d . u s
ful fbod plants.includingsmallcamas(Camcssia
qranrash)(Norton1979,Agee 1996;Tvetenand
Fonda119991providea recentreview).Fire, mild
climate, and diversephysiographyled to diverse
plantassociations
includingkettlewetlandcommunities.riparianhardwoodforests,Douglas-fi
r
(Pseudotstrgttmenzierii) westemhemlock(?srga
heterop hyIIa) -w estemrc dcedar(Thui u p I iet o) old
grcwth lbrests, Douglas-fir fire-climax forests,
Idahofescueprairies,ponderosapine (Plrls pon
derosc) savannasand tbrests,Oregon white oak
(.Que
rcusgarryana) savannas,
woodlands,fbrests.
and ecotones.including wetland oak grassland,
wetland-oak-tir,
riparianhardwood-oak-grassland,
a n dg r a s . l a n d - o a l - fTi rh. e . eb i o t i Lc u r n m u n i t i e s
and their ecotonescomprisedthe PSA lowland
ecosystem-a dynamic,shiftingmosaicof diverse
plant communitiesmaintainedby indigenous
people.
Soon after Europeansettlementin the 1850s,
gr;zing animals.especiallysheep,wereintroduced
to PSA prairiesand, certainly.exotic plantswere
inlroducedandbecamenaturalized(Meany l9l8).
Usurpationof most land by white settlerseliminatedtheindigenes'bumingandwildfire. allowing
North$,estScience,Vol.75. No. 3. 2001
ol0(ll br-rh.Nrnherrs.i.
,l,.Aso.,if
or ,^llrigh6r.irrv.d
219
Douglas fir to encroachboth on prairiesand oak
comInunities(Leighton1918.Ituckcberg 1991,
Ryan and Carey 1995b,Agee 1996).Develop
mentoltlansporlation networks,agriculture.and
scttlementsconcentratedinthe lowlandsandcontinues to destroyprairies,wetlands,sayannas.
woodlands,and forests(McGinniset al. 1997).
Prairieswereinvadedby exoticgrasscs(e.g.,colonial bentgrass,Agt'o.tti.\capilLaris)and Scot's
broom (Cltl.!r.! scopariLts).
Scot'sbroom also
invadedmanyoak dominatcdsites.Wetlandswere
invadedbycxotic speciessuchasreedcanarygrass
(Phaleris arundinacr.?).Numerousexotic plants
now compete u'ith indigenous. espccially rare,
plants(ThomasandCarey1996.ThysellandCarey
2000).Although Oregonwhite oak extendsnorth
to the islands of Puget Sound and southeastern
VancouverIslrnd (Stein 1990),relarivelyintact
oakcommunitiesexistprimarilyon areasprotected
tiom humandevelopment,particularlyon thc Foft
Lewis Military Rescrvation.At risk of loss wirh
the destructionof oaks. prairics,and lowland
wetlands are the western gray squirel (S'cfurar
g/lsE&srlistedbytheStateof WashingtenasThreatenedanda FedcralSpeciesofConcem (Ryanand
Carey 1995n,BayrakEiet al.2001);the western
pocket gopher (.Thonomysnnz.atna),a Federal
SpeciesofConcern (RyanandCarey 1995b);and
severalspeciesofbirds, reptiles.amphibians,and
butterfliesincluding the FcderalCandidateSpe
cies, mardon skipper (PoliteJ mardon), and lhe
FederalSpeciesol Concenr,valley silverspot
(Spel:eriaTerenebrcrirrerli) (T.Thomas.U.S.Fish
andWildlife Service.personalcommunication),
as well as severill plant species,including
Columbian whitetop aster(Seriorcaryusrigidus
lAster cu rtusl), longhair sedge(Carex contosa),
greenfruit sedge(Crirex irterruptal. smallflower
wakerobin (Trillium pawiflorurz) (Thomas and
Carey 1996. WashingtonNatural Heritage Pro
gram 1997), Torrey s pea (Lathrrus toue,\-i),a
Federal Speciesof Conccm. and golden Indian
paintbrush(Casrillr7rlelisectur),a FcderalThreatenedSpecics(T.Thomas.U.S.Fish andWildlifc
Service,personalcommunication).Thus,the citi
zenso1Washingtonare in dangerof losing a signitlcant part oftheir naturalhcritage(Larsonand
Morgan 1998),the lcgaciesof the VashonGlaclatlon.
Our objectivesin this paper are to assessthe
status,condition. and trend olthe oak dominated
vegetationassociationson Fort Le*,is by: ( | ) de220
ThysellandCarey
temining total area and number of sites occupied by oak dominatedvegetation.(2) charactcrizing overstory and understoryvascularvegeta
tion, including cxtentofoak regeneration.degree
of invasionby exoticplantspecies,and impacts
of Douglas-1irencroachmcnt,(3) cornparingoak
community diversitl' to that of prairies and
Douglas-tir fbrests two donlinant types on the
Fofl Lcwis landscape,(:l) detennining the landscapecontext of. or the nature of the two biotic
communitiesadjacentto, the 20 or so largestoak
communities.and (5) developinga conceptual
model of the prevailing influenceson oaks and
associatcdvegetationin PSA. Finally, we discuss
the implications of our findings for management
anq consetvauo[.
Methods
Study Area
Fort Lewis Military Reservationis in Pierceand
Thurston counties in the southernPugetTrough
ofWashington(Flanklin and Dyrness1973).Thc
areais nearthe southemlimit of the PugetLobe
ofthe VashonStadeofthe continentalglacierthat
retreated13,000-15,000years ago (Kmckeberg
1991).Relief is moderatcto rdling, elevation
rangesfiom 120 to 160 m, and annualprecipitation is 800-900nrm with onlv l0-157oofannual
precipitationfalling during the peak growing
(Pringle 1990).Bemonthsof June-September
neathoaksaredeep,coarse-textured.
well drained
soilsof the SpanawayNisquallyassociation
de
rived frorr glacial till and glacial outwashdepos
ited during thc retreatof the continentalglacier
Becauseol thc int'luenceof the VashonGlaciation. FofiLewis is characterized
by alack ofsharp
relief and by an absenceof markedly divergcnt
soil types(Zulauf 1979,Pringle 1990,Kruckeberg
1991).
Of 34,:100
ha within FoIt Lewis. 1.200-1,400
ha (3-,+%)in 573 sitesaredefinedasOrcgonwhite
oak woodlands(seeRyanand Carey 1995a:206
fbr a map). Some sitesare inaccessible(in artilleryimpactareas)andsomcmappedsitesno longcr
havcoaks.Msits to 333 accessible
sitesrevealed
that 85 siteshad <5 oak treeson areas<0.1 ha or
were within developedareas (Ryan and Carcy
199512).
The remaining siteswere 0.2-4,1ha and
usuallycontainedmixturesoftree species oak.
Douglas-fir,Oregonash(.Fnainuslat(il ia),bigleal
TABLE L Chafacteristics(01 SE. , = 8 plots) oi:2 Oregon rhite oak (pu?\:ur gat\-ana) ca]mtllunjtics,Fort Leu is. Washing
ton. 1999.
Sitc
No.
Slope
22
l8
1,1
8l
92
t71
183
lt5
213
265
t93
3t.l
tl5
Basal area"
PSNTE
(mr/ha)
\{odal
aspcct
QC;A
(m:/ha)
02
010
sw
sE
2 11 5
2,{t5
0-15
03
0 ,{2
0-8
01,1
03
0 l0
010
0-22
8 :0
ltuied
flat
NW
lla!
E
flat
varied
flar
S
sE
2l + l
812
1i:l3
ll1l
1711
1!l
913
161l
l:l 1'1
ll1:
1216
1 31 l
812
1lr,l
11 1
12l6
0r0
0
913
511
8l I
9r3
0-13
laried
2\ !2
Ir3
l:])
3,13 012 \'aried 10t,1
S
l51l
l-18 312
161 5
SE
167 0-22
399
0
515 0 10
528 0 .10
530
0
5.11 05
0
550
flat
flal
\'aried
flat
llar
ilat
61 2
Il t l
17t l
11 |
llt2
t] t1
QUGA
no./ha)
QLIGA
dbh (cm)f
395i75
3 2 0 16 7
3 5 5t l 1 3
11012'1
260119
r 5 0 13 8
225!69
250:t,tl
235!lr2
3 3 5r 3 3
2 7 0r 8 . 1
l55r2l
.1012
. 1 11 2
371,t
l:t,l
3l12
12:r,t
,t0tl
2 2! 2
32tl
3112
3 11 , t
t5r2
Q. I (Frla. Prar)
Q. P. (Frla)
Q.P
P,Q
Q, (Psnrc)
230138
,+213
Q, (Psne. Acna.
