Alpine Plant Community Trends on Elk Summer Range 

of Rocky Mountain National Park, Colorado: 

An Analysis of Existing Data 

By Linda Zeigenfuss 

Open-File Report 2006–1122 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

P. Patrick Leahy, Acting Director 

U.S. Geological Survey, Reston, Virginia 2006 

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Suggested citation: 

Zeigenfuss, L., 2006, Alpine plant community trends on elk summer range of rocky mountain national park, 

colorado: an analysis of existing data: U.S. Geological Survey, Open-File Report 2006-1122, 21 p. 

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ii
Contents 

Contents ..............................................................................................................................................................................iii

Abstract................................................................................................................................................................................1

Introduction .........................................................................................................................................................................1

Study Area ...........................................................................................................................................................................3

Methods ...............................................................................................................................................................................3

Results ..................................................................................................................................................................................4

Discussion..........................................................................................................................................................................13

Acknowledgments............................................................................................................................................................15

References Cited ..............................................................................................................................................................16

Appendix ............................................................................................................................................................................18

Figures 

1. Decreases in percent cover and height of Salix planifolia on alpine and subalpine transects in Rocky 

Mountain National Park, Colorado 1971–96.....................................................................................................5 

2. Decreases in percent cover and height of Salix brachycarpa on alpine and subalpine transects in Rocky 

Mountain National Park, Colorado 1971–96.....................................................................................................6 

3. Percent cover and height of Engelmann spruce (Picea engelmannii) measured on alpine and subalpine 

transects in Rocky Mountain National Park, Colorado, 1971–96 .................................................................7 

4. Changes in tufted hairgrass (Deschampsia caespitosa) and litter cover in subalpine krummholz and 

alpine tundra transects in Rocky Mountain National Park, Colorado, 1971–96 ......................................11 

5. Changes in moss and stonecrop (Sedum spp.) frequency in subalpine krummholz and alpine tundra 

transects in Rocky Mountain National Park, Colorado, 1971–96 ...............................................................12 

Tables 

1. Significant changes in vegetation types on alpine and subalpine transects in Rocky Mountain National 

Park, Colorado, 1971–96.......................................................................................................................................8 

2. Significant changes in vegetation genera found on alpine and subalpine transects in Rocky Mountain 

National Park, Colorado, 1971–96 ......................................................................................................................9 

3. Individual species that showed significant changes in cover and frequency on alpine and subalpine 

transects in Rocky Mountain National Park, Colorado, 1971–96 ...............................................................10 

iii
Effects of Elk Herbivory on Alpine Plant Communities 

on the Elk Summer Range, Rocky Mountain National 

Park, Colorado—An Analysis of Existing Data 

By Linda Zeigenfuss1

Abstract 

The majority of the elk (Cervus elaphus) population of Rocky Mountain National Park in 

Colorado summer in the park’s high-elevation alpine and subalpine meadows and willow 

krummholz. The park’s population of white-tailed ptarmigan (Lagopus leucurus altipetens) 

depends on both dwarf and krummholz willows for food and cover. Concern about the effects of 

elk herbivory on these communities prompted the monitoring of 12 vegetation transects in these 

regions from 1971 to 1996. Over this 25-year period, data were collected on plant species cover 

and frequency and shrub heights. These data have not been statistically analyzed for trends in the 

measured variables over time to determine changes in species abundance. Krummholz willow 

species (Salix planifolia, S. brachycarpa) declined 17–20 percent in cover and about 25 centimeters 

in height over the study period. Graminoids (particularly Deschampsia caespitosa, Carex, and 

Poa) increased slightly from 1971 to 1996. No significant increases of nonnative plant species 

were observed. An increase in presence of bare ground over the 25-year period warrants continued 

measurement of these transects. Lack of good data on elk density, distribution, or use levels 

precludes correlating changes in plant species cover, frequency, or heights with elk population 

trends. I recommend development of a more rigorously designed monitoring program that includes 

these transects as well as others chosen on a random or stratified design and consistent 

measurement protocol and sampling intervals. Some method of quantifying elk use, either through 

measurement of plant utilization, pellet counts, or census-type surveys, would allow correlation of 

changes in plant species over time with changes in elk distribution and density on the park’s alpine 

and subalpine regions. 

Introduction 

The elk (Cervus elaphus) population that winters along the eastern boundaries of Rocky 

Mountain National Park (RMNP) and in the Estes Valley of Colorado currently numbers around 

2,200 elk. Approximately 75 percent of this population summers in the alpine and subalpine 

regions of the park. This population has been increasing in recent decades (Lubow and others, 

2002). Approximately 150–200 elk have also been observed to winter at these high elevations and 

may be browsing alpine willow communities to a great extent during winter. Park management is 

concerned about the effects of large numbers of elk on alpine and subalpine willow and tundra 

 

1

 Linda Zeigenfuss, U.S. Geological Survey, Fort Collins Science Center, 2150 Centre Avenue, Bldg. C, Fort Collins, 

CO 80526, (970) 226-9329, Email: Linda_Zeigenfuss@usgs.gov 

1
communities located in the park’s high central mountains (Stevens, 1980; Therese Johnson, Rocky 

Mountain National Park, oral commun., 2005). Alpine willow communities are crucial to the 

park's population of white-tailed ptarmigan (Braun and Rogers, 1971; Braun and others, 1976). 

State of Colorado biologists have reported declines in white-tailed ptarmigan (Lagopus leucurus 

altipetens) in core areas along Trail Ridge and have attributed the decline to willow habitat declines 

due to high densities of elk (Braun and others, 1991). Former park biologist David Stevens 

reported significant declines in willows at long-term sites monitored in the 1970s and 1980s 

(Stevens, 1993). Stevens’ work, however, was limited in inference to those few plots he monitored 

and not to landscape scale. 

