Many alien plants depend on humans toexpand their range (Hodkinson and Thomspon1997, Mack and Lonsdale 2001). Human activ-ity can introduce new plants both intentionallyand unintentionally and often creates habitatsthat favor alien plant establishment (Mack andLonsdale 2001, Mack 2005). Managers of Na -tional Parks and Forests and other natural areas
are becoming increasingly concerned aboutinvasive alien plants (Marler 2000). Past re -search has shown a positive relationship be -tween visitation rates and the presence of alienplants (Lonsdale 1999). As recreational use innatural areas increases, the number of alienplants and the area they occupy can also be ex-pected to increase, especially in sites disturbed
Western North American Naturalist 72(4), © 2012, pp. 507–533
RECREATIONAL TRAILS AS CORRIDORS FOR ALIEN PLANTS IN THE ROCKY MOUNTAINS, USA
Floye H. Wells1, William K. Lauenroth2, and John B. Bradford3
ABSTRACT.—Alien plant species often use areas of heavy human activity for habitat and dispersal. Roads and utilitycorridors have been shown to harbor more alien species than the surrounding vegetation and are therefore believed tocontribute to alien plant persistence and spread. Recreational trails represent another corridor that could harbor alienspecies and aid their spread. Effective management of invasive species requires understanding how alien plants are dis-tributed at trailheads and trails and how their dispersal may be influenced by native vegetation. Our overall goal was toinvestigate the distribution of alien plants at trailheads and trails in the Rocky Mountains of Colorado. At trailheads, wefound that although the number of alien species was less than the number of native species, alien plant cover (x– = 50%)did not differ from native plant cover, and we observed a large number of alien seedlings in the soil seed bank, suggest-ing that alien plants are a large component of trailhead communities and will continue to be so in the future. Alongtrails, we found higher alien species richness and cover on trail (as opposed to 4 m from the trail) in 3 out of 4 vegetationtypes, and we observed higher alien richness and cover in meadows than in other vegetation types. Plant communitiesat both trailheads and trails, as well as seed banks at trailheads, contain substantial diversity and abundance of alienplants. These results suggest that recreational trails in the Rocky Mountains of Colorado may function as corridors thatfacilitate the spread of alien species into wildlands. Our results suggest that control of alien plants should begin at trail-heads where there are large numbers of aliens and that control efforts on trails should be prioritized by vegetation type.
RESUMEN.—Las especies de plantas exóticas generalmente utilizan áreas de gran actividad humana como su hábitaty para su dispersión. Las carreteras y los corredores de utilidad albergan más especies exóticas que la vegetación circun-dante y, por lo tanto, se cree que contribuyen a la persistencia y propagación de plantas exóticas. Los senderos recre-ativos representan otro corredor que podría albergar estas especies y contribuir a su propagación. El manejo efectivo deespecies invasoras requiere comprender de qué manera se distribuyen las plantas exóticas en las entradas de lossenderos y en los senderos en sí y cómo su propagación puede estar influenciada por la vegetación nativa. Nuestro obje-tivo general fue investigar la distribución de plantas exóticas en las entradas de senderos y en los senderos de las Mon-tañas Rocosas en Colorado. En las entradas de los senderos, descubrimos que, a pesar de que la cantidad de especiesexóticas fue menor que la cantidad de especies nativas, la cobertura de plantas exóticas (un promedio del 50%) no fuediferente de la cobertura de plantas nativas, y observamos un gran número de plántulas exóticas en el banco de semillasdel suelo, lo que sugiere que las plantas exóticas son un gran componente de las comunidades que habitan las entradasde los senderos y continuarán siéndolo en el futuro. A lo largo de los senderos, encontramos mayor riqueza y mayorcobertura de especies exóticas en los senderos (en lugar de a 4 metros de distancia desde el sendero) en tres de cuatrotipos de vegetación y observamos más riqueza y cobertura de plantas exóticas en praderas que en los otros tipos de veg-etación. Las comunidades de plantas en las entradas de los senderos y en los senderos, así como los bancos de semillasen las entradas de los senderos, contienen una diversidad y abundancia sustancial de plantas exóticas. Estos resultadossugieren que los senderos recreativos en las Montañas Rocosas de Colorado pueden funcionar como corredores quefacilitan la propagación de especies exóticas en tierras silvestres. Nuestros resultados sugieren que el control de plantasforáneas debería comenzar en las entradas de los senderos donde existen grandes cantidades de estas especies exóticas yque se deberían priorizar los esfuerzos de control en los senderos según el tipo de vegetación.
1Former Graduate Student, Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523.2Corresponding author. Department of Botany, University of Wyoming, Laramie, WY 82071. E-mail: [email protected]. Geological Survey, Southwest Biological Science Center, Flagstaff, AZ 86011.
507
by human activity because of the strong linkbetween disturbance by humans and the es -tablishment of new plants (Hobbs and Huen-neke 1992, Burke and Grime 1996).
There is evidence that human-made corri-dors often harbor alien plants. Roadsides andutility corridors both have been shown to har-bor more aliens than surrounding vegetation(Tyser and Worley 1992, Panetta and Hopkins1993, Rubino et al. 2002, Pauchard and Ala -back 2004). Since human-made corridors linkthe front country to the backcountry, trails areof particular concern to managers of naturalareas because they may provide a route foralien plant dispersal into wildlands. Severalstudies have documented higher numbers ofalien species and cover directly next to thetrail compared to the surrounding vegetation(Benninger-Truax et al. 1992, Campbell andGibson 2001, Dickens et al. 2005, Potito andBeatty 2005, Gower 2008).
To understand the threat posed to naturalareas by trails, trailheads deserve special con-sideration. Trailheads tend to be heavily dis-turbed areas with regular vehicle traffic andmay provide a site for alien plant establish-ment. If trailheads harbor alien species, it isthen possible for those plants to disperse alongthe trail corridor either by slowly establishingalong the trail edges or by attaching to trailusers (Mount and Pickering 2009).
Understanding the role of trailheads in har-boring alien plants requires characterizing boththe existing vegetation and the soil seed bank.Species that produce persistent soil seed banksusually have small seeds without additionalstructures for dispersal, such as awns or hairs(Thompson and Grime 1979, Thompson 1987).It is common for alien species with seeds thathave these characteristics to travel as a conta-minant in soil on the vehicles (Hodkinson andThomspon 1997) or footwear (Clifford 1956,Salisbury 1961) of humans. The presence ofsignificant alien seed abundance in the trail-head seed bank implies the potential for thosealien species to disperse along the trail.
The few studies that directly link trails withthe presence of alien plants focus on the dif-ference between trails and roads (Tyser andWorley 1992, Stroh and Struckhoff 2009) ordifferences in use levels and types of trails,particularly if trails are used by horses andpack stock or by hikers alone (Benninger-Truaxet al. 1992, Gower 2008). Hikers and horses
have different types of impacts on the vegeta-tion and soils (Pickering et al. 2010, Quinn etal. 2010). Horses pose a special concern sincehorse feces contain viable alien seeds that canthen be deposited into natural areas (Camp-bell and Gibson 2001, Wells and Lauenroth2007, Quinn et al. 2008).
Vegetation type may influence plant com-munity resistance to alien establishment (Lons-dale 1999). In fact, some studies have found asignificant relationship between vegetationtype and the number or cover of alien plants(Larson et al. 2001, Pysek et al. 2002, Vilà etal. 2007, Stroh and Struckhoff 2009). Unlikemany regions, where a trail passes throughone dominant vegetation type, in the RockyMountains, trails generally pass through sev-eral distinct vegetation types. We explicitlyincluded vegetation type in our study to deter-mine whether vegetation type could be usedby land managers to prioritize areas that aremore prone to alien invasion.
We examined both trailheads and trails inthe Colorado Rocky Mountains to determine ifhuman activities were influencing alien plantestablishment and spread. For trailheads, wehad 2 objectives: (1) to determine the similaritybetween seeds in the seed bank at trailheadsand seeds at adjacent (~200 m away) siteswithout trailheads and (2) to determine thesimilarity between the plant communities attrailheads and those at adjacent sites withouttrailheads. For trails, we had 3 objectives: (1)to determine if trailsides harbored more alienplants than the adjacent plant communities,(2) to find out if some vegetation types weremore heavily invaded than others, and (3) toexamine use patterns to see if there was a con-nection between the level of use or the type ofuse and the presence of alien plants.
METHODS
Site Description
TRAILHEADS.—We sampled a total of 9 trail -heads in the Colorado Rocky Mountains: 3mountain trailheads on the western slope (west -ern side of the Continental Divide), 3 moun-tain trailheads on the eastern slope, and 3foothill trailheads on the eastern slope (Table1). The trailheads were located in aspen forests,open meadows, and evergreen forests. Thetrailheads in the western slope mountainswere in the White River National Forest at
508 WESTERN NORTH AMERICAN NATURALIST [Volume 72
elevations between 2500 and 2800 m. Thetrailheads in the eastern slope mountains werein the Arapaho–Roosevelt National Forest atelevations between 2400 and 2620 m. Theeastern slope foothill trailheads were in a statepark, a county park, and the Arapaho–RooseveltNational Forest at elevations between 1600and 1800 m.
TRAILS.—We sampled 4 trails in summer2003 on the western slope of the Rocky Moun-tains in the White River National Forest and 4trails in summer 2004 on the eastern slope ofthe Rocky Mountains in the Arapaho–Roo-sevelt National Forest (Table 1). Although itwould have been preferable to sample all thetrails in one season, this was not possible.However, since each plot was being comparedonly to other plots on that same trail, the dif-ference in collection years should not greatlyaffect the core question, which is whether thetrailside plot has more aliens than the adjacentplot.
Data Collection
TRAILHEADS.—We collected seed bank sam -ples in early June 2004. We chose this datebecause it was early enough that few newseeds had dispersed. Seeds in the seed bankhad overwintered and therefore received acold treatment if necessary for germination. Ateach trailhead, we established 2 samplingsites: a trailhead site and an adjacent site. Thetrailhead site was directly at the trailhead(where the trail departs from the road or park-ing lot), and the adjacent site was approxi-mately 200 m away from the trailhead andconsisted of the same vegetation type, slope,and aspect as the trailhead site. We placed theadjacent site at the same distance from theroad as the trailhead site to ensure that wewere sampling a trail effect and not a roadeffect.
Our seed bank methods are similar to thosedescribed by Coffin and Lauenroth (1989). Wetook 5 samples at each site. Each sample wasrandomly located by distance (0–10 paces) andcardinal direction either from the corner ofthe trailhead signpost closest to the trail or froma random center at the adjacent site. Each sam-ple consisted of 2 pooled subsamples. Eachsubsample was a soil core 7.5 cm in diameterand 5 cm deep. When possible, we took onesubsample in the vegetation and the other inbare soil. We allowed samples to air-dry for
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 509
TA
BL
E1.
Cha
ract
eris
tics
of tr
ails
in th
e C
olor
ado
Roc
ky M
ount
ains
, USA
.
Trai
l nam
eE
leva
tion
(m)
Fore
st/p
ark
Loc
atio
nPr
imar
y us
ers
Use
rs p
er y
ear
Mea
sure
men
ts
Hor
seto
oth
1655
Hor
seto
oth
Mtn
. Par
kE
ast S
lope
Foo
thill
sH
iker
sn/
aaTr
ailh
ead
Wel
ls G
ulch
1700
Lor
y St
ate
Park
Eas
t Slo
pe F
ooth
ills
Hik
ers
n/a
Trai
lhea
dYo
ungs
Gul
ch17
80A
rapa
ho–R
oose
velt
N.F
.bE
ast S
lope
Foo
thill
sH
iker
sn/
aTr
ailh
ead
Boo
th F
alls
2560
Whi
te R
iver
N.F
.W
est S
lope
Mou
ntai
nsH
iker
s62
30B
othc
Buc
hana
n Pa
ss26
21A
rapa
ho–R
oose
velt
N.F
.E
ast S
lope
Mou
ntai
nsH
iker
s, h
orse
sn/
aB
oth
Fish
Cre
ek24
38A
rapa
ho–R
oose
velt
N.F
.E
ast S
lope
Mou
ntai
nsH
iker
s, h
orse
s70
0B
oth
Gor
e L
ake
2645
Whi
te R
iver
N.F
.W
est S
lope
Mou
ntai
nsH
iker
s33
20B
oth
Pine
y R
iver
2795
Whi
te R
iver
N.F
.W
est S
lope
Mou
ntai
nsH
iker
s, h
orse
s50
0B
oth
Wes
t Bra
nch
2609
Ara
paho
–Roo
seve
lt N
.F.