Frla)
Q, P. Pra\. (Frla)
.113 1E5189 15t6
l,lt5 .125tlll 3012
1615 1801,19 .10:!,t
3t2
512
9tl
l0t3
5:13
2! r
Understory'
No. Exotics
Nlajor (minor)
overstory Species' spccics (%)
1 , 1 0 1 . 1 52 6 1 1
1001:18 331,1
3101'11 3212
105137 1611
295158 1913
. r 5 0 16 5
3 11 l
P.Q
Q. (P\ne. Frla)
a
P Q
Q.P
Q. P (Acma)
Q. I Frla.
Q.P
Q. P (Acma,
Frla, Pra\ )
Q.P
Q.P
Q,P
P,Q
Q.P
Q. (P,in,e)
813
1211
t3t5
3115
Adjonring
15tl
2 3 1 3 1 9t . r
22!2 3 t i 5
161l
1 9 1 1 ,ltl
WL. DF/RD
PR. DFA4F)
RD/SH, DF/MF
WL. DF/SH
RD/SH, RT/SH
PR/SH. DF
WL. SV
I)1,.DFA,IX)
WL, SH
DF MX
PR/RD. DF
P R .W L
l,lt2
1616
PR,/SH.WL
1 9+ ) 2 9 . t 1
1611 19r5
15rr 813
PR, DF,IIX
PR, DF/MF
PR. WL
l8tl
21!2
tM
2 2! 2
1 9 1I
1,{lr
DF. DF
PR, DF
PR. DF/I,IF
PR. DF
PR. DF/MF
PR. DF
l 2t
lt t
r81
1',7
!2
1 l i1 2
12!6
5515
26!,t
2t!3
2 . 6! 1
27+1
2317
3615
'Includcs only
0. gdr./tdr.r (QUC;A) and Prerl.i.,trr3d ,1o1./'r,i (PSVE) >10 cn dbh
'Bas.d on the 2 lugesl (liancter oak tfees per plo!. 8 plots per site.
'ln order of doninancei tree speciescodcs: majot species.Q = Q gatra d,P = P m(t.i.rii; minor species.Acna = A.r.r
ittctoph,-llu"t, Fna = Frcritut\ lutit) Iid, Pfti\ = Prunus driuin. Psne = P m(,t.ielii
r\iscular phnt specicsnchnesvpkn. 8 plots pcr ritel exotic specicsas a percentageof |oul vascularplant speciesrichncss.
.Adjoining hndscape features:DF = Douglas-fir fofest: PR = prairie; MF = mixed oak and Douglas-lir lbreni RD = roadr RT =
rjdee toD:WL = wetland SH = shJubland;MX = niredt SV = oak or mixed salanna.
maple (A<:ernttcrophtllun). and others(Tables
I and 2). Other plants frequentlytirund with Oregon white oaks includc common snowbef)'
(Slmphori<:.trpos dlbirs).Indian plum (Oemlerlc
t erasilb nnis) , P acifrc poison oak (To.ricodendron
di versil obum), y anpth (Perideridia gttinlneri).
sanicles(Saricirlaspp.).tnd snowqueen(S-vtth-r'ds
reneJormis)(Stein 1990,Ryan and Carey 19950,
ttrisstudy).Otrkswerecommonlyecotonal wherc
tbrcsts,prairies.or wetlandstransitionto another
community type and often found at breaks in
the terrain, such as the bottom or tops of hills
(Table 1, Ryan and Carey 1995a,0).The lbrmer
extentofoakson Fort Lewis is unknown,butour
observationsol deadoaksunder Douglas-tir and
distantfrom remainingliving oaks.suggestoaks
were more widespreadin the past. Analysis of
Iand survey notesfroln 1853 suggestsa marked
declinein areacoveredby oakssincethen(Tveten
andFonda1999).
F l e l dS a m p l i n g
Basedon previousvisits to 333 siteswith oaks
(Ryan and Caley 1995a),we identified sitesthat
were cither large enough to be consideredoak
communities(i.e.,>8.0ha,dominaledor co dominatcd by oaks), as opposedto prairie or conifer
comrnunitieswith a few happenstanceoaks. or
>,1.8ha and that had llnctioned historically as
Quertus gttrr.r'arnin Washington 221
T A B L E 2 . D e n s r t ia n d p r e ! . r l e n c e osf e c d l i n g s a r ds a p l i n g s
olmator trec spcciesand ofstens >10 cn dbh of
ninor speciesfound in 22 oak comnumries on
Fo Lewis Washingron.1999.
\ ariabLe
Quetl:u\ ran\untl
Seedlings/suckcrs 9611226
Saplings
205t 56
I'seudot.\Ltgu t net taiesi i
Seedlin-ss
1i6169
Saplings
3 , 1I 1 5
T r e e s> l 0 c l n d b h
Seedlings
Saplings
tu t nktrtophrllunt
Trees> l0 cln dbh
Seedlmgs
Saplings
Tfees > l0 cm dbh
Seedtings
Sapiings
0 ,1.150 96
51025
100
12
01300
0-ll5
rn
55
5
2l
l0 t 6
230i l9l
2618
0-105
0.1250
0 115
7l
32
+b
11
I ):1
ll !'7
5 1.1
0-55
0 r00
0-90
18
l.l
9
ItJ
2
5
23
3l
l.l
6
1
I
,l1l
0 55
1 6 1 r7 5 0 1 2 5 0
9r5
0105
' Mean aDdrangeol 22 site mean\ of plots/sxe.
8
b Perccnrof 22 siies containing an) ofthis |ariable
' P e r c e n to f I 7 6 p l o t sc o D t a i n i n g
a n ) o l t h i sl a r i a b l e .
oak habitat lbr westem gray squinels (Ryan and
Carey l995a,b).We visited 133ofthese(Bayrakgi
et al. 2001) and found 22 that were lar-qeenough
to be considercdoak communities:mosr were
ecotonalbetweenDouglas-fir tbrestand prairies.
For each site, we circumscribeda core ereathat
includedthc living oaks.Visuallydrawinglines
from one exte or crown point 10 anotheralong
l h eo u t e r m u :ot a k su t . ( h eo n l ) o b j e c t i r e p r o c <
dure we could deviseto identify the actualextent
of thc oak community.
We devclopeda samplingschemefor core areasbasedon reconnaisslnce
of all 22 sites.We
sampled corc areaswith eight nestedplots. To
place the plots. wc establisheda 240-m transect
\\"ith eight stations.+0-mapart, >60 m from the
delineatedperimeter,andpalallel to the long axis
ofthe core.In largesites,we systematicallyplaced
consecutjve
tanscctsalong the long axis of the
core,with onc transect/8ha. up to thrcetransects/
core. Where size or shapeof the site precluded
use of a single transectof cight stations,we establishedtwo parallel lines of four stationseach
with 80 m betweenlines.At eachstatiorr,we rarr
222
Thysell and Carey
domlv sclecteda bearing and a distance(30 m
tiom the station.but alwayswithin the delincated
corearca.to locateeachofeight centcrstbr nested
plots (at every,every other.or every third station
in siteswith one. two, or thrce transects,respectively). We chose30 nr becauseit ( I ) nude availablc tbr samplinga largeproportionofthe points
within delineatedsites,and. thus. our samplcs
would approximatenndom samples,(2) prevented
sempling ovcrlap among consecutivelransects,
and(3) provided,then,unbiasedsamplesofcore
areas.
During Juneand July. 1999.we recordedrhe
octave-scalepercentcover of all v:tscularundelstory spcciesandnumberandspeciesoftree seedlings ('1 cm basaldiameteron 2.8 m-radiusplots
(25-m') centeredon samplepoints.We uscd the
octavescalerecommcnded
by Gauch( 1982.)as
appopriatcfbr visualestimationofspecrcscover
allowing preciseestimatesof the abundanceof
rare plants and avoiding estimationeror due to
poor visualdiscriminationbetweencoversofhigh
value in abundantplants(Bonham 1989,Carey
et al. 1999a).Scalevaluesare: I (0 < 7ccover<
0.5),2 (0.5< 7ccover< 1).3 (1 ( 7ocovcr< 2). :l
(2 { % cover< 1%). ....9 (64 ( Tr coverI 100).
We definedcover as fte vertical projectionof the
vegetationontoahodzontalplane(i.e..theground).
Forrecordingandanalysis.u'e usedthe mid point
0f eachcover category.We did not distinguish
betweenoak seedlingsand oak suckers.