White-tailed ptarmigan populations have declined about 55 percent during the period 1975-

1999 in a study area on Trail Ridge in RMNP (Wang and others, 2002). This period of decline 

roughly corresponds to a period of substantial increase in the Estes Valley elk population (Lubow 

and others, 2002), which summers in the alpine/subalpine areas of the interior of RMNP. The elk 

increases were once thought to be related to the ptarmigan decline (Braun and others, 1991), but 

Wang and others (2002) found no correlation between the Rocky Mountain National Park/Estes 

Valley elk population size and the ptarmigan population growth rate. Elk, however, may still have 

a long-term, time-lag negative influence upon ptarmigan populations through slower decline in 

willow abundance due to the elk increases. Willows might take a decade or more to decline in 

response to overabundance of elk, and the Wang and others (2002) analysis did not search for timelag effects. 

Ptarmigan population cycles, however, may be correlated to weather. Willow communities 

may also be affected by changes in the climate, and climate records indicated a warming (+0.89o

C) 

and drying (–101.4 mm annual precipitation) trend on the low-elevation winter range of the park 

from 1948 to 1997 (Singer and others, 1998). Similar climate change is likely occurring in the 

park’s alpine regions. Average May and June temperatures recorded at Niwot Ridge Long-Term 

Ecological Research Site, 40 km south of the Trail Ridge area of RMNP, showed a significant 

increase of about 2o

C over the 2 decades from 1976 to 1996 (Wang and others, 2002). While high 

levels of elk herbivory alone may not cause willow decline, herbivory coupled with climate 

changes may be contributing to decline of lower elevation willow communities in areas such as 

Yellowstone and Rocky Mountain National Parks (Wagner and others, 1995; Singer and others, 

1998). 

White-tailed ptarmigan are obligate habitat specialists that require willows. White-tailed 

ptarmigan may use two height strata of willows. Short, often dwarf, willows or willows only 7–24 

cm in height are preferred during the summer months (Frederick and Gutierrez, 1992) and during 

the winter months, when these areas are blown largely snow free (Braun and others, 1976; Francis 

Singer, U.S. Geological Survey, oral commun., 2003). Taller shrub willows (>90 cm), more 

typically found at or below the treeline, are avoided when there is minimal or no snow cover 

(Frederick and Gutierrez, 1992), but crowns of taller willows may become more accessible when 

snows get deeper and the birds gain access to buds and smaller shoots of the crown by walking on 

deeper snow (Braun and others, 1976; Francis Singer, U.S. Geological Survey, oral commun., 

2003). 

Vegetation data were collected on 12 transects in subalpine krummholz and alpine tundra 

plant communities in RMNP at varying intervals over a 25-year period from 1971 to 1996. These 

data were never subjected to any rigorous statistical analysis to detect trends over that time period. 

Data that were collected include plant cover and willow height and cover. No data were collected 

on percent leader use of willows by elk or elk fecal pellet counts; therefore, one could not correlate 

trends observed in plant cover and shrub heights to any trends in elk use or increased utilization of 

willows. Therefore, any conclusions that changes in alpine and subalpine vegetation types are the 

2
effect of increased levels of elk herbivory are speculative. The study objectives will address the 

following questions: 

1. What was the trend in plant cover, heights, and species composition from 1971 to 1996? 

2. Was there a decline in alpine/subalpine willow heights that may have indicated decreasing 

habitat for white-tailed ptarmigan over the 25-year study period? 

Study Area 

Description of the study area has been taken from Stevens (1980) and Hobbs and others 

(1982). Subalpine krummholz was defined as the ecotone between the subalpine forest and alpine 

tundra occurring at about 3,300–3,600 m elevation in Rocky Mountain National Park. It is 

characterized by an intermingling of species from both habitats. Primary plant species include 

stunted Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa), often mixed 

with willows (Salix planifolia, S. glauca, S. brachycarpa) and low blueberry (Vaccinium spp.); 

sedges (Kobresia, Carex spp.), tufted hairgrass (Deschampsia caespitosa), alpine timothy (Phleum 

alpinum), alpine avens (Geum rossii), and clover (Trifolium spp.). 

The alpine tundra zone is located above the subalpine krummholz at elevations over 3,600 

m. Tundra vegetation consists of a heterogeneous cover of low sedges, Juncus spp., cushion plants, 

bistort (Polygonum spp.), and dwarf shrubs. 

Elk migrate through these alpine and subalpine areas in large numbers in the spring and fall, 

and many spend the majority of the summer on the tundra slopes (Bear, 1989; Braun and others, 

1991; Larkins, 1997). A small group of elk also has wintered on the tundra (Bear, 1989; Braun and 

others, 1991). Diets of elk summering in these areas consisted primarily of graminoids (62–67 

percent of total diet), followed by shrubs—particularly willow (11–21 percent), with forbs 

accounting for the remainder of the diet (9–27 percent, Hobbs and others, 1982). 

 

Methods 

In 1971, park biologist David Stevens established twelve 100-ft (30.5-m) transects in alpine 

tundra (n=8) and subalpine krummholz (n=4) areas of Rocky Mountain National Park in Colorado. 

Stevens selected representative sites in those vegetation communities and locales receiving the 

highest elk use (Stevens, 1980, 1992). Transects were chosen nonrandomly and were distributed 

across the alpine range in easily accessible areas of highest elk densities. Seven of these 12 

transects (3 alpine, 4 subalpine) had substantial willow cover. Data on average height and percent 

cover of shrub species were collected, approximately once every 5 years, using the line intercept 

method (Canfield, 1941). A modified Daubenmire (1959) technique was used to determine 

occurrence, and percent cover of herbaceous and small shrub species on transects. These samples 

were intended to be collected approximately once every five years. This technique involved 

sampling 21 (20 x 50 cm) plots distributed at 5-ft (1.52-m) intervals along the 100-ft (30.5-m) 

transect line. 

