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Perspectives
in Plant Ecology,
Evoliiation and
Systematics
1
SCIENCE
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Pel-spccli~cs In Planr Ecology, Evolution and S!~~rcnialics7 (7005) 1-37- 158
Natural and land-use history of the Northwest mountain ecoregions (USA)
in relation to patt rns of plant invasions
J"
J
dZ
J
Catherine G. ~arks"?",Steven R. ~ a d o s e v i c hBryap
~,
A. ~ndress",Bridgett J. Naylor",
Dawn ~ n z i n ~ e r Lisa
" : J. RewC, Bruce D. Maxwellc, Kathleen A. wire" '
Received 25 April 7005; accep~ed35 September 3005
Abstract
Althougli the Northwest currently has the least proportion of non-native irlvasive plant species relative to other
regioi~sor North A~.neric;i.im~asionscontinue to increase illto the ~nountainous:ueas of the rezion. Lnndscalx
structure, such as the viu-ia~ionfound along the complex gradients of the Northwest mountain ecoregions, affects the
Also, the history of land use and current
expansion of illvasive plant species and the invasibility of pla~ltcorn~~lunities.
use patterns affect the expansion of invasive plants. and many of the deteriorated environme~~ts
in tlle region's
mouuttlins may invite and stabilize pinnt invasions. We examined the patterns of invnsive pla11t diversity in Nortl~west
mountain ecoregions. as derived rrom literature sources. to analyze wl~ichfactors influence plant invasions. Our
analysis found allel-ed riparian systems and disturbed forests to be especially v~~lnerable
to plant invasion. Conversely.
alpine and wilderness areas are still relatively uimfrected by invasive plants. Both riparian and alpine communities,
while making LIPa relatively small area across Nor-thwest mountain ecoregions, have significant ecologic;il importance
and deserve special protection from invasive plant introductions. Hur-nan settlement
,at low elevations and intense lund
use of upl~tndforests will likely continue to enl3ance invasive plant in~roductionsinlo Northwest mounttlin ecosystems.
Knowledge of the relationsllips between biological and envirc71111lentalfactors, distul-bnnce, and hu~naitland use will be
critical for future manngemel~tstrategies that proactively locate. prevent, or contain plant i~lvasiollsin the mountains
of the Northwest.
( . 3005 RtibeI Foundation. ETH Ziirich. Published by Elsevier GmbH. 4 1 1 rights ~.eserved.
I~cj-it~ord.v:
Exotic plan 1s: Inv;~sive plant management; Landscape clia~ige:M o u n tail1 ecosystems; Pacific Northurest; Setllement
histol-y
Introduction
Plant inbasions orten occul. across broad landScalles,
stafes
ille
b ~ 1)lo\\.
1
~ ~ ~ l tpatlelll
i a l affects the
"'Ct,rr-osponcI~~~~
;lulIlor.
L-imii/ ( I C / ( / I Y ~ S \ : c p c ~ r 1 ~
I Is~(I-s.I-ccI.LIs
~I
(C.G. Parks).
invasion process is not well known (With. 2002).
Landscape structure. srtclt as found aloilg the cot~il~les
gradients of mountain ecoregions, will likely arrect the
f ~ ~ t u reeup:ulsion
e
of invasive plant species and the
i~tvasibilityof plant communities. Thus, understanding
the landscape patterns of non-11:ltive plmt illvasio~lsill
111ou111ainecoregions, especially as they interact with the
1333-X319:'$ -scc h-ont mattcr (.' 2 0 0 Riihcl F-ounctatinn. ETH Ziirich. Published by Elscvicr G m h H . All rights rcscrvcd.
doi: 10.10 16~~j.ppccs.7905.0~~.007
Fig. 1. Position ol' the Northwest in the conterminous US.
dynamics tltr~t follocv local disturbance. afrords new
insigh~sTor rnana~iitgplant invasions.
The states of Oregon. Washinglon, Tdaho, and
western Montana occupy the Tar i~ortltwestcorner of
tlte contiguous US and for111 tlte 'Nortl~west'(Fig. I ;
.Jackson itncl ICin~erli~~g,
2003). The Nor~hwest is a
region of shared history, cvilderness. and natiu-a1 areas
that is eliceptionally I-ich i l l ngricultural. forest, and
ng co~tcern to land
fishery resources. An i~icr-easi
managers is the invasion and expansion of non-native
plruit species ii-ito the mountain ecoregions of lhe
Northwest. We c o ~ ~ s i d ethe
r n~ountainousecoregions
of tlie No~-tfi\x,estto be the Cnsc:.tde Pro\~ince(M343;
B ~ ~ i l e 1995).
y,
which iitcludes the Pacific Coast, Cascade.
aitd OIy111pic Mouiit;lii~ranses: portions of the Sierran
Steppe Province (M26 1 ) that el~colt~passes
tlte I<lnmath
and Siskyou ranges in soutltern Oregon; a11 of the
Middle Rocky Mouiitains Province (M332). which
i ~ ~ c l u d ethe
s Blue Mou~ttains,Salmon River Mountains,
iutd ranges of southwester^^ Montrina; part o r tlte
Nortller~tRocky Mountain Province (M333): and tlte
portioit of the Southern Rocky Moul~tailt Steppe
Province (M33 1) tltat extends throughout the Grealer
Yellowsto~teEcosystelll ( F i g . 2). R;tiloy f 1()95) provides
detailed descriptioils of the biogeocli~tlaticcollditio~lsof
these 1x-01
'1ltces.
'
The specific goaIs or this paper are to ( I ) exalnille the
geogrnpl~ic patterns of iitvasive plant diversity in
Nortltwesl ~llo~~lltaill
ecoregions. as derived from
l i teratul-e sources; (2) suggest aplx~rentbiogeographic
filctors that influence patterns of plant invasion; (-3)
exalttine the iitflueltce of disturba~tceon the dist~.ibution
of invasive plants within the ecoregions; and (4) evaluate
the susceptibility of native plant communities to plant
illvasioils by spatially integrating plailt tiistribi~tiolts
with e1evatiol-r and land cover of the ecoregions.
This review focuses on the striti~sof non-native plant
invasions in Northwest mountain ecoregions. We also
discuss Itow natural 31td land-uhe history influences
plant invasion. We first present :m overview or tlie
settle~nenthistory and ~eiieral131td uses for the Nor-thwest. We then introduce tlte general c1t;lracteristics of
the ecoregions and present important gradients across
these areas as they relate to non-native plai~tinvrlsions.
Altltough the available literature is disproportion~~te
among the ecoregions, ufe indicate plant species that 31-e
of pr~rticular concern under specific environ~xe~ital
condilions or management circumsta~tces. With this
b3ckgrou1td, we characterize e:tcIt ecoregion ernpltasizing differences ancl commonalities among tl~entand how
tltese chriracteristics interact with local observations of
plant invasions. I n syntltesis. we analyze tlte susceptibility of particular land-cover types, or 11,'t b'ltats, to
plant invasion. aitd discuss these findings with respect to
landscape ecology and land uses. Areas are pointed out
where additional reserzrclt is needed to better understand
the fi~ctorstltat affect plant invasions and their Illanagenleitt ill ~ o u l t t a i i ecoregions.
i
History, general land uses, and trends in nonnative plant invasions
After the well-known Lewis and Clarlc expedition in
1805-1806 (Pl~ilfips,2003). settlers of European origin
Tront tlte eastern US began to occupy the Nortltwesl.
The arrival of railroads in tlte mid- t o l;~te-l9tltcentury
C.G. Parks
CI
:\I. / Pcrspcctivcs in Pla111Ecology. Evolu~ionand Systemalics 7 (2005) 137-158
ater YetlowatMn
Cascade Ecoregion
IIP Sierran Steppe Ecoregion
.f!
Ir-
akyou Ranges
Middle Rocky Mountains Ecoregion
Northern Rocky Mountain Ecoregion
Southern Rocky Mountain
Steppe Ecoregion
Fig. 2. A map of the mountainous ecoregions of the Pacific Nortllwest. The associr~~ed
Bailey's ecoregioti bouridaries are shown
(Bailey, 1995). Ecoregions iriduded are: R4232, Cascade; A4361, Sierran; M332, Middle Rocky Mountains: M333. Northern Rocky
Mountains; M331, Soulhern Rocky Mountains.
Fig. 3. Land under redera1 ownershil:, in the Northwest.
made fru-ming and irtdustrial ntining possible to satisfy
the resource de~nandso r the i~idustrialrevolution in
Ellrope and the eastern US. The cornbilled mining and
agriculturrzl boom drew an estrenlely diverse ethnic
population to Nol.tliwest towns and cities. At about the
same ti111e. livestock-raising spreitd across the federal
gl-asslaiids of tlte region, which foreshadowed high171aii1s cattle arlct sheep r;~ncl~ing,
and the wheat Lir111ing
industry. Timber IYBS 11ni-vested as both all obstacle to
agricultr~re and :I natural resource tllat becante an
im17ortant industry in the Northwest (Franklil-t and
Dl rneli. 1988).
Land o ~ v n e r ~ h istill
p shapes tlie geographic, socioeconomic. and environmental landscapes of the Northwest. Over KO(%/;, o r the now I1 nill lion people in tlie
region live in ~i~etropolitail
areas (US Census Bi11-ea~1,
2000). People in these large pol>ulation centers dominate
politics in each state. especially concerns about environmental preservation and land-use planning Rural land
use and low Iiuntun populr~tio~l
density c1i;lracterize
areas that are yredomjllately federal lr~nds.~vllichslill
have the traditional resource-based economy of ;~gr-iculture. timber, livestock ra~lching,and mining. Federal
g o v e r n ~ ~ l e agencies
~lt
mailage nl~lcho r tile resioil as
national forests, rt~ngelands,parks, monuments, and
wilderness (Fig. 3). Some snlaller communities, particularly aloilg the roo tl~illsof the mountains. have becon~e
aitrr~ctive locations for ne\v residents interested in
retirement. recreation, and tourism. ilbout 4Ol/b of
federal lands provide primitive or semi-pi-irl~itiverecreational opportunities (Quigle> and Arbelhide. 1097) to
people who live in or visit the region.
The North~vestlandscapes encountered 200 years ago
by Lewis and Clmk are vastly t1.ansrormecl by the trail
140
C.G. Parks ci :\I. ; Pcrspcctivcs in P1;1nt Ecology. Evolu~ivn2nd S\:stcm;ltics 7 (3005) 137.- 158
of non-native plants that arrived, either accidentally or
gr;tsslands; Bunls and Hou1ic)l:i. 1990),and proximity to
deliberately. ~lit11the people ~ v h osettled the region.
water. i.e., riparian areas. A susceptibility rating for
h4rlny invasio~~s
of non-native 17l:lnts established in the
each vegetation type to the non-native p l u ~ t slisted in
Nortllwest between 1850 ;~nd 1920 during the region's
the database for each ecoregion was then made
great influx of agrarian settlers. Port cites such as
followi~~g
Rice (200-5) and Rice ;rnti Rider ( 1995). The
P~>rtl;lnd.Oregon, and Seattle, Washington were notasusceptibility latinps are 'U' (uninvaded by non-native
ble entry points for foreign plants. Historically, trade
plant), 'I' (invasible without disturbance). or ID'
\lessels brought grain and livestock shipments contiumi(invasible when the intact veget~ltionis disturbed).
nated with foreign seeds, while freighters cluinped huge
We then calculated the floristic similarity of non-native
ore deposits and ship ballast laden with foreign plant
plants listed in Tablt. 1 among and within ecol-egions
material oilto tile shores and ; ~ S O L Idocks
~ ~
of these
using Sorensen's con~rnunity similarity index. T l ~ eSo.
Tinlber pl-oduction, li\/estock
cities ( K ~ t r t e ~11399).
rensen con1111unity similarity index is a measure of
ranching. and fi~rmingactivities throughout the region
c o ~ n m u ~ ~similarity
ity
between two sites, or as is t11e case
continue to pro\~ide endpoints for introduction and
here. between two different elevation-based tegetation
al
subsequent seed dispersal. as well 3s the e n v i r o ~ ~ l l ~ e ~ ~ t cover
types. The Stirensen community sirni1:ll-i ty index
distul-bnnce that enl~nncesger~nination and establisl1was calcu1:lted usins the equ:itioi~: 2C,'(N1+ N?). \vllere C
merit o r non-native plant species (Mack. I 986: 'lVi fcovr.
is the number of non-native species in commol~between
1989; Tone)( et a[., 1908; Situ~zc.tersel a].. 199 1 ; Mrootan
the communities, and N1 and AT3 are the ~ o t a number
l
of
LIIICJ. Mort-isoi-t, lt 005).
11011-nativespecies of the two separate communities. To
liej~nitnek( 2000 j iildic:~testhat nlore illan 2 lo/;, of the
determine the siil~ilarityof non-native species among the
22000 vascular plant species found in North America
different ecoregions. the Sorensen's index was calculated
are non-native. However. the proportion of non-native
by comparing the species in common of each ecoregion at
to
species is least in the mountain Northwest con~l~nred
each of the six vegetation cover types. To deterrnille the
other North American regions (Willless et al.. 1999).
si~.nila~-ity
of non-native species within an ecoregion. the
Rice (3005) lists IS3 non-native plants that occur in the
index was calculated by cornparins the similarity or nonNorth\vest that are considered noxious
species
native species occurring along the vesetution cover types
specified by law as being especially undesirable. troublewith a n indi\~idu;llecoregion.
some, or difficult to control. Mounlaitls, ill general, have
We then exalvined the suxeptibility of plant commufewer non-native plan1 introductions relative to lo~vland
nities no re closely by integrating data from Rtce (2005)
areas in the region. The prevalent systetll of 11;ltional
rind Rice ;~ndRider- (1995) with a land-cover map of
parks and forests are believed to account for this paucity
O r e m (Northwest Habital Instit~lle.1998). Thus, tile
of non-native plill~t invasions relt~tive to lot+~l:lnds
susceptibility of particular land-cover types, or habitats.
because early establishmel~t of areas wit11 low human
to invasion in the nlountain ecoregions of Oregon wits
impact probably restricted p1;int introductions. Nonedetermined. Taxono~llicinformation related to plants
theless. plant invasions occur in 111e mountains. and
non-native to the Nortl~westthat are referenced in this
land-use and land-cover change has ~u~~doubtediy
been
paper can be f o ~ ~ nond tlte National PLANTS Database
the underpinnii~gfor the successful establishment of
(USDA. NRC'S. 2005).
these plant species.