Eas
t Slo
pe M
ount
ains
Hik
ers,
hor
ses
3000
Bot
hE
ast P
orta
l28
08A
rapa
ho–R
oose
velt
N.F
.E
ast S
lope
Mou
ntai
nsH
iker
s, h
orse
sn/
aTr
ail
Pitk
in L
ake
2545
Whi
te R
iver
N.F
.W
est S
lope
Mou
ntai
nsH
iker
s12
80Tr
ail
a n/a
= d
ata
not a
vaila
ble
b N.F
. = N
atio
nal F
ores
tc U
sers
mea
sure
d bo
th a
t the
trai
lhea
d an
d on
the
trai
l.
5–10 days and then passed them through a0.5-cm2 screen. The sieved soil was evenlydistributed on sterile potting soil in standardtrays in the greenhouse, watered daily, andfertilized with a commercial fertilizer (Scott’sMiracleGroTM) every 2 weeks. Seedlings wereidentified and removed from the trays as theyemerged to ensure that space and nutrientswere available for new seedlings. If a seedlingcould not be identified, it was transferred to alarge pot and identified at a later growth stage.We identified plants and assigned their originas native or alien using Weber and Wittmann(2001a, 2001b). Seedling emergence was moni -tored for 4 months, at which point the trayswere discarded. Following Coffin and Lauen-roth (1989), we reported seedling abundancein units of the number of seedlings per m2 ofground area.
To measure plant cover, we used four 1-m2
plots located at random cardinal directionsand distances (0–10 paces) from the trailheadsignpost closest to the trail for the trailheadsites and from a random center for the adja-cent sites. Using cover classes (Daubenmire1959), we recorded the species within the plotand estimated percent cover for each species.We averaged the values for the 4 plots to get asingle description of the plant community ateach site.
TRAILS.—In the first 2000 m of each trail,we measured the distance occupied by 4 vege-tation types (aspen forest, evergreen forest,meadow, riparian area) using a distance mea-suring wheel. We calculated the percentage ofthe trail that fell within each vegetation typeand allocated 20 sampling points proportion-ately so that if 20% of the first 2000 m passedthrough meadow vegetation, 20% of the sam-pling points were located in meadows. Thesampling points were randomly located withinvegetation type. Two trails, Gore Lake andLower Piney River, had only 19 points.
In order to determine which environmentalvariables were correlated with the presence ofalien species, at each sampling point, we re -corded a GPS coordinate, elevation, percentslope, aspect, and the width and depth of thetrail. We established two 1 × 3-m quadrats, onedirectly adjacent to the trail, with its long axisparallel to the trail’s edge (the “on” quad rat),and another 4 m from the trail’s edge (the “off”quadrat). Within each quadrat, we recor dedunderstory species presence, understory spe -
cies cover according to established cover clas -ses (Daubenmire 1959), and tree canopy covermeasured with a densiometer. We identifiedplants and assigned their origin as native oralien, using definitions of Weber and Witt -mann (2001a, 2001b).
We considered Poa pratensis L. to be a na -tive. Poa pratensis L. is usually recorded as analien grass, but we chose not to do so since ithas a closely related native species, Poa agas-sizensis B. Boivin & D. Löve, which is difficultto distinguish from the alien species. In orderto ensure that we did not overreport the num-ber of alien species, plants that we could iden-tify to genus but not to species were includedas natives.
We gathered trail-use data from the USDAForest Service. The White River National For-est provided use estimates from trail registers,and the Arapaho–Roosevelt National Forestprovided estimates based on volunteer obser-vations. We analyzed total visitor estimates asa continuous variable and whether or not packstock commonly used the trail as a categoricalvariable.
Analysis
TRAILHEADS.—We used Jaccard’s coefficient(Krebs 1989) to determine the similarity be -tween the species in the seed bank at eachpaired trailhead and adjacent site, the similar-ity between the vegetation at the trailhead andadjacent site, and the similarity between theseed bank and the vegetation at each site. Weused a weighted coefficient for cover and anunweighted coefficient for the vegetation andthe seed bank. The weighted coefficient com-pares percent cover, while the unweightedcoefficient compares only species presence.Jaccard’s coefficient provides an index of simi-larity between 2 communities and is reportedas percent similarity.
We used linear regression in SAS PROCGLM (SAS 2001) to model the number of na -tive and alien species and the number of nativeand alien seedlings from the seed bank as aresponse to site (trailhead or adjacent). Thevariable assessing whether the trail was on theeast slope or west slope of the Rocky Moun-tains was removed from the analysis because itwas not significant. We used linear regressionto model the number of alien and native spe -cies (species richness) and alien and nativecover classes as a response to site. Cover class
510 WESTERN NORTH AMERICAN NATURALIST [Volume 72
values were square-root transformed to meetthe assumption of normality. Statistical signifi-cance is α = 0.05 unless otherwise stated.
TRAILS.—To determine the importance ofvegetation type and proximity to the trail (onor off), we used a split-plot design with trail asblock, vegetation type as whole-plot treatment,the 20 sampling locations as subsamples nestedwithin trail and vegetation type, and the onand off quadrats as a split of the subsample.We used the SAS program PROC MIXED(SAS 2001). We used a square-root transfor-
mation for percent cover calculations to nor-malize variance and increase the linearity ofthe response. We tested the importance of useby adding it to the PROC MIXED model.
In addition to use and vegetation type, wealso included environmental variables andcommunity similarity between the on and offquadrats in our analysis. We used linear re -gression to determine the importance of theenvironmental variables (percent slope, aspect,elevation, and tree canopy cover), and we com -pared the plant communities by calculatingJaccard’s coefficient of similarity for each on-off pair (Krebs 1989).
RESULTS
Trailheads
SOIL SEED BANK.—We encountered 29 alienspecies and 52 native species in our seed banksamples (see Appendix 1 for a complete list ofspecies). The number of species in the seedbank at trailhead and adjacent sites was simi-lar (Fig. 1A). There was a mean of 7 alienspecies (range 5–10) and 6 native species (2–8)in the seed bank at the trailhead sites and amean of 7 aliens (4–12) and 7 natives (2–12) atthe adjacent sites. The difference between siteswas not significant.
The number of seedlings emerging fromthe soil seed bank (sampled to 5 cm depth)was significantly dominated by aliens at bothtrailhead and adjacent sites (Fig. 1B). Therewas a mean of 3746 alien seedlings (range408–8470) and 702 native seedlings (159–1585)per m2 at the trailhead sites and a mean of2415 alien seedlings (113–6907) and 1507 na -tive seedlings (159–6183) per m2 at the adja-cent sites. There was no significant differencebetween the number of alien seedlings at thetrailhead sites and the adjacent sites, nor wasthere a significant difference between thenumbers of natives. However, similarity be -tween the species in the seed banks at thetrailhead sites and the species in the seedbanks at the adjacent sites was low (Table 2).The mean Jaccard’s coefficient (J) was only28% and ranged from 19% to 42% (Table 2).
On a per species basis, aliens had a mean of206 seedlings per species and natives had 74seedlings per species. Native and alien seed -ling numbers had a similar frequency distribu-tion, but aliens were more evenly distributedwhile natives had more species with low
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 511
Fig. 1. The number of species per sample in the soilseed bank at the sites with trailheads and adjacent sites(A), the number of seedlings per m2 at trailhead and adja-cent sites (B), species richness at trailhead and adjacentsites for aliens and natives (C), and percent cover foraliens and natives at trailhead and adjacent sites (D).Error bars represent standard errors, and lowercase let-ters indicate significant differences between alien andnative plants. Overall differences between trailhead sitesand adjacent sites was not significant for any comparison.
numbers of seedlings (Fig. 2). Out of the seed -lings that sprouted in the trays, there were 7alien species with over 200 seedlings (in as -cending order): Poa compressa L., Bromus iner-mis Leyss., Poa annua L., Verbascum thapsusL., Verbena bracteata Lagasca & Rodriguez,Spergularia rubra (L.) Presl., and Bromus tec-torum L. There were only 3 native specieswith over 200 seedlings: Silene antirrhina L.,Sporobolus cryptandrus (Torrey) Gray, and Jun-cus bufonious L.
TRAILHEAD VEGETATION.—Overall, the plantcommunities at trailhead and adjacent siteswere dissimilar, with a mean J value of 23%,ranging from 7% to 56% (Table 2). We found26 alien species and 111 native species (seeAppendix A for a list of species). Two speciesthat we could not identify were removed fromthe analysis. These species were rare, withfewer than 10 seedlings each. There were sig-nificantly fewer alien species than native spe -cies at both trailhead and adjacent sites (Fig.1C). However, the difference between aliensat the trailhead sites and aliens at the adjacentsites was not significant, nor was the differ-ence between natives at the trailhead sites andnatives at the adjacent sites. There was a meanof 6 aliens (range 1–9) and 12 natives (6–22) atthe trailhead sites and a mean of 3 aliens (1–8)and 13 (2–24) natives at the adjacent sites.
Even though the number of alien specieswas significantly less than the number of na -tive species, cover values contributed by aliensdid not differ from cover contributed by na -tives (Fig. 1D). At the trailhead sites, the meanalien cover was 51% (range 28%–94%) and themean native cover was 46% (16%–119%). Atthe adjacent sites, the mean alien cover was
42% (1%–86%) and the mean native coverwas 52% (8%–80%).
On a per species basis, aliens had a highermean cover than natives. Aliens had a meancover of 10% per species and natives had amean cover of 4% per species. Overall, alienswere more evenly distributed between lownumbers and high numbers per species, andnatives were heavily weighted by a large num-ber of species with low cover values (Fig. 3).
The species that were dominant in the seedbank were poorly represented in the vegeta-tion plots. The mean J value for the similaritybetween the seed bank and the vegetation wasonly 15% and ranged from 4% to 26%. Someexamples of this dissimilarity include the alienspecies Verbascum thapsus L. and the nativespecies Spergularia rubra (L.) Presl. Verbas-cum thapsus L. was present in the seed bankat every site, but recorded only once in thevegetation survey, and Spergularia rubra (L.)Presl, which was the most abundant species inthe seed bank at many of the trailhead sites,occurred at only 2 trailhead sites, where it hada cover of <1%. The native grass Bromus iner-mis Leyss. was the only species that was abun-dant in both the soil seed bank and the plantcommunity of the vegetation plots.
Trails
VEGETATION TYPES.—We sampled a total of158 plots: 35 in meadows, 57 in aspen forests,57 in evergreen forests, and 9 in riparianareas. These plots were dispersed throughoutthe first 2000 m of the 8 trails (Fig. 4). Aspenforest vegetation type plots were equallydistributed throughout the entire distance;meadow plots were generally concentrated at
512 WESTERN NORTH AMERICAN NATURALIST [Volume 72
TABLE 2. Jaccard’s coefficient of similarity between trailheads and adjacent sites (trailheads vs. adjacent) in the seed bankand the existing vegetation (seedbank vs. vegetation) and between the germinable seed bank and the existing vegetation attrailheads and adjacent sites. Jaccard’s coefficient is reported as a percentage between 0 and 100, with high values indi-cating high similarity.
Trailheads vs. adjacent Seedbank vs. vegetation___________________________ __________________________Trailhead Seed bank Vegetation Trailhead Adjacent
Booth Falls 19 23 19 22Gore Creek 18 14 19 12Piney River 42 16 12 19Buchanan Pass 27 13 15 8Fish Creek 15 56 14 9West Branch 25 7 17 26Horsetooth 36 41 4 10Wells Gulch 39 12 17 26Youngs Gulch 31 27 11 13MEAN 28.0 23.2 14.2 16.1
intermediate distances; evergreen forest plotswere generally farther from the trailhead; andriparian plots were mostly located in the firstand last 500 m of our sampling distance.