On 8.9 m radius(250 m') plots.\\,erecorded
octa!c percentcoyersofvascularplant life forms:
canopy trees.shrubsand understorytrees>2 m
tall but below the forest carop)'. shrubs0.5 2.0
ur tall, trailing shrubsand vine species<0.5 n
tall or scandenton other pl nts oI snags,tbrbs,
lerns,and graminoids.We alsorecorded(1) the
numberof tree saplings1-5 cm bas l diamelct
(2) number of live and dead overstory trees by
speciesanddiameter-breasrheighr
(dbh)category
( 5 - 1 0c m . I l - 2 0c m , 2 l 3 0 c n . 3 l - , 1 0 c m , 4 1 - 5 0
cm, and> 50 cm) andwhetheroaksweresinglestemmedor palt of a cluster (> 2 stems),such as
may developfiom suckersarounda stumpor root
coilar, (3) bole and canopy dimensionsfbr the
two largestdiameteroaks including dbh. tree
height. and canopydiameter,and (4) evidenceof
iire,logging (species,nunber. and sizeofstumps,
andpercentcoverof skid trailsandroads),manual
b r u ' h c o n t r o l p. i l d l i n go t n o n - o a kt r c e\ p e c i c \ .
soil excavation,andpastsetdement(e.9.,foundations.
fences,fruit trees).From eachplot. we estimated
, l i r c c t i o rnn d d i . t u n c cl o l h el $ o n e r r c spt r i r n f f \
(c.g..road,wetland,
f'eatures
adjoininglandscape
prairie, conifer forest).
Vascularplant nomenclaturelbllows Kartesz
(1994) as updated(USDA, NRCS 1999) with
vascularplant spcciesconceptsandidentifications
basedon Hitchcockand Cronquist(1973).Regional floristic guides(Hitchcock and Cronquist
1973.Klinka et al. 19ii9.Hicknan 1993.Pojar
andMacKinnon 1994)providedfurther intbrmation aboutspeciesorigins(nativeorexotic).natural
histories,and prefened habitats.
Ana ytical l\,4ethods
We calculated(l) mean cover fbr each species,
speciesrichness(the number of species/plot).
(E),
Shannon-Wiener
diversity(H'),andevenness
the ratio of observedH' to the maximum H' that
would occur ifall speciesin the plot were equa]ly
abundantfor eachsitc (Maguran 1988)i(2) the
pcrcentageof vasculal plant speciesthat $ere
exotic: (3) basalarea(n2,4ra)anddensitiesoftrees
>10cm dbh:and(4) numberofsaplings
andseedlings tbr eachtree species.We usedthe midpoint
for eachdbh categoryfbr basalareacalculations
exceptfbr the largestcategorywherewe usedthe
categoryvalue: thus basalareasmight be biased
downwrlrdswheretreeswerclargc-lew oal$ were
>50 cm dbh (Table l). We report meanst standard errors (SE) exccpt where otheN,ise noted.
Ws u.qfl p1q.encq-rh.en\'e
Jrtr lor .ftccic. or
groupsto calculateprevalencevaluesby site and
by plot. We assessed
the correlationbetweenoak
height and dbh basedon the two largestoak ffees
per 25(!mr plot.
To assess
nativeand gxoticspeciescontributions to total spccicsrichnessandto contrastrichnessof sampledoak sitesto similararcasin prairiesand Douglas-firforcsts.we genentedspecies
accumulationcur.res,includingall understoryand
overstoryspecies.We plottedthc cumulativenumber of 25-m: plots ve$us the cumulativenumber
plant species(McCunc and Mefford
of vasculeLr
1999).Directcompadsons
with prairies nd fbrests were possiblc becauseall sampling efforts
u.ed 25 In plots nd 2.5rn i. rn Jffropriirlr'drcr
with which to samplcvegetationin grass.$,eed.
andshrubcommunities(Gauch1982).Prairiedata
are from Thonas and Carey ( 1996); managed-
lbrest data are fiom Thysell and Carey (2000).
We calculatedthe correlation betweenthe total
numberof vascularplant spcciesand the total
s n t h eu a ks i t e : . .
n u m h e or [ e r o l i cr p e c i e o
We perlbrmedBray-Cuftis(BC) ordinationwith
square-roottransfollnedpercent-covervaluesfor
all speciesencounteredon all 176plots.We chose
BC ordinationbecauseit is easyto interpretecologically asenvironmentalor compositionalgradicntsandit hasdocumentedutility forplant comBC, asin dher indirect
nunity data(Beals198.+).In
ordination methods(Kent and Coker 199,1),or
dinatiol axes aLrederived from the tloristic data
andareinitiallyundcfincdin termsof ecological
or environmental variables.We used variance
regressionendpoint selectionand the Sorenson
d i " t u n c em e u : u r eT. h e u m o u n lo l ' \ J r i J n c ee \ plained by each ordination axis was computed
b)' subtractingthe ratio of the sum of squaresof
the residualdistancematrix to the sum of squitres
of the original distancematrix tiom one and expressingit as a percentage.
For combinations
of
speciesor selectcdderived variablesof interest
and eachordinationaxis. we calculatedthe value
of the Pearsonproduct momentcolTelationcoefticient,r. Usingt?= 116 (.dJ= 174),the critical
value(twolailed)of r at a = 0.01was0.25l (Zar
198,11.
We reportonly conelationswithP < 0.01.
To furthcr assessspeciesrelations. we perforned an ordination on all species and used
weighted averagingto locate the averageposition of eachspeciesin the BC plots-ordination
space(McCune and Mefford 1999).We grouped
. p e c i e su i t h l h e S o r e n s o dn i s t u n c em e u ' u r ei n
the farthestneighbor linkage method of cluster
analysisto identily recurrjngvegetationsitetypes
andusedthis site-typemembership
asa variable
in the erdination.Weightedaveragingwasbased
on all species,but we graphedonly locationsof
speciesfound on )l0c/a of the 176 p)ots.Then
we usedindicatorspecies
analysisto idcnlifyspccies characteristicof sitc typcs (Dufr6ne and
Legendre1997,McCuneandMefford 1999).We
evaluatcd statistical significance of maximum
indicatorvalues(IV max) for theresultinggroups
$ith a Monte Carlo methodemploying 1.000
pcrmutationsof the data whele the resultantP
valuewastheproponionofpermutationsin which
the IV max ftom the rundomizeddatasetequaled
ol exceededthe observedlV-max. Thus. a signilicant IV-max indicated r speciesthat was
Quercusgarrtant rn Washington 223
characteristicof a site type and thar the indicator
valuewaslargerthanwould beexpectedbychance
in a pcrmutationset(Dufr€neandLcgcndre 1997,
McCuneaurdMefford 1999).All calculationswere
made with fhc SPSSstatisticalprogram relcase
9.0.1(Nomsis1999)or with PC-ORD,a program
for multivariate analysis of ecological data
(McCuneand Mettord 1999).
Results
Adjolning
Landscape
Features
and
D sturbance
All the oak communitieswe sampled(all thelargc
arcasofoirk) $'ereon levelto gentl)'slopingground
(generally<15% slope),with viLriousaspects(Tablc
1). A11the communitiescould be considered
ecotonal, with adjoining landscapefeaturesin
cludingroads,prairies.saviurnas,
andforests(Table
1). The distance fiom plot centersto adjoining
plantcommunitiesor landscape
components
ave r l g e dl m c r n o [ . i t c m e . r n ' r6 0 = 5 m : I n e a n r
r a n g c dl i u m 2 - +t o l 1 5 l n . T h u : . r u k r ' o m m u n i
ties were linear and narrow in tbrm. on average.
Douglas-fir or Douglas-fir/mixedhardwoodfbrest was nearcstto 39clc.prairies lo 387., aDdwet
Iandsto 16% of plots (r = 176 plots).Thc remaining 77owere nearestto roads(4dl.) and shrub
lands(3%) (Table1).
area.All but one ofthe sitescontaincdtreesother
thanoaks(Tablel). Douglas-fir$'asthe second
most abundanttrcc species.averaging7 l 1 mrl
haor 28 t 2% ofthe totalbasalarca.All but three
sitescontainedDouglas-fir,which accounted
for
>2070oftotal basalareain 6.1%ol'the sites(Table
l). Treedensiticswere25:1115 oakfta and60 t
7 Douglas-fir,4ra,
with sitcaverages
fbroakranging
from 105 to .150stems/ha(Table2). Oregonash.
bigleaf maple. and the non-native su'eet cherry
(Pnrnusatiurn)werethenextmostconmontrees.
found in seven,tbur, and four sitesrespectively;
eachrepresented
<0.5% oftotal basalarea(Tables
I and 2). Ponderosapinc was on two sites:and
black cottonwood (.Populusfulsan(era tricho
crzrpa)and Pacific madrone(Arbuttrsmertzie.sii)
wereon onc siteeach.All in all. )257r of plotsin
all but I site and 6.1%of all plots contained>1
tree speciesbesidesOregonwhite oak (Tables 1
and2).