An a1y sis
Knowi11g the susceptibility of different plant cornmunities to plant invasion provides insigllt on 11on-i~ative
plant spread and call help design programs to manase
i~on-11ativeplants 01- restore native habitats. I11 Table 1.
we explore the relationsl~ipbetween vegetation type,
elevation, and disturbailce on the presellce of non-native
plants in each ecoregion. The Invaders database (Rice
ancl Rider, 1995; Rice. 2005), which contains nearly
10.000 records of iilvasive plan1 presence ranging over
76 plant communities across five North\vest slates. was
used in 111is i l l l ; ~ l y ~
(Table
i~
I). We conlbined these plant
co~~lmunities
into six general vegetation cover types
based on elevation (alpine to low itplaild forests and
Climate and physiography, natural vegetation,
land uses, and plant invasions of Northwest
n~ountainecoregions
Variation in climate, elevation, soils. and topography
contributes to differences in vegetation that distinguish
each ecoregion. A climatic gradient across the Northwest exists froill west to east besinning at the Pacific
Ocean. Clinlate is wettest and nlildest nl the Pacific
Coast, which beco~nes drier 311d cooler tocvard the
interior of the region (Fig. 4). Winter r ~ ~ iand
n snow
~~t
provide most of the precipitation t l ~ r o u g l ~ othe
Northwest.
Conifers generally dominate Nortllwes~ mountains.
except alo~lgrivers and streams where they are replaced
by broadleaf species of Populus and A1rnr.s. Dense, nloist
C.G Pal Ls cr ;\I.
Table 1.
Lwnri-cover 5usceplibili~yto
Pcrspcctir cs In Plant Ecolo!z\~.Er 01~11011 and Systcmrttlc\ 7 (1005) 137-1 58
11011-naiikei n ~ u s i v eplants 111the
Cascade
Abutiron theophrasti
Acrop tilon repens
Agmstis gigantea*
Ailarzthlss altissimaU
Anchusa oBcinalis
Anthriscus sylvestris
Arctitlm minus
Arlemisia absinthium
AzolZa pinnata
Bromus inermis*
Bromus japonicus*
Bromus lectorurn
Brpnkz alba
Cardaria draba
Cardaria pubescens
Carduus acanthoides
Carduus nutans
Cenchrus longispinus
Cenfaureu hiehersteinii
Centaurea debeauii
Centaurea dijfma
Centaureajuncea x nigra
Centarea nigra
Centaurea nigrescens
Centaurea solstitialis
Centaurea trizinzfettii
Chondrilla jtuzcea
Cirsiwn arvme
Cirsim oulgare
Conium maculatum
Coizuo1u:ulus amensis
Crupina uulgaris
Cuscuta approximata
Cuscuta spp.
Cynoglossurn oficinale
Cyperus esculentus
C y t i m scoparizss
Dactylis glutnerata*
Daucus carota
Echiuin vulgare
Egeria densa
Eichlzornia azurea
Elyrnus repens
Einex spinosa
Equisettkm arve~lse
Equisetum telmateia
Euphorbia esula
Gypsopltila paniculara
Halogeton glorneratus
Hernizonia pungens
Herracleunz nzanf egazzimzmz
Hihiscus trionum
Hieraciuin aurantiacurn
Hieracium caespitosrtrn
Hydrilla verticillata
Nol-~l~ues~
Sierran Steppe
Mid-Rocky Mountains
H M L R
A S H M L R A S H , M L R
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Rocky Mountains
A S H M L R
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1 1 1 1 1
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1 1 1 1 1 1
DI D I I I
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112
C.G. T',irks ct a1
Pcrspccti\c~rn P l ; t l ~Ecology.
~
Evolution and S!\~cmat~cs7 (2005) 137- 158
Table 1 ( ( * o t l t i ~ r i ~ ~ ~ i l )
Cascade
1 id-~ock
Sierran Steppe
Mountains
Rocky MounLlins
A S H M L R I A S H M L R
Hyoscyamus niger
Hyperimn perforaturn
Hypochaeris radicatn
Isatis tinctorb
Kocllia scoparia
Lagarosiphoil: major
Lepidiunz li-tt$oliwn
Lqtoc!zloa chi~zensis
Leucanthenzum vulgare
Limnophila sessiliflora
Linaria dalmalica
Linaria vulgaris
Lythruwr salicaria
Medicago iupulina*
Melilotus officinalis*
Mirabilis nyctaginea
Monochoria hastata
Monochoria vagimlis
Myriophyllum aquaticum
Myrioph-ylim spicatum
Nardus stricta
O n o p o r h acant/ziurn
Opuntia aurantiuca
Orobanche spp.
Oryza longistanzi~lata
Oryza ptinctata
Oryza rujpogon
Ottelia alismoides
Panicum miliaceunz
Paspcriu~nscrobiculatum
Phleum pratense*
Poa pratensis*
Polygonum cuspidarum
Potenlilla recta
Proboscidea louisianica
Rorippa sj~lvestris
Rubus discolor *
Rubus fruticom agg.
&bus rnofuccanw
Sagitturia ,sagittifolia
Secale cereale
Seneciu jacobaea
Silene latgolicz
Silybum marianum
Solanum dukarnara
Solanunz, rustraturn
Sonchus aruensis
Sorghum haiepense
Spargarzium erecturn
Sparti~zaaaglica
Sphaeroyhvsu salsuia
Sf ratiotes n ioides
Taeniatherum caput-medusae
T m a r i x ramosissinaa*
Tanacetzklvt vulgare
D
D
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C.G Parks ct al. ,' Pcrspcc~ivcsin Pl~tnlEcology. El olut~on.~ndS>sccmat~ch7 (1005) 137- 15s
Tahle I (cw~lrirzucdl
Sierran Steppe
Cascade
A S H M L R
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Taraxactawl laeoigatzzm*
Taraxacum officinale agg. *
Tribulus terrestris
Tripletuosper~y~um
mritinza
Ulex europaeus
Ventenatu dubia*
Verbrssnun thapsw
Xanthium spirroswn
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Ecorcgions arc C~iscadc,Sicrran Stcppc. Middlc Rocky h~lount;tins,and Northern and Southcrn Rocky Mountains combined. Vcgctation typcs arc
composcd fro111 tlic plant colnmunitics listcd in Ricc (2005) and l'iicc and IiitIcr (1095) rind groupcd according to clcvation or prosimiig to wutcr
(Horns ;inti f-lonliol;~.1990). Vcgcration typcs arc alpine (A), subnll7inc (S). hi211 (Hj. middlc ( M j . or low (L)upland forests 3lld gra~~I:inds.and
riparian arcrs (Rj.Susccptihility c:itcporicb of ~cgctationtypes arc uninvadcd by non-iiiitivc plants ( U ) , invasiblc \~ithoutdisturbance (1). and
invasihlo with disturl-rvncc (D). Susceptibility ratings arc idcntic;il to tl~oscSound in iiicc i7(#,5) ;ind Kicc and Ridcr I lt)'l.f!csccpt in cases whcrc an
:islerisk occurs tiftcr thc plant name indicated tlic susccptibility I-ating wcrc clcrivccl Fro111 USDrZ I:ol.cst Scrvicc Fire Effccts Inibrn~ationSystem:
http:~.:w~~~w.fs.ft~tl.~~~~ii~~~~~h:ts~~fcis;~~liii-~~s~i~~cci
;indcs.i~rmi.,2 hlatik in ~1 cc)Iumn indiattcs that cithcr no vr itlsufticicnt infornlnlion csists for tl1;rt
spccics ~ i n dvcgcration ~ypc.
Topography and $redpitation (cm)
~ocicyMountains
73-9Qcm
Approximate Distance to Coast
As mod$& fmm Jacbon 8 Hrnerfing 2003
Fig. 4. A lineal- transecl d r ~ t w na b o u ~1000km fi-om west LO east along the 45tli pnr:tllel includes climate types t h a l range TI-om the
tnilci 111al-ine e n v i ~ - o n m e n t sof the Pacific C o a s t t o he continental climates of the R o c k y M o u n t a i n s . In b e t w e s l ~are fou~tcithe
bleditet-ranenn-like climes. steppes and deserts.
forests of prin~arilyT . Y ~ II~~~~L' tI t ~ r o j and
~ l ~ jP~SICl L
~ /~( ~ I I . S I I ~that
I I r ~ i nnortll lo south along the westernmost portion of
western edse of the Cascade
tl-te region. The Coast Range and Olympic Mountc~insrise
Province. However, tlte Sierra11 Steppe Province supI500 117 above sea level; wi tli n local selief of 300-900 111.
130rts diverse n ~ i x t ~ ~ofi -drought-tolerant
e
conifers and
The more interior Cascade Rrlnge has lllou~ltai~ls
hardwoods. a result of locver precipitr~tionand geologi2400-2700 111 in altitude, don~inrztedevery 8--135 k111 by a
cal and ecological history. Moving eastward, increased
volcallo of muc11 higher elevation. ?\/it. Rainier, in the
aridity, and fire li-ecluency promote ol-xn. park-like
Cascades, e.g., rises Inore t l ~ r ~4300
n m above sea level.
Pilllrs liol?tortrr, and L L I ~ ~ . Y Areas thi-ou~houtthe three m o ~ ~ n t a iranges
stands of Pi17l,ls po~~tlei-o.rti,
n
have bee11
oc~,itk~~rinli.s
in the Northern and Middle Rocky Mounglaciated. Western Washington rtnd Oregon (Fig. 4) are
tain Provinces and Greater Yelloc\lstone Ecosystem.
~llaritinlein cli~uatewith mild temperatures and prolonged
cloudy periods. wet mild winters and cool. dry summers, a
long Ssost-free season, and heavy precipitatioi~during the
Cascade Ecoregioii
winter months, most of which Etlls as rain. Rriinf~tll is
heavy, 770 -3800mm/yew, with a general decrease in
Cli~nateand physiography
precipitation TI-o~nnorth to sou~11.The ~nountainmnges
The Cascade Ecoresion (M242; B~tile)!.1995; Fig. 2) is
create rain sl~adowsto their leeward side. The climate of
chm-actesized by three steep, rugged mountrtin ranges
the eastern slope of the Casc~ide Ranse is more
I I I C I I ~ ~lnredo~lliilate
L ~ , ~ ~ ~
the
114
C.G. Parks cr ill. ' Pcrspcc~ivos~n Plan1 Ecology. Evoluriou and Systcma tics 7 ( 2 0 0 ) 137- 158
contii~ental~vithcooler \nilinters and hotter suminers tI1311
its western slope. Enst slopes of the Cascades are also
n ~ u c ldrier
~
than west slopes, ~zcciumulatii~gless than
51 1 111111 of precipit~~tion
per year, 111ost of which falls as
snow (FI-:inklin and Dyrness. 1973).
Natural vegetatiorl
Pacific Cortst forests are 131-oductiveand economically
\ial~inbleforests (Now. 1993). The coniferous forests of
this ecoi-e~ionexceed other prtrts of the world for size
irlld longevity of the dominant species with every conifer
genus represented finding its largest (rrnd often oldest)
represeiltative in the Pacific Coast and Cascade Mountains (Franklin and Elyrness, 1988). All but the highest
peaks are covered by forest. Abo1.e timberline, there are
alpi11e plant con1n1utlities of s h r ~ ~ band
s forbs. The
temperate r'orests of the Olympic Mountains. Coast
Range. and western slope of the Cascade Range are
~~~enric,sii,
Tslrgglr hctc~rophj~llcr.
composed of Pscil~lut,s~~lcr
and Tilr!jci plic,crt[r at low elevations. and /il-iie,s fitllahilis
and T,~lr{gclori~ol.t~~~~.sitrrltr
at higher ele\lations. Pic+c~r
sitc'l~cnsisare common along the coastal margin of the
Coast Range and Olympic Mountains. The easterll
Cascades are dominaied by a mix of species, so111e
represented on the \vestern slope of the range n~hile
others ;ire representative of the Roolcy Mo~~iltriins
farther to the east. Pimus yon~ic~ro.rcr
is conl~llonat lo\ver
e1ev:rtions and Ahic~.s 1r.riocurpu at higher elevntions
( FranAlin and Dyr'ness. 1973).
Land uses
Forest management practices have shaped m u c l ~of
the Cascade Ecoregion. Tniti;tlly, logging concentruted
on Io\vlands. but gradually shifted to l~ighereIev:~tions.
P:~st fires, extensive I-oac?building, land cleasing, and
over nearly a century of clearcut logging characterize the
iiltensive forestry managenlent of the Coast Range
forests. The suititbility of clearcuts for the i n ~ a s i o nof
11011-native plants is \\fell docr~niented(Appleby. 1998).