We found a total of 210 native species(Appendix 2). Native species richness differedamong the 4 vegetation types (Fig. 5A). Themeadow and aspen forest vegetation types
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 513
Fig. 2. Histogram of seedlings per m2 per species for aliens and natives in the seed bank.
Fig. 3. Histogram of percent cover per species for alien and native plants at trailhead and adjacent sites. Aliens had amean cover of 10% per species, and natives had a mean cover of 4% per species.
Fig. 4. The distribution of plots among vegetation types and distances (the first 2000 m of a trail).
differed from each other, but neither was sig-nificantly different from the riparian areas,and all 3 had significantly more species thanthe evergreen forest. The number of nativespecies on trail and off trail did not differ inany vegetation type.
Native percent cover followed a patternsimilar to that of native species richness (Fig.5B). The meadow and aspen forests differedfrom each other, but not from the riparianareas, and all 3 had significantly greater nativecover than the evergreen forests. There wasnot a significant difference between nativecover on trail and off trail in the aspen forestsor the riparian areas, but there was a signifi-cant difference between the native cover ontrail and off trail in meadows and evergreenforests, with meadows having greater nativecover off trail and evergreen forests havinggreater native cover on trail.
The overall percent similarity between thevegetation along the trails and the vegetationin the adjacent lands was low. Jaccard’s coeffi-cient of similarity (J) for the comparison be -tween the on trail and off trail in meadows was23% (range 3%–36%). In aspen forest vegetationtypes, J was 21% (1%–34%); in evergreen for -ests, 16% (0%–44%); and, in riparian areas, 10%
(0%–22%). In addition, trail width, but notdepth, varied among vegetation types. Trailswere significantly wider in evergreen forests(145 cm) and riparian areas (129 cm) than theywere in meadows (96 cm) and aspen forests(91 cm).
Tree canopy cover showed high cover val-ues in evergreen forests, low cover values inmeadows, and intermediate values in both as -pen forests and riparian areas (Fig. 6A). Wedid not find a difference between tree canopycover on trail and off trail. Percent cover ofbare ground followed the same pattern as treecanopy cover, with high values in the ever-green forests and low to intermediate valuesin the meadow, aspen forest, and riparian areas(Fig. 6B). Riparian areas were the only vegeta-tion type with significant difference betweenthe bare ground on trail and off trail, exhibit-ing more bare ground off trail.
ALIEN SPECIES.—We found a total of 27alien species (Appendix 2), but no more than 7species in any quadrat. We observed signifi-cantly more alien species and alien percentcover on trail than off trail in all vegetationtypes except evergreen forests (Fig. 5C). Themeadows had a mean of 3 species on trail(range 0–6) and 2 off trail (0–6); the aspen
514 WESTERN NORTH AMERICAN NATURALIST [Volume 72
Fig. 5. Native species richness (A), native species cover (B), alien species richness (C), and alien species cover (D)for the on- and off-trail locations within each vegetation type. Bars represent standard error; different small letters indi-cate significant differences between on- and off-trail locations, and different uppercase letters indicate significant differ-ences between vegetation types. Statistical significance for alien cover was determined using data that had been roottransformed.
forests had a mean of 3 species on trail (0–5)and 1 off trail (0–4); the evergreen forests hada mean of 1 species on trail (0–7) and <1 offtrail (0–4); and the riparian areas had a meanof 3 species on trail (2–6) and 1 off trail (0–2).
ENVIRONMENTAL VARIABLES.—We excludedaspect from our analysis because most of thetrails were on south-facing slopes, and weused distance from the trailhead rather thanelevation since the 2 were highly correlated.All the trails gained elevation from the trail-head. The combination of percent slope, dis-tance, and tree canopy cover accounted for30% of the variance in percent cover for aliens.Percent slope had a negligible effect, whiledistance and canopy cover were both signifi-cant for explaining the presence of alien spe -cies. All 3 variables interacted significantlywith vegetation type.
USE.—We obtained trail-use data for 6 ofthe 8 trails (Table 1). The number of visitorsper year ranged from <1000 visitors per yearto >6000 visitors per year. Five of the 8 trailswere used by horses, but estimates of the
number of visitors on horseback and thosehiking were not available. Neither the numberof visitors, analyzed as a continuous variable,nor whether or not the trail was used byhorses, analyzed as a categorical value, wassignificant for explaining either the number ofalien plants or the percent cover of alien plantsalong the trail.
DISCUSSION
Trailheads represent the point where thefront country meets the backcountry and theseresults underscore the role that trailheads andtrails may be playing in alien species dispersalinto the backcountry. At the trailheads weexamined, both the seed banks and the vege-tation contained considerable numbers of alienspecies, and trailhead seed banks and vegeta-tion differed from adjacent areas without trail-heads. Although the trailheads and adjacentareas that we examined contained significantlyfewer alien species than native species, thepercent cover of aliens and natives did not
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 515
Fig. 6. Tree canopy cover (A) and percent bare ground (B) in the on- and off-trail locations within each vegetationtype. The difference between the on- and off-trail locations in A is not significant. Bars represent standard error of themean; different lowercase letters indicate significant differences between the on- and off-trail locations, and differentuppercase letters indicate significant differences between vegetation types.
differ. Aliens had a higher percent mean coverper species, in addition to a higher number ofseedlings per species. Species-specific studieshave shown that alien species can have highcover values, as well as many seedlings in theseed bank within a plant community (Vitousek1990, D’Antonio and Vitousek 1992, Humphreyand Schupp 2001, Alexander and D’Antonio2003).
Although the number of aliens did not differbetween trailheads and adjacent sites, speciescomposition between these locations were dif-ferent. This difference cannot be entirely ex -plained by the presence of alien species andmay be partially a result of more frequent dis-turbances at trailhead sites (e.g., trampling).Our observation of high exotic species coverin both sites may be a consequence of closeproximity to roads, which have been shown toharbor alien species (Tyser and Worley 1992,Pauchard and Alaback 2004).
Plant species in the seed bank and the plantsgrowing at our sites were not similar, a rela-tively common finding in seed bank studies(Thompson and Grime 1979, Coffin and Lauen-roth 1989, Leck et al. 1989, Jalili et al. 2003).In fact, it is common to find some species ex -clusively in the seed bank and some speciesexclusively in the vegetation and vice versa(Maccherini and De Dominicis 2003). In astudy comparing the forest edge to the interiorvegetation, Honu and Gibson (2008) foundthat over 50% of the native plants in theirstudy were unrepresented in the seed bankand that over 50% of the alien species werefound in the seed bank but not in the extantvegetation. Many alien species have seeds thatremain viable in the soil seed bank for a longtime (Burnside et al. 1996, Alexander andD’Antonio 2003). Fluctuations in resource lev-els are tied to the invisibility of communities(Davis et al. 2000). If resources become avail-able and if there are alien propagules availableto take advantage of those resources, then in -vasions are more likely to occur. In the case ofthe soil seed bank, there are abundant propa -gules that are poised to take advantage of ad -vantageous resource fluctuations at the trail-head, as well as at locations farther along thetrail if those propagules are transported as acontaminant on shoes, etc. (Clifford 1956, Sal-isbury 1961, Mount and Pickering 2009).
The patterns of alien species along the trailswe examined, when contrasted with the sur-
rounding vegetation, imply that trails may beserving as invasion corridors. Vegetation nextto the trail contained more aliens than plotslocated only 4 m from the trail’s edge in 3 outof the 4 vegetation types, implying that thereplacement of native species by aliens maycontribute to the low compositional similaritybetween the trailside vegetation and the sur-rounding vegetation. Similarly, the percent co vercontributed by aliens was significantly highernext to the trail in all community types exceptevergreen forests. The presence of alien spe -cies along the edge of the trail is consistentwith other work (Benninger-Truax et al. 1992,Tyser and Worley 1992, Dickens et al. 2005,Potito and Beatty 2005, Gower 2008) and de m -onstrates that propagules are arriving at thosesites and that conditions for growth are suit-able. In addition, the greater abundance of alienspecies along the trail compared to surround-ing areas implies limited successful mi grationaway from trails, perhaps because the alienspecies are less able to compete with the na -tive vegetation farther away from the trail wherenatives may have a competitive advantage inthe absence of trampling stress.
Vegetation type appears to influence themagnitude and pattern of alien plant speciesinvasion along trails. Specifically, meadows, as-pen forests, and riparian zones are likely toharbor alien plants, and evergreen forests arelikely to contain a negligible number of alienplants. In addition to harboring alien plantsalong the edge of the trail, meadows had sig-nificantly higher alien species richness andcover at the off-trail location (4 m from thetrail’s edge) than the other 3 vegetation types.
We expected to confirm the findings ofLonsdale (1999) that a positive correlation ex -ists between visitors and aliens, but we did notfind a significant relationship between thenumber of visitors and the presence of alienspecies. Although pack stock cause additionaldisturbance and have the potential to intro-duce seeds as both contaminants in their dung(Campbell and Gibson 2001, Wells and Lauen-roth 2007) and external contaminants, we didnot find a relationship between the presenceof aliens and whether or not the trail was usedby pack stock.
We found that trailheads and trails both al -ter native plant communities. Trailheads rep-resent the first point of contact between visi-tors and wildlands. Though our results suggest
516 WESTERN NORTH AMERICAN NATURALIST [Volume 72
trailheads are not significantly more invadedthan adjacent sites without trailheads, trail-heads are heavily invaded, and managementshould focus on trailheads as locations fromwhich introductions of new plant species canspread along trail corridors to the backcountry.The greater number and cover of alien plantsalong trails than in the adjacent vegetationsuggest that trails are indeed corridors alongwhich alien plants move. Furthermore, the ap -parent success of alien plants that dispersealong trail corridors depends upon vegetationtype. Control of alien plants should considerthe potential impact of trailheads, where thereare large numbers of aliens, and efforts to mini -mize or mitigate invasion along trails may bemost effective if focused on the most invadedvegetation types.
ACKNOWLEDGMENTS
We thank Chris Warren for help with thetrailhead data collection. This work was sup-ported by the Colorado State University Agri-cultural Experiment Station through grantnumber 1-57661 and by the National ScienceFoundation through grant number 0217631.Any use of trade, product, or firm names is fordescriptive purposes only and does not implyen dorsement by the U.S. Government.
LITERATURE CITED
ALEXANDER, J.M., AND C.M. D’ANTONIO. 2003. Seed bankdynamics of French broom in coastal Californiagrasslands: effects of stand age and prescribed burn-ing on control and restoration. Restoration Ecology11:185–197.
BENNINGER-TRUAX, M., J.L. VANKAT, AND R.L. SCHAEFER.1992. Trail corridors as habitat and conduits for move -ment of plant species in Rocky Mountain NationalPark, Colorado, USA. Landscape Ecology 6:269–278.
BURKE, M.J.W., AND J.P. GRIME. 1996. An experimentalstudy of plant community invasibility. Ecology 77:776–790.
BURNSIDE, O.C., R.G. WILSON, S. WEISBERG, AND K.G.HUBBARD. 1996. Seed longevity of 41 weed speciesburied 17 years in eastern and western Nebraska.Weed Science 44:74–86.
CAMPBELL, J.E., AND D.J. GIBSON. 2001. The effect ofseeds of exotic species transported via horse dung onvegetation along trail corridors. Plant Ecology 157:23–35.
CLIFFORD, H.T. 1956. Seed dispersal on footwear. Pro-ceedings of the Botanical Society of the British Isles2:129–131.
COFFIN, D.P., AND W.K. LAUENROTH. 1989. Spatial andtemporal variation in the seed bank of a semiaridgrassland American Journal of Botany 76:53–58.
D’ANTONIO, C.M., AND P.M. VITOUSEK. 1992. Biologicalinvasions by exotic grasses, the grass/fire cycle, andglobal change. Annual Review of Ecology and Sys-tematics 23:63–87.
DAUBENMIRE, R. 1959. A canopy-coverage method of vege -tational analysis. Northwest Science 33:43–64.