Douglas-fir treeslarge enough()30 cm dbh)
to dominatemature oaks u'ere found on ,10%of
plots. Domirant oaks (r = 340) averaged33 | I
cm dbh (maximum= 84 cm dbh) and 161 I m
tall (naximum = 30 m), with 807cof the dominants<20 m tall (Table1.Fig. I ). Heightanddbh
of dominantswasstronglycorrelatcd(transfomed
by the natuml logarithm,r = 0.80).Most oaks
were (30 cm dbh (5% werc ).10 cm dbh) while
Douglas-firs>50 crndbh werecommon(Fig. l).
Alnrost all (94q.) plots containedmole than one
singlestenmedoaktree(i 1SE, -51 1) and6l7o
containedmore than one cluster-stemmedtree (4
t I clusteredstems)thatmayhavearisenassuckers
from the baseof a stump or root collar.
Dislurbance.as sampledby plots. was not
widespreadin the communitieswe sampled.We
observedstumpsof recentlyfelled Douglas-fir
(pan of oak restorationefforts) on 23% of plors
(<l% rclativecovcr).We tbundevidenceofhomesteads(e.9..orchards,ornamentalspeciessuch
as periwinkle Iyl7ra mclor], or old foundations)
on 227o(<l% relativccover).Roadscrossed157r
ol plots ( 137.relativecover)andexcavations(e.g.,
army fbxholes)were in 107r(rt7orelativecover).
On plots in four areas.however.we found 8 maturc oaks (>15 cm dbh and >,10years old) that
appearedto have been killed by intensc fire resultinglrom buming ofScot's broom.During our
study, we actually observedcrown fires in one
oak-Douglasfir standand in one ponderosapinc
standduringprescribed
bums.
Oak seedlingsor saplingsu,erepresenton all
sites (N = 22) but in <50c/. of plots (.n = 176)
(Table 2). Of the four other common lrcc specres,only Douglas-fir saplingswere on >507r:of
sitesor>207, ofplots.Douglas-firseedlings.
whilc
locally abundant.wcre obsen'edin onlv 57r of
plots (Table2). Oregonashseedlingsor saplings
were locally abundant(presentin 457e of sites
and 177rofplots). Bigleaf mapleandswectcherry
seedlingsand saplingswere common on some
sites.but werefound in <10% plots(Tablc2).
Overstory
Treesand Begeneration
Speces-areaCurves
Total basal area averaged22 1 | mr/ha with a
range of 7-3li m2/ha (Table 1). Oak basal area
averagedl,1t I m2/ha, 66 t 37oofthe total basal
Cunrulativenumberof speciesincleasedntore
r a p i d l yi n o r l e o m m u n i t i et.h l n i n p r r i r i e : o l
Douglas fil forests.Fufthemtole.the species- ea
22,+ Thysell und CaLrey
species(Thomasand Carey 1996.Thysell and
Carey2000.Fig. 2). Exoticscornposed3l% of
the speciesin oak communitiesand thc exoticspeciescuNe was more asymptoticthan the na
curve for oak communities rvasnoLasymptotic.
evenaflcr accumulating17| species.$hilst the
othercommunitiesreachedasymptotesof approximately 100 (prairie) and 90 (Douglas-fir fbrest)
70q
60q
o
o)
.: 50q
o
a LiveOregonwhiteoak
I DeadOregonwhiteoak
l
LiveDouglasJir
g DeadDouglasjir
3 4oc
E
f
c 30d
E
F zoo
5-10
11-20
21-30
31-40
41-50
50+
Dbh class (cm) of live and dead trees
Figure L I)iainerer clas\ dislibulions ofli!eanddead Oregonwhite oak(0r?rc.6 g.r't.r'rir) and Douglasfit \Psetulotstsu mlr:i.-rii) tees on 116 250'ln: plots in 22 oak communities on Forl Lewis.
$ ' a s h i n g i o n ,1 9 9 9 .
.9
E 100
E
.z
-g
j.;."""".":::r;;;^^-^
t8";^^^^
l'^^^^^^
"""":::::::::::1fl:r:*rltri*tr**r'r*rn*rl
li::,1"
*:i^
ooo"
50
75
100
125
Cumulative number of 25-m'zplots
Figufe 2. Speciesaccumulatior curlcs for Otcgon wlite oak (Qrirfcrr gdnrrrz) communilics (* = rll
\ f e c i e s . l = n a l i v es p c c i c s .^ = c x o t i cs p e c i e s )plr a i e s ( a = a l l s t e c i e s , a = n a t i v c s p c c i c s . x =
exotrc spccics):and nanaged Douglas fir (Pr.rdotsugd m .ie\ii) forcsts (+ = all species)on
F o d L e l v i s .W a s h i n e t o n1. 9 9 2 1 9 9 9 .
garryonurn Washington 225
Quercus
tive-species
curvc (Tablc 1. Fig. 2). Native and
exotic specieswere equally representedin prai
rie comr.nunities,but exotics werc only 18% of
thc spcciesin Douglas-firtirests.
Understory
(overstuyandunderstory)
Wc found171species
i n t h eo c k c u m r n u n i l i e \ : 5133 l i I w e r ee x u t i e
(TablesI and 3). Oak communitiescontained
numerousinfrequentspecies;only 46 (27%) wcre
lound on > 10%of plotsand | 03 (607.)$'eretbund
on <57. of plots. Exotics were 28?, of both the
;f6 most fiequentspeciesandthe 103inliequently
encountered
species.Plot-lcvclspcciesrichness
(r= 176)averaged17.2t 0.,1(range6 37.)inoak
conmunilicsand was intermediate
bgt$,eenthat
of prairies(22..1I 0.5,rr = l68) andthatof man
agedDouglasfir lbrests(11.81 0.3, n = 24{)).
Exoticsaveraged23 1 17a(range0-787o)oftotal
speciesacrossthe 176plots.Averagcspccicsrichness in oak communities ranged from I I to 27
(Table3). The total numberof
spccics/plorsite
exotic species/sitewaspositively correlatedwith
thc total numberof speciesper site (r = 0.66).
Plot-levelspeciesrichness,diveISity(H'), percent
TABLE L Nlcrns (1 I SE) .rnd runge of means ibr undefstor,"'speciesrichness.percentexotic\. di\'ersit),.
a n d e \ e n n e s sa. n d p e r c e n tc o v e ro f l 0 c o m m o n
species(tbund on > 50t of 116plors) in 22 oak
col runities on Fort Lervis. ['ashington. 1999.
\'{eiln t SE
S p e c i c sr i c h n c s s
Shannon $iener di\.'ersit,v(H )
S h a n n o n - \i\e n e fe ! e n n e s s( t )
Coler(?)
S\nph.tt utpot dlbul
Muhontd dquiftnit!nl
0(nluie (ru\it1Dlti\
N?tnothilu pdrtilloftl
PolIsIi(lun nunituIt
CJtisussco?arius'
Atnekorhi.r dlnil.lid
1711
2-t1l
It0
r10
Rangc
tt 21
'155
ii
r0t3
ll
1!
31
0 l0
0 -1 7
0,15
0 18
It0
2:t
2!
0t0
0-12
012
0 l.r
' lvleanand rangc of 22 sitc ncans of 8 ploty\ilc.
L Exotic specjesrichncssas a pcrccnlagcoftoul spccicsdch
' E x o t i cs p e c i e s . l | e m b o l d e n e d .
226
Thysell and Carey
exotics species,and percent cover of common
understoryspeciesvariedgreatlywithin andamong
sites(Table3). Much of the vadanceencountered
acrossall 176plotsalsowascontainedwithin each
of the 22 sites.Except for common snowberry.
understory specieswcre found at low average
coversand frequencies:only 10 undcrstorl,specieswere found on >50c/rof the 176plots.The
tenmostcommonunderstoryspeciesincludedlling
native speciesand one exotic species;all werc
widespreadbut variablein distribution(Tables1.
3).
Ordlnat
on,C usterAnalys
s, Indlcator
Speces
Our ordination (Fig. 3) produceda two-dimensionalmodelthat explained8l7c oftotal variance.
Axis I explaincd477r andAxis 2 explained3,1%
of thevariancein coverof 171species.Pkrtswithin
the 22 communitieswere widely distributed in
ordination space(Fig. 3a). exccpt for oak sites
28,92.and314.Thus,we evaluated
gradients
and
-specicr
76
plots
7
acro\\
dll
i
in
I
|
:prrce
fru\'e\\e\
nther than cxamining statisticsaveragedfor the
22 communitiessampled.ln addition to oak and
snowberry,only eightspecieswerefoundon >507.
of the plots. Howevel numerousnative and exotic specieswere correlatedwith ordinationAxcs
I and 2 (Table4).