However, the resulting forest p1ant;ttions form :I landscape o r Y O L I I I ~ , even-aged. closed canopy stands. These
young forest stands tend to have species-poor understories due to ciense sllildii~gand intense competj tion. A
somewhat difi'ereilt situation exists on the easterll slopes
of the Cascades where a century of fire suppression has
allowed dense understory vegetatioil to develop. These
forests are ilow at risk to severe fire events. The coinmon
timber removal nietl~od in the eastern Cascades is
selective tree 11:lrvest :IS opposed to the typical clearcutting ~ ~ s eond western slopes of the Cascades, Olylllpics
and tllroughout the Coast Range.
Plant invasions
111 the Coast Range and western slopes of the Cascades
(T;t ble I ) , non-native ruderal plant species ase largely
co~lfined to early sera1 coil~il~uilitiesfor 3. 5 year:,
folloiving disturbance (DeFerrnri. 1993; DeFerrar~3rd
N a i r n ~ ~ u1993;
.
Planry-Tabncchi et 21.. IC)C)h; P:~rendes.
1 997). AIt11ougl.i non-native l-dants are well represented in
the seed bank oS old-~rowthforests, these species ;ire
rarely present under the dominant vegetation (Ingersoll
and %'iIson, 1989). Size and intensity of disturbiince are
significailt factors for invasio~~
by grasses and (orbs
(Tab12 1). The proportioil of non-native species is
positively correlated with edge leugth of tlle disturbance.
suggest in^ that larger disturbance yaps are nlore rer~dily
in\laded th~rnsmaller gaps (PIanty-Tahitcclii et a!., 1996).
Clearcut logging is the most widespread disturbrrnce in
\vesten1 mountains of the province (Moi-ris. 1 958:
Ilyrnesc;, 1971; Kraerncr. 1977; Ste~v:rrt. 1978; /%gee anci
HuK, IYtYO; I-fufll 1984; Scltc?onmrzker.;1nd McKee. 1088:
I-4alpei.11,1989; De12errari. 1993; Hrij1-xr.n rt uI., 1997). but
non-native herbaceous or shrub species that donlinate
sites early are replaced by native shrubs or trees 11s
succession prozresses (Heckmani~.lC)99).Advancement
c/ii;fius(i.C.
of long-establislled iilvnsive species (Cc~lltr~urc~r
tlc~l~cvrlr.\-ii,
C, ,sol.stiticili,s, Cj*iisus sc.r)plrr.iirs. fipericrrrll
p~t;f.:fl~rotlilli.
Li~z~ricu
ci~rlt~~l~tic~i,
S C ~ M C J ( * ~ ~ , ~etc.)
[ I ( *will
O~-~LIPL~,
probably continue into ne~viydisturbed or clearcul areas
(Toney et al., 1998).
While most nail-11:rtive species are unable to persisi in
coili fei-ous Sorest understol-ies, thel-e are u Te\v excepii ons . h.ij~<~c~/i,s
11rrrrcrli.sand hfj'ccli,~
.scrrioif~are frecjuen t
along shaded abandoned roads and streanls of the
western Cascades (Pureildes. 1997; P;~rendes:1nd Jones.
2000), and have been observed in boll1 yo~ingrind
mr1ture conifer forests or the Otyillpic Ranse (DcFc.1-ritri.
1 993; Halpern c t id., 1999). Brcrch?.l~otli~ii~r
sj.lr*ciric.u~i~
and G C ~ L C T ~r~h~'l'tillnlilii
~LIIII
illso invade matt~re Y.
i.lic~nric,siiand T. lletc~~-o~~hylllr
forest st;lnds.
~~~~~~~e riparian forests contain a sjgnificanlly greater
nuntber and cover of 1101-1-nativespecies than conifei-ous
ttpland forests. Flood and high flow events both disperse
non-native propngules along riparian corridors and create
new unvegetrzted floodp1:tins fol- colonizatio~~
(Thon~pson.
20(!I; \4';lttcrson, 2004). Though riparian areas are
vulnerable to non-native species suc11 as Rrihus cli,scolor.,
the patchiness of riparian habitats often allows coexistence of native and non-native species (Planty-Tal-~acohi
et al.. 1996). P O ~ J Y J O I ~~zispid~lt~ili7
~L~IIT
is beginning to
agpl-essively invade riparian areas of the Coast and
Cascade ranges (Toney et 31.. 1998). In the sleep and
highly dissected inouiltain ranges of the Cascade Province, landslides are n c o ~ ~ ~ i l ldisturbance
on
on both
managed and unmanaged forests (Miles a~lclSwanson,
1986). and uplaild siles nlay be import:unt sources of nonnative propag~~les
for riparian comidors. In a study of C
,sco~~lrriri.s
and Di<gitcrlisplrlplir-ecr in the western Oregon
Cascades. W;~ttet.son(2004) concluded that seeds of these
species move down the ,nradient fro111 uplands to riparian
areas via flood and debris flow events. Furthermore.
11uman dist~~rbances
nlay accelerate the dispersal process
#
C.G. Pai-ks ct
;I/.
/ PCI.S~CC~~J.CS
in Plant Ecolc
fro111uplands to rip;iri;tn areas (P:~l.endes.1997: Parencles
and Jones, 2000). Although riparian areas serve as
species. they do not appear to be
corridors for i~~vasive
sources of propagules for uplil~ldsites (LIeFerral-i. 1 W?).
Natural disturbance gaps in alpine and many
subnIpine environments are largely free of non-native
plants (Table 1). For exal~ilple,lligh-elevation environlllents in the Cascades tend to have fewer non-native
plants t l ~ a n lower elevation sites (DeFerrari. 1993:
Parendes, 1997; Oriiou et al., 2005). Most non-native
D. I I Z ~ I ~ U ~ - C JR.
N.
plants, particularly C, .scopii~-izr~s,
tli,vrolor, and Cir,~iii117
U~L?CII.SC,
decrease i l l abu~lda~lce
with increased elevatioil (DeFerrari, 1993: Parendes,
1qC)7).The fewest plant i~~vasions
are observed in ~ilature
forests located in high-elevation wilderness area of the
Olympic Range (DzFerr-asi and Naiman, 1993). In
general, a n inverse relationship between non-1-12tive
plant species and elevation exists in a11 of the mount;iin
ranges of t11is ecoregion (Table I : DeFerrari and
Nairnan, 1 i)5)4; Paszndes, fOSl7). Fire-effects studies
conducted in wilder11ess and ;la tioilal parks located
along the crest of the Cascades I~avenot found 11011native plal1t species (Dorrglas and Ballard, 197 I ; Miller
a n d Milier. 107h; Hemct~-c~i-rt
and Fr:~nkIiil. 1982);
whether tiis absence is due to lack or seed soul-ce or
to environmental barriers to es~ablishmentis unknown.
Heavily disturbed suballine and alpine. meadows may
support persiste~~t
populations of non-natives. 111 an 8year study of a closed parking lot located in an alpine
i-neaclow do~ninated by native Fc..r.trrc.u itliihocr~.sis.
Schr-eincr t 1982) monitored established non-n;ltive
species for persistence. Three non-native species were
~111d Ttrrctsobserved, Poi/ pi.crtc~rrsi,s, Plrlc~unI ~~~.c~tcvl.se.
C I ( * I I I I I (?tfi('i~liiI~.
Of these. T. c?fjf'cii~nI~
had a negligible
erfec~,P. piwtcil,~~
occurred only where there \.sJas no
other vegetation, and P. ~~rutcn.si.sescluded na t h e
colonizers for a short time. While there was 110
indication illat P. ~ ~ N ~ C I I \ SI ~~OSL I I ~ eventually be
excluded fro117 tlle area by native plruilts. there was also
no indication that it corild invade the undisturbed 12ative
mertdow (Sch rcincr. 1982). However. there is concern
that non-native l>lants that perfor111poorly under forest
canopies, but are tolerant of a wide range of climatic
rrilcl soil conditions, pose a threat to disturbed and
therefore open subalpine and alpine er~vironments(see
Recket- et al., 2005; h4cDotrgalI et al., 2005). For
example, C. oi.Lrn.vc (T;ablc I), corninon in clearcuts.
nlay spread to open alpine meacio\vs of the Olympic
Range (DeFel-I-ar-i.$993).
Sierran Steppe Ecoregion
Climatc and physiography
I11 southwest Oregon between the Cascade hlountains
and the Pacific Ocean is the nortkernmost portion of the
Sierran Steppe Ecoregion (N1261; BaiIeg.. i995; Fig. 3).
These mountains form a uniclue topographic. geologic,
and ecological transition zone tvith elevations from 600
to 2900m. An i~~lportantfactor in the ecological
makeup of the area is the east-west orientation of the
Siskiyou Mountains, a n unusual orientation for a large
mount;~inrange. The climate is warnler and drier than
either the Coast or Cascade ranges (Fts. 4). Annual
precipitation is between 600 :ind I700 m m or nlore,
depending on elevation and distance from the coast.
kEin
Less than 30'?4 falls during the gro~tlingseasoil (Friia~
:~ntf Dyrness. 1988). East slopes are n ~ u c ldrier
~
than
west slopes.
Natural vegetation
The mountains are covered with steeply sloping
forests crossed by valleys. The species composition of
these forests is more native to C:rlifori~i:t. such as Pir?r/,s
Iir/~rbcr~icrrln,Ciilocc~tlr-1i.s~k~czrrr.crl.s.and Liflroc.trrprts
tk~~r~.s{fk)ru.s.
Thus, the forests of this ecoregioll also
represent the northernmost range of the mixed-conifer
and mixed-sclerophyll forests typical of the Sierra
Nevada and C;~lifornia Coast ranges. Forests and
woodlands of the TClamath-Siskiyou are. in certain
locations, Inore open than the conirer forests described
in the previous section.
Land use
Prinlary laud uses of the Klanlath- Siskiyou Moiuntain
ranges are timber Ilar\~est,wilderness recreation. and
conservation. The ecoregion is highly valued for its I~igl-I
botanical diversity. Many eildenlic species occur in this
area of the Northwest. The Siskiyous 131-ovideplant and
animal species with critical connections betiveen the
Cascade Mountains and the wet forests of the western
Coast Range. In addition. the Siskiyou and I<l;imatl~
mountains were not heavily gl~iciatecland served as a
refuge for species whose former habitats disappeared
during the last ice age. T l ~ eWorld Conservation U 11ion
(IUCN) co~lsidersthe Kla111ath-Siskiyou to be a place
of global botanical significance, and the World Wildlife
F L I I Ii~lcluded
~
it in its global 2000 list of 1110st vnluable
and threatened ecoregions of tlle \vorld (Strittholt atld
DellaSala. 200 1 ). Almost 13'!/0 of the region is protected
21s wilderness area, prii~~arilyat higher elevations
(Stri ttllolt ant1 De1laS:tla. 3001 ).
Plant invasions
Tn an examillation of non-native plant species in sis
national parks located withi11 this ecoregion, Odio11 et
:xi. (2OOi) fou~ldan inverse relationship betwen nonnative species richness and elevation. and a \?leak
relationship between soil surface ciisturb:ince and pi-esence of non-native plrunt species. Since srtnlpli~lgtook
place near roads and trails where abund~intsources of
non-nrltive seeds were presei-it. the aulhors believe that a
146
C Ci. Parkx ct
21.
Pcrbpcc~i~cs
~n Plant Ecology. E\-olul~onand S j \ ~ c r n a t ~7c >(2005) I j 7 - 158
cliillntic barrier to est:lblishment For many species maq
with ;tltitudes ranging fro111 900 to 2130 111. East of the
exist at 11i~l-ielevations. They also found :in inverse
Batholith is a basin-and-riinge area consistii~g or
pi elution ship betc+.een non-native plmt species ricl~ness
n~ountains with alluvial Tr~nsat their buses and floodand fosest canopy cover. suggesting that non-nrtti~.e
pl:iins along strea111s draining the valleys. To the west lie
species may be i1lore li~niledby l i ~ h tawilability Lhan
the Blue Mountains, which seldom exceed 3400111. but
seed source (Cldion et ;ll., 3005). Due to decades of fire
I ~ a sone peak 3050 m in height. The Sniike River crosses
suppression. closed cnnopies of trees are i~~creasingly the province at the bottom of Hells Canyon, the deepest
com~nollin hig1-1-elevation forest environments of the
~-ivergosge in North America. Most high reaches have
K1~11atlt-Siskipou region, but moist, open me1
<Id ow
been glaciated.
en\~ironmentsmay be particulitrly \fulnerr~blelo 11011and high rtltitudeb o f
Despite the nortllerly latit~~des
native plant invasion (Ociion et :%I..2005).
this regio11. the climate remains re1;ltively rnild due to
Non-native plallts are pr~rticularlyabundant along
proximity to the Pacific Ocean and protection fro111
streams 3116 rivers in the Sierrian Steppe Ecoregion
Arctic cold fronts. Mean mo~ithlytemperatul-es in the
('Tii hlt. 1 ). L o i ~
ele~ationrip;ti.ian areas thi-oughout the
vaJleys of the Blue Mountains i n northeast Oregon
I<lnmath Park network are inllabited \zit11 dense thickets
range frc)111just above freezii~gto 20 -C. I11 the mountrtin
of R~lhrlsclisi.o/or. ;ind other non-native species (Ckliou el
valleys of Montana. Jai~ilarytempercttures a\>erage its
ti1..