DAVIS, M.A., J.P. GRIME, AND K. THOMPSON. 2000. Fluctu-ating resources in plant communities: a general the-ory of invasibility. Journal of Ecology 88:528–534.
DICKENS, S.J.M., F. GERHARDT, AND S.K. COLLINGE. 2005.Recreational portage trails as corridors facilitatingnon-native plant invasions of the Boundary WatersCanoe Area Wilderness (USA). Conservation Biol-ogy 19:1653–1657.
GOWER, S.T. 2008. Are horses responsible for introducingnon-native plants along forest trails in the easternUnited States? Forest Ecology and Management256:997–1003.
HOBBS, R.J., AND L.F. HUENNEKE. 1992. Disturbance,diversity, and invasion: implications for conserva-tion. Conservation Biology 6:324–337.
HODKINSON, D.J., AND K. THOMSPON. 1997. Plant disper-sal: the role of man. Journal of Applied Ecology34:1484–1496.
HONU, Y.A.K., AND D.J. GIBSON. 2008. Patterns of inva-sion: trends in abundance of understory vegetation,seed rain, and seed bank from forest edge to interior.Natural Areas Journal 28:228–239.
HUMPHREY, L.D., AND E.W. SCHUPP. 2001. Seed banks ofBromus tectorum–dominated communities in theGreat Basin. Western North American Naturalist 61:85–92.
JALILI, A., B. HAMZEH’EE, Y. ASRI, A. SHIRVANY, S. YAZ-DANI, M. KHOSHNEVIS, F. ZARRINKAMAR, M.A. GHAH -RAMANI, R. SAFAVI, S. SHAW, ET AL. 2003. Soil seedbanks in the Arasbaran Protected Area of Iran andtheir significance for conservation management. Bio-logical Conservation 109:425–431.
KREBS, C.J. 1989. Ecological methodology. Harper andRow, New York, NY.
LARSON, D.L., P.J. ANDERSON, AND W. NEWTON. 2001.Alien plant invasion in mixed-grass prairie: effects ofvegetation type and anthropogenic disturbance.Ecological Applications 11:128–141.
LECK, M.A., V.T. PARKER, AND R.L. SIMPSON. 1989. Ecologyof soil seed banks. Academic Press, San Diego, CA.
LONSDALE, W.M. 1999. Global patterns of plant invasionsand the concept of invasibility. Ecology 80:1522–1536.
MACCHERINI, S., AND V. DE DOMINICIS. 2003. Germinablesoil seed-bank of former grassland converted toconiferous plantation. Ecological Research 18:739–751.
MACK, R.N. 2005. Predicting the identity of plant in -vaders: future contributions from horticulture. Hort -science 40:1168–1174.
MACK, R.N., AND W.M. LONSDALE. 2001. Humans as glo balplant dispersers: getting more than we bargained for.BioScience 51:95–102.
MARLER, M. 2000. A survey of exotic plants in federalwilderness areas. USDA Forest Service ProceedingsRMRS-P-15 5:318–327.
MOUNT, A., AND C.M. PICKERING. 2009. Testing the capac-ity of clothing to act as a vector for non-native seedin protected areas. Journal of Environmental Man-agement 91:168–179.
PANETTA, F.D., AND A.J.M. HOPKINS. 1993. Weeds incorridors: invasion and management. Pages 341–351 in D.A. Saunders and R.J. Hobbs, editors, Nature
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 517
conservation 2: the role of corridors. University ofMinnesota, Minneapolis, MN.
PAUCHARD, A., AND P.B. ALABACK. 2004. Influence of ele-vation, land use, and landscape context on patternsof alien plant invasions along roadsides in protectedareas of south-central Chile. Conservation Biology18:238–248.
PICKERING, C.M., W. HILL, D. NEWSOME, AND Y.-F.LEUNG. 2010. Comparing hiking, mountain bikingand horse riding impacts on vegetation and soils inAustralia and the United States of America. Journalof Environmental Management 91:551–562.
POTITO, A.P., AND S.W. BEATTY. 2005. Impacts of recrea -tion trails on exotic and ruderal species distributionin grassland areas along the Colorado Front Range.Environmental Management 36:230–236.
PYSEK, P., V. JAROSK, AND T. KUCERA. 2002. Patterns ofinvasion in temperate nature reserves. BiologicalConservation 104:13–24.
QUINN, L.D., M. KOLIPINSKI, V.R. COELHO, B. DAVIS, J.-M.VIANNEY, O. BATJARGAL, M. ALAS, AND S. GHOSH. 2008.Germination of invasive plant seeds after digestionby horses in California. Natural Areas Journal 28:356–362.
QUINN, L.D., A. QUINN, M. KOLIPINSKI, B. DAVIS, C.BERTO, M. ORCHOLSKI, AND S. GHOSH. 2010. Role ofhorses as potential vectors of non-native plant inva-sion: an overview. Natural Areas Journal 30:408–416.
RUBINO, D.L., C.E. WILLIAMS, AND W.J. MORIARITY. 2002.Herbaceous layer contrast and alien plant occur-rence in utility corridors and riparian forests of theAllegheny High Plateau. Journal of the Torrey Bo -tanical Society 129:125–135.
SALISBURY, S.E. 1961. Weeds and aliens. Collins, London.[SAS] STATISTICAL ANALYSIS SYSTEM. 2001. System for
Win dows. Version 8.02 of the SAS System for Win-
dows. Copyright 1999–2001, SAS Institute, Inc.,Cary, NC.
STROH, E.D., AND M.A. STRUCKHOFF. 2009. Exotic plantspecies associations with horse trails, old roads, andintact native communities in the Missouri Ozarks.Natural Areas Journal 29:50–56.
THOMPSON, K. 1987. Seeds and seed banks. New Phytolo-gist 106:23–34.
THOMPSON, K., AND J.P. GRIME. 1979. Seasonal variation inthe seed banks of herbaceous species in ten contrast-ing habitats. Journal of Ecology 67:893–921.
TYSER, R.W., AND C.A. WORLEY. 1992. Alien flora in grass-lands adjacent to road and trail corridors in GlacierNational Park, Montana (USA). Conservation Biol-ogy 6:253–262.
VILÀ, M., J. PINO, AND X. FONT. 2007. Regional assessmentof plant invasions across different habitat types.Journal of Vegetation Science 18:35–42.
VITOUSEK, P.M. 1990. Biological invasions and ecosystemprocesses: towards an integration of population biol-ogy and ecosystem studies. Oikos 57:7–13.
WEBER, W.A., AND R.C. WITTMANN. 2001a. Colorado flora:eastern slope. University Press of Colorado, Boulder.
______. 2001b. Colorado flora: western slope. UniversityPress of Colorado, Boulder, CO.
WELLS, F.H., AND W.K. LAUENROTH. 2007. The potentialfor horses to disperse alien plants along recreationaltrails. Rangeland Ecology and Management 60:574–577.
Received 16 November 2011Accepted 29 July 2012
518 WESTERN NORTH AMERICAN NATURALIST [Volume 72
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 519
APPENDIX 1. Attributes of plant species at trailheads. B = Booth, G = Gore, Pr = Piney River, P = Pitkin, E = EastPortal, V = Buchanan, W = West Branch, F = Fish, H = Horsetooth, L = Wells Gulch, Y = Youngs Gulch.
Trail and Number ofSpecies name Location position % Cover seedlings
ALIEN SPECIES
Agropyron cristatum (L.) Gaertn. White River N.F. B TH 9 —Lory State Park L adj. — 68Arapaho–Roosevelt N.F. Y adj. — 23
Alyssum desertorum Stapf White River N.F. Pr TH 5 —Amaranthus palmeri Watson Arapaho–Roosevelt N.F. F adj. — 23
W adj. — 23Lory State Park L TH — 23White River N.F. Pr adj. — 91
Bromus inermis Leyss. White River N.F. B TH 61 113B adj. 39 68G adj. — 45Pr TH 2 45Pr adj. 14 113
Arapaho–Roosevelt N.F. V TH 1 —F TH 23 747F adj. 63 657W TH 5 0W adj. 4 23Y TH 44 113Y adj. 56 408
Lory State Park L TH 37 929L adj. — 1042
Horsetooth Mtn. Park H TH 68 566H adj. 63 159
Bromus tectorum L. White River N.F. B adj. — 68Arapaho–Roosevelt N.F. Y TH — 317
Y adj. — 204Lory State Park L TH — 4371
L adj. — 5367Horsetooth Mtn. Park H TH — 249
H adj. — 181Camelina microcarpa DC. Arapaho–Roosevelt N.F. W TH 1 —Capsella bursa-pastoris (L.) Medik. White River N.F. Pr TH 5 362
Pr adj. — 23G TH — 45
Arapaho–Roosevelt N.F. Y adj. — 23W TH 3 272W adj. — 45
Chenopodium album L. White River N.F. B adj. — 23Arapaho–Roosevelt N.F. F adj. — 45
Y TH — 113W TH 0.25 —
Cirsium arvense (L.) Scop. White River N.F. B TH 11 —B adj. 2 23G TH 4 —G adj. 9 —
Arapaho–Roosevelt N.F. F adj. — 45Y TH — 113
Cirsium vulgare (Savi) Ten. White River N.F. G TH 6 —Convolvulus arvensis L. Arapaho–Roosevelt N.F. F TH 1 —
Y adj. 9 —Lory State Park L TH 8 —
L adj. — 23Conyza schiedeana (Lessing) Cronquist White River N.F. G adj. — 23
Arapaho–Roosevelt N.F. V TH — 23F — 23
Horsetooth Mtn. Park H TH — 679H adj. — 68
Dactylis glomerata L. White River N.F. B TH 11 340B adj. 16 —
520 WESTERN NORTH AMERICAN NATURALIST [Volume 72
APPENDIX 1. Continued. B = Booth, G = Gore, Pr = Piney River, P = Pitkin, E = East Portal, V = Buchanan, W =West Branch, F = Fish, H = Horsetooth, L = Wells Gulch, Y = Youngs Gulch.
Trail and Number ofSpecies name Location position % Cover seedlings
G TH 9 23G adj. 28 23Pr TH 2 —Pr adj. 0.25 —
Erodium cicutarium (L.) L’Hériter White River N.F. B TH — 68B adj. — 23Pr adj. — 91
Arapaho–Roosevelt N.F. Y TH — 181Y adj. — 1019
Gnaphalium uliginosum L. White River N.F. Pr adj. — 45Arapaho–Roosevelt N.F. V TH — 23
Lepidotheca suaveolens Nuttall. White River N.F. Pr TH — 91Arapaho–Roosevelt N.F. F TH — 45
Linaria vulgaris Miller White River N.F. B adj. — 23Lonicera morrowii Gray White River N.F. G TH 9 —
G adj. 1 —Malva neglecta Wallroth Arapaho–Roosevelt N.F. Y adj. — 23Medicago lupulina L. White River N.F. B adj. 1 —
G adj. 1 —Arapaho–Roosevelt N.F. F TH 5 —
Medicago sativa L. White River N.F. B TH — 23Arapaho–Roosevelt N.F. Y TH 23
Y adj. 18 23W TH 9 —
Lory State Park L TH 1 —Melandrium dioicum (L.) Cosson & White River N.F. B TH — 113
GermainMelilotus officinalis (L.) Lam. White River N.F. B adj. 1 113
Arapaho–Roosevelt N.F. F TH 12 23Y TH — 23Y adj. — 294
Nasturtium officinale R. Brown Arapaho–Roosevelt N.F. V TH — 91Phleum pratense L. White River N.F. G TH 9 —
G adj. 2 —Pr TH 4 —Pr adj. 12 —
Arapaho–Roosevelt N.F. V TH 2 —Plantago major L. White River N.F. G adj. 0.25 45
Pr TH — 23Arapaho–Roosevelt N.F. V TH — 23
V adj. 5 23Poa annua L. White River N.F. B TH — 91
G TH — 45Pr TH — 91Pr adj. — 1291
Arapaho–Roosevelt N.F. F TH — 136V TH — 6432V adj. — 498
Lory State Park L adj. — 91Poa compressa L. White River N.F. B adj. — 906
Arapaho–Roosevelt N.F. F TH — 136V TH — 113V adj. — 1540
Lory State Park L TH — 91L adj. — 23
Poa trivialis L. White River N.F. B TH 15 —B adj. 2 —Pr TH 16 —Pr adj. 6 —
Polygonum arenastrum Jord. ex Boreau White River N.F. B TH 1 —G TH 1 —
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 521
APPENDIX 1. Continued. B = Booth, G = Gore, Pr = Piney River, P = Pitkin, E = East Portal, V = Buchanan, W =West Branch, F = Fish, H = Horsetooth, L = Wells Gulch, Y = Youngs Gulch.