Prior analysis of similar data from low-elevation winter range transects has identified trends 

in species diversity and shrub cover decline (Zeigenfuss and others, 1999). However, as pointed 

out in the earlier analysis (Zeigenfuss and others, 1999), these plots were limited in number and not 

randomly selected, so inference may be limited. Subalpine krummholz transects were sampled in 

1971, 1975, 1979, 1984, 1989, and 1996. Tundra transects were sampled in 1971, 1976, 1979, 

3
1985, 1989, and 1996; however, those with willow associations were measured in 1984 instead of 

1985, and one tundra turf site was only sampled in 1971, 1976, 1991, and 1996. Orthogonal 

polynomial contrasts were developed to estimate linear and quadratic polynomials. The data were 

transformed using contrast coefficients, and the linear and quadratic effects over time were 

estimated by summing the transformed data for each transect. A one-sample t-test was used to test 

whether the effects over time were different from zero (no time effect). Analyses were performed 

using SAS 9.1 (SAS Institute, 2002) statistical software. Percent cover, frequency and height of 

shrubs for each species, genus groupings (Daubenmire data only), and major vegetation groups 

(graminoids, forbs, and so forth—Daubenmire data only) were analyzed over time. 

I compiled a complete list of species found in the dataset and included current and former 

scientific names, as well as common names, for each species (see Appendix). Only two species 

entries out of 5 sampling sessions on 12 transects could not be discerned from the raw data. In 

many cases, genus and species information was included in one year, but only genus was recorded 

in subsequent years. When possible to determine the species (for example, only one species of the 

indicated genus is found in the region/habitat), I added species data to the genus data obtained from 

the raw data. Because in many years only genus data were available, and therefore, the genus data 

may fill in missing gaps for a particular species in a given year, I also ran all analyses after 

grouping all individual entries by genus. 

Results 

Average cover and height of planeleaf willows (Salix planifolia) and short-fruit willow (S. 

brachycarpa) declined over the 25-year period from 1971 to 1996 (figs. 1, 2). S. planifolia cover 

decreased 17.8 percent (P=0.1376), but this decrease was not significant at the 0.05 level. 

However, the average decline of 25 cm in height over the 25-year period was significant 

(P=0.0199, fig. 1). S. brachycarpa decreased an average of 20.3 percent in cover (P=0.0321) and 

24 cm in height (P=0.0258, fig. 2) over the 25 years. Engelmann spruce (Picea engelmannii) cover 

and height increased coincidentally with the decrease of Salix on three transects (fig. 3), from no 

cover in 1971 to an average of 6 percent cover on two subalpine transects and 0.6 percent cover on 

one tundra transect, but these changes were not different from zero (P=0.13). Percent cover and 

frequency of grasses and lichens increased over the sampling period (table 1), while overall shrub 

cover and frequency decreased over this period (P<0.05), as measured using the Daubenmire 

technique. Percent litter cover and frequency observed responded in a quadratic fashion, increasing 

initially and then decreasing toward the end of the sampling period (table 1). The frequency of forb 

and nonvegetative cover types (rock, water, bare ground) were observed to decrease initially and 

then increase toward the end of the sampling period. 

4
0

10

20

30

40

50

60

70

1971 1976 1981 1986 1991 1996

YEAR

PERCENT COVER

s-1 s-2 s-3 s-4 t-6 t-7

0

0.25

0.5

0.75

1

1971 1976 1981 1986 1991 1996

YEAR

HEIGHT (m)

s-1 s-2 s-3 s-4 t-6 t-7

Figure 1. Decreases in percent cover and height (in meters) of Salix planifolia on alpine and subalpine 

transects in Rocky Mountain National Park, Colorado 1971–96. “s” prefix denotes subalpine 

transects, “t” denotes alpine tundra transects. 

5
0

0.25

0.5

0.75

1971 1976 1981 1986 1991 1996

YEAR

HEIGHT (m)

s-1 s-2 s-3 s-4 t-6 t-7

0

10

20

30

40

50

60

70

1971 1976 1981 1986 1991 1996

YEAR

PERCENT COVER

s-1 s-2 s-3 s-4 t-6 t-7

Figure 2. Decreases in percent cover and height (in m) of Salix brachycarpa on alpine and subalpine 

transects in Rocky Mountain National Park, Colorado 1971–96. “s” prefix denotes subalpine 

transects, “t” denotes alpine tundra transects. 

6
0

0.5

1

1.5

1971 1976 1981 1986 1991 1996

YEAR

HEIGHT (m)

s-1 s-3 t-7

0

2

4

6

8

1971 1976 1981 1986 1991 1996

YEAR

PERCENT COVER

s-1 s-3 t-7

Figure 3. Percent cover and height (in meters) of Engelmann spruce (Picea engelmannii) measured 

on alpine and subalpine transects in Rocky Mountain National Park, Colorado, 1971–96. “s” prefix 

denotes subalpine transects, “t” denotes alpine tundra transects. 