Of l8 speciesconelatedwith Axis 1 with r >
l2 werepositivelycorrelared:
of these,g
10.351.
wereexotic.The remainingsix speciesu,erenegatively correlatedwith A\is I andwerenative(Table
:1).weighted averagingof the 46 most frequcnt
speciesrevealedtwo broadgroupsofspecies(Fig.
3b). Of the 16 speciesthat groupedon the right
of Axis l. I I were exotic. Of 30 speciesthat
g r o u p eo
d n t h el e f to ! ' A r i . l . r ' n 1 12 u e r ee r o l i c .
Ari. I u rr po.itirelyconellledu ithper.cntcr,'ti,.'
specics,percentexotic cover, graminoid cover,
r n d o r k s l p l i n gL l c n \ i l )A. m o n ! n ; 1 1 i ' , q . p s c i e . .
the graminoidslong-stolon sedge(.Carexinops)
andblue wildrye (EA nir.r g/a/./cr./.r)
hadthe stron
gest positive corelations (Fig. 3a). The species
mostnegativelyconelatedwithAxis 1 wcreSaskaloon servicebery (AnrelanchieralnifoIia), Indran
plum,commonsnowben),smallenchanter's
night
shade(Circaea ulpina), and westem swordf'ern
(Pol;"stichum
nunittor). Treespeciesrichness,oak
height, tall shrub cover, and native shrub richnessalso were negativelycorrelatedwith Axis I
l i e u r el
A
AX
-n
r44K
l
Al AA
r (A
l
,1\
trt
r* i
' 4 ,
St-
+
*
td"
x
7X
Al
I
t^
I
/l a ^ ^
*
cLsl
FRIA
FRVE --.,,,
CIAI POTU P8flE
oEcE RUUR
rorA
8A0op5g q6g6tIXE
ROGYIiEPA
coco x 6firE I
LOCI FH'U GA P
A
ttrE
fltc
*
ih.
1'l_
trHl Egr!
Bra! Cuflis ordinarionof 176sampletlots (a) and
\|eighlcd a!cfagirg of the ,16most common rpc
cies (b) iiom 22 ]arye oak communities on Forr
L e u i . . \ \ i . h 1 e l . , r .l q u u A \ i . | . i n c e - . i n e
J o r nr r n c e o [ r \ o r r c . f ( . r . . J n J \ \ i . 2 i . u , m nancechangingiiom Oregon lvhite oak (0r.r.&r
gal?r.rrd)loDouglas-lir (Pseudolsugu en.ietii)
and siles grading fioln dry to mesic. Samplc plols
are displayedin legetation si!e lypcs dcliyed hom
cluster analysis.Vectorsindicatethe dircclion tlnd
. r r c n ! t ho l . u | | ( l - r i u n b
, e t ue e I a \ i . . 1 d r h ( \ - r .
ablesi EXOTIC7.. eiolic richness as t of total
richncss: CRASS7.. % grass covefr NAI1VE9,.
natirc dchness as * of total richness; PSME7..
Douglaslirbasal area(BA) as a perccnlagcof to
tal BAI QLIGAf.. oak tsA ar a pcrccnrageLrftoral
BA; QUGA HGT. heigh! oI largestoaksr
S H R U B D V R S . r i c h n e s so f n a l i \ c s h r u b s . , { c r o ,
nlms e plant names (exotic spccicsare underl i n e d ) : A C M A . A c e r n i d c r o p h ' " l l u , n tA . C C A .
A8,.rrtir..rpi1ldr.tr;AMAL. AnrcLtn hiet ahtilil ie I
BRVU. Br..]r,llr rrlgd,.lr; CA1N. Car^ inopsl
CAPE. Carddnine Fn',\ltutliu|
CIAL. Cucded
dlpi a; CLPE. Clalto,iia petJblidu: C.LSI. C.
sihericdtCOCO, Co\ lu.!.rr.nurd; CYSC. C}rvr.r
st:optt I i us; D AGL, D ac! )^Ii s ll I ot neI ata I ELGL.
tll,r/r Sldrcrr: FltVE. F,?s.rt.r r,.,rc./:FRVL I:
ri/gnrid,?dr FRPU f rangule putthiok\ FRLA.
Fmit
s ldtifolidt GAA.P.Gahm updritrc: HODI.
H o l o L l i s c u sd i s . n b \ H O t . A . H o k u s L a n a u 5 l
H\PE.
H,"perit:un pcrforutuw
H\RA.
Htpo<hu{i\ rudkatd. LACO. Iatpsdnd .otntnu
rt. lOCl. LDn,t\,.,rJ,d. \'{\AQ. r.rnr.',,/
aq u iJaI iulni t l AST. Ma ianthehLtnt ste I I dt r"t :
\ttsl . l,r1l,,',,lrrrlr,r: \4o\lA. v.,/r,;,.,;.,
nncftUht"ILut NEPA. N?rrrplild pan ilorrr:
OECL. Otnl.riu | {a\ilbmir;OSP,E, Osntvntl
befteroi; PO\[U. Pol)"sti(hutn munitur POPR.
PoL.prdt(nsis PS\{E. Pr.r/d.7/vrgd,ren.i.,.il?:
QUCTA, Qr.f.rr
Bdr.rud,rd; ROCY. /ir).!.r
g\tntbcdrpa. RUAC Rrlraf d&1,re//.| RUUR.
Rltbt5 ursinus SACR. .tdri.rald .rd!1k.ll.r/irj
\ADO. sdrrf,/d d.,:/..;;. Sl\ll . \/,//.,,,./
neluttt S\AL. S\mplrcticarus d1r,r; SYllE.
\ ; n t ' h .t , , t r p r , i , , p , , / , , : S Y R f . \ , , . , r , r ; ,
r , r , / u , n r ' : \ ' l H T I i ' 1 , / r l r l . / / , , : V l \ A .l \ a / . . .
a&1
(Fig.3a,Table5). Thus.we interpreted
Axis I as
a gradientof increasingdomiDanceot cxotic
species.with Scot's broom. sod-tbrming colonial bentgrassand Kentucky bluegrass(Poa
protensis),common St. John's-wort(I1_tperl
cun perlbrutum), and common shecp sorrel
(Rumet acetosella) most positively correlated
(Tables,1.5).
Axis 2 wasa bipolargradientrepresenting
shifts
in dominancetrom oak to Douglas-llr and fiom
dry to mesicsites(Fig. 3a.Tables,l.5). All nine
speciescorrclatingwith Axis 2 wirh r > 10.351
were native. Sevenwere associatedwith wet to
mesiofbrest Oregon ash, bigleaf maple, Sibe
(Cla\tonio sibiri('d),Ir,dixnplum,
dan springbeauty
\\,estem swordlcm. Douglas-fir, and bigflowcr
Quertus gttrry^anain Washington 227
TABLE ,1.Corelalion coefficients bclsccn plxnt speciesand Brat-Curtis ordiiation axes. d rheir indicalor !alues fbr three
v e g e t t i o n s i t et ] p e \ f o u n di n 2 2 o a k s i l e so n F o f i L e $ , i s .W a s h i n g t o nl .9 9 9 . S p e c i e s s h o w n h a v e / >0 . 3 5 . i r d i c a t ( t
\ a l u e s> 1 0 . o r l i e q u e n c i e >
\ l o t t ( , 1= 1 7 6p l o t t .
InJiL.uor Value for Sitc T\ Dcs
Species'
A.et inaor4lh\llutit
Agrostit utpilla s
A ielatrchieraln$)lid
Ca a,nine pefisJlwnica
C!tisus scoparius
Eht,us gluu.u\
Geru iun nlunhinun
perf1ratutn
Hlpericu
I4psana commu,tis
Leucanthemun ,ulgare
Mdh) id dqLtitoli t
N e t n o p l t i kpta ^ i f l t ) t u
OunlIri0 ctrasilonni:
Oeltothi.a b?t(roi
Pol\\tk hun rwtlitu'n
Pseudot\ugd']1?'t. ie \ ii
QLkrcus pt nand
S\,tph0ridrpos dlhus
Teesdalia udi.aulis
Te!Iin1asr i litl0ta
-0.21
(lfil
0.11
0.20
0.36
0.68
0.12
-0.31
-0.11
0.61
0..15
0.t l
-0.06
0.1:
0.35
0.61
-0.07
0.36
0.30
0.09
-0.11
0.:0
0.39
-0.10
0..1I
-0.+0
0.37
0.01
-0.17
0..1:
0.,10
0.16
-0.1I
0.13
0.36
,{xis 2
npe | 0r = 8.{)
t}pe 2(/1=,10)
typc3('] = 52)
0.12.
