Investigating Vegetation and Small Mammals in the Cloud Peak Wilderness Area of the Bighorn Mountains in Wyoming

Part of the Young Naturalist Awards Curriculum Collection.

YNA 2001 Winners Hero
by Jennifer, Grade 11, Pennsylvania - 2001 YNA Winner


A group of about 35 or 40 people sitting or standing on grass posing for the camera.
Figure 1. The American and Scottish contingents
A group of eight people outdoors smiling and posing for the camera, with trees in the background.
Figure 2. The Members of the "Bio Group"

In the summer of 2000, I had the opportunity to spend three weeks camping and performing fieldwork in the Cloud Peak Wilderness Area of the Bighorn Mountains of Wyoming. Accompanying me were 16 of my fellow students from State College Area High School in Pennsylvania, as well as 17 students from James Gillespie High School in Edinburgh, Scotland (Figure 1). The purpose of the expedition, organized and headed by State College Area High earth science teacher Dr. Thomas Arnold and Edinburgh geography teacher Mr. George Meldrum, was to conduct various studies of the region, including a heat-budget determination, a lake water analysis, and a mapping of the valley. My research focused on the vegetation and small mammals present in the riparian area of Oliver Creek. As a member of the "Bio Group" (Figure 2), I studied the changes in vegetation with increasing distance from the stream across three habitats, and determined the types and diversity of small mammals present in those three habitats. Additionally, I collected and analyzed soil samples in the three habitats, monitored air conditions, and determined the types of macroinvertebrates found in Oliver Creek. The Bio Group was assisted in these tasks by field biologist Julie Roth, a graduate student at the University of Nevada. This expedition provided me with a unique opportunity to directly study the biology of a wilderness area while interacting with a diverse and international group of students who are as interested in science as I am. Furthermore, since I had never gone camping before, this research endeavor meant that I also had to meet the challenges of learning to properly pitch a tent, sleep on the hard ground, and prepare meals on an outdoor cookstove.

A young woman smiling at the camera wearing a backpack and a field hat and holding books in one hand, with a map in the background.
Figure 3. The Oliver Creek research site. Figure 4 insert; The daily climb
A small pond or body of water in a green field with trees and mountains in the background under a blue sky with a few cumulus clouds.
Figure 5. Oliver Creek at the location of the vegetation transect.

We set up base camp at the Hettinger Rest Area in the Bighorn National Forest near Buffalo, Wyoming. Our research site, located at an elevation of 8,750 feet in the Cloud Peak