7
Table 1. Significant changes in vegetation types on alpine and subalpine transects in Rocky 

Mountain National Park, Colorado, 1971–96. [+ = increasing; – = decreasing; U = quadratic response, 

decreasing initially then increasing; • = quadratic response, increasing initially then decreasing, < = less than]

Vegetation type Variable P-value T-statistic Degrees of 

freedom 

Increase/ 

decrease 

Forbs Frequency 0.0247 2.60 11 U 

Graminoids Cover 0.0133 2.95 11 + 

Frequency 0.0027 3.86 11 + 

Lichens Cover 0.0213 3.09 11 + 

Frequency 0.0216 3.08 11 + 

Litter Cover 0.0074 –3.28 11 • 

Frequency <0.0001 –8.20 11 • 

Shrubs Cover 0.0073 –3.74 8 – 

Frequency 0.0302 –2.71 8 – 

Non-vegetated Frequency 0.0296 2.50 12 U

Species data indicated changes in cover of many species over the 25-year period (tables 2 

and 3). In agreement with observations of earlier reports of Stevens (1980) and Braun and others 

(1991), I found increases in percent cover of tufted hairgrass (Deschampsia caespitosa), but cover 

of sedges (Carex elynoides), bistort (Polygonum viviparum), and bluegrasses (Poa spp.) also 

increased. Cover of windflower (Anemone spp.) was found to be decreasing. My analysis of the 

Daubenmire species composition data also found decreasing cover of willow (both S. brachycarpa

and S. planifolia) similar to the line intercept data and as was observed by Stevens (1980) and 

Braun and others (1991). Several species showed a quadratic response over time. Cover of 

bedstraw (Galium spp.) and violets (Viola spp.) increased initially, but then decreased, while alpine 

sandwort (Arenaria obtusiloba), chickweeds (Cerastium spp.), and king’s crown (Sedum rosea) 

decreased early in the sampling period followed by an increase (tables 2 and 3). 

The observed frequency of several species also changed over time (tables 2 and 3). 

Decreases in frequency of asters (Aster spp.) were observed, while frequency of C. elynoides, P. 

viviparum, Trisetum, Poa, fescues (Festuca spp.), gentians (Gentiana spp.)—particularly alpine 

gentian (Gentiana algida)—, nailworts (Paronychia spp.), clovers (Trifolium spp.) and Engelmann 

spruce (Picea engelmannii) increased. 

8
Table 2. Significant changes in vegetation genera found on alpine and subalpine transects in Rocky 

Mountain National Park, Colorado, 1971–96. [+ = increasing; – = decreasing; U = quadratic response, 

decreasing initially then increasing; • = quadratic response, increasing initially then decreasing, < = less than] 

Genus Variable P-value T-statistic Degrees of 

freedom 

Increase/ 

decrease 

Anemone Cover 0.0409 –2.50 7 – 

Arenaria Cover 0.0348 3.14 4 U

Aster Frequency 0.0286 –2.01 7 –

Bare ground Frequency 0.0222 2.66 11 U

Cerastium Cover 0.0083 3.37 9 U

Frequency 0.0004 5.48 9 U

Erigeron Frequency 0.0451 2.33 9 U

Festuca Frequency 0.0378 2.36 11 + 

Galium Cover 0.0245 –4.21 3 • 

Frequency 0.0019 –10.39 3 • 

Gentiana Frequency 0.0061 4.13 6 + 

Paronychia Frequency 0.0323 3.22 4 + 

Pedicularis Frequency 0.0055 4.23 6 U

Poa Cover 0.0531 2.17 11 + 

Frequency 0.0039 3.64 11 + 

Polygonum Frequency 0.0232 2.63 11 + 

Potentilla Frequency 0.0092 3.22 10 U

Salix Cover 0.0066 –3.81 7 – 

Frequency 0.0246 –2.85 7 U

Sedum Frequency 0.0042 3.69 10 U

Trisetum Frequency 0.0479 2.23 11 + 

Trifolium Frequency 0.0145 2.95 10 + 

Viola Cover 0.0492 –2.58 5 U

9
Table 3. Individual species that showed significant changes in cover and frequency on alpine and 

subalpine transects in Rocky Mountain National Park, Colorado, 1971–96. [+ = increasing; – = decreasing; 

U = quadratic response, decreasing initially then increasing; • = quadratic response, increasing initially then decreasing, 

< = less than] 

Species Variable P-value Tstatistic Degrees of 

Freedom 

Increase/ 

decrease 

Arenaria obtusiloba Cover 0.0189 3.81 4 U 

Carex elynoides Cover 0.0149 3.38 6 + 

Frequency 0.0134 3.47 6 + 

Carex scopulorum Frequency 0.0417 –2.49 7 U 

Deschampsia caespitosa Cover 0.0126 3.20 8 + 

Gentiana algida Frequency 0.0325 2.93 5 + 

Kobresia myosuroides Frequency 0.0052 5.55 4 U 

Pedicularis bracteosa Frequency 0.0241 4.24 3 U 

Picea engelmannii Frequency 0.0263 6.05 2 + 

Polygonum viviparum Cover 0.0169 3.12 7 + 

Frequency 0.0061 3.88 7 + 

Salix brachycarpa Cover 0.0281 –3.06 5 – 

Salix planifolia Cover 0.0481 –2.39 7 – 

Sedum rosea Cover 0.0335 2.51 9 U 

Frequency 0.0055 3.63 9 U 

The sedge, Carex scopulorum, willows (Salix spp.), and bedstraw (Galium spp.) showed 

initial increases in frequency followed by declines. Cinquefoils (Potentilla spp.), fleabane 

(Erigeron spp.), chickweed (Cerastium spp.), stonecrop (Sedum spp.)—particularly king’s crown 

(Sedum rosea)—, bog sedge (Kobresia myosuroides), louseworts (Pedicularis spp.)—particularly 

bracted lousewort (Pedicularis bracteosa)—, and bare ground decreased initially and then 

increased later in the sampling period. In only a few cases were significant changes in cover or 

frequency found on only subalpine krummholz or alpine tundra transects. Tufted hairgrass 