3005). whic.11 mriy be explained by frequent
much as 6 C higller and summer temperatures 3-6 C
disturbance and abundant soil i-uoisture. In the Klnmath
lower thail on the Great Plaiils to the east. The average
Nationrll Forest ( K N F . 2003). riparian areas are
length of the growing season is about 130 days.
vulnerable to 11oi1-native species invasions due to
Temperature and snowfall vasy with altitude. Wind is
rreque~ltflood events and high recreatio~iuse.
generally fioin the west, wit11 111ost nloist ure 17recipitated
Non-native plant species that nl-e especially probleucl-oss the Cr~sc~tdeEcoregion. Consecl uent ly, ~ h i s
niatic in the I<lamath -Siskiyoii Mountains inclr~cle
portion of the Rocky Mountains is semi-arid; vrllleys
C.'cwt[/ln-er~
.sol,\titiolis. C. ~liffi/.sn,C. hic~her..vic~irlii.
and
receive less than 5 10 111111 of precipitation each yerlr \vith
Eltphor-l~icre.5 r//(l (T:117le f ). Ccnticllr.rw .sol,sij~icrli,s is
up to 1700 mm fi1lli11gin the mountains mostly as snow
ilb~11lda11till the foothills o r the Siskiyou Mountai~ls
(Fig. 3 ) .
(12r~?ulcf:lnd :\~-I~I~c)II). 7(100; Iitrches ant1 CVll~tc..2000).
Altho~1211C. .sol.stiticr/ics no st I-eadily ins!ades sor~tll
Natural vegetation
slopes and dislurbed sites, the specie5 also v\rill invade
Low elevatioils ( < 1000111) of the Middle Rocky
forest ope~lingsin the conifer transition zone above oak
are co~nprised111ai11lyof arid gt-asslanct and
Mountains
woodlands in the absence of conlpetii-ig pere~~nirtl
shrub
steppe
vegetation. dominated by ,41.tcllrisirt spp.
vegetation (Rocl~cand Whitc, 2000). State :tnd natio~lal
and
perennial
bunchgrass communities. Forest covers
lxu'ks have high levels of i~on-native plants. For
increase
at
mid-elevations
(c. 1000-lh00n3) and tire
exilmple. 25% of the flora in Red\+rood National Park
, don1iilated by Pi11lus j?o~?c/e~-ri.sa
rind P.rc~ii~/ot,\n(gci
fllc.f?riccis believed to be non-nalive (Cldion ct a]., 2005).
.sii.
Higher
elevation
roresls
(
u
p
to
approxiilzalely
CI1;~pnrral and low elevatiorl woodla11ds are invrtded
~
L(1ri.y
by Aikrr~t11ri.safti.s.si~~~c~,
G'cnist~rr ~ ~ o n . s ~ ~ c l s . silnci
r ~ l t C'
~.~ ~ ~ ~ , 1900 111) ;Ire domiilated by P. I I I C / ~ : ; C S ~and
oc'c2it/~~~i~(/i,r.
wit11
A/7ic,s
gr.cn~c/i,~
as
;ti1 associate west of
sal.stiti~~/i~~.
Aillong the most widespread non-nati.\~e
the contineutnl divide, chiefly on west-htcing slopes.
plants in the Klnmath Park network are &y~ci-ic,iiiil
Picc~crcngol~llunuii,Ahies I~~,sioc.trrl~c/
and Pilzzr,r cilhic*rnrlis
p ~ ~ t : f O r ~ tand
~ i i iHi j y ~ o i ' l ~I Y~I C~/ ~ (~* C iI CsL I (0cfi011ct 31.. 2005).
are
the
prirnrtsy
trees
in
subalpine
ar-eas
(c. <20OOn1).
Coastal invaders are typically herbaceous pereilnials.
Due
to
aridity.
forests
directly
east
of
the
Salmon River
such as C'ori~llicl-injiil~lifc~
and /11ftllo.~l1lltlllili~
o~lor~/tzil~~
and eastern
Mountains
are
usually
restricted
to
northern
(Sass et ;d.. 2003).
slopes. Although south- and west-facing slopes recei\le
co111parable precipitation, they are llotter and evaporation is higher as compared to ~lorthern and eastern
Middle Rocky Mountains Ecoregion
slopes. Consecltiently, south- and west-facing slopes
support Sew trees, and are covered by sl~rubs and
C1intat.e and physiography
grasses.
The Middle Rocky Mountains Ecnregioil is comprised o r the Blue hlountrtins. Sr11111on River k,$ountains,
Bitterroot Mountains, Pioneer Mountains, Butte Highland Mountains, Tobi~ccorootMountains, and portions
of the Madison and G;lllatin Mountain ranges (M332:
Bailey. 19C15; Fig. 3). Most of ce11tr;ll Idaho and the
Sah1-1011 River mountains are fc~rnled by granitic
intrusior~stllnt collecliilely m:~kt:up the 1d:tho Batholith,
Land use
Over 40% of the land is federally owned, of which 1 7")
is designated for recreation or wilderness management
(Qrrisley and Arbelbide, 1997). Low- l o mid-elevation
sagebri~sh(il~.t~~~lli.sic~
SF.) steppe and ope11 P. pc~ilcIcro.vcr
commt~nities have been greatly impacted by cursent and
C.G. P;\rks cl ;\I. ,' Pcrspccti\ci in Plant Ecol ogy. Evolu~ionand Systcmalics 7 (20051 137- i 58
past land use such as intensive livestock grazing. scattered
s ~ ~ i asettlements.
ll
and wide-scale tjn~berharvests.
147
nutrien~s (Table 1). Post-fire seeding of non-native
grasses to stabilize soil, contributes to a n increase in
non-native plants at mid- and lligh-elevation. Over the
Plant invasions
last few years, controlled fi res have been widely applied
In common with the rest of the Northwest (Tal-tle I ) ,
across the Middle Rockies to reduce forest file1 loads.
p l a ~ l t il~vasions in the Middle Rocky Mount:iins
Fuels reduction programs may enhance the spread of
Ecoregion vary depending on elevation, past Iilnd use,
existing non-native species since sites itre more suscepand disturbai~cel~istory.Lower elevation shrub steppe,
tible to plant invasions rifter fire (h~filhergancf L:~rncltlt,
forest are inost
grassland, and xeric P. ~~o~~clc~ro.scr
1995; D'Antonio, 3000; Good\vin ;lnct Sheley. 3001).
impacted by invasive plants. Pastic~~larly
problematic
An important qnrility throughout the Middle Rocky
us
non-native plants include ani~ualgrasses ( B r o ~ ~ l spp.,
Mountaii~sis the espansive ro;idless wilderuess areas
I,'c,lrtc~nerta clrrhirr, Tcrcr?icrt/~et-u~~~
c ' e r ~ ~ r r t - r 7 i c ~ c 1 ~ r rllizoLs~~),
that O C C L I P ~ the ecoregion's higl~estelevations. Nonmatous perennial grasses ( B ~ O I I I~ZILZ.C~ P IPOL/
I ~ ~~ I. -~N ,~ C J I ? - native plants are less frequent in wilderness areas than in
sis), and perennial forbs (including species in the genus
the other land-use categories. When they are found, the
C~~~itrrrrrccr,
and Hypcric'iilir pcl:fi,rcr tltt~i;H:II-I-o~,
200 1 ).
plants are mostly restricted to access trails. paths,
trailheads. and campsites (Cole, 1982; hElarirr~iel id..
The knapweed complex is especially troublesome since
niore than 1.4 n~illionha of Oregon, W:isltington, Idaho.
1986). Cc~rztrr~ur-ccr
hichc~l..stt~ir~ii,
C/~orltli.illerj l l l i i ' ~ ~i111d
~ . P.
and h4 ontana are cover-ed wi th Cc~itrizrrc~tr
/~ichsr;sfcil?ii r.ccstlihave beell found in the Frank Church River of Noitlone (Lal-tsi-ierand Flather-. 1904; Wilson et ill., 2003).
Return Wildenless, the largest wilderness :ire3 in the
It is estimated that 8% of the Payette and S:tlmonco11tinent:ii US (\Wood rlnd Lyman. 2004).
C11;lllis National forests are inhabited by C. ,sol~s~iiicrli.v.
Hic.rrrc.ir~~rlc.cic~.vpirusu~~
and H. ~irr~~~rntiric~i~t~~
are of
, J3ip/1(cl*hiri
~J,SIIILI,
or C ~ I ~ L lllrt~ll~s
~ L L I S(Joh-tson, 2000).
concern in moist pastures and mid- to high-elevation
Pofciltillc~ r-~~c~ttr
is a long-lived perenilia1 that 1x1s
meadows (Table I ) . Extensive inrestations of H.
become one of the most serious invaders of the Middle
cvre,sj~iro.szn~ihave beell disco\ered recently in the
and Northern Rockies (Sheley and PetroSS. 1999).
Wallown Mountains of nortl~eastern Oregon (Dwir-e
Po tell tilkr I - C ~ ~ ~ipent
N
unnoticed in many parts or its
and Parks. 2002). Non-native grasses :ind rol-bs were
range because it is similar in appea~xnceto 11;ltive cooften seeded in ~nontanemeadows to increase rorage
OCCLII-ri
119 congeners. pa rticularl y Potci?tillcr g~vic.ilis
value of the native vegetation, a11d several of these
(Aitkem and Pal-Ls, 2004). Other invrisive species found
introduced species now persist as do~llinants even
in the Blue Mountains are in limited areas or in low
with011t livestock gl-r~zing (Cron t tind C'larrsnitrer.
abundance. These species include E. c~slrlll, Lillc~ric~ 1997). E1rpl1ol'l)ie1r~i11rris found along many rivers and
tlrrl~~~crtic~r,
L. ~ ! ~ ~ l g i ~
C r' Ci sI ,~ C / C
~ ?IZI I. ~~C~~L
S C ~ (and
J I I . S ,C'l1011streams, and appears to be spreading upstrean1 to higl~er
tli.ill~r,jrmi*ccl(Table 1 ). Othel- invusive species common
elevatio~is. C'cl~tcrzri.c~~~
rl'c~/>c.rlrr.~ii
is a relatively new
tllrougl~outthe Salmon River R:inge include C ~ l ~ ~ o g l o s - introduction to the Norti~west (Roche :tnd Roche,
,srirrl r?f;fic.i~icrlc~,
Cir.sizr17.rr*ul$jclr.c.Trif~zr1tr.stc;.re.'ifr.is,;1nd
I99 f ). Ci~trtciiir.cclc/e~c.hr~rlrsii
grows best on ~lloistsites,
Ci-~~l~iliil
t-~~l~jc~ris.
includin~pastures and nieado\vs aloi~grivers, streams,
The ~n;~-iorityof high-elevation uplands in the
and irrigation ditches, and in openings in forested areas.
ecol-egion are managed by the federal govern~lleittwhere
Seeds are carried in watern~ays.I~~festations
of T ~ I I I I C I ~ ~ . Y
plant invasions are currently less pronounced and
i.cu~lo.sissiilicz,/Iilrrnrhr is c~ltis.sir~lrr,Rrrh~rs ~/i.si'olor,and
litostly restricted to early successional plant comn?uPO~~Y~O
L * IL I~S Z
~ I I~ ~I ~~C have
/ ~ L ~ I ~been
I
discoyered in the
nitie:, (Tablc I ) . These areas are generally forested and
~ ~ p p reaches
er
of the Snake Rillel-. Currently. alpine and
dominated by 111ixed-coniferI'orests. C'ir.sirirr1 I-r11gclr.rand
s~ibalpineareas have few non-native plants (Tablc I),
C. cr~.r.e~tscare ofieil found followiilg prescribed or
though there is concern about invasion by Lj.tlzi.ur~l
wildfires, logging or heavy grazing. Additionally, re.scrlic.rri.irr, H. cut~.s~?iro.szrr~~,
and H. c ~ ~ r ~ r r t i c i ~ * ~ r ~ r .
seeding prograrl-is to reduce soil erosion rollowing
ti111ber harvest have resulted in wide distl-ibutions o r
111~11iyilon-native grass species such as T1ri1iopj.rz1111 Northern Rocky hlourltain and Southern Rocky
i ~ ~ t c r - ~ ~ ~ c B.
> t l ~i ~I rI ~~lJ~~, ' IP.~ Ipi-iit~~~.si,s,
LIS,
; ~ n d P111c~z1117
Mountain Steppe Ecoregions
J ? ~ L I ~ C J I IPast
S O . fire suppression has resulted in heavy fuel
~iccum~~lations
and high tree stand densities in many
Climate and physiography
areas of the Midclle Rocky Mountains. and have put
The Northern Rocky Mountain Ecoregiott (M33-3;
these forests at risk to stand-destroying wildfires. In
RtiiIey , 1995; Fig. 2) consists of high. rugged mountains
2000, wildfires prevailed throughout the Middle Rocky
rising to more than 2700 m with local relief in excess of
Mountains and created optilnal conditions for invasive
900 m.hlost o r the ecoregioll has been glaciated. Many
plant establishment by decreasing tree, sill-ub and
valleys are nearly flat with some being several niiles
herbaceous cover and illcreasiitg light le\lels and
wide. Sno\vf:~il is heavy, but perm:~nent sno~~~fields
and
118
C.G. Parks ct al.
'
Pcrhpcc\i\;cs in Plant Ecvlcjgy. Evolution and S>.s~cmatics
7 [3!)05)137- 158
gl~iciers ;\re s111all. The average lenlperature of 111s
coldest month is below 0 ' C , and the average temperature of the w:lrmest month is below 22 -C. Summer days
are cool. Precipitation averages
are often 1101, but 11i~hts
5 10- 1030 mm:year and is c o n c e ~ ~ ~ r a tine d
winter
and sprii~g.Si~nirnersare U S U ~ I I dry
~ (Fis 3 ) .