Trail and Number ofSpecies name Location position % Cover seedlings
G adj. — 45Pr TH — 23
Arapaho–Roosevelt N.F. V TH 3 —V adj. 0.25 23F TH 3 —W TH 3 181Y TH 4 23
Rumex crispis L. Arapaho–Roosevelt N.F. V TH 1 —Sonchus asper (L.) Hill White River N.F. B TH — 68
G TH — 23Arapaho–Roosevelt N.F. Y TH — 45
Y adj. — 23Lory State Park L adj. 1 23Horsetooth Mtn. Park H TH — 181
Sonchus oleraceus L. Arapaho–Roosevelt N.F. Y TH — 23Spergularia rubra (L.) J.& K. Presl White River N.F. Pr TH — 2084
Pr adj. — 1178Arapaho–Roosevelt N.F. V TH 1 566
W TH 0.25 6885Taraxacum officinale G.H. Weber White River N.F. B TH 1 136
ex Wiggers G TH 3 272G adj. 11 23Pr TH 5 136Pr adj. 3 —
Arapaho–Roosevelt N.F. V TH 3 —V adj. 2 45F TH 2 294F adj. 7 —W TH 13 91W adj. 5 23Y TH 1 —
Lory State Park L TH — 23L adj. — 45
Thinopyrum intermedium (Host) Arapaho–Roosevelt N.F. Y adj. 4 —Barkworth & D.R. Dewey
Thlaspi arvense L. Arapaho–Roosevelt N.F. W TH 0.25 —Tragopogon pratensis L. White River N.F. G TH 5 —Trifolium repens L. Arapaho–Roosevelt N.F. V TH 11 —
F TH 0.25 —Verbascum thapsus L. White River N.F. B TH — 362
B adj. 3 385Arapaho–Roosevelt N.F. Y TH — 1676
Y adj. — 3963Lory State Park L TH — 204
L adj. — 91Horsetooth Mtn. Park H TH — 23
H adj. — 159Verbena bracteata Lagasca & Rodrigues Arapaho–Roosevelt N.F. Y adj. — 91
Lory State Park L TH — 2831L adj. — 136
Horsetooth Mtn. Park H TH — 204H adj. — 476
NATIVE SPECIES
Achillea lanulosa Nutt. White River N.F. G TH 4 —G adj. 2 —Pr TH 2 —Pr adj. 9 —
Arapaho–Roosevelt N.F. V TH 2 —V adj. 2 —F TH 3 —F adj. 2 —
522 WESTERN NORTH AMERICAN NATURALIST [Volume 72
APPENDIX 1. Continued. B = Booth, G = Gore, Pr = Piney River, P = Pitkin, E = East Portal, V = Buchanan, W =West Branch, F = Fish, H = Horsetooth, L = Wells Gulch, Y = Youngs Gulch.
Trail and Number ofSpecies name Location position % Cover seedlings
W TH 2 —Achnatherum nelsonii (Scribn.) Barkworth White River N.F. G TH 0.25 —
Arapaho–Roosevelt N.F. V TH 1 —V adj. 1 —W TH 3 —W adj. 2 —
Agrostis scabra Willd. White River N.F. Pr adj. 0.25 —G adj. 0.25 68
Arapaho–Roosevelt N.F. V TH — 91Lory State Park L TH — 181
Allium cernuum Roth White River N.F. Pr TH 0.25 —Pr adj. 1 —
Amaranthus albus L. White River N.F. B adj. 9 —G adj. 4 —
Ambrosia psilostachya DC. Horsetooth Mtn. Park H TH 1 —Lory State Park L adj. 6 —
Amerosedum lanceolatum (Torr.) White River N.F. Pr TH 1 —A.& D. Löve Arapaho–Roosevelt N.F. V adj. 2 —
W adj. 2 —Androsace occidentalis Pursh Arapaho–Roosevelt N.F. W TH 0.25 —Androsace septentrionalis L. White River N.F. Pr adj. — 91
F adj. — 23V TH — 23W TH — 340W adj. 1 996
Horsetooth Mtn. Park H adj. — 68Antennaria corymbosa E. Nels. White River N.F. B TH 1 —
G adj. 1 —Pr TH 1 —
Antennaria rosea Greene Arapaho–Roosevelt N.F. V TH 1 —V adj. 1 —
Arabis L. White River N.F. G TH 0.25 —Pr TH 0.25 —Pr adj. 0.25 —
Arapaho–Roosevelt N.F. V TH 1 —V adj. 1 —F adj. — 23Y TH — 45
Artemisia frigida Willd. Arapaho–Roosevelt N.F. V adj. 2 —F adj. — 45Y TH 1 23Y adj. — 23
Lory State Park L adj. 4 —Horsetooth Mtn. Park H TH — 23
Artemisia ludoviciana Nutt. Lory State Park L TH 3 —Horsetooth Mtn. Park H TH — 23
H adj. 2 317Arapaho–Roosevelt N.F. Y adj. — 23
Artemisia tridentata Nutt. Arapaho–Roosevelt N.F. W TH 9 —Asclepias macrotis Torr. Horsetooth Mtn. Park H TH 3 —Aster adscendens Lindl. Lory State Park L TH 1 —
L adj. 1 —Astragalus laxmannii Jacq. Arapaho–Roosevelt N.F. F TH 0.5 —Aster L. White River N.F. B adj. — 136
G TH 0.25 —Pr adj. — 23
Arapaho–Roosevelt N.F. F TH 0.5 23V TH — 23
Lory State Park L TH 2 —L adj. 11 91
Horsetooth Mtn. Park H TH 1 —
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 523
APPENDIX 1. Continued. B = Booth, G = Gore, Pr = Piney River, P = Pitkin, E = East Portal, V = Buchanan, W =West Branch, F = Fish, H = Horsetooth, L = Wells Gulch, Y = Youngs Gulch.
Trail and Number ofSpecies name Location position % Cover seedlings
Bassia sieversiana (Pallas) Weber Arapaho–Roosevelt N.F. Y TH — 23Boechera drummondii (Gray) Arapaho–Roosevelt N.F. V TH 1 —
A.& D. Löve V adj. 2 —Bromus carinatus Hook. & Arn. White River N.F. G TH 2 —
G adj. 2 —Pr adj. 1 —
Bromus ciliatus L. Arapaho–Roosevelt N.F. V adj. 1 —F TH — 23
Cactaceae Jussieu Lory State Park L TH — 23Campanula rotundifolia L. Arapaho–Roosevelt N.F. Y TH 0.25 —Carex L. White River N.F. G TH — 45
G adj. — 68Pr TH — 249Pr adj. 4 498
Arapaho–Roosevelt N.F. V TH 24 —V adj. 10 45Y adj. 23
Horsetooth Mtn. Park H TH 23Cerastium L. West Branch off 7 —Cercocarpus montanus Raf. Arapaho–Roosevelt N.F. Y TH 1 —Chamerion angustifolium (L.) Holub White River N.F. G adj. 6 —Chenopodium berlandieri Moq. White River N.F. G TH 0.25 —Chrysothamnus nauseosus (Pallas ex Arapaho-Roosevelt N.F. Y TH 1 —
Pursh) Britt. Y adj. 2 —Horsetooth Mtn. Park H TH 5 —
Cirsium Mill. White River N.F. Pr TH — 23Cirsium centaureae (Rydb.) K. Schum. Arapaho–Roosevelt N.F. F adj. 1 —Cirsium eatonii (Gray) B.L. Robins. White River N.F. B adj. 2 —
G TH — 23G adj. 1 —
Clematis ligusticifolia Nutt. Arapaho–Roosevelt N.F. Y TH 4 —Y adj. 20 45
Collomia linearis Nutt. White River N.F. Pr TH 1 —Arapaho–Roosevelt N.F. V adj. 1 —
W TH 1 —Dasiphora floribunda (Pursh) Kartesz White River N.F. Pr TH 1 —
Pr adj. 6 —Elymus canadensis L. White River N.F. G adj. 5 —Elymus trachycaulus (Link) Gould
ex Shinners Arapaho–Roosevelt N.F. F TH 1 —W TH 13 —
Epilobium L. White River N.F. Pr adj. 3 —Epilobium brachycarpum Presl. White River N.F. B TH — 23Epilobium ciliatum Raf. Arapaho–Roosevelt N.F. V TH 3 45
Y adj. — 226Erigeron L. White River N.F. B adj. 2 —
G TH 2 —G adj. 3 —Pr TH 2 —Pr adj. 2 —
Arapaho–Roosevelt N.F. W adj. 3 —Y adj. — 45
Erigeron compositus Pursh Arapaho–Roosevelt N.F. V adj. 2 —Erigeron divergens Torr. & Gray Lory State Park L TH 2 —Erigeron flagellaris Gray Lory State Park L adj. — 68Erigeron formosissimus Greene White River N.F. B adj. 2 —
G TH 1 —G adj. 3 —Pr TH 5 —Pr adj. 7 —
Arapaho–Roosevelt N.F. V TH 1 —
524 WESTERN NORTH AMERICAN NATURALIST [Volume 72
APPENDIX 1. Continued. B = Booth, G = Gore, Pr = Piney River, P = Pitkin, E = East Portal, V = Buchanan, W =West Branch, F = Fish, H = Horsetooth, L = Wells Gulch, Y = Youngs Gulch.
Trail and Number ofSpecies name Location position % Cover seedlings
V adj. 7 —Erigeron speciosus (Lindl.) DC. Arapaho–Roosevelt N.F. F TH 9 —Eragrostis trichodes (Nutt.) Wood White River N.F. Pr TH 1 —
Pr adj. 4 —Eriogonum umbellatum Torr. Arapaho–Roosevelt N.F. W adj. 4 —Festuca arizonica Vasey White River N.F. G adj. 1 —Festuca idahoensis Elmer Arapaho–Roosevelt N.F. F adj. 57 —
W adj. 33 —Festuca rubra L. Arapaho–Roosevelt N.F. F TH 16 —Festuca saximontana Rydb. Arapaho–Roosevelt N.F. V adj. 1 —
W TH 14 —Fragaria virginiana Duchesne White River N.F. G TH — 91
G adj. 3 —Pr adj. 5 —
Arapaho–Roosevelt N.F. V TH — 45V adj. — 23F adj. — 23Y TH — 23
Frasera speciosa Douglas White River N.F. Pr adj. 1 —Galium septentrionale Roemer & White River N.F. B TH 1 —
J.A. Schultes Pr adj. 0.25 —Arapaho–Roosevelt N.F. V TH 2 —
V adj. 2 —F adj. 1 —
Geranium richardsonii Fisch. & Trautv. White River N.F. B TH 5 —G TH 32 23G adj. 7 —
Geum macrophyllum Willd. White River N.F. G TH 2 —Gnaphalium L. Arapaho–Roosevelt N.F. V adj. — 91
Horsetooth Mtn. Park H TH — 45Gutierrezia sarothrae (Pursh) Britt. & Lory State Park L TH 8 —
Rusby L adj. 10 —Horsetooth Mtn. Park H adj. 4 —
Hedeoma hispidium Pursh. Horsetooth Mtn. Park H adj. — 249Heliomeris multiflora Nutt. White River N.F. G TH 1 —Heracleum maximum Bartr. White River N.F. G TH 6 —Heterotheca villosa (Pursh) Shinners Arapaho–Roosevelt N.F. V adj. 3 —
Y TH — 113Lory State Park L TH 2 45
L adj. 1 249Horsetooth Mtn. Park H adj. — 91
Hordeum brachyantherum Nevski. White River N.F. Pr adj. 2 0Juncus L. White River N.F. Pr TH 2 91
Pr adj. 2 544Arapaho–Roosevelt N.F. F TH — 23
F adj. 2 91Juncus balticus Willd. White River N.F. Pr TH — 566
Pr adj. — 4099Arapaho–Roosevelt N.F. V TH 2 —
Juniperus communis L. White River N.F. G adj. 2 —Juniperus scopulorum Sarg. Arapaho–Roosevelt N.F. V adj. 2 —Lepidium densiflorum Schrad. White River N.F. G TH 1 —Liatris punctata Hook. Horsetooth Mtn. Park H adj. 0.25 —
Lory State Park L TH 1 —Lupinus argenteus Pursh Arapaho–Roosevelt N.F. F TH 1 —
Horsetooth Mtn. Park H TH 1 23Mahonia repens (Lindl.) G. Don White River N.F. B adj. 1 —Maianthemum stellatum (L.) Link Arapaho–Roosevelt N.F. V adj. 2 —
White River N.F. Pr adj. 1 —White River N.F. Pr TH — 45
Mimulus glabratus Kunth White River N.F. Pr adj. 1 68
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 525
APPENDIX 1. Continued. B = Booth, G = Gore, Pr = Piney River, P = Pitkin, E = East Portal, V = Buchanan, W =West Branch, F = Fish, H = Horsetooth, L = Wells Gulch, Y = Youngs Gulch.