(Deschampsia caespitosa) cover tended to increase on krummholz transects while remaining rather 

stable on alpine tundra transects (fig. 4a). Cover of litter increased at a much greater rate on 

subalpine transects than alpine tundra transects (fig. 4b). A pattern of initial increases in cover, 

followed by declines was observed for Festuca on subalpine krummholz transects and Anemone

and Carex on alpine tundra transects. On alpine tundra transects, cover of chickweed (Cerastium) 

and rock showed decreases in cover, followed by increases over the sampling period that were not 

observed on the subalpine krummholz transects alone. Moss frequency increased on subalpine 

krummholz transects over the 25-year period while it decreased, but not significantly on alpine 

tundra transects over the same period (fig. 5a). Stonecrop frequency decreased in subalpine 

krummholz transects, but not on alpine tundra transects (fig. 5b). Marsh marigold (Caltha leptosa), 

bedstraw (Galium) showed initial increases in frequency, followed by declines on subalpine 

krummholz transects. The opposite trend (decreasing then increasing frequency) was observed for 

Pedicularis in subalpine krummholz and bare ground, fleabane, stonecrop, and globeflower 

(Trollius laxus) on alpine tundra transects. 

10
Deschampsia caespitosa

0

10

20

30

40

1971 1976 1981 1986 1991 1996

YEAR

PERCENT COVER

subalpine tundra Linear (subalpine) Linear (tundra)

Litter

0

15

30

45

60

75

90

1971 1976 1981 1986 1991 1996

YEAR

PERCENT COVER

subalpine tundra Linear (subalpine) Linear (tundra)

(a)

(b)

Figure 4. Changes in tufted hairgrass (Deschampsia caespitosa) and litter cover in subalpine 

krummholz and alpine tundra transects in Rocky Mountain National Park, Colorado, 1971–96. 

11
Moss

0

20

40

60

80

100

1971 1976 1981 1986 1991 1996

YEAR

PERCENT FREQUENC

Y

subalpine tundra Linear (subalpine) Linear (tundra)

Sedum spp.

0

5

10

15

20

25

30

35

1971 1976 1981 1986 1991 1996

YEAR

PERCENT FREQUENC

Y

subalpine tundra Linear (subalpine) Linear (tundra)

Figure 5. Changes in moss and stonecrop (Sedum spp.) frequency in subalpine krummholz and alpine 

tundra transects in Rocky Mountain National Park, Colorado, 1971–96.

12
Discussion 

Alpine willow cover and height decreased strikingly from 1971 to 1996 in the surveyed 

subalpine and tundra communities of Rocky Mountain National Park. The collected data did not 

focus on the dwarf willow species (S. arctica [synonymous with S. anglorum antiplasta], S. nivalis

[synonymous with S. reticulata nivalis], S. reticulata) that might provide more desirable summer 

forage to white-tailed ptarmigan. May and Braun (1972) found that willow species make up a 

smaller percentage of summer diets (6 percent) than winter (89 percent) and spring (85 percent) 

diets for white-tailed ptarmigan throughout Colorado. But observations of foraging behavior of 

hens and chicks in Rocky Mountain National Park indicated that as much as 38 percent of hen 

summer diets and 26 percent of chick diets consisted of S. reticulata (Allen and Clarke, 2005). So 

decreases in these species, while important, might not have as significant an effect on white-tailed 

ptarmigan populations as the non-dwarf species. However, these dwarf species, can still form a 

portion of winter diets in areas blown free of snow by winter winds. 

Analysis of winter ptarmigan habitat in Colorado indicated that ptarmigan use feeding sites 

with mean snow depths of 72.3 cm in April and mean willow height above snow of 12.4 cm 

(Giesen and Braun, 1992). This would indicate that as willow heights drop below 85 cm, willow 

begins to become unavailable as a food for ptarmigan. Currently mean heights of S. brachycarpa

and S. planifolia in the transects are well below 85 cm. However, Giesen and Braun (1992) 

conducted their studies in an area 80 km south of the Trail Ridge area of RMNP and snow depths 

may have been considerably deeper in their study area. Studies of winter habitat of white-tailed 

ptarmigan in Colorado indicate that female ptarmigan winter at or near timberline in dense stands 

of tall willow, while males winter in krummholz dominated by willows and spruce (Hoffman and 

Braun, 1977). When snows are deep, these willow species are typically tall enough that the birds 

access them by walking on top of the snow crust, but at shorter heights the willows may now 

become completely covered by snow. Therefore, decreasing heights of S. brachycarpa and S. 

planifolia should be of concern regarding the future of white-tailed ptarmigan in the park. 

Regardless of whether the heights of alpine and subalpine willows are optimal for whitetailed ptarmigan, the fact remains that these data indicate decreasing cover of willows. Based on 

the information available, I cannot assess whether these transects are representative of all alpine 

regions in the park. They were selected nonrandomly to reflect areas of heavy elk use and typically 

tend to be close to the Trail Ridge Road corridor. If all alpine habitats in the park have received 

similar elk use and have experienced similar weather and human impacts, then alpine krummholz 

willow can be assumed to be declining throughout the park and, therefore, potentially habitat for 

white-tailed ptarmigan can be also be assumed to be declining. I recommend a resurvey of the lineintercept work on these transects, if feasible in 2006, to determine whether the downward trend is 

continuing since the previous measures in 1996. If only the line intercept sampling were done, this 

work could be conducted in a few days. It would also be useful to have data on percent leader use 

of shrubs, particularly at the end of summer, to index the degree of ungulate use of shrub species. 

These data were begun by David Stevens, but only for winter use, and were abandoned because of 

difficulty in determining use before shrubs had begun a new year’s growth. 