0.07
-0.16
0.26
0.01
-0.22
0.31
0.,t3
0.0,1
0.12
-0.11
0.31
0.09
-0.l9
0.02
0.01
0.ll
0.08
-0.09
0.01
0.l2
0.05
0.36
0.09
0.21
0.36
0.5.1
0.7,1
0.2,1
,0.08
0.,11
0.06
0.,13
-0.28
0.06
U
6
26
0
t2
21
2
0
.18
1
l
2l
6t
5
1
6
5
3
36
6
32
t2
l3
-l,l
u
:l
l0
23
0
)1
15
1
l2
1u
2
19
11
l
0
(l
.l
U
5
3
0
tl
21
2t
21
5l
1
0
60
l8
3,1
0
l3
36
0
l9
22
l9
l8
l
)1
2
26
6
,l
t9
30
I
I
l8
31
20
t/
29
(l
t,
0
2',7
16
I
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
0.19
<0.01
<0.01
<0.01
0.11
<0.0t
<0.{11
<0.01
<0.01
<0.t)l
<0.01
0..18
<t-).01
<0.01
<0.01
0.02
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
'/r-valuesbascdon Monle C rlo simulations(\,lccunc and Nlcltbd 1999)
"Er0lic speciesare emboldened.
tell,imx(Tellilnagrar./ifl.r?) (Klinka et al. 19E9,
PojarudMacKinnon 199:1)-and werepositively
correlated$'ith Axis 2. Axis 2 uas positively
correlatedwith native shrub richness.h'eedchness.percentbasalarcathat wasDouglasfi1.basal
areaof bigleaf maple and Oregon ash,and den
sity ofDouglas-fir')30cm dbh.Only Oregonwhite
oak andcon]mon snowberrywerc negativelycorrelatedwith Axis ?. Percentbasalareathat was
oak and dcnsityof oaks210 cm dbh were ncga-
228
ThysellandCarey
tively conelated with Axis 2 (Table5). The species nrost highly correlatcdwith Axis 2 were
Douglas-fir (r = 0.5.1)and Oregonwhite oak (r =
-0.11).
Clusteranalysisproducedthrecgroupsofplots
representingthrcevegetationsitetypesthat made
(Fig.3a).The eighrplors
up theoakconrmunities
sampledin eachofthe 22 oakcommunitieswere
widely variable as to site-typemembershipand
o n a \ c r i r g . , , ( \ ' u l T ei nd2 . 4\ e g e l l l i o ns i t et y p e s .
T,ABLE 5. Cofelationcoellicienb belweense]cct.d!adablcs
and BIay Curlis spccics ordination arc\ lin 22
oak comnrunilics on For! I-c\,"i\. Was|ingron.
1999.
A*i'
Total understorycovef
Percenteriotic coler
Percentgramiroid cover
Pcrccn!la]l shrub covcr
l b l a l s p e c i e sr i c h n e s s
Percentexotic species
\a(ive shrub richness
Trec spccicsrichncss
Shannon Wiencr divcrsit) (lJ=)
S h a n n o n - W i e n e r\ e n n e s s( E )
Toral basalarea (BA. m /h.r)
Q ctrussarrlana BA
I ' s e u d o l l u q ai n e , . i e s i i t s A
Frarinus ldtifolidBA
Ac(r tnaLroph\ ||um BA
Dcnsiw 01 livc oaks >10 cm dbh
O. 3.r/,r.rnd sapling dcnsjty
0. gal,rdnd seedlingdensit_v
Density ofdead 0. ,q."r1.rId >10 cln dbh
Dersit) ofP ,r.,r.icrii >10 cm dbh
Hcight oftallesr O. gdrDUra
1
-0.09
0..16
0.70
0.52
0.l5
0.81
0..19
0.5,+
0.05
0.0E
-0..13
0.10
-0.12
'0.21
0.25
0.12
0.31
0.2.1
-0.30
0.33
0.52
A"ir 2
-0.15
-0.05
-0.l5
0 .t 6
0.15
-0.29
0.52
0.5-l
0.17
0.35
0.13
0.3.1
0..10
0.38
0.37
0.13
0.01
0.r6
0.03
0.37
0. ()
Indicatorspeciesanalysisrevealedthateachsite
type had characteristicspecies(Table4). while a
number of species,notably beaked hazelnut
(Con ltrsutrnuta ), strLckywilly(.Galiurnaparite l,
and hollyleavedbarbeny [ta]l oregongrapel(Malnnia ucluifoliurn).werecommonto all tluee veg
etationsite types.Site type 1 contained;187c
of
plots, and was charactelizedby oak in the overstoryandthe nativeshubs sen'icebern'andsnow
The nativevines.orange
berry in the undgrstory.
honeysuckle (Lonicera tiliosa) and California
blackberry(Rubusursinus),were also common
in this site type. The native herbssticky\\"i1lyand
paniflora)
smallflower nemophila (.NemophiLtt
were common in site type I but did not distin
guish this group fiom other groups. Except tbr
commonnipplewon (.ldpstutaconrnunisl. cxotic
speciesu'ere rare in site type I (Fig. 3a.b;Table
4, 5). Thus we labeledsiLetypc I thc white oak/
nativeshrubgroup.
The threespeciescharacteristic
ol'sitc typc 2
were Douglas-fir, Indian plum. and western
swordtern. with the moist-site herbs small
enchanter'snightshade.Siberianspringbcauty.
and
bigflowertellima (Klinka et al. 1989,Pojarand
MacKinnon199,1)
rlso common;sitetype2 contained 237cof the plots. Site type 2 had the lo\\"
est densityand basalareaof oaks,the lowest fre
quencyandabundance
ofexotic species.
thchighcst
tree speciesrichness(and the largestnon-oak
hardwoodcomponent).andthe highestShannonWienerdiversity(H') ard evenness(E) of the three
site types (Fig. 3a.b;Tables,1,5). We labeledsite
l y p c2 I h e D o u g l a . - l ' i r + r U r n o ih: ct r h: i t c t r p e .
Site type 3, with oak asits overstoryindicator
species.contained29% of ploLs.lts undcrstory
wascharacterized
by nativegraninoids (long sto
lon sedgeand blue wildryel andby cxotics(colonial bentgrass.
Scot'sbroom, and St. John's
wofi). Other exoticssuchaslong stalk cranesbill
lGeruniton coI urnbin urn),common vclvct-grass
(Holcnslanatus),oxcye daisy (Leucqrihemum
L,algare).
Kentucky bluegrass.comrnon sheep
sonel, barestemteesdriia (.Teestlalia
nudicauli.s),
andvetches(yrcld ftl,a!l/d,al]d ll sdtir,,]/alsowefe
charactedsticof site type 3 and virtually absent
liom the othersitetypes.Diversity (H') andeven
ness(E) were lessin site type 3 than in other site
typesand, in shalp contrastto site types I and 2,
poftionof total
exoticspccieswerea substantial
speciesrichness.Olk seedlingsandsaplingswere
morc abundantin sitetype 3 than in sitetypes I
and2 (Fig. 3a,b;Tables4, 5). We labeledsite type
3 r s t h ep i o n e eor l V g l a ' . l l n d - c r o t i c. i r c t 1 p e .
Discussion
Statusof OakCornrnun
t es
Oak sitescover <,17rof Fon Lewis (Ryan and
C r r e ) l g 0 5 4 . l , rl 'e w r r e > 5 h ar n d n t u n lc o n t a i n
few oaks.Most are ecotonesu'ith sharpergradi
cnts and greater influencestiom adji,rcentcommuniticsthan in the 22 largesiteswe describe.
Early in the 20thcenturv.Rigg ( I9l8) desc bed
the oaksofFort Lewis aslbrming a "fringe alound
the edgeofthe praide. next to the forest.The forestis evideDtlyadvancingslowly uponthe prair i c ' . t i g h t 1 ) e a r . l d l e r o. u r a : \ c \ \ m e n li : \ i n r i lar. but human dominanceof the landscapehas
resultedin establishmenlofexotics and advancementof Douglas-firinto woodlandsandprairics
and.off Fort Lcwis, a continuinglossof wood(McGinniset
lands,e.g.,>25% from 1982-1992
al.1997).