The Southern Rocky h4ountains Province includes
the Yellowstone Highl:~nds. Bigl~orn Mountains. and
Overthrust Mount~~ins.The Yello\vstone Highlands
encon1y:tsses rnilcll of the Greater Yellowstone Ecosystem (M33 1 ; Bailtt! , I9c)i; Fig. 3). The E--ello\vstoi~e
Plateau was formed from t ~ v o~ o l c a n i cepisodes. Other
areas iiiciude high rugged moul~tainswith ridges and
circlues at highe~. olevations, and narrow to broad
v~~lleys.Much of this area has been gl~lciatecl, and
moraines are comnlon. Elevation ranges from 1800 to
4100m in the mountains, and 763 to 1983 m in the
basins and valleys. Precipitation ranges froim 5 I0 to
1140 n1rn annrrally; 1110sf O C C U ~ Sdi~ringf i l l . winter, and
spring. Above 1800 m, precipitation falls mostly as
snow. Rain is commoli during the growins season.
Climate is cold, moist continental. The growing season
lasts 25-120 days.
lnter~ulsbetween fires typically range from 100 to 300
years ( R o n ~ r n ea ~ t c iK u ~ g l ~I98
t , I ) . As evidenced by the
extensive fires in the Yellowstoiie Nation;~lPark in 1988.
Pirlrrs c~)ntur.t[r
forests are rejuvenated by crown fires 11i:it
replace tree stands. Alt11ougl-r Po11~rlu.s~ ~ L ' I I I L I I O ~stands
CI~~S
gener;~lly cover less than I ' X of the la11dsc;lpe (e-g.,
Rocky Moimtain National Park, Grand Teton National
Park). they are keystone plr~ntcommunities for birds
and mammals, and are especially important forage for
deer and elk (Mueggtel- and Stewart. 1980).
Land use
An important quality of the Northern Rocky
Mountain Ecoregion is the. expansive roadless wilderness areas that are linked by ~ninii~~ally
ronded
submountain ranges. This ecoregion is irnportanr
habit:it Tor many anill~alspecies including large carnivores like the grizzly bear. wolf, aiid other animals
reliant on large tracts of land (Ament :rntJ Craighead.
1908). The ecoregion is, however, becoming increasingly
fi-agmented by roads (Noss. 1993). encroached upon by
exurban developmei~t (H~rnsen el al.. ZOO'),
and
intensively used for recreation ( J t ~ h ~ ~ seto nal.. 2003).
Incre;~singnumbers o r elk may have an adverse efrect on
Natural vegetation
cluality or the available wji1te1-forape (Kn~ght.1994) and
Well-marked elevation zones o r vegetation are a
:ilso increase the occurrence of plailt invasions.
striking featitre of the NorChern Rocky Mouiltain
Human-caused pressures in the Greater Yellowstoi~e
Ecoregion. 111 the uppermost alpine belt, trees are
Ecosyste~ll include commercial development, lo~ging.
absent. The subalpine belt is domin~tted by Picw
exploitation of geothermal resources, and tourism. The
~~r~gebrl~rrznii
and Ahic,~l~/,sior~ir~ci.
In the Bitterroot
park's visitation rate is about 3.2 million visitors /year
Rllnge. Tstlyri 17lei*tc~i?.sil~rlu
is the clil~l:~xtree of the
(Knigh t. I99 I ) and increasing (Johnson et 31.. 200.3).
subalpilie belt. Tllrijii l~lic,iitcr:~nd Tsrrya I ~ ~ ~ t c l - o ~ ~are
l r j , l l ~ i A l t h o ~ ~ g hlivestock :~llotn~ent:razing intensity has
chai-acteristic of [he monlane belt, along with Pscliriotdecreased :is in 111ost of tlie Mountain West, livestock
,s~iiglj~l
17lol1zic~~ii.
round t h r o i ~ g h o ~the
~ t ecoregion. :\long
glazing is still perinitted on about 40% of the Greatelwith Pirl~{srllcnitirolir, Llrrix occii/'o/itc/li.\.Ahic.s gr~i~ldi,s, Yellowstoile Ecosyste~l~
(Keiter and Boyce. 1991 ).
ailci Pi77il.s J~OIIL/OI'O,CI/,
f o ~ ~ ii l~l dthe south. In these
l'orests, areas that have been burl~ed or cut are
Plant invasions
regenerated first by L. orrill~r~tolis,
a deciduous conifer.
There are 125 1 vr~scular plant species in western
Pil7lr.s rnor~tic.olcrcrowds out the L. occi~Jc.rtt~rlis,
and tlletl
Moiltana and 250 non-native species in the area
is replaced by T. 11lc.rtc.ir.rie1izt1.
T. Ilctcrophy/I~r.T. l?/icertil,
(Whipple, 2001. modified from Rcimanck and Randutl.
and Ahics corico/oi-. Depending on latitude, the lower
1994). 111 Glacier National Park. a total of 1131 plant
part of the Inonta~lebelt may be interspersed with srass
species have bee11 foui~dof whicl~126 ( I l'%) are 11011and sagebrush. Throughout the ecoregion, mixed-connative (Tyser- and ~Yorley. 1993). In Yellowstoi~e
ifer-deciduous forest, sucli as P. 171i)rizi~~ii
and T.
National Park, 1265 plant species have been recorded
l~licarrttr-T. ~l~er.tc~rl.si~/r~~r---P.
111~11:iesii
forests. predonliand 187 (14.7%) are non-native species (Whippls, 200 1 ).
nate.
In a survey of noii-native plant species adjacent to
For the Southern Rocky hlountain Ecoregion, I-ISDA
Ilighways between Glacier National Park and Grzrnd
FOI-cst Scrvicc (1905) iilapped potential vegetation as
Tetoli National Park. Weaver ei n l . (2001) observed 39
P.rcl~cioi.ocg~ic.~.ir/--Ac~h~~crt/ter.~/n~-sl~r~ib
steppe in drier,
non-native plant species. Most of tlie doniinant plants
Iower elevation valleys (55x1, aiid P. 17rcrrri~sii-Piare intentio~~nlly
illtrocliiced grasses (Ayrosti.~~ ~ ~ C I M T P C I ,
cetr-/l hies forest (45':)l) between 1667 and '879 m. Pirrzrs
B P O I I ~ ir1er117i.s,
NS
B. ttlctorl~~li,
B. ,jl~po~licri~.
D(~~*tj)lix
c80iltortir is the common tree cover type, with an
~ I O I ~ J I .;ind
N ~ Lparticiilarly
/,
Pot[ prcfcl~i.sca11d P I I I ~ J ~ { I ~ ~
r~nclerstory of l 'crc.c+ir~iunl.sc.o~~~rririri
1, C~i/~~/~icryrr~.rti.s
/ I I - N t~/lf.si.s)and l e p 111es s LICII ;IS A41~liIo
t1l.s ~fJI~ir~iili.~.
~.rrhr~.sc.cils,
Arr~icairrot.d(fblill, or hfc~lzoniur c p ~ i s Afpiiie
.
i\.I~~cli<.t/~o
Ilrl~uli~~n,
TrifOli~iii~
~ > I ' ~ I ~ C811d
' I ? . YTl.ifi)Iill~~l
C~,
vegetalion, iilcludii~g P. rrl1~ic~arrli.sand A. I ~ ~ . s i o ~ ~ i i r ~I~~iI~I ,I I I I I L\!fea\rer~ S ~ P C Jet. ;I I . (300 t ) ri>iind non-native plant
occu~-sabove 2878 m.
species in both grasslands and dry Sorests (Table I ).
Table 2.
Floristic similarity of non-11;l~iveplants \ ~ i ~ l l i 1;e~el;ltion
ll
t!~l,es of Norlliwest mountain ecol-egions uslng data Srolii
T'tl7t~ 1
Vegetation types
Alpirle
Cir.sc~orlt)
Alpine
Subalpine
High Sorest
Middle li~rest
Losv forest
Rip:tri;tl~
Subalpine
Higli fwest
Middle forest
Low forest
Riparian
--
9I
95
S7
85
72
Sic>/.r.~/r~
Sfqy~c~
41pine
Subalpine
High forest
Middle forest
Low r c ~ r e s ~
Riparian
~Zlitl-Rocnlcj- hlorrntlrirl.5
.Alpine
Subalpine
High forest
Middle fol-est
Low forest
Riparian
Roc*l;j. A'IOIIII
~LI~II.S
Alpine
Subalpine
Higli Sorest
Middle Sorest
Low forest
Ripari:~n
1
1
1
I
I
.-
40
40
38
36
30
-
94
94
92
90
72
Namhcss arc pcrcctit similarity of tlic non-native IIora, caIcuiatccI usitlg thc S3rcnscn incics tllc cq~;ltii)n:2C/(.iY1 + 11'2). whcrc C'is tl~cnu11ihcr or
spccics in common hct\vc.cn thc communities. anci ,W,and A?? ;~rcS P C C ~ C S i.ichncss 01' the two scp;ir;ii~conim~i~litics.
" N o or insut'licicnl inft)t.m~ttioncsists l'or spccics i n \:cgctation type.
We coilfirn~ed(Fig. 5 ) that different land-cover types
are susceptible to invasive species, but the range oS
invasive species richness plants ai~longthe habitats is
coilsiderable (Fig. h). Drier climates, such as that of the
Middle Rocky Mountain Ecoregion a i d tlte eastern
portions of the Cascade a ~ t dSierra Steppe ecoregions
are at greater risk to invnsive species than tlie ltlore
mesic western portioits of the Cascade Ecoregion (Fig.
5 ) . In Oregon, xeric grassl~~nds
comprised lltostly of
perenitial bunchgrass coil-lmunities, upland shrub cornm~rnilies,and riparian areas are susceptible to the itlost
iton-native plant species, wllile subalpine meadows r~nd
salt-desert shrub are susceptible to the fewest invasive
plant species (Fig. 0 ) . Using the data froin Fig. h a
calculatioit of Ihe pel-centage of land area in suscel3tible
plant comit~unitiesin each ecoregioil (Table 3) i1ldic:ttes
the over:ill level of risk for mountains in Oregon.
Specific areas of risk are d s o indicated. e.g., the Cascade
ecoregioi~has less land cover i l l the invasive species-rich
xeric grassiand category but twice the a r n o u ~ tof land
cover in the riparian categorq than tlte otl~erOregon
mountain ecoregions.
Discussion
The il~ourttain ecoregions of the Northwest have
fe\ver non-native invasive plailts tltait other regions of
tlte US because of (1) climate Sactors including a short
growing season at high elevations and lack or moisture
diiriilg tlte growi~12 seasoit, (2) LL limited settlenlent
history. (3) relatively low freqitency of seed sources, and
(4) \videspread forested areas cvitlt closed canopy
conirers that li~ltillight and ;tcidify the rorest floor with
needle litter. Thus, comp:tred to more invaded forest
C.G. Parks ct
ill.
' Pcrspccti\.cs i n Plant Ecology, Evolution
xnd Systc~ualics7 (2005) 137-1%
,
lnvasive Species Richness
1 1 6 - 2 0
-
20 40
-
40 60
-
60 80
ao-.roo
--
:
'
Cascade
'\/
Ecoregion
-
100 120
f No Available Data
Middle Rocky
Mountain Ecoregion
Fig. 5. (a) Numbers of non-native invasive plants to which mountain ecol-egions of Orezon are suscep~ibleand (b) elevation
gradients of mountain ecol-egions in Oregon.
steppe grasslands. high-elevation North\vest forests
experience lilnitecl invasion by 11011-native plant species,
except where ~nodifiedby natural or human-mediated
clist~rrbal~ce
(Table I. Figs. 5 and 6 ) .
Non-native plant invasions within and among North~t.lestmou11taii-r ecoregions vary accol-ding to clii~~ate,
elevation, soils, and topography that contributes to
differences ill vegetation that distinguish each ecoregion.
C.C; Pal-kh ci al. Pcl-spcctivc~111 Plan1 Ecology. E\-olutinn xnd S!hlcmatics 7 (2005) I37 - 158
Land Cover Type
Xeric Grasslands
Upland Shrublands
Riparian
-
1
I
i
1
Wlesic Decid. Forest
Mixed Xeric Conif. Forest
.
Mixed Subalpine Cunif. Forest
<
"
A
-
'
Xeric Pseudotsuga menziesii
-7
:
"0
,
a
.
,-
I
I
Mixed Coastal Forest
Other Aftemisia spp.
-
Shrubland Purshia spp.
invasive with disturbance
Subalpine Meadow
Saltdesert. Shrub
0
ID 20 30 40 50 60 70 80 90 100 110 220
Ilnvasiva Species Richness
Fig. 6. The number of non-n:~~ive
plant species. listed as noxious by the state o f Oregon that can pote~itiallyinvade different landcover 1yiJes in the mountain ecoregions of Oregon. A species is calegori~edas 'invnsive' if the species c ~ t nobtain dominance 01-coclomillnnce in the absence of intense or li-ecluent disturb~inceevents. 'Invasive with cIisturb;itlce' refers to noii-11a~i1~e
species t l x ~ t
recluire ciisturbance that ilnprtcts the soil S L I S ~ ~ or
I C ~vegetation layer to es~ablish.
Thus, the western slopes of the Cascade ecoregion (Fig.