The decrease in alpine willow cover may or may not be associated with increasing elk 

population in the park. While many of the roughly 2,000–3,000 elk that winter on the eastern 

winter range inside and outside the park, spend part or all of the spring and summer on alpine 

ranges, there are no accurate numbers on summering elk populations. In addition, there is little 

information on the current size and distribution of the elk population that actually winters on the 

13
alpine range. Recent observations of elk in the alpine regions during winter aerial surveys seem to 

indicate that fewer elk, perhaps only 50–60, are currently wintering on the tundra (Kathryn 

Schoenecker, U.S. Geological Survey, unpub. Data, 2000–2005). Park management should 

consider monitoring the summer elk population size and distribution in alpine and subalpine 

regions of the park and also should attempt to conduct a winter survey whenever feasible. 

However, winter weather conditions often make it impossible to fly over the alpine regions at an 

altitude appropriate to observe and count individual elk. It may be possible to conduct ground 

surveys in both summer and winter, which may not provide an accurate population size but would 

at least give a minimum number of animals using even the most accessible and visible areas of the 

park’s alpine regions. Alternatively, pellet count transects might be used to get an index of the 

degree of use these areas are receiving, though pellet counts are considered to be somewhat 

unreliable and are not good indicators of population size. 

Forb and graminoid species of the subalpine and tundra did not seem to show any major 

declines from 1971 to 1996. There was no significant increase of exotic species in these plots. 

Alpine tundra environments tend to have the advantage of having low invasibility for most 

common North American exotics, even in disturbed areas (Weaver and others, 2001). Weaver 

attributed the poor performance of exotics on disturbed alpine areas to physical limitations that do 

not allow them to thrive under the short growing season in alpine regions. This fact is particularly 

important when considering the opportunities for exotic invasion on these grazed sites. There was 

overall a significant increase in frequency of bare ground, but no coincident increase in bare ground 

cover was observed. The increases in frequency of observations of bare ground are of interest 

because they could indicate that while mean bare ground cover does not appear to be increasing, 

the number of locations where bare ground was found increased over the 25-year period. Increases 

were concentrated on alpine tundra transects, which are likely the more sensitive of the two 

community types. If such increases were observed to continue, this could indicate problems from 

overgrazing and hoof action. While the concerns about invasion of exotic plant species may not be 

of as great a concern in the alpine as other vegetation zones, there could be loss of species and (or) 

loss of overall plant biomass and cover with an increase of bare ground, and recovery could take 

decades in this fragile environment. The absence of a significant decline in bare ground cover may 

be an artifact of the way the Daubenmire cover classes are set up. Four of the cover classes span a 

20–25 percent range of cover. Therefore, it is possible that cover of a species, or in this case, bare 

ground, could change as much as 25 percent and not be detected when this method is used. 

There is not a great wealth of research on the effects of grazing on alpine systems, 

particularly in the Rocky Mountains. Much of the work that has been conducted focuses on the 

Alps, Asia, and Australia (where a large component of the overall grazing pressure is from 

domestic livestock) or on the arctic tundra systems. Galen (1990) investigated the effects of 

grazing by aphids and mammalian ungulates in limiting distribution of skypilot (Polemonium 

viscosum) in the Rocky Mountains. This study indicated that in this species, grazing was greater on 

krummholz than tundra populations and that grazing led to complete loss of current year’s seed 

crop and an 80 percent loss of net seed production over 3 years. No significant decrease in this 

species over the 25-year period was observed from the current data set. Similarly, a study of the 

subalpine forb, Ipomopsis aggregata, indicated that browsing delayed flowering phenology, and 

while this late flowering led to lowered rates of seed predation, the conclusion was that overall, in 

areas where the growing season was short, browsing led to reduced plant fitness (Freeman and 

others, 2003). One might assume a similar effect of high rates of herbivory on many alpine and 

subalpine forbs. 

Del Moral and others (1985) found that simulated grazing of a subalpine Festuca species 

that was dominant in fell fields reduced its yield relative to subordinate species, but a study of 

14
green fescue (Festuca viridula) in alpine regions of Mount Rainier National Park, indicated that 

this species is very tolerant of herbivory (Sharrow and Kuntz, 1999). Festuca species on the 

RMNP transects increased in frequency of occurrence from 1971 to 1999, so there does not appear 

to be an adverse effect of grazing on Festuca in the park despite its moderate palatability to grazers. 

Two graminoid species identified by Hobbs and others (1982) as major elk diet components 

increased in cover on the transects described in this study, Deschampsia caespitosa and a Carex 

species (C. elynoides). Deschampsia is considered to be of low palatability to grazers, but alpine 

Carex species tend to be moderately palatable. These increases may or may not be due to grazing 

by elk. Without further information on the levels of elk use at these and other sites in the park, one 

cannot conclude any reason as to the cause of these increases. 

Long-term grazing can alter carbon dioxide and nitrogen dynamics in alpine grasslands 

(Welker and others, 2004). Grazed areas had higher soil carbon and nitrogen concentrations, but 

lower plant biomass, lower grass leaf N concentrations, and lower early and late summer N 

mineralization rates at some sites. This could have implications for plant production and cover 

under high levels of herbivory in alpine areas, but further data would need to be collected to 

determine whether herbivory levels in RMNP have been high enough, and for a long enough period 

of time, to cause these types of changes. 

While there is value to continuation of the Daubenmire transects, it appears that the amount 

of information gained may not warrant the time and expense of monitoring more frequently than 

every 10 years. Furthermore, if the park wishes to have a more statistically rigorous sampling of 

alpine regions, more transects should be added in areas that are less accessible from the road to be 

sure that effects, positive or negative, of human activity on elk distribution and density are 

accounted for. Such a design should include random placement of transects, or stratification based 

on observed elk distribution and density, so that a range of elk use levels is included in the 

sampling. 

I also recommend that there be greater consistency in the sampling, with regular sampling 

intervals, and consistent use of species identifying information. The data presented here suffer 

from this lack of consistency where one year a plant might be identified to species, another year 

only to genus, another year only by common name, and so forth. This leads to confusion in data 

analysis that might be avoided. 

