Recreational trails as corridors for alien plants in the ...

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.

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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

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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


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


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


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


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


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


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


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.

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Received 16 November 2011Accepted 29 July 2012



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 —


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.


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 —




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 —


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



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 —




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 —




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 —




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




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


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 —




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


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


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 —


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


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


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


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


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


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


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

Recreational trails as corridors for alien plants in the ...

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