7), illfl~~e~lced
by a maritime climate, support dense
conifer forests with a subcanopy of trees and many
understory sl~rubs.ferns, herbs. bropl~ytes,and lichei~s
(Franhli 11 and Dyrness, 1973). Similar vegetation
extencts inland, on west-fi~cingslopes. to the Middle
Rocky Mour~tains us a peilinsula created by storm
tracks that extend as far soutl~east as Yello~i!stone
National Park in the Southern Rocky Mountains
ecoregion (Brouillet and \Vl~etstone. 1993). Therefore,
the il~ostmesic sites or the Rocky Mountains ecoregions
and the Siersan Steppe Ecoregion in 01.epol1 have
vegetation remarkably similar to those of pasts of the
Cascade ecnregioil in western Oregon and W a s h i ~ ~ s t o i ~
(Brvt~illetaitcl ?t7htjls~one.IC)93).The eastern mounlain
slopes of tile Cascacle ecoregic>n, however, and he
southern and eastern edges of the Sierran Steppe
Ecoregion, are characterized by a drier conti~lental
cli~llalewith cold winters and hot summers similar to
I I I L I C ~ or the Middle Rocky ecoregion that exhibit a
no re open vegetation coil~piexthat proceeds ~ I I ~ c > L I ~ I I
zones of Jui~i/~c.rus
oc,c.ic/c~j~
i c r l i , ,I - ~ P II ~ S ~ SCLII V ;11~lla, a 11d
P ~ ~ ~I O~I I I~ IsC ' I ' O S Lforest,
I
to a nlesic A h i ~ ~i cst ~ i o ( ' ~ or
rp~~
T,sligc~ rlrc~r.tcn.~ici~~(
forest a bot'e 1 500 111 elevation
(Hrouillct and LVhctstone, 199-3). Tl~roughout the
Northwest, climate, physiograpl~y.and vegetation define
the plai~tinvaders that are shared anlong the ecorepions.
For exalnple, coi~stalinvaders are typically herbaceous
perennials, such as Cor.tocit~r-icr Jlihat~~ and Antho.~lri?th~,nr
ot/or.trtu~~l,
whereas drier interior areas are invaded by
Eurasian annuals. Across the Northwest mountail1
ecoregioils the mid- and lo~ver-elevation valleys of
of Great
grasslands and shrublands have a i~u~mber
Basin attributes and associated species, such as BI.OIJIZIS
frctcjrrrrll. We found little evidence in the literature to
suggest t h ~ l tnon-native plant species that are sflared
;rmong ecol-egions beilaile differently in the different
ecoreglons.
Land-use and 1:ind-cover change has undoubteclly
bee11 the underpinning for the successful introducof non-native plants in the
tion and estitblish~~~ei~t
Northwest mountains. Current ;tnd historic land use is
15-3
C.G. Parks ci al. ,' Pcrspcc~i\:csin Plan1 Ecolog>. E\olui~onand Systcmutica 7 (3005) 137-158
Tahle 3.
Percent:~geor area in t h e three mount:iin ecoregions of Oregon in each Irtnci-cover category presented in Fi:.
6
Ecoregion
Vegeta lion types
Cascade
Sierra11Steppe
hliddle Rocky
Xeric GI-asslands
Uplnnd Shr~~blnnds
Riparian
Mesic Deciduous Forest
hl ixed xeric coniferous forest
Misecl Subalp. Coniferous Forest
mcr~rii~,sii
Xeric P.sc~r0ot.s~r~gcr
Pillll,~c'olltor'to
P I I I ZII) U. ~I I C / ~ ~ I . O S N
Mised Coastal Forest
~~,sILI
Other A I * ~ c ~ I ~spp.
A~.tmii.s.c;iotri~kwtcritr
.lztni~x~ru.s
c~~~c~itkent(rli,r
C?~~r.c.oc.rrry)zt.s
T,~zr[lrr
11ic~r.tcw.sion~1
Shrubland - PIII-.VI~~LI
spp.
Subalpine Meadow
Salt-desert Shrul-,
an iml3ortailt Fzictor in non-native in~asive plant
management. particularly as it relates to grazing, forest
urban develmanagement, fire and fuels mnnageme~~t,
opment, and recreation. The ecoregions or concern in
this paper fill1 into three general lai~d-usecategories -a~~thropogenic
systems. 11unla11 imp;icted natural systems, and wilclerness areas and some national parks
(W~lliams.f 993) - tllrit are spatially interwoven, t h o ~ ~ g h
orten discernrible by elevation and terrain. Because the
human use ~ ~ n t t e r nare
s different for ex11 of these
c;ltegol-jes, the threat of non-native plant invasions to
then^ also dirfers.
The first category of land use is anthrol-~icsystems,
iv11icil have a high degree o f 11uma11 use and impact.
These systems are often at low- to mid-elevations and
i~lcl~lde
E i r i ~ ~forests
s,
near towns. roads. rights-of-way,
homesites. and illanaged parks and camlxites. Human
settlement and intense 1;lnd development will likely
continue to transfer non-native plnitt species into these
areas. but they will probably be concentrated in the
mountain footl~illsbecause of extensive federally owned
lands and rugged topography at lligher elevations.
Roads and riparian areas are the major conduits for
dispersal of 11011-nativespecies in this land-use category,
with tlie degree o r pe~letration of non-native plant
species into associated natural areas depending 011 the
letel o r disturbance to theln.
The second category o r land use, human iillpncted
natural systems. eixmmpasses areas that have experienced intense or prolonged anthropogenic animr~l
grazing, logging, an altered fire regime, or old fields
fro111 pr~st rarmi~tg activity. Roads create significant
palhways for pl:int intl-oductions, and forests in this
land-use category are extensively logged. In such areas,
herbaceous non-native species can be locally abundant
depending 011 the degree of disturba~~ce.
r~itesuccession
to native sllrubs and trees, and amount of co~l~lecting
roads. Recently. large tracts o r lands in the region have
experienced stand-replacin: wildfire. Howe~ler,tlle role
o r wildfire on the introduction and establishment of
alien pl:lnts remains ullclear, except for tlleir association
with the soil disturb;~nce o r roads and road building.
Non-native plrint iilvasio~lsi l l severely grazed ~neadours
and old fields are often the ob-ject of local site
restoration.
Wilderness areas and solme natioilal parks colllprise
the third category of land :it risk to 11011-native plant
invasion. These are areas designated for limited ltun~an
use, preservation of nat ui-a1 biota, and mriintenance of
ecological integrity. The intact vegetation cornmoll in
such areus co~nn-ronlyliillits the ir~trusionor non-native
plants to within a few meters of trails. Ripal-ian areas
withill wilderness often have the l~ighestoccurrence of
11011-native plant illvasiolls because they experience the
most hurn:~n use. while wilderness alpine areas I-en~ain
relatively free of plant invasiolls.
Our analysis found altered riparian systenls to be
especially vulnerable to plant invasions. Studies show
tlli~t species-I-icll r~parian con~~nunities
that receive
an iiltermsdiate level of disturba~~ce(fire. flood,
herbivory) have more reso~trcesavailable Tor invading
species (Planty-T:i bacchi er xi.. 1496: Slohlgren et a]..
154
C'.G. Park3 cl al
,
Pcrbpccli~~cs
i n P1:ini Ecology.
I qCIC)tt.1 ) ) . Riparian habitats, while making 111-1 u
relatively small area acl-oss the mouiit~~in
ecoregions of
the Northwest, have significant ecological. cultural, and
econo~nicimport:~nce. For example, an estimated
of wilcllife species depend at sonie tinie dill-ing the year
011 this limited area for llabitat ('Thontah. 1979; Tcnigh~.
IClCl-2).
Alpine and subalpine areas of tlie Nortliwest :Ire
still rel:ttively uli1111p:tcted by invasive plant species.
These co~nmunitiesnirtke a critical contrib~~tiolito
overall biodiversity and deserve special protection fro111
threats caused bq increased humrtn activity. including
i~l~lrtsi\je
plant i~~troductions
(R:tph;tcI rt ;I].. 11003).
\Vilclerness areas and ilational parks. in general. may
be at particular risk to new pla~-rtinv;tsions. Macf>onalrl
et ul. ( I
obserlled sigl-rificant correlatioi~sbetween
the number of visilors to natural areas and the i~umber
of non-native invitsive plants in those reserves. Positive
correl:~tion between visitor numbers and invasive plant
richness suggests that visitors are either increasing
r~ccidei-ital introductions or that more visitors cause
more disti~rbnlicestliat facilitates invasive plant establisl~ment,or both (X,o~lsdaIe,109%). This indicates that
the Irtrger North\vest parks that crin hold Inore visitors,
e.g., Yellowstolie National Park. are potentially at
higher risk th:~ii sllialier parks to plant invasions nt all
elevations. M7ilderness areas and parks tliut are contigi~ousto one of the other land-use categories. human
impacted systems or anilirol>ic systems, are also likely to
be at higher risk to plant illvasions than ~vildernessareas
and parks that are continuous.
As pointed out by Lol~sd;tli: ( 1999). to simply
determine which ecosystems have {nore invasive species
does not answer the cluestion of wl~icliecosystems are
intrinsically more invasible. In 1111 anitlysis of native and
non-native pl:tnts along the lalitudinal zradient i l l the
US, Stohlgrcn ci a!. ( 2 0 0 5 ) conclude that Iiirm;~ns
f;lcilit:lte the initial estal~lisli~iieni
of lion-native plants,
but the spread and subseqt~entdistributions of nonnative plallts are controlled by biotic ancl enviro~lmental
factors. For example. a biotic factor limiting invasion o S
coii~monnon-native plants into alpine zolles may be
growth rate. Most alpine plants exl~ibilI-elatively low
growtll rates rind exhibit vegetative developmental
patterns that lilllit tl~eir growth capacity, includiiig
preformation of bi~ds2-4 years in advnnce of emergelice
and reduced cell numbers relative to lowlaild congeners
(HC~M'RI;III
and F>amn~. 2002). However, since some
species. including grasses and solne herbs, can PI-oduce
vegetative shoots ill the salile growilig season in which
they emerge, their likelihood of becoming a sticcessfi~l
plant invader into ~llpineecosystenls may be illcreased
over non-n:lti\/e plants without this ability.
Clearly. the interaction among suitable habitrtt,
c1ispers;tl potential, prop;lgule production, and absence
of biotic u i d iibiotic hazards determines the I-elr~tive
success of 1: no~l-n~ttive
p1i111t introductiotl (l-ctr~sdali..
SO'Yij
1999). However, little cluaiititative data 011 these fnctors.
other t h ~ t nthe largely descriptive information reported
in this paper, is mailable to determine the risk of
dirferent plant communities to non-natl~eplant invusioiis or to project their r:~les of spread. Thus, land
Iiianagers in the region now nii~stconsider ewry nonnative pla~itinvasion tliat occurs in any habitat a risk
and attempt to eradicate the plants, rather t1ia11
systematically locate plant invasions or to prevent their
occurrences in particularly risky l-rnbitats. Slraf i eL xi.
( 2 0 0 3 ) and I<c.u t ' ~: t i . (2005) propose methodologies to
determine Iinbitrtt risk and rates of expansion of milnative plant species. K~~ciow\.ich
et .d. (7005)describe a11
approach to project invasive plant expansion that relies
on proximity of 11011-native species to susceptible
habitats, empirical information on not?-native plant
species population cfynamics, and their dispersal distances. Reliable and consistent spatial databases among
land management agencies to doculnent ~~oiz-native
plant presence in distilrbed and undis~urbed plant
communities will be required for managers to pror1ctively prevei~tor contain invasive plant species in the
mountains of the Northwest.
Several global processes, including climate. eco~-io~nic
globalization, and alteration of nutrient cycles itre
predic~ed to contribute to escalating rates of species
invasions and impacts (C'ilornesky et 21.. 2005). How
will mountain ecoregions respond to these processes?
Mountain ecoregions have a unique complex lrindscape
struct~tre.land-use histoi-y, and current laud-use patterns that influence their susceptibility to non-nat ive
plant invasions. Under-standing [lie landscape patterns
of non-nat ive plant invasions in mountain ecoregiot-rs.
especi;llly us they interact with the dynamics tliat follow
local dist u~.b;~nce.;tTfords new insights for managing
piant invasions. Accomplisliing these management
objectives. however, will recluire a new level of
cooperation ariiong international, national, and local
governniel-it agencies. private l~tnclonners.and general
citizens.
We thank J.L. Hayes, L. Spiegel, D. Sal-r. two
anonymous reviewers, and especially H. Dietz for their
critical insigl~ts on drafts of tlie m;tnusci-ipt. We
appreciate tlie technical support ancl editing provided
by J. Wells, J. Harper, and 3.Stewart.
References
Agee. J.l<., Huff. M.H., 1980. First year ecologic:tl effecls of'
tlie Hoh fire, Olympic Mountains, Wasliington. In: Mat- in.
R.E., Ed~nonds. R.L., Faulkner-, D.A.. Hart-ington, I.R.,
C.G. Pal-ks cr ;\I. / Pcrspuct~vcsin Plant Ecolog). E~olu~ion
iind Sys~cmatica7 (1005) 137-158
155
wa -IVII~LIII;IIINx~ional Forests. R6-N R-ECOL-TP-22-97.
Fuiluny. D.M., Sti,cks, B.J.. Rarr, S. (Eds.), Fire and Forest
US Department of Agriculture, Forest Service, Pacilic
Meteorology Conference Proceedings. vol. 6. Society of
Northwest Region.
Auiierican Foresters, Wr1~11i11,nton.DC, pp. 175-1 81.
D;lIe. D., Weaver. T., 1973. Tranipling effects on vegetation of
Aitken, M., Parks, C.G., 2004. Guide to the Coni~lion
the trail curl-idors of north Rocky Mountain forests.
I ' o t ~ i z t i l l i ~ Species of the Blue hllountains Ecoregion.