My recommendation is that these transects become part of a larger and appropriate 

inventory and monitoring program. Such a program should have a predetermined level of 

measurable change that is acceptable to elk and vegetation management goals of the park 

management staff. Data collection methods should be designed so that (1) the acceptable level of 

measurable change can be detected, and (2) to the greatest extent possible, existing data previously 

gathered on the established transects can be compared with data collected in the future under the 

new inventory and monitoring protocols. 

Acknowledgments 

This analysis was funded by Rocky Mountain National Park. I appreciate the assistance of 

Brian Cade, statistician, U.S. Geological Survey, for his guidance on appropriate statistical methods 

and comments on drafts of the report. David Stevens, National Park Service (retired), was helpful 

in providing information on data collection. Therese Johnson, Rocky Mountain National Park, 

provided raw data files and assistance with reviewing draft reports. Kate Schoenecker, ecologist, 

U.S. Geological Survey, provided helpful comments on the draft. 

15
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17
Appendix 

Complete species listing and codes used in electronic data spreadsheets for David Stevens’ alpine 

and subalpine vegetation transects. Collected 1971–96 in Rocky Mountain National Park, Colorado. 

Code Vegtype 

g=grass, f=forb, 

s=shrub, 

x=other 

Genus Species Common name Currently accepted 

name, or older 

names 

Genus grouping 

for statistical 

analysis 

able ? Not determined Not 

determined 

ablexx 

achlan f Achillea lanulosa Yarrow achxxx 

achxxx f Achillea spp. achxxx 

acocol f Aconitum columbianum Monkshood acocol 

agoxxx f Agoseris spp. False dandelion agoxxx 

agrscr g Agropyron scribneri Spreading wheatgrass Elymus scribneri agrscr 

agrxxx g Agrostis spp. Bent-grass agrxxx 

aneome f Anemone spp. Windflower aneome 

angxxx f Angelica (grayi) Angelica angxxx 

aquxxx f Aquilegia spp. Columbine aquxxx 

araxxx f Arabis spp. Rockcress araxxx 

arefen f Arenaria fendleri Fendler's sandwort arexxx 

areobt f Arenaria obtusiloba Alpine sandwort Minuartia 

obtusiloba 

arexxx 

arexxx f Arenaria spp. Sandwort arexxx 

argxxx f ? argxxx 

arncor f Arnica cordifolia Heart-leaved arnica arnxxx 

arnxxx f Arnica spp. Arnica arnxxx 

artarc s Artemisia arctica Arctic sagebrush/ 

Boreal sagebrush 

artarc 

artbor f Artemisia borealis Field sagewort Artemisia 

campestris borealis 

artxxx 

artsco f Artemisia scopulorum Alpine sagebrush artxxx 

artxxx f Artemisia spp. Sagebrush artxxx 

astxxx f Asteraceae spp. Aster artxxx 

betgla s Betula glandulosa Bog birch/ Dwarf 

birch 

Betula nana betgla 

bg x Bare ground bg 

bromar g Bromus marginatus Mountain brome broxxx 

broxxx g Bromus spp. Brome broxxx 

calcan g Calamagrostis canadensis Canadian reed-grass calxxx 

callep f Caltha leptosepala Marsh marigold callep 

calxxx g Calamagrostis spp. Reed-grass calxxx 

camxxx f Campanula spp. Harebell camxxx 

camrot f Campanula rotundifolia Common harebell camxxx 

caraqu g Carex aquatilis carxxx 

carely g Carex elynoides carxxx 

carrup g Carex rupestris carxxx 

carsco g Carex scopulorum carxxx 

carxxx g Carex spp. Sedge carxxx 

casocc f Castilleja occidentalis Western yellow 

paintbrush 

casxxx 

casxxx f Castilleja spp. Paintbrush casxxx 

18
cerarv f Cerastium arvense Field chickweed cerxxx 

cerbee f Cerastium beeringianum Bering chickweed cerxxx 

cerxxx f Cerastium spp. Chickweed cerxxx 

colpar f Collinsia parviflora Maiden blue-eyed 

Mary 

colpar 

cruxxx f Cruciferae Unidentified crucifer unkxxx 

danxxx g Danthonia spp. Oatgrass danxxx 

delxxx f Delphinium spp. Larkspur delxxx 

desalp g Deschampsia alpicola Tufted hairgrass Deschampsia 

caespitosa 

descae 

descae g Deschampsia caespitosa Tufted hairgrass descae 

epixxx f Epilobium spp. Willow-herb Eritrichium nanum 

var aretioides 

epixxx 

eriare f Eritrichium aretioides Arcticalpine forgetme-not 

eriare 

erigxx f Erigeron spp. Fleabane erigxx 

eryniv f Erysimum nivale Alpine wallflower Erysimum capitatum 

var. purshii 

eryniv 

fesxxx g Festuca spp. Fescue fesxxx 

fraxxx f Fragaria spp. Strawberry fraxxx 

fungi x Fungi Fungi fungi 

galxxx f Galium spp. Bedstraw galxxx 

genalg f Gentianodes algida "Alpine gentian, 

whitish gentian" 

Gentiana algida genxxx 

genama f Gentianella amarella "Little gentian, dwarf 

gentian" 

genama 

genxxx f Gentian spp. Gentian genxxx 

geuros f Geum rossii Ross' avens Acomastylis rossii 

(Weber) 

geuxxx 

geuxxx f Geum spp. Avens geuxxx 

harxxx f Harbouria spp. Harbouria harxxx 

helian f Helianthus spp. Sunflower helian 

helmor g Helictotrichon mortonianum Alpine oat helmor 

hiealp g Hierochloe alpina Alpine sweetgrass hiealp 

hymxxx f Hymenoxys spp. hymxxx 

junxxx g Juncus spp. Rush junxxx 

kobmyo g Kobresia myosuroides Bog sedge kobxxx 

kobxxx g Kobresia spp. Bog sedge kobxxx 

kolcri g Koeleria cristata June-grass Koeleria macrantha kolcri 

lichen l Lichen Lichen lichen 

lilxxx f Liliaceae Lily lilxxx 

litter r Litter litter 

luzspi f Luzula spicata Spiked woodrush luzspi 

lloser f Lloydia serotina Common alplily lloser 

mervir f Mertensia viridis "Oblongleaf bluebells, 

green mertensia" 