Quercusgarnana in Washington 229
The statusofthe oak cornmunities
is still pri
marily a resultof humanactivities:fire exclusion,
introductionand sprcadof exotic species,military activities.and conservlrtion
activities.Dis
turbancesaffecting Fofi Lewis woodlands and
prairies are dominated by militaq/ activity and
conservation
cftbrts.Tveten and Fonda (1999)
describedone fire policy on Fort Lewis: 80% of
the area undgr flre exclusion, 8c/ounder annual,
a n i i l e r )i n d u c e di i.r e .r n d 8 i u n d e lr 3 - ' 5 - y e r r
rotationof lo\\ intensityprescribedbums. But
various efforts enploy diversetechniquesto address ditTerentoonseryationobjectives on (and
ofll Fofi Lewis (DunnandEwing 1997providea
pafiial compendium).Goalsinclude reductionof
Scot's broom. nraintenanceof the structuralap
pearanceof oak, pine, and prairie communilies,
restorationof Lhehistoricalvarietyof oak, pine.
or prairie communities.and maintenanceof vi
ablepopulationsof varioussensitivespeciesof
p l a n t si.n re r l e b r a t easn. dr e r t e b r a t e . .
C o n d i t i o no f O a k C o m m u n i t i e s
Although the large oak communitieswere influ
encedby adjacentcomrnunilies,
most remained
structurallyand compositionallydominatedby
oaks:most seedlingsand saplingswcrc oaksas
well. Most sitesaveraged>200oak n'ees,&a
within
thc rangesof sizes,densities,and basalareasreponedasnormalby Stein(1990).Largcoakswere
rare-most oaks were <30 cm dbh and <20 m
tall. Clustefs of oaks, such as develop from cut
stumpsoI root collars(Stein 1990),were common, but we saw almost no direct evidence of
felling.Abundantsmall.clusteredstemssuggests
that cunrnt oak densitiesmay be higher,and averageoak sizesmaller,thanin thepast(Stein1990)
and that natural,accidental,and prescribedtires
had not beenfrequentenoughto prohibit oak re
S.m a l lo r k . . u h i l ep r o ri , - l i n o
gp t i o n .
eeneralion
for future management,are more susceptiblgto
fire thanlargeoaks(Stcin l990,Agee 1996.Tveten
and Fonda 1999).Densesmall oaks, small Douglas-firs,and Scot'sbroom in understoriesofoak
communitiescreateconditionswhereby fire can
bl: more damaging to maturc oaks than where
matureoaks are large and widely separatedwith
grassy unde$tories. In the tbrmeq understory,
espeoiallymature standsof Scot's broom, provides fuel for intense,high severityfire (Tveten
and Fonda 1999) and a ladder to the crowns of
mature ollks, whereasin the latter grassessup230
Thysell and Carey
port only a mild fire conlined to the vicinity of
oaktrunks.Consequently.
we observedtlre-killed
mature oaks. Douglas-firs.and ponderosapines
in sone oak sites.Repeatedbuming on FofiLewis
hasreducedfuel loads on some sitesand low intensity fires have been shown not to affect mature oaks (Tevetenand Fonda 1999). Fire mortality wasnot con'monamonglargeOregonwhite
oaks;suppressionby Douglas fir was more common.
trr a aa aq
I lninr ona<c nf Aak
Commun
t es
The ecological uniquenessof oak communities
rests on the physical, architecturalprcsenceof
Oregonwhiteoakitself.itsrole in providinghabitat
for the threatenedwesterngray squirrel(Ryanand
Carey 1995b).and the contdbution of the communilieu
. se l e m e n lor l t h eP S A m o s r i (c c o \ ) . tem-an ecosystemwhose properties(e.g., speciesdiversity)aregreaterthanthesumof theunique
characteristicsof each componentsystem.Few,
if any, vascular plant specieswere found to be
obligateassociates
ofoaks. We did not studynonvascularplantsor fungi. however.Nonetheless,
oak communitieshad high plant speciesrichness
comparedto similar areasofprairies orDouglas
fir forests,reflectingthe transitionallature ofthe
oak communities.Most specieswere 'rare ' spe
cies,in the tail of the rank-abundance
curve.Only
one,however.u'as"everywheresparse"(Murray
et al. 1999)and affofded specialprotectivestatus
in Washington(WashingtonNaturalHeritagePrcgram 1997) the smallflower wakerobin.Other
fare spgcleswelg speclesmole common rn pralries,Douglas-frrforests,mixed hardwoodforests,
or wetlands(Thomas and Carey 1996; Carey et
al. 1999c:Thyselland Carey2000).
Oak communities used by the westem gray
squirrelon Fort Lewis werc >2 ha. <0.6 km from
water and had a mixture of trce species,including co-dominanceby Douglas-fir, and a diversityofmast-prcducingnativetreesandshrubsRyan
andCarey(1995a,b).Westemgray squirels were
negativelyaffectedby fiagmentationofoak comm u n i t i e sT. h u s ,f u l l f u n c t i o no l ' o a k e o m m u n i
rie\ in the! reaterecos)stem depend\.in prn. on
their size.contiguity.arldecologicalcontext.The
extant oak communitieson Fort Lewis are small
in size.relativelyhigh in number,but widely dispersed(Ryanand Carey l995a,b).
Conceptual l\,4odeland Oak Trends
PugetSoundoak conmunities \\"eremore extensive a te* hundredyearsago than today and oc
curred under a broaderrange of conditions than
theydo now (Stein1990,Iirckeberg 1991,Ryan
andCarey19950.TvetenandFonda1999).Thus.
u e conslrucledu con(eptuirln rodclrhdlincorporatesa narro\a,ingofthe breadthofhabitat conditionsoccupiedby oakcommunities(Fig.4).Present
oak communities are physically narower, more
disjointed, and more influenced by Douglas-fir
apparentthroughout
thanin the past.a phenomenon
the rangeof Oregonwhite or* (Thilenius1968:
Reed and Sugihara1987;Bamhartet al. 1987,
1996;Srcin1990:TvetenandFonda1999).Consequently,the contribution of oaks to landscape
and biologicaldiversityin the PSA has diminished substantively.On Fort Lewis, oak commu-
nitiesarecommonlyboundedon onesideby glacial
outwashprairies a maiorlloristjc influencethat
i r i n c r e a r i n ! l )J r \ m i n i r l ehJ1 e r o t i c : p c c i c .
(Clampitt 1993,ThomasandCarey 1996)andthat
was evident in our pioneer oak-/grassland
exotic
vegetationtype. Thus, one of the two chief intluenceson oak communitiesin our model(Fig. 4)
is the prairie/exoticinfluence.
The other community exerting strong intluenceon oaksis Douglas-firlowlandfbrcst.ln the
absenceof tirc and during years of above aver
agerainfall.Douglas-firsreadilyestablishon prairies and amongoaks.Rapid height and diameter
growth of Douglas firs can quickly transibrm
prairie or oak sitesinto homogeneoustir fbrests
( L e i g h t o n l 9 l 8 : R e e d a n d S u g i h a r a1 9 1 3 7 ;
B a r n h a r det t a l . 1 9 8 7 .1 9 9 6 ) .O u r r e s u l t sa l s o
show this processis ongoingin most largeoak
Dduobsnr o. hadwood forssl
'innu;ne"
,
_tossof oat"e
_i;";;r"s
-iJ.i"Ji.1.o
Furu.e ranse o'osk condrtions?
!
randscap€
€remenl
"p."r""
ho.nooenizaton
p isducion in hebiratbrcadth
i
"_
v
fudhe'oiakloss
::v.?
!!:11
l79/
r.,'
'
J \
-/
=g
-e
*
psME
...
io-u'dir
to.est
Fi€suppression
psMEo.
Psuri
PSME/
(oucA)
49lv!
FRLA
I
'
iitr
;::.,:"-tg,:'*"
rrougas-ft
<
)
i,liiirll"i'^
ws and
o.k:
/ quoA
\,
on :p.iiri'u'
^4444
Hldh
int nsltv nr
H,shintenstv
ur€;
ooisibrebsdofoaks:
;xotics favored ,i
a,
-l l
Nascent
fflXli35i
,t
!3L'*
--
PSME/OUGAJ
OECE/POMU
-QucA;natle
shrub
Site type I
"n't ot'
I.
=
j'
Prarne"innuence
-numerous exotiG
-oak rogen€ration?
.mairtain {weedy) p6 rie
pioneer
\-
9"y9n--,
o..-
6xotic
:;;''"-
sitetvle 3
.--l
;;;Pred
'
a r.€ suppresslon, oss ofPrairies
Co-iGr enq@chmenl.