Trail and Number ofSpecies name Location position % Cover seedlings
Muhlenbergia filiformis (Thurb. ex S. White River N.F. Pr adj. 2 91Wats.) Rydb. Arapaho–Roosevelt N.F. F adj. — 91
W adj. — 45Muhlenbergia minutissima (Steudel) Arapaho-Roosevelt N.F. F TH — 23
SwallenOpuntia polyacantha Haw. Horsetooth Mtn. Park H adj. 1 —Pascopyrum smithii (Rydb.) A. Löve White River N.F. B TH 2 —
B adj. 0.25 —G TH 16 136G adj. — 45Pr TH 11 23Pr adj. — 45
Arapaho–Roosevelt N.F. V adj. 5 —W adj. 1 —Y adj. — 23
Horsetooth Mtn. Park H TH 1 —Penstemon cobaea Nutt. Arapaho–Roosevelt N.F. V adj. 5 —Pinus contorta Dougl. ex Loud. White River N.F. G adj. 2 —Pinus ponderosa P.& C. Lawson Arapaho–Roosevelt N.F. Y adj. 9 —
Horsetooth Mtn. Park H adj. — 23Poa L. Lory State Park L adj. 21 —Poa pratensis L. White River N.F. B TH — 272
G TH 10 0G adj. — 91Pr TH — 23Pr adj. — 204
Arapaho–Roosevelt N.F. V TH 7 —V adj. 5 —F TH 3 —F adj. — 136W TH 20 23Y TH — 136
Lory State Park L TH — 430L adj. — 68
Horsetooth Mtn. Park H adj. — 45Poa secunda J. Presl Pr TH 3 —
Pr adj. 1 —W TH 1 —W adj. 4 —
Polygonum douglasii Greene White River N.F. G TH 4 —Pr TH 16 —Pr adj. 1 —
Arapaho–Roosevelt N.F. W adj. 4 —Populus angustifolia James Arapaho–Roosevelt N.F. F TH — 23
F adj. — 23Y adj. — 23
Horsetooth Mtn. Park H adj. — 23Potentilla concinna Richards. Lory State Park L TH 1 —
L adj. 1 —Potentilla fissa Nutt. Arapaho–Roosevelt N.F. V TH — 23Potentilla hippiana Lehm. Arapaho–Roosevelt N.F. W TH 1 —Potentilla norvegica L. Arapaho–Roosevelt N.F. V adj. 3 —Potentilla pensylvanica L. Arapaho–Roosevelt N.F. F adj. 1 45Potentilla pulcherrima Lehm. White River N.F. B adj. — 23
G TH 4 181G adj. — 23Pr TH 2 —Pr adj. 0.25 23
Arapaho–Roosevelt N.F. W TH 1 —W adj. 2 45
Horsetooth Mtn. Park H adj. 1 —
526 WESTERN NORTH AMERICAN NATURALIST [Volume 72
APPENDIX 1. Continued. B = Booth, G = Gore, Pr = Piney River, P = Pitkin, E = East Portal, V = Buchanan, W =West Branch, F = Fish, H = Horsetooth, L = Wells Gulch, Y = Youngs Gulch.
Trail and Number ofSpecies name Location position % Cover seedlings
Potentilla rivalis Nutt. Pr TH 3 —Pr adj. 1 —
Prunus virginica L. var. melanocarpa White River N.F. B adj. 4 —(A. Nels.) Sarg.
Pseudocymopterus montanus (Gray) Arapaho–Roosevelt N.F. V adj. 2 —Coult. & Rose
Psoralidium tenuiflorum (Pursh) Rydb. Lory State Park L TH 15 —L adj. 4 —
Horsetooth Mtn. Park H TH 4 —Ratibida columnifera (Nutt.) Woot. Lory State Park L adj. 1 —
& Standl. Horsetooth Mtn. Park H TH 1 —H adj. 1 —
Rhus aromatica Ait. ssp. trilobata Arapaho–Roosevelt N.F. Y TH 5 —(Nutt.) W.A. Weber
Ribes cereum Dougl. Arapaho–Roosevelt N.F. Y TH 5 —Ribes inerme Rydb. White River N.F. G TH 6 —
G adj. 4 —Arapaho–Roosevelt N.F. Y TH 1 —
Rosa woodsii Lindl. White River N.F. B adj. 28 —G adj. 6 —
Arapaho–Roosevelt N.F. V adj. 7 —Y TH 2 —
Rubus idaeus L. White River N.F. G TH 4 —G adj. — 68
Sagina saginoides (L.) Karstens White River N.F. Pr adj. — 476Salix L. White River N.F. G TH 14 —
G adj. 2 23Sambucus microbotrys Rydb. White River N.F. G adj. — 23Saxifraga L. Arapaho–Roosevelt N.F. G TH — 113
Arapaho–Roosevelt N.F. W adj. — 23Sedum lanceolatum Torr. Arapaho–Roosevelt N.F. F TH — 23Senecio eremophilus Richards. White River N.F. B TH — 23
G TH — 23Senecio spartioides Torr. & Gray Lory State Park L adj. — 23
Horsetooth Mtn. Park H TH — 45H adj. — 23
Silene antirrhina L. Horsetooth Mtn. Park H adj. — 589Solidago missouriensis Nuttall White River N.F. Pr adj. 1 —
Arapaho–Roosevelt N.F. V TH 3 —V adj. 3 —
Sporobolus cryptandrus (Torr.) Gray Arapaho–Roosevelt N.F. Y TH — 929Y adj. — 861
Lory State Park L TH 4 883L adj. 21 996
Horsetooth Mtn. Park H TH — 294H adj. — 589
Stellaria umbellata Turczaninow White River N.F. Pr adj. — 23Symphoricarpos rotundifolius Gray White River N.F. B TH 1 —
B adj. 4 —Thalictrum occidentale Gray White River N.F. G TH 4 —Thermopsis divaricarpa A. Nels. Arapaho–Roosevelt N.F. V adj. 13 —Tradescantia occidentalis (Britt.) Smyth Arapaho–Roosevelt N.F. W TH 1 —
Horsetooth Mtn. Park H TH 1 —Valeriana edulis Nutt. ex Torr. & Gray Arapaho–Roosevelt N.F. F TH 1 —
F adj. 1 —Veronica americana Schwein. ex Benth. Arapaho–Roosevelt N.F. V TH 1 —Vicia americana Muhl. ex Willd. White River N.F. B adj. 0.25 —
Pr adj. 0.25 —Arapaho–Roosevelt N.F. V TH 0.25 —
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 527
APP
EN
DIX
2. A
ttri
bute
s of
pla
nt s
peci
es a
t tra
ils in
the
Col
orad
o R
ocky
Mou
ntai
ns, U
SA. N
= n
ativ
e, A
= a
lien,
B =
Boo
th F
alls
, G =
Gor
e L
ake,
F =
Fis
h C
reek
, Pr
= P
iney
Riv
er,
P =
Pitk
in L
ake,
E =
Eas
t Por
tal,
V =
Buc
hana
n, W
= W
est B
ranc
h.
Num
ber
Num
ber
Mea
nM
ean
Spec
ies
Ori
gin
Trai
ls
on p
lots
off p
lots
on c
over
off c
over
Abi
es b
ifolia
A. M
urra
yN
G, E
, V, W
2120
1712
Ace
r gl
abru
m T
orre
yN
V0
2—
1A
ceto
sella
vul
gari
s(K
och)
Fou
rrea
uN
B, G
, E, V
57
98
Ach
illea
lanu
losa
Nut
tall
NB
, G, P
r, P,
E, V
, W, F
8989
54
Acn
athe
rum
nel
soni
i(Sc
ribn
er) B
arkw
orth
NB
, G, P
r, P,
V, W
3943
75
Aco
nitu
m c
olum
bian
um N
utta
llN
G, P
r, E
, V, W
55
96
Ade
nolin
um le
wis
ii(P
ursh
) Löv
e &
Löv
eN
P 0
1—
6A
gata
che
urtic
ifolia
(Ben
tham
) Kun
tze
NB
, Pr,
P 9
115
9A
gose
ris
Raf
. spp
.N
B, G
, Pr,
P 20
83
5A
gose
ris
glau
ca (P
ursh
) Raf
ines
que
NG
, E, V
, W, F
85
11
Agr
opyr
on d
eser
toru
m F
isch
erA
E1
01
—A
gros
tis e
xara
ta T
rini
usA
G1
00
—A
gros
tis s
cabr
aW
illde
now
NG
20
8—
Agr
ostis
sto
loni
fera
L.
AE
01
—30
Alli
umL
.spp
.N
Pr, V
, F7
105
6A
lnus
inca
na (L
.)M
oenc
hsu
bsp.
tenu
ifolia
(Nut
tall)
Bre
itung
NW
01
—5
Am
elan
chie
r al
nifo
liaN
utta
llN
B, G
, P
68
814
Ana
phal
is m
arga
rita
ceae
(L.)
Ben
tham
& H
ooke
rN
Pr, E
, V, W
32
48
Anc
husa
offi
cina
lis L
.A
V1
00
—A
ndro
sace
sep
tent
rion
alis
L.
NB
, Pr,
F5
20
1A
nem
one
mul
tifid
aPo
iret
sub
sp. g
lobo
sa(N
utta
ll) T
orre
y &
Gra
yN
F5
61
2A
nten
nari
a G
aert
n. s
pp.
NG
, Pr,
E, V
, W, F
3422
46
Ant
icle
a el
egan
s(P
ursh
) Ryd
berg
NPr
10
1—
Api
acea
eL
indl
.N
B, G
, Pr,
P 4
62
8A
quile
gia
coer
ulea
Jam
esN
G, P
r, P,
F4
35
2A
rabi
s L
. spp
.N
B, V
, F1
21
3A
rcto
stap
hylo
s uv
a-ur
si L
.N
B, G
, Pr,
P, W
, F15
239
11A
rnic
a co
rdifo
liaH
ooke
rN
G, P
r, P,
E, V
, W18
188
8A
rtem
isia
frig
ida
Will
deno
wN
F5
48
3A
rtem
isia
ludo
vici
ana
Nut
tall
NW
, F6
107
3A
rtem
isia
trid
enta
taN
utta
llN
B, P
, W6
319
19A
ster
L. s
pp.
NB
, G, P
r, P,
V, W
, F15
73
4A
ster
folia
ceus
Lin
dley
NW
11
11
Ast
er la
nceo
latu
s W
illde
now
NG
, P
21
21
Ast
er la
nceo
latu
s W
illde
now
sub
sp.h
espe
rius
(Gra
y) S
empl
e &
Chm
iele
wsk
iN
P, W
22
91
Ast
erac
eae
Mar
tinov
NB
, Pr
32
28
Ast
raga
lus
L. s
pp.