Mertensia 

oblongifolia 

merxxx 

merxxx f Mertensia spp. "Chiming bells, 

bluebells" 

merxxx 

moss m Moss Moss moss 

orexxx f Oreoxis spp. Alpine parsley orexxx 

parpul f Paronychia pulvinata Rocky Mountain 

nailwort 

parxxx 

parses f Paronychia sessiliflora Creeping nailwort parxxx 

parxxx f Paronychia spp. Nailwort parxxx 

pedbra f Pedicularis bracteosa Bracted lousewort pedxxx 

pedgro f Pedicularis groenlandica "Elephantella, pedxxx 

19
elephanthead 

lousewort" 

pedxxx f Pedicularis spp. Lousewort pedxxx 

penxxx f Penstemon spp. "Penstemon, beardtongue" 

penxxx 

phlalp g Phleum alpinum Alpine timothy phlxxx 

phlcon f Phlox condensata Dwarf phlox phlxxx 

phlxxx f Phlox spp. Phlox phlxxx 

phlxxx g Phleum spp. Timothy phlxxx 

piceng s Picea engelmannii Engelmann spruce piceng 

poaalp g Poa alpina Alpine bluegrass poaxxx 

poagla g Poa glauca Glaucous bluegrass poaxxx 

poaxxx g Poa spp. Bluegrass poaxxx 

polbis f Polygonum bistorta Bistort polxxx 

poldel f Polemonium delicatum Jacob's ladder Polemonium 

pulcherrimum 

polexx 

polexx f Polemonium spp. Jacob's ladder polexx 

polvis f Polemonium viscosum Sky pilot polexx 

polviv f Polygonum viviparum Alpine bistort polxxx 

polxxx f Polygonum spp. Bistort polxxx 

potxxx f Potentilla spp. Cinquefoil potxxx 

psemon f Pseudocymopterus montanus Yellow moutain 

parsley 

psemon 

ranxxx f Ranunculus spp. Buttercup ranxxx 

ribaur s Ribes aureum Golden currant ribxxx 

ribxxx s Ribes spp. Currant ribxxx 

rock x Rock rock 

rumden f Rumex densiflorus Dense-flowered dock rumxxx 

rumxxx f Rumex spp. Dock rumxxx 

salbra s Salix brachycarpa Short-fruit willow salxxx 

salgla s Salix glauca Grayleaf willow salxxx 

salniv s Salix nivalis Snow willow salxxx 

salpla s Salix planifolia Planeleaf willow salxxx 

salxxx s Salix spp. Willow salxxx 

saxixx f Saxifraqa spp. Saxifrage saxixx 

saxodo f Saxifraqa odontoloma Brook saxifrage saxixx 

saxrho f Saxifraqa rhomboidea Diamondleaf 

saxifrage 

saxixx 

sedlan f Sedum lanceolatum Stonecrop sedxxx 

sedros f Sedum rosea King's crown Rhodiola 

integrifolia 

sedxxx 

sedste f Sedum stenopetalum Wormleaf stonecrop sedxxx 

sedxxx f Sedum spp. Stonecrop sedxxx 

selsco cm Selaginella scopulorum "Lesser spikemoss, 

Rocky Mountain 

spikemoss" 

Selaginella densa selxxx 

selxxx cm Selaginella spp. "Little clubmoss, 

spikemoss" 

selxxx 

sentri f Senecio triangularis Arrowleaf ragwort senxxx 

senwoo f Senecio wootonii Wooton's ragwort senxxx 

senxxx f Senecio spp. Ragwort senxxx 

sibpro f Sibbaldia procumbens Creeping sibbaldia sibpro 

silaca f Silene acaulis Moss campion silxxx 

silxxx f Silene spp. Campion silxxx 

solxxx f Solidago spp. Goldenrod solxxx 

20
stexxx f Stellaria spp. Chickweed stexxx 

sweper f Swertia perennis Star gentian sweper 

tarxxx f Taraxacum spp. Dandelion tarxxx 

thaalp f Thalictrum alpinum Alpine meadow-rue thaxxx 

thaxxx f Thalictrum spp. Meadow-rue thaxxx 

thlalp f Thlaspi alpestre Alpine pennycress Thlaspi montanum thlx 

tridas f Trifolium dasyphyllum Alpine clover trixxx 

trinan f Trifolium nanum Dwarf clover trixxx 

tripar f Trifolium parryi Parry's clover trixxx 

trispi g Trisetum spicatum Spike trisetum trisxx 

trisxx g Trisetum spp. Trisetum trisxx 

trixxx f Trifolium spp. Clover trixxx 

trolax f Trollius laxus Globeflower Trollius albiflorus 

(older name) 

trolax 

unkxxx f Forb Unknown forb unkxxx 

unkxxx g Grass Unknown grass unkxxx 

vacsco s Vaccinium scoparium Broom huckleberry vacxxx 

vacxxx s Vaccinium spp. Huckleberry vacxxx 

verbxx f Verbena spp. Verbena verbxx 

verxxx f Veronica spp. Veronica verxxx 

viobel f Viola bellidifolia Mountain blue violet Viola adunca vioxxx 

vioxxx f Viola spp. Violet vioxxx 

water x Water water 

21