Exobc species irlroductions
Measure of habitat bresdlh
Figure,l. Conceptualmodel of Oregon whie oak (Quexv; eur,!-ana) community developmenton Folt Le$is. \!'ashington.CIa]
boxesindicate non oak conmunitics. Site types l. 2, and 3 fefef \egetation site typesthal composeoak coilnunidcsi
exotic group. Acronln\ arc:
ot*./native shrub group, Douglas fir oak/nroist herb group, and pioneer oak-/grassland
ACMA = Ac.r ndcrophlllftrTr: AGCA = ,,lgforrir .drrilldrlr; AMAL = A nelanchiet alnilblia: CAIN = Cdr"cirtr.,,p.r;
CYSC = C[lskr J.opd,ill stFRJ,A= Fruinus latilblia. OEC.E= Oenleria cerus{or//.tstPOMU = Pol;"stichu]nnnnitult:
PSNfE = 1'r€rd.rhrgd ,i.,,?iirrtt; QUCA = Quorus surtlunut S\AL = St q*oricdryor dlr'lr. Minor speciesare
indicaled bv Darentheses.
Quercusgarryuna rn Washington
231
conxnunilics;we do not believethatany PSAoak
siteis immunefrom succession
to Douglas-firor
Douglas-1ir/ash/mrple
fbrest.Thus,theothermajor
i n l l u c n i e i n u u r n r o d e lr : r r p i L l\ u ( \ ' e \ \ i o nl o
Douglas fir or Douglas-fir/mixedhardwood forestswith fire exclusion.
theothertwo oak types.Douglas-firwasherealso.
suggestingthat, with exclusionof fire, succession to Douglas-fir tbrests could occur here as
well (Fig.4).
The nrodel incorporatesour three vegetation
site types(Figs.3.4) to suggestpossibletrends
in future oak developmcnt.Although the types
resemblecommunity types(Thilenius 1968).they
arc not discretecommuDities.Rather.they repre
sgnt responsesof vegetation to environmental
gradientsatrdcomposefine-grainedmosaicswithin
oak communities.Nearly 50% of plots werc in
the oak/native shrub type. This type is thc least
inlluencedby nearbyplant communitiesandmay
be the most indicative of interior oak dominated
forests (and $estern gray squirrel habitat). Becausetheseplots otten containedDouglas fir or
were in closeproximity to arcasthatdid. this type
will continue to conveft to a Douglas-fir typc in
the absenceof disturbancc.The olk/native shrub
type containedtew exoticspecies.
\ \ r t h o u t r p p r o p r i a t em l n a g e r i r l i n r e r v e n r i , ' n .
encroachmentby Douglas fir and other invasive
spccies$'ill continueanddeveiopnentol classical oak communitiesin the future is unlikely.
Among the ever-increasingnumber of invasive
plantspeciesin thePaciticNorthwest.Scot'sbroom
(HitchcockandCronquist
andcolonialbentgrass
l973.Toneyet al. 1998,UsseryandKrannitz 1998,
Tvetenand Fonda 1999,this study)presentthe
greatestthreat to oak comntunities by altering
regene[tionnicherrGruhhI q77r.pron]oling.r\1'm
decayand altcring litter deconposition (Jackson
ct al. 1998).alteringsoil moisture.precludingoak
(DanielsonandH?Llvorson
seedlingcstablishment
1990),andincreasingtire intensityandfrequency
(D'AntonioandVitousek1992.Agee1996).Such
complex rclationshipssuggesLthat both a comprehensiveset of conscryationobjectivesand
comprehensivcassessment
of techniquesf or pro
moting indigenousspecies.includingoaks,and
controllingindividualexotic speciesis needed.
For example,exclusionof fire, without other
managcrialinteryention.leads
to succassion
to a
D o u g l r . l i r c o m r n u n i tO
; . n o a k - p r l i r i em u r g i n s .
fire usedto control Scot's broom can pose risks
to oaksunlessit is usedfiequently enoughto pre
vent excessiveaccretionoffuel. If fire is too frequent. ho\vevet exotic speciesmay bc tat'ored
ovcr nativespecies(Tvetenand Fonda1999).The
frequency.intensjty.and seasonof buming to
control exotic speciesmust be carefully chosen
to a!oid damagingnativespcciesand mechanical destructionof Scot s broom and Douglas-1ir
beforebumingwill reducethepotentialtbrnegative
effectson oaks (Tveten and Fonda 1999).
The Douglas-fir-oak/rnoisthelb type is in the
proccssofconversionto Douglas-firor Douglas
tir/ash/mapleforest. Plots within this group containcdlarge.rapidly growing Douglas-tirsin close
proximity to matureoaks.TheseDouglas-fir can
rapidlyovetop theslower-growingoaks.Although
oaksarelong-lived, they a.reshadc-intolerantand
declinerapidly whcn overtoppedby Douglas-fir
Here, n'e often lbund oakswith small live crowns
at the end of long. arcuatestems.We often encounteredDouglas-tir. Oregon ash, and bigleaf
maple seedlingsand saplingsbut rarely oak rcgeneration.This vegetationtype containedfew
exotlcspccles.
Thc pioneer oak/grassland-exotictype representsareasthat are most intluenced by glacialoutwashprairies.This type hasabundantand di
verse cxotic species, often dominated by
sod-forminggrassesand Scot'sbroom.Prior to
introduction of Scot's broom and colonial
bentgrass.liequent tires in grassy understories
andat prairie-oakmarginsu,ouldhavebeenpatchy
and of low intensity,but sufficientto kill invad
ing Douglas-flr.In contrast,exotic understory
species.especially Scot s broom. now have thc
potentialto fuel highcr intensity.more severefires
thatcouldkill evenmatureoaks(TvetenandFonda
1999,this study).Although lessfiequent than in
232
Thysell and Carcy
I\,4anagement
mpllcatons
Currently managemcntis not effectively addressingissuesof decreasing
iand areaavailablc
fbr naturalcommunities.maintenance
of landscape
processessuch as dispersaland colonization by
westem gray squirrcls, landscapedynamics. or
valuesattributableto the PSAnosaic perse. Such
issucstranscendany onc managementgroup.
Land:cJpeproce\\e.camelo lhr.ft)rein alletnpl.
to lbmulate managementrccommendations1br
thc western gray squirrcl. whose population
vilbility may clcpcnduponan interconnectednetwolk of low density local populationsthat fbrm
a rcsilicnt mctapopulation(Ryan and Carey
l995a,D).RyanandCarey( l995a,b)recommended
management.
both comnlunityand landscapc
Maintainingoaksas paft of a dynamiclandscaperequiresmanagementof contemporaryprocessesthat are reducingthe i,rrea
of oak communities.Our nrodelgivesinsightintosomcofthese
proccsscs.But thc model is inadequateto describe
how eitherindividualoakcommunitiesol a greater
PSA systemmight behaveunder comprehensive
landscapemanagement.A more sophisticated
modcl is ncededto suggesthypothesesthat could
be tcstcdin managcrnentexperiments.This model
would be necessarilycon.rplexand incoryorate
perhapslike the qualitative
r,arioussubrnodels.
model oftlre and vegetationinteractionprescntcd
b 1 M r e r sr l q 8 5| J u d i \ ' i , r uu\' . cr , l ' i i r ci . . r n i m portanttool fbr sustaining
valuesassocinted
with
Oregonu'hite oak woodlands(Reedand Sugihara
1987,RyanandCareyJ9950,Agee1996.Tveten
and Fonda 1999).Fire holdspromisefbr rcducing Scot'sbroonrandprcvcntinginvasionofDouglas-lir Douglas fir. ho$'ever.andvariousdeciduous treesare important membelsof certaintypes
of oaks
of oakcommunities.If simplemaintenance
is thc conservationgoal, one could remove all
othcr trees.lf maintenanceof either the oak fir
ccotonalconmunity with its threatenedflagship
species,the \\,estem gmy squirrel, or the landwetlands.praiscapemosaicof oak u,oodlands,
ries. andconiler fbrestswith the ilttendantmyriad
goal, then a balof speciesis the conservation
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Acknowledgments
This researchwas funded by the Environmental
and Natural ResourcesDivision, Depanment of
Army, Fort Lewis, and the Pacific Northwest
RcsearchStation,U.S. Deparlmentof Agriculture Forest Service.We thank Fofi Lewis Miliin selectionand
tary Reservationfbr assistance
identification of the study sites. We thank personnelofthe EnvironmentalandNaturalResources
Division,and membersof the EcologicalFoundationsofBiodiversity Teamofthe PacificNorthwest ResearchStation for invaluable assistance
during the study. We particularly thank Stacey
Brewstertbr herassistance
in thetleld.We thank
Rich Fonda,David
Jim Agee,Allan Branscomb,
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Receied I 1 Septenber2000
Acceptedfor publication 27 March 2001
Quercusgarmana ln Washington 235