NE
, W, F
34
12
Ast
raga
lus
tene
llus
Purs
hN
F1
32
5
528 WESTERN NORTH AMERICAN NATURALIST [Volume 72
APP
EN
DIX
2. C
ontin
ued.
N =
nat
ive,
A =
alie
n, B
= B
ooth
Fal
ls, G
= G
ore
Lak
e, F
= F
ish
Cre
ek, P
r = P
iney
Riv
er, P
= P
itkin
Lak
e, E
= E
ast P
orta
l, V
= B
ucha
nan,
W =
Wes
t Bra
nch.
Num
ber
Num
ber
Mea
nM
ean
Spec
ies
Ori
gin
Trai
ls
on p
lots
off p
lots
on c
over
off c
over
Bal
sam
orhi
za s
agitt
ata
(Pur
sh) N
utta
llN
P 0
1—
13B
oech
era
diva
rica
rpa
(Nel
son)
Löv
e &
Löv
eN
E0
2—
1B
oech
era
drum
mon
dii (
Gra
y) L
öve
& L
öve
NB
, G, P
r, P,
E, V
, W12
102
1B
oech
era
fend
leri
(Wat
son)
Web
erN
V, W
20
6—
Bra
ssic
acea
eB
urne
ttN
G, E
, W4
20
1B
rom
us L
.spp
.N
W, G
31
40
Bro
mus
car
inat
us H
ook
& A
rn.
NB
, G, P
r, P,
E, V
, W, F
2224
58
Bro
mus
cili
atus
L.
NB
, Pr,
P, E
, W9
96
3B
rom
us in
erm
isL
eyss
.A
B, E
, W, F
2114
1920
Cac
tace
aeJu
ssie
u N
F1
01
—C
alam
agro
stis
can
aden
sis
(Mic
haux
) P. B
eauv
ois
NE
, V, W
28
623
Cal
ocho
rtus
gun
ison
iiW
atso
nN
B, G
, Pr,
P, V
, W20
192
2C
aloc
hort
us n
utta
lliiT
orre
y &
Gra
yN
Pr2
28
10C
ampa
nula
rot
undi
folia
L.
NB
, G, P
r, P,
E, V
, W, F
4650
22
Cap
sella
bur
sa-p
asto
ris
(L.)
Med
ikus
AB
, V4
10
0C
arex
L. s
pp.
NB
, G, P
r, P,
E, V
, W, F
9510
114
12C
astil
leja
Mut
is e
x L
. f. s
pp.
NP
01
—5
Cas
tille
ja s
ulph
urea
Ryd
berg
NB
, Pr,
P, W
55
45
Cea
noth
us fe
ndle
riG
ray
NB
10
13—
Cer
astiu
m L
. spp
.N
E, W
, F11
74
5C
eras
tium
nut
ans
Raf
ines
que
NW
01
—0
Cer
astiu
m s
tric
tum
L.
NV
12
01
Cer
coca
rpus
mon
tanu
s R
afin
esqu
eN
F0
1—
0C
ham
aepe
ricl
ymen
um (C
ornu
s)ca
nade
nse
(L.)
Asc
hers
on &
Gra
ebne
rN
E0
1—
2C
ham
erio
n an
gust
ifoliu
mD
anie
lsN
B, G
, Pr,
P, E
, V, W
1527
46
Che
nopo
dium
L. s
pp.
NB
, F2
33
2C
heno
podi
um a
trov
iren
s R
ydbe
rgN
B, P
r2
27
3C
heno
podi
um b
elan
geri
Moq
uin
NB
, G, P
r, P,
V, F
1623
23
Chl
oroc
repi
s fe
ndle
ri (S
chul
tz-B
ipon
tinus
) Web
erN
V1
27
1C
hrys
otha
mnu
s vi
scid
iflor
us (H
ooke
r) N
utta
llN
P 0
1—
5C
irsi
um M
ill. s
pp.
NB
, G, P
r, P,
E, V
, W, F
2525
48
Cir
sium
arv
ense
L.
AG
, Pr
24
199
Cir
sium
cen
taur
eae
(Ryd
berg
) Sch
uman
nN
V1
11
7C
irsi
um e
aton
ii(G
ray)
Rob
inso
nN
B, G
30
3—
Col
lom
ia li
near
isN
utta
llN
B, G
, Pr,
P, E
, V, W
3330
45
Con
ium
mac
ulat
um L
.A
Pr, P
, E7
810
10C
onvu
lvus
arv
ensi
s L
.A
Pr1
05
—D
acty
lis g
lom
erat
aL
.A
B, G
, Pr,
P, V
163
94
Dan
thon
ia in
term
edia
Vas
eyN
G, P
r, V,
W8
510
3
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 529
APP
EN
DIX
2. C
ontin
ued.
N =
nat
ive,
A =
alie
n, B
= B
ooth
Fal
ls, G
= G
ore
Lak
e, F
= F
ish
Cre
ek, P
r = P
iney
Riv
er, P
= P
itkin
Lak
e, E
= E
ast P
orta
l, V
= B
ucha
nan,
W =
Wes
t Bra
nch.
Num
ber
Num
ber
Mea
nM
ean
Spec
ies
Ori
gin
Trai
ls
on p
lots
off p
lots
on c
over
off c
over
Del
phin
ium
L. s
pp.
NB
, G, P
r, P,
W11
131
1D
esch
amps
ia c
espi
tosa
(L.)
P. B
eauv
ois
NE
21
911
Ely
mus
ele
moi
des
(Raf
ines
que)
Sw
ezey
NB
, G, P
, W, F
910
32
Ely
mus
gla
ucus
Buc
kley
NB
, G, P
r, P,
E, V
, W25
265
8E
lym
us tr
achy
caul
usL
ink
NG
, P, W
41
20
Ely
trig
a re
pens
(L.)
Nev
ski
AB
10
0—
Epi
lobi
um c
iliat
um R
afin
esqu
eN
Pr2
18
2E
pilo
bium
hor
nem
anni
i Rei
chen
bach
NE
31
61
Equ
iset
um L
.spp
.N
G, E
, V, W
35
1015
Ere
mog
one
cong
esta
(Gra
y) I
konn
ikov
NW
55
56
Ere
mog
one
fend
leri
(Gra
y) I
konn
ikov
NV,
F11
91
2E
rige
ron
L. s
pp.
NB
, G, P
r, P,
E, V
, W, F
7867
88
Eri
gero
n co
mpo
situ
s Pu
rsh
NE
, V2
17
23E
rige
ron
coul
teri
Por
ter
NG
01
—7
Eri
gero
n fla
gella
ris
Gra
yN
B, G
, Pr,
P, V
, W15
179
7E
rige
ron
form
osis
sim
usG
reen
eN
G, P
r, P,
E, V
, W22
1911
10E
rige
ron
pere
grin
us (B
anks
) Gre
ene
NV
34
73
Eri
gero
n sp
ecio
sis
(Lin
dley
) de
Can
dolle
NB
, E2
515
7E
riog
onum
um
bella
tum
Tor
rey
(incl
udes
E. s
ubal
pinu
m)
NB
, G, P
r, P,
V, W
, F25
3112
13E
rysi
mum
cap
itatu
m(D
ougl
as) G
reen
eN
F1
21
0E
upho
rbia
ceae
Juss
.N
F0
1—
0Fe
stuc
a L
. spp
.N
B, P
r, V,
W, F
69
310
Fest
uca
ariz
onic
aVa
sey
NP
10
5—
Fest
uca
idah
oens
is E
lmer
NB
, G, P
5
118
30Fe
stuc
a th
erbe
ri V
asey
NB
, G, P
r, P
2232
2019
Frag
aria
vir
gini
ana
Mill
er s
ubsp
. gla
uca
(Wat
son)
Sta
udt
NB
, G, P
r, P,
E, V
, W, F
4740
88
Fras
era
spec
iosa
Dou
glas
NB
, Pr,
W4
56
9G
ailla
rdia
ari
stat
aPu
rsh
NV
01
—5
Gal
ium
sep
tent
rion
ale
Roe
mer
& S
chul
tes
NB
, G, P
r, P,
E, V
, W, F
3848
44
Gal
ium
trifl
orum
Mic
haux
NG
, E, W
510
42
Gay
ophy
tum
diff
usum
Tor
rey
& G
ray
subs
p.pa
rvifl
orum
Lew
is &
Szw
eyko
wsk
iN
P 1
01
—G
entia
nella
acu
ta (M
icha
ux) H
iiton
enN
E1
10
1G
eran
ium
ric
hard
soni
iFis
her
& T
raut
vett
erN
B, G
, Pr,
P, E
, V, W
, F34
494
5G
eum
mac
roph
yllu
m W
illde
now
NE
10
1—
Geu
m tr
iflor
ium
Pur
shN
Pr, W
04
—5
Gly
ceri
a el
ata
(Nas
h)Jo
nes
NG
10
0—
Hac
kelia
flor
ibun
da(L
ehm
ann)
Joh
nsto
nN
Pr0
1—
1H
erac
lium
sph
ondy
lium
L. s
ubsp
. mon
tanu
m(S
chle
iche
r) B
riqu
etN
B, G
, Pr,
P, W
2326
49
Hel
iant
hella
qui
nque
nerv
is(H
ooke
r) G
ray
NB
, Pr,
P, V
, W, F
1511
812
530 WESTERN NORTH AMERICAN NATURALIST [Volume 72
APP
EN
DIX
2. C
ontin
ued.
N =
nat
ive,
A =
alie
n, B
= B
ooth
Fal
ls, G
= G
ore
Lak
e, F
= F
ish
Cre
ek, P
r = P
iney
Riv
er, P
= P
itkin
Lak
e, E
= E
ast P
orta
l, V
= B
ucha
nan,
W =
Wes
t Bra
nch.
Num
ber
Num
ber
Mea
nM
ean
Spec
ies
Ori
gin
Trai
ls
on p
lots
off p
lots
on c
over
off c
over
Hes
pero
stip
a co
mat
a (T
rini
us &
Rup
rech
t) B
arkw
orth
NB
11
71
Het
erot
heca
vill
osa
(Pur
sh) S
hinn
ers
NG
, W, F
42
512
Hie
raci
um a
lbifl
ora
(Hoo
ker)
Web
erN
P, V
30
1—
Hor
deum
bra
chya
nthe
rum
L.
APr
10
0—
Hor
deum
pus
illum
L.
NE
10
1—
Hyd
roph
yllu
m c
apita
tum
Dou
glas
NB
01
—1
Junc
us L
. spp
.N
G, P
r, E
, V, W
, F17
129
2Ju
ncus
bal
ticus
Will
deno
wN
E3
19
6Ju
nipe
rus
com
mun
isL
.N
G, P
, E, W
, F5
75
32Ju
nipe
rus
scop
ulor
um S
arge
ntN
V, F
33
614
Koe
leri
a m
acra
ntha
(Led
ebou
r) S
chul
tes
NV,
F5
43
3L
athy
rus
leuc
anth
usR
ydbe
rgN
B, G
, Pr,
P, W
5362
67
Lep
idiu
m L
. spp
.N
B, G
10
0—
Leu
cant
hem
um v
ulga
reL
amar
kA
E1
011
—L
euco
poa
king
ii (W
atso
n) W
eber
NF
1716
1211
Ligu
lari
a bi
gelo
vii (
Gra
y) W
ebbe
rN
G, V
21
20
Ligu
stic
um p
orte
ri C
oulte
r &
Ros
eN
B, E
, V, W
67
57
Lim
norc
his
dila
tata
(Pur
sh) R
ydbe
rg s
ubsp
.alb
iflor
a (C
ham
isso
) Löv
e &
Sim
onN
P 1
11
1Li
nari
a vu
lgar
is M
iller
AB
11
210
Lon
icer
a m
orro
wiG
ray
AE
, V, W
16
55
Lup
inus
arg
ente
us P
ursh
.N
F2
30
4L
uzul
a pa
rvifl
ora
(Ehr
hart
) Des
vaux
NE
01
—0
Mah
onia
rep
ens
(Lin
dley
) Don
NB
, G, P
r, P,
V, W
2533
811
Mai
anth
emum
am
plex
icau
le (N
utta
ll) W
eber
NG
, P, V
22
133
Mai
anth
emum
ste
llatu
m (L
.) L
ink
NB
, G, P
r, V,
W, F
611
13
Med
icag
o lu
pulin
a L
.A
G1
01
—M
elic
a sp
ecta
bilis
Scri
bner
NB
, G, P
r, P,
W17
243
3M
elilo
tus
offic
inal
e (L
.) Pa
llas
AE
11
3019
Mer
tens
ia c
iliat
a (J
ames
) G. D
on.