J. Appl. Ecol. I I. 767-772.
PNW-GTR-607. US Dep:\rtment of Agriculture, Forest
D'Antonio, C.M., 2000. Fire, pliint in\r:~sio~is:~nd global
Service, Pacific Northwest Research Station, Portl:~nd.
cliangzs. In: Mooney. H., Hobbs, R. (Eds.). Invasive Species
Ament, R.. Cr~~ighead,
L., 1998. An~ericanwildlands coniin a Chnnging Q70rld. Islr~ndPress. Co\pelo,pp. 65-94.
pletes model-building phase of vital land linkage corridors
DeFerrari, C.M ., 1993. Non-indigenous plant invasions across
in tlie Northern Rockies. J. AIII. Wildlands 9 11ttp:i;
landscape patch types on the Olympic Peninsula. M.S.
\v.~vw.wildln1ids.org/u~ildsidejspr9S/~~g
13.11tml.
Thesis. University of Washington, Seattle.
Appleby, M.W..4., 1998. The incidence of exotic species
DeFel-rari, C.h4., Naiman, R.J., 1994. A multi-scale assessfollowing clearfelling of Er~c.c~/jy>tlu
r.cJgrz[nrs forest in the
ment of the occurrence of non-indigenous plants on the
Central Highlunds. Victoriil. Australian Journal of Ecology
Olynipic Peninsula, Washingtou. J. Veg. Sci. 5, 347-258.
23, 457-465.
Douglas. G.W., Ballard, T.M., 1971. Effects of fire in alpine
Arnold, S.J., Anthony, J.A., 2000. Suninl;~ryof cursell t status
plant conin~unitiesin the N o r t l ~Cascades, \Vashington.
of exotic species in Oregon. Oregon State of the EnvironEcology 52. 1058-1064.
111ent Report 2000. Oregon Progress Board. pp. 127-1 3 1.
Doyle, K.M.. Knight, D.H.. Taylor, D.L., R:~rryil~ore.W.J..
( k r i g~:,';egoi..ore~on
.$oil/]>AS ~OI'i3:'tlo~s~SOE:
R3000
Renedict, J.M., 1998. Sevenleen years ol' [orest succession
Ch3-12.pcli') ( 10 Decern ber 3004).
following tlie \Vaterf:tlls Canyon Fire in Grand Teton
Bailey. R.G., 1995. Description of tlie Ecoregions of the
National Park, M;yoniing. I n t . J . Wildlancl Fire 8, 45 55.
LJnited States. US Depnrt~nent of Agriculture, Forest
Dwire, K . 4 . . Parks, C.G.. 2002. Noteworthy collections,
Service, Misc. Publicaiion No. I39 I l ~ t t pi~\\l\~.f~.fed.us/l.~~/
:~
Iiic.1.rrc.ii1111 cvti~.s~~ito.~irtil
DLIIIIO~~.,
an iii11asii.e species new
colo~iniage~iiapieco~-egl
provinces.lit~iil.
lo Oregon. Mudrono 4, 58.
Recker, T., Dieiz.. H., Billeter, R., Ruschri~;~~ln,
H., Edwards,
Dyrness. C.T., 197.3. Early stages of plant succession fi>llowing
P.J., 2005. Altitudinal distribution of alien plant species i n
logging and burning in the \vestern C;~scudesof Oregon.
the Swiss Alps. Perspect. Plant Ecol. Evol. Syst. 7. 173-1 83.
Ecology 54. 57-69.
R o ~ ~ l m a W.D.,
n,
D:l~lim, M., 2002. Causes and consequences
Fr~lnklin. J .F.. Dyrness, C.T., 1973. Natural vegetation of
of alpine \~ascularplant diversity in the Rocliy Mountains.
Oregon and Wasliington. General Technical Report GTRTn: I<ijrner, C.H., Spehn, E.M. (Eds.), Mountain RiodiPN'M7-8. US Department of Agriculture, Forest Service,
versity: a Global Assessn~ent.P:irthenon Publisl~inp.New
Pacific Northnest Forest and Range Experi~nentStation.
York, pp. 101-197.
Franklin. J.F., Dyrness, C.T., 1988. Nntrtrnl Vegetation of
Broi~illet,L.. Whetstone, R.D., 1991. Climate and physiograOregon and Washington. Oregon Strite University Press,
phy. In: Co~nrnittee (Eds.), Flora of North Anierica.
Oxford University Press, New York, 1313.131 - I 35.
Corvallis.
Goodwin. K.M.. Sheley, R.L., 2001. What to do when fires
Burns, R.M., Honl<oIa, R.M. (Eds.), 1990. Silvics of North
fuel weeds. Rangelands 33, 15-2 1.
America. US Depart~nentof Agriculture. Forest Service,
Hulpern, C. R., 1989. Early successional patterns of forest
Washington, DC.
species: interactions. of life history traits and disturbance.
Chornesky. E.A., Rartuska, A.M., Aplet, G.H., Britton, K.O.,
Ecology 70, 704-720.
Cunimings-Carlson, .I., Davis, F.W., Eskow. J . , Gordon,
Hi~lpern.C.R., Antoh, .I.A., Geyer. M.A., Olson. A.M., 1997.
D.R., Go~tschalk, I<.\V., Hnack, R.A.. Hansen, A..I.,
Species replaceriient during early secondary succession: the
Mack. R.N.. Raliel, F.J., Shannon, M.A.. Wninger, L.A.,
abrupt decline of n winter r~nnual.Ecology 78. 62 1 - 63 1.
\Vigle~r,T.B., 3005. Science priorities for reducing the threut
Halpern. C.B., Evans, S.A., Nielson, S., 1999. Soil seed banks
of invasi~especies to sustainable forestry. BioScience 55.
in young, closed canopy forests of the Olympic Peninsula,
335-349.
Washington: potential contributions to understory reinitiaCole, D.N., 1983. Veget~~tion
of Two Drainages in the Eagle
tion. Can. .I.Bot. 77. 922-935.
Cap Wilderness. Wallowa Mountains, Oregon. INT-388.
Hansen, A.J.. Rasker, R., Maxwell, B.. Rotella. J.J., Johnson,
US Depart~i~ent
of Agriculture, Forest Service. IntennounJ., M7rlght Parillenter, A,. Lnngner, U., Colien. 'A",
t:~inForest and Range Experinlent St~ition,Ogden.
Lawrence, R., Kraska, M.V., 2002. Ecolcjgical causes and
Cook. J.G.. 2002. Nutrition and food. In: Toweill. D.E.,
consequences of demographic change in the new West.
T h o ~ n ,J.W. (Eds.), Nol-th An~erican Elk: Ecology and
BioScience 52, 151- 168.
Manr~gement.Sn~ithsonianInstitutioi~Press, Washington,
Harrod, R.J.. 2001. The effect of invasive lttld novious plants
DC, pp. 250-349.
on land management in eastern Orzgon and Washington.
Cc~oper, S.V., Jean. C.. 2001. Wildfire succession in plant
North~bestSci. 75, 85-90.
comn~unitiesnatural t o 1112 xlhali creek vicinity, Charles M .
Heckmann. C.W., 1999. The encroachment of non-indigenous
Russell National Wildlife Refuge. Montana. Unpublislied
Iierbaceous plr~nis into the Olyn~pic Natio11;~I Forest.
Report to the US Fish and Wildlife Service, Montana
Nortl~~vest
Sci. 73. 2614-276.
Natural Heritage Profram, Helena.
He~nstrom. M.A., Franklin, J.F., 1982. Fire and other
Crowe, E.A., C1:iusnitzer. R.R., 1997. M icl-montane Wetland
disturbances of the forests in T~louiit Rainier National
P1:int Associr~lions of he Malhuer, Un~atilln,and LVrlllo-
156
C.Ci. Parks
C I ill.
Pcl-.\l~oc~l\~c.s
111 Pl;int Ecology. E\olulion and S)slun:llics 7 (2005) 137- 1 %
Park. USDA Forest Senice, Willamette National Forest.
Eugene. Oregon. USDA Forest Service. Pacific Nortli\\est
Forest and Range Experiment Station, Corvallis. Oregon.
Quat. Res. 1 S, 32-5 1.
Huff, M.H., 1984. Post-fire succession in the Oly~iipic
Mountains. W ~ ~ s h i n g ~ oforest
n:
vegetation, fuels. xnd
avifi~una.PI1.D. Thesis, University of \Vrtshington, Seattle.
Ingersoll. C.A.. Wilson, M.V.. 1989. Buried propagules in an
old-growth forest and tlieir response to esperiine~ital
disturbances. Cali. J. Bot. 68, 1 156-1 162.
Jackson, P.L.. Iiimerlin~,A.J.. 2003. Atlas of the Pacific
Northwest. Oregon State U niversity Press.
.lohnson, C., 2000. Noxious Lveed inrestations by forest 111;~~.
IJSDA Forest Service. (Iit~p:,\~~1n.t~s.lirl.us~r'-I-Il1~oize
11)trnl resources no.i1c3us-needs regweed rnap.pdf ) .
Johnson. J., h4as~vell.R., Aspinall, R., 2003. Moving nearer to
Iieaven: 21-ou:th and change in the Greater Yellowstone
Region, USA. I n : Bucliley. R., Pickesing. C., Weaver, D.R.
(Eds.), Nature-Based Tourism, Environment, and L:tnd
Munagernent. C24BInternational Publication. W~tltingford,
Oxon, pp. 77 -88.
Kartesz, J.T., 1999. 4 syiiony~iiizedchecklist and atlas with
biological attributes for the vascular flora of the United
States, Canada, and Greenland. In: K~trtesz,J.T., Meachum, C.A. (Eds.), Synthesis of the North American Florrl.
North Carolina Bot;ruical Gitrden, Chapel Hill.
Iceiter, R.B., Boyce, M.S., 1991. Tlie Greater Yellowstone
Ecosystem: Redefining America's Wilcierness Heritage.
Yale University Press, New Haven.
Klamrith National Forest (I< NF), 2004. iilamu~hNational
Forest Nosious, lnvasive Weed Project. (I-rt~p:::u.n~\~.li.fed.usrr5 'kinn~atli:ptojects no.titruswt.eds'index.~l~itril) (73
N ove~iiher 2004).
Knight, D.H.. 1991. Tlie Yellowstone fire controversy. In:
Keiter, R.B., Boyce. M.S. (Eds.), Tlie Gre~tterYello~i~stone
Ecosysterii: Redefining Ariierica's Wilderness Heritage.
Yale University Press, New Haven, pp. 87-103.
Knight. D.H.. 1994. Mvuntains and Plains. the Ecology of
\T1yoming Landscapes, Yale University Press. New Haven.
Kr:ienier. J.F., 1977. The long-~ermeffects of burning o n pla~it
succession. M.S. Thesis, Oregon State University, Corvallis.
Langner. L.L., Flather, C.H.; 1994. Biological Diversity:
Status and Trends in the United States. US Department
of Agl-iculture. Forest Service, Rocky Mountain Forest and
Range Esperi~iientStation, Fort Collins.
Lonsdnle, W.M., 1999. Global patterns of plant invasions and
the concept of invasibili~y.Ecology 80, 1522-1 536.
Macdonald. I.A.. Lrjope. L.L., Usher. M.B.. Harnrinn. 0 . . 1989.
Wildlife conservation and the invasion of nature reserves by
introduced species: a global 1x1-spective. In: Dsrtke, J.A.,
Mooney. H.A., dicastri, F., Groves, R.H., Krugel-, F.J..
Rejmanek, M.,Williamson, M . (Eds.), Biological Inv;\sions:
a Global Perspective. Wiley, Cliichester, 1113.2 15-255.
Mack, R.N., 1986. Alien plant invasion into the Inteniiount~~in
West: it case history. In: Mooney, H.A., Drake, J.A. (Eds.),
Ecology of Biological Tnvasions of North America and
Hatvaii. Springer, Berlin. pp. 19 1-2 13.
Marcus. W.A., h/lilner, G., M;tx~vell. B., 1998. Spotted h a p weed distribution in stock camps and trails of the SelwayBilterroot M!ilderness. Great Busin Nat. 58, 156-1 66.
Marion, J.L.. Cole. D.N.. Bratton. S.P., 1986. Esotic
vegetation in wilderness areas. In: Luals, R.C. (Ecl.),
Na~ional Wilderness Research Conference: Current Research. USDA Forest Service, Intermount~ti11 Research
Station, Ogden, pp. 1 13-120 (General Technical Report
INT-212).
Markin, G.P.. 2003. Weeds of National Forest Lttnds of the
~
Northern Rockies. Retrieved from: (http:, , w u ' .f\.fed.us,
rm /ecology,st~1clies~\~ic~ci~t~tro1I'~~~eecis~NFL~re~~or1.~~dS)
(25 February 2004).
McDougall, K.L., Morgan, J.W., Walsli. N.G.. Williams. R.J..
2005. Plant invas~o~is
in treeles vegetation of the Australian Alps. Perspect. Plant Ecol. Evol. Syst. 7. 159-1 71.
Merrill, E.H.. Maryland. H.F., Peek, J.M., 1980. Effects of a
fr~llwildfire on herbaceous vegelrttion o n xeric sites rn the
Sel~vay-BitterrootWilderness, Idaho. J. Range Manage. 33.
363 367,
Milberg, G.P.. Laniont, B.B.. 1995. Fire enhances ckeed
invasion of roadside vegetation in southwestern Australia.
Biol. Conserv. 73, 45-49.
Miles, D.W.R., Slyanson, F.J., 1986. Vegetation composition
on recent landslides in the Cascade Mountains of ivestern
Oregon. Can. J. For. Res. 16, 739-744.
Miller, M.M., Miller, J.W., 1976. Succession after wildfire in
the North Cascades National Park coniplex. In: Proceedings of the Annual Tall Tinibers Fire Ecology conference:
Pacitjc Northwest. Tall Timbers Research Station. Tallahassee, pp. 71-83.
Morris, W.G.. 1958. Influence of slasli burning on regeneration, other plant coI1er, and fire hazard in the Douglas-fir
region ( a progress report). Research Paper PNW-2'). US
Department of Agiculture, Forest Service. Pacific Northwest Forest and Range Experinlent Station, Portlrtnd.
Mueggler, W.F., Stewart, W.L., 1980. G ~ i s s l a n dand slisubland habitats of Western Montana. USDA Forest Service.
General Technical Report INT-66. lntermountai~iForest
rind Range Experi~nentStation. Ogden.
Northwest I-labitat Institute, 1998. Oregon GAP Analysis
Vegetatioti. Midcontinent Ecological Science Center. US
Geological Sur-vey, Fort Collins.
Noss, R.F.. 1993. A conservation plan for the Oreson Coast
Range: some preliminary suggestions. Nat. Areas Ass. J.
13. 376--390.
Odion, D., Sarr, D., Truitt, B., Duff, A.. Smith. S.. B~unl.W..
Beever, E.. Sliafes, S., S~iiitli.Rocchio, J.. Hoffnian. R..
Currens, C.. Made-j, M., 2005. V~talSigns Monitoring Plan
for the IClamatli Network: Pliase 11 Report. K1~1ii1atI-r
Network-National Park Service. Aslilitnd.
Parendes, L.A.. 1997. Spatial patterns of invasion by nonindigenous plants in a forested landscape. M.S. Thesis,
Oregon State University, Corvallis.
Parendes, L.A., Jones. J.A.. 2000. Role of light availability and
dispersal in non-indigenous plant invasion along rortd and
stsexills in the H.J. Andre~vsExperimental Forest, Oregon.
Conserv. Biol. 14, 64-75.
Phillips. H.W.. 2003. Plr~ntsof the Lewis and Clark Expedition. klountain Press Publishing Company. Missoul:~.
Planty-Tabacchi, ,4.,
Tabacchi. E., Naiman, R.J., DeFesrari.
C.. Deca~iips.H.. 1996. lnvasibility of species-rich cornmunities in riparirtn zones. Conserv. Riol. 10. 598-607.
C.G. Piirks ot aI. / Pcrspcciivcs in P1:11itEcology. Evolution :)lid Sysicm:~iics7 (2005) 137-158
Qu~glfy, T.M ., Arbel bide, S.J ., 1997. An assess~nent of
ecosystetii components in the interior Colun~hia Basin.
Landscape dynan~icsof the basin, vol. 11. General Technical
Report PNW-GTR-405. US Department of Agriculture.
Forest Service, Pacitic Nolzliwest Research Station.
Ritdcrsevich, S.R.. Endress, R.A., P~trks,C.G., 2005. Defining a
regional r~pproaclifor invasive plant research and m:~nage~iient. 111: Inderjit (Ed.). Ecological and Agricultural
Aspects of lnvusive Plants. Birkhiiuses, Basel, pp. I4 I - 166.
Raphael, M.G., \I~isdum, M.J., Wales, B.C.. 3003. Status and
trends in diversity of alpine vertebrates in the Northwestern
United Stntes. 111: Korner, C.H., Spehn, E.M. (Eda.).
hgo~~ntain
Biodiversity: a Global Assessment. Parthenon
Publisl~ing,New York, pp. 191--197.
Re.jiiianek, M.. 2000. A must for North American biogeographers. Divers. Distrib. 6, 208-2 1 1.
Rejnx~nek.M., Randall, J.M.. 1994. Invrlsive alien plants in
California: 1993 summary and comparison Llith other areas
in North America. Madrorio 42, 161-1 77.
Rew, L.J., Maxwell. B.D., Aspinall, R., 3005. Predicting the
occurrence of non-indigenous species using envirc3111ilent:tl
and remotely sensed data. Weed Sci. 53, 336-241.
Rice, P.M., 2005. INVADERS Dr\t;tbase Sjtstem (http://
:nvad~r.tIl-ls.un.iiL.c:~111).
Division of Biological Sciences,
Univel-sity of Montana, Missoulri.
Rice, P.M., Rider. .I., 1995. L;indscal-le ecology. nosious weeds
invasion analysis. Final Report for Interior Colu~nbiaBasin
Ecosysten~ Mi~n~zgen~ent
Project. (tlttp., inv;~der.dhs.~~m1 &ti 1?~r:t1e~csl?-sep.!i1rn
).
Roche, C.T., Roche. B.F., 199 I . Meadow knapweed invasion
in the Pacific Northu.est, USA, and Brit~sh Columbia,
Canada. Northulest Sci. 65, 53-61.
Roclie, C.T., Mrliite, G.R., 3000. Managing J'ellon Starthistle
in Southwestern 01-egon. Oregon State University. Extension Service, Cor~fallis.
Romme, W., I<niglit, D.H., 1981. Fire frequency and
subalpine forest succession along a ropogr;tphic gradient
in Wyon~ing.E c ~ l o g y62, 3 19--326.
S:~rr. D., Shufelberger. A., Con~mons.M.. Runn. W., 2003.
Non-native plant inventory. I<la~iiathnetctlork inventory
and monitoring progrLun. Unl?ublished Annual Repost for
tlie Klamatli Network Inventory Program, Available from
Daniel Sarr: tian.s;trrlcr rlps.gov.
Saundel-s. D.A., Hobbs, R.J., Margules, C.R., 1991. Biological
consequences of ecusyste~nf r a g ~ i ~ e n l a t i ao ~review.
~:
Consel-I!. Biol. 5, 1 8 32.
Schoonmaker, P.. McKee, A., 1988. Species co~iipr)sitioriand
diversity during secondary succession of coniferous forests
in the western Cascade Mountains of Oregon. Forest Sci.
34. 960-97'1.
Schreiner. E.G.. 1982. The role of non-ind~genousspecies in
plant successton following Iiu~iiandisturbance in an alpine
itsea of Olympic National Pnrk, Washington. Ph.D. Thesis,
University of Washington, Seattle.
Seln~runtb,P.C., ICnight, H.D., 3003. Understory pliint species
composition 30- 50 years after clearcut tine in southeastern
Wyonling coniferous forests. For. Ecol. Manage. 185.
275- 2x9.
Sh~llii,B., Price, U'.J..
Pruther, T.S.. Lass, T.W., Thill, D.C..
2003. Predicting the likelihoc)d of Yellout St;tstliistle
I57
( ( . ' c w t ~ ~ l ~ r.sol.stiti~~ii,s)
-c~~
occurrence using landscape charac-
teristlcs. Weed Sci. 51, 718-751.
Sheley, R.L.. Petroff. J.K. (Eds.), 1999. Biology and Management of Nosious Rangeland Weeds. Oregon State University Press, Corvallis.
S~eiirart,R.E.. 1 978. Origin and develop~nent of vegetation
after sllruying and burning in a coastal Oregon clearcut.
Research Note PNW-317. US Department i4griculture,
Forest Service. Pacific NortlIuest Forest and Range
Experiment Station. Portland.
Stickney. P.F., 1980. Data base for post-fire successiori, first
6 - 9 years. in Mont3na Larch-fir forests. General Technical
Report, GTR-1NT-63. US Department of Agriculture,
Forest Service, Intermountain Forest and Range Esperiment Station, Ogden.'
Stohlgren, T.J., Binkley. D.. Chong, G.\V., Kalklian, M.A.,
Scliell. L.D., Bull, 1<.4., Otsukl, Y., Newnian, G.. Brtshkin,
M., Son. Y .. 19993. Exotic plant species invade hot spots of
native plant diversity. Ecol. Monogr. 69. 25-46.
Stolilgren, T.J.. Scl~ell.L.D., Heuvel, B.V., 1999b. How grazing
and soil q u a l i ~ j:tffect native and exotic plant diversity in
Rocky Mountain grasslands. Ecol. Appl. 9, 45- (-4.
Stolilgren, T..].,Rarnett. D., Fluther, C., Kartzsz, J., Petel-.john,
B., 2005. Plant species :tlong the latitudinal gradient in the
United Slates. Ecology 86. 2798-7309.
Strittholt, J.R., DellaS~tln,D.A., 2001. Tmportance of roadless
areas in biodiversity conservation in forested ecosyslems:
case study of the Klaniath-Siskiyou ecoregion of tlie
United States. Conserv. BioI. 15. 1737-1 754.
Thomas, .I.W., 1979. Wildlife habitats in nianaged fores~s:tlie
Blue Mountains of Oregon and Washington. Agric. Hr~ndb.
553. US Departnlent of Agriculture, Forest Service.
Washington. DC.
Thompson. R.L.. 2001. Botanical survey of Myrtle Island
Reseitrcli N ntural A rea. Oregon. General Technical Report
PNW-GTR-507. US Departnient of Agriculture, Forest
Service, Pacilic Northwest Forest and Range Experi~ilent
Station. Portland.
Toney. J.C.. Rice, P.M.. Forcella. F.. 1998. Exotic plant
rccords in the ~~ortli\vestUnited States 1950-1 996 ;ind
ecological assessment. Northwest Sci. 72, 198-213.
Turner, M.G., Ronlrne, W.H., Gardener, R.H., Haifpove.
W.W., 1997. Effects of fire size and pattern on early
succession in Yellowstone National Park. Ecol. Monogr.
67. 41 1 3 3 3 .
Tyser, R.W., Worley. C.A., 1992. Alien flora in grasslands
acl-jacent to road and trail col-ridors in Glacier National
Park. Montana (USA). Conseri,. Biol. 6, 253-363.
US Ce~isus Rurei~u, 2000. Census 2000 Su~s~nlrtryFile 1,
Matrix PI.
USDA Fore91 Service, 1995. Kuchler's Potential Naturrll
Vegetation - Point. Portland. 1 nterior Colun~bia Basin
Ecosyste~nManagement Prqject. ( http: \i'u9\i.icheti>p.ytn'
sp;~~i~tl:\,eg
).
USDA, NRCS, 2005. The PLANTS Database, Version 3.5
(http: ':j>l:~nts.u~ci:t.go\). Data coinpiled from various
sources by M;~rkW. Skinner. National Plant Data Center,
Briton Rouge, LA 70874-4390, USA.
Wnttersoti. N.. 3004. Noti-indigenous plant invusioris Troll1
roads to stream networks in sleep forested 1:tndscapes of
158
C.G. P;~rkscl ;11.
Pcrspcctivcs i n P l a n t Ecolog)/. Evolutivn 21nct Systcmalics 7 (2005) 137- 1 %
ttlestern Oregon. h1.S. Thesis. Oregon State Uni\lersi~y,
Corvrillis.
Weri\ er. T.. Gust~~rbon.
D.. Licht11;trdt. S., 200 1. Exotic pl:t~lts
in early and Ii~tesera1 vegetation of fifteen 1101-tliei-n Rocky
blounlain env~ron~iients.West. North Am. Nni. 61,
Witliers, M.A.. P;~Iiiier,M.W., Wade, G.L.. White. P.S., Neal.
P.R., 1999. Changing pallerns in tlie number of species in
on
North American floras. In: Sisk, T.D. (Ed.),Perspecti~~es
the Land-use Hislory of Nortli America: a Contest for
Understanding our Cliangrng Environmen~.US G z o l o ~ ~ c a l
4 1 7-427.
Sur\fey. Biological Resources Division, 1311. 73- 32. (BiologiWliipple, J.J., 2001. Annotated checkli5t of exotic ~ a s c u l ~ u
cal Science Report USGS/RRD:BSR 1998).
plants in Y e l l o ~ ~ \ t o nNe ~ t ~ i o n aPark.
l
West. North Am.
Wood. W., Ly~iian,H., 2.003. The Frank Church-Ri~erof No
Nat. 61, 336-346.
Return Wilderness Noxious Weed Treatments: D r a f ~
Wilcoce. D.S.. 1989. Protecting biodi\lersity in multiple-use
Supplemental Environn~ental T~iiprtctStatement. US Delands: lessons from the US Forest Service. TREE 3.
partment of ,4griculture, Forest Service. ( h r ~ p : fi~~.nrsv.fs.Sc;
355 -358.
cl us,r3 sc recrent~onfcr-onrl\ieed ltoc.pclS).
\Villiaii~s,T.. 1997. 1Ciller Weeds. Audubon, Net31 Yorlc.
Wooten, G., Morrison, P., 1995. Biologicul invtls~onsof alien
Wilson. L.M.. Jette. C.. C'or~nett.J., McCaffrey. J.P., 3003.
plants in the interior Columbia River Bas~n.In: Nelson, C.
Biology and Biological Control of Yellow St;~rtli~stle.
(Ed ), I<ey Ele~ne~lts
for Ecolog~calPl:inni~ig: Man;~gzment
FHTET- 1998-17. secorid ed. US Depart~nentof AgriculPrinciples. R e c o ~ ~ ~ ~ i i e n d ~and
~ t iGuideline\
o~~s,
for Federril
ture, Forest Sel-vice. ( I i t t p : 'u\\.u.~nr~;~s~vc.c~rgiweccis Lands East of the Cascade Crest In Oregon anci W;isl~ingstu~'tl~is~itt~chaptt.r.t
.ht~-111).
ton. a Report to tlie Interior Columbiit Basin Ecosystetn
With, K.A., 2002. The landscape ecology of i~ivasi\~e
spread.
Management Project. Columbia River Rial-egion CamConserv. Biol. 16, 1 192-1 203.
paign, Science Working Group. Walla Walla.