NE
, W2
39
3M
oss/
Lic
hen
NF
13
2326
Muh
lenb
ergi
a m
onta
na(N
utta
ll) H
itchc
ock
NV,
F9
79
8N
emop
hilia
bre
viflo
raG
ray
NB
, G2
53
13O
ligos
poru
s dr
acun
culu
s (L
.) Po
ljako
vN
Pr, E
12
214
Ore
ochr
ysum
par
ryi(
Gre
y) R
ydbe
rgN
G, P
1
215
28O
smor
hiza
dep
aupe
rata
Phi
lippi
NPr
, P, E
, V, W
1419
32
Oxy
trop
is la
mbe
rtii
Purs
hN
V, F
52
25
Oxy
trop
is s
eric
ea N
utta
llN
E, F
21
96
Padu
s vi
rgin
iana
(L.)
Mill
erN
G, P
5
313
15Pa
sopy
rum
sm
ithii
(Ryd
berg
) Löv
eN
B, G
, Pr,
P, E
, W37
314
4
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 531
APP
EN
DIX
2. C
ontin
ued.
N =
nat
ive,
A =
alie
n, B
= B
ooth
Fal
ls, G
= G
ore
Lak
e, F
= F
ish
Cre
ek, P
r = P
iney
Riv
er, P
= P
itkin
Lak
e, E
= E
ast P
orta
l, V
= B
ucha
nan,
W =
Wes
t Bra
nch.
Num
ber
Num
ber
Mea
nM
ean
Spec
ies
Ori
gin
Trai
ls
on p
lots
off p
lots
on c
over
off c
over
Pedi
cula
ris
race
mos
a D
ougl
as s
ubsp
.alb
a Pe
nnel
lN
E, V
55
72
Pens
tem
on S
chm
idel
spp
.N
B, G
, P, V
, F9
103
4Pe
nste
mon
ryd
berg
ii N
elso
nN
P 1
06
—Pe
nste
mon
whi
pple
anus
Gra
yN
V1
010
—Pe
ntap
hyllo
ides
flor
ibun
da(P
ursh
) Löv
eN
Pr2
33
22Ph
leum
alp
inum
L.
NP,
V2
11
15Ph
leum
pra
tens
e L
.A
B, G
, Pr,
P, E
, V, W
, F43
209
7Pi
cea
enge
lman
ii(P
arry
) Eng
elm
ann
NPr
, E, V
, W, F
,P4
64
4Pi
cea
pung
ens
Eng
elm
ann
NE
21
30
Pinu
s L
. spp
.N
E, F
22
00
Pinu
s ar
ista
taE
ngel
man
nN
V1
02
—Pi
nus
cont
orta
Dou
glas
NG
20
11—
Pinu
s fle
xilis
Jam
esN
P, W
21
518
Pinu
s po
nder
osa
Dou
glas
NV,
F3
72
5Pl
anta
go m
ajor
L.
AE
40
13—
Pneu
mon
anth
e af
finis
(Gri
seba
ch) G
reen
eN
F0
1—
1Pn
eum
onan
the
parr
yi(E
ngel
man
n) G
reen
eN
Pr, E
, V, F
35
42
Poa
L. s
pp.
NE
, V, W
54
711
Poa
annu
a L
.A
E2
023
—Po
a fe
ndle
rian
a (S
teud
el) V
asey
NE
, F2
12
23Po
a pr
aten
sis
L. (
incl
udin
g Po
a ag
assi
zens
is B
oivi
n &
Löv
e)N
B, G
, Pr,
P, E
, V, W
, F95
7418
11Po
a re
flexa
Vas
ey &
Scr
ibne
rN
P1
25
6Po
a se
cund
aPr
esl.
NP
12
11
Poa
trac
yi V
asey
NB
, Pr
11
1910
Poac
eae
Bar
nhar
tN
B, G
, P, E
, F6
31
6Po
lygo
num
are
nast
rum
Bor
eau
AB
, Pr,
P, E
, V, W
, F37
267
8Po
pulu
s tr
emul
oide
s M
icha
uxN
B, G
, Pr,
P, V
, W, F
3738
54
Pote
ntill
a L
. spp
.N
E, F
, W24
195
5Po
tent
illa
ovin
a M
acou
nN
G1
05
—Po
tent
illa
pens
ylva
nica
L.
NP,
E3
25
1Po
tent
illa
pulc
herr
ima
Leh
man
nN
B, G
, Pr,
P, E
, V, W
, F50
3313
10Po
tent
illa
pulc
herr
ima
×hi
ppia
naN
F0
1—
7Po
tent
illa
rubr
icau
lis L
ehm
ann
NF
30
5—
Pote
ntill
a un
iflor
a L
edeb
our
NV
11
72
Pseu
docy
mop
teru
s m
onta
nus
(Gra
y) C
oulte
r &
Ros
e N
V, W
, F21
161
3Ps
eudo
roeg
neri
a sp
icat
a (P
ursh
) Löv
eN
B, G
, Pr,
V3
311
7Ps
eudo
tsug
a m
enzi
esii
(Mir
bel)
Fran
coN
W0
1—
10Pu
lsat
illa
ludo
vici
ana
(Nut
tall)
Hel
ler
NV,
F3
24
6Pu
rshi
a tr
iden
tata
(Pur
sh) d
e C
ando
lleN
F11
518
10
532 WESTERN NORTH AMERICAN NATURALIST [Volume 72
APP
EN
DIX
2. C
ontin
ued.
N =
nat
ive,
A =
alie
n, B
= B
ooth
Fal
ls, G
= G
ore
Lak
e, F
= F
ish
Cre
ek, P
r = P
iney
Riv
er, P
= P
itkin
Lak
e, E
= E
ast P
orta
l, V
= B
ucha
nan,
W =
Wes
t Bra
nch.
Num
ber
Num
ber
Mea
nM
ean
Spec
ies
Ori
gin
Trai
ls
on p
lots
off p
lots
on c
over
off c
over
Pyro
la c
hlor
anth
aSw
artz
NE
35
54
Pyro
la r
otun
difo
lia L
. sub
sp.a
sari
folia
(Mic
haux
) Löv
eN
E, V
, W7
122
5R
anun
cula
ceae
Juss
ieu
NV
01
—0
Rib
es c
ereu
m D
ougl
asN
B, E
, V, W
, F7
911
5R
ibes
iner
me
Ryd
berg
NV
01
—6
Rib
es m
ontig
enum
McC
latc
hie
NB
, G, E
, W4
911
4R
ibes
wol
fiiR
othr
ock
NB
01
—14
Ror
ippa
sin
uata
(Nut
tall)
Hitc
hcoc
kN
E1
05
—R
orip
pa s
phae
roca
rpa
(Gra
y) B
ritt
onN
E1
03
—R
osa
woo
dsii
Lin
dley
NB
, G, P
, E, V
, W, F
2832
116
Rub
acer
par
viflo
rum
(Nut
tall)
Ryd
berg
NB
, G1
15
5R
ubus
idea
usL
.N
B, G
, E, V
, W10
107
6Sa
gina
sag
inoi
des
(L.)
Kar
sten
sN
E, V
31
10
Salix
L. s
pp.
NG
, P, E
, W3
79
18Sa
mbu
cus
mic
robo
trys
Ryd
berg
NB
, G, E
23
198
Saxi
frag
acea
eJu
ssie
uN
V0
1—
2Se
dum
lanc
eola
tum
Tor
rey
NG
, E, W
, F9
62
1Se
neci
o L
. spp
.N
B, G
, Pr,
P, F
1011
12
Sene
cio
inte
gerr
imus
Nut
tall
NPr
01
—5
Sene
cio
serr
a H
ooke
rN
B, G
, Pr,
E3
87
7Se
neci
o tr
iang
ular
is H
ooke
rN
V0
1—
1Sh
epar
dia
cana
dens
is (L
.) N
utta
llN
G1
00
—Si
lene
ant
irrh
ina
L.
NB
, G, P
, E3
31
0So
lidag
o L
. spp
.N
P 1
06
—So
lidag
o m
isso
urie
nsis
Nut
tall
NP,
W3
36
1So
lidag
o si
mpl
ex H
umbo
lt, B
onpl
ant &
Kun
th v
ar.s
impl
exN
Pr, V
, F7
33
2Sp
ergu
lari
a ru
bra
(L.)
K. P
resl
.A
E1
01
—Sp
orob
olus
cry
ptan
drus
(Tor
rey)
Gra
yN
E1
11
1St
rept
opus
fass
ettii
Löv
e &
Löv
eN
E, V
22
32
Sym
phor
icar
pos
albu
s(L
.) B
lake
NV,
W, F
43
78
Sym
phor
icar
pos
rotu
ndifo
lius
Gra
yN
B, P
r, P
1012
2419
Tara
xacu
m o
ffici
nale
Web
erA
B, G
, Pr,
P, E
, V, W
, F98
477
4T
halic
trum
L. s
pp.
NB
, G, P
r, P,
E, V
, W18
268
10T
herm
opsi
s di
vari
carp
aN
elso
nN
V, F
68
108
Thl
apsi
arv
ense
L.
APr
, E2
01
—To
xico
scor
dion
ven
enos
um (W
atso
n) R
ydbe
rgN
E, V
44
23
Trag
opog
on d
ubiu
sSc
opol
iA
B, G
, Pr,
P, W
2716
22
Trag
opog
on p
rate
nsis
L.
AB
, G, V
, W6
57
4Tr
ifoliu
mL
. spp
.A
B, G
, Pr,
V14
45
2
2012] ALIEN PLANTS ON TRAILHEADS AND TRAILS 533
APP
EN
DIX
2. C
ontin
ued.
N =
nat
ive,
A =
alie
n, B
= B
ooth
Fal
ls, G
= G
ore
Lak
e, F
= F
ish
Cre
ek, P
r = P
iney
Riv
er, P
= P
itkin
Lak
e, E
= E
ast P
orta
l, V
= B
ucha
nan,
W =
Wes
t Bra
nch.
Num
ber
Num
ber
Mea
nM
ean
Spec
ies
Ori
gin
Trai
ls
on p
lots
off p
lots
on c
over
off c
over
Trifo
lium
hyb
ridu
m L
.A
Pr1
06
—Tr
ifoliu
m p
rate
nse
L.
AE
56
53
Trifo
lium
rep
ens
L.
AB
, P, E
, V, W
278
1012
Tris
etum
spi
catu
m(L
.) R
icht
erN
B, P
r, E
, V10
72
3Va
ccin
um m
yrtil
lus
L. s
ubsp
. ore
ophi
lium
(Ryd
berg
) Lov
e et
al.
NG
, Pr,
P, E
, V, W
1315
1318
Vale
rian
edu
lis N
utta
llN
Pr, F
13
018
Vale
rian
occ
iden
talis
Hel
ler
NB
, Pr
78
59
Verb
ascu
m th
apsu
sL
.A
B0
1—
1V
icia
am
eric
ana
Mül
enbe
rgN
B, G
, Pr,
P, W
5466
45
Vio
la L
. spp
.N
B, G
, Pr,
P, E
, V, W
, F46
433
2V
irgu
last
er a
scen
dens
(Lin
dley
) Sem
ple
NW
54
414
Wye
thia
am
plex
icau
lis (N
utta
ll) N
utta
llN
P1
118
5U
nkno
wn
NB
, G, P
r, P,
E, V
, W, F
4838
14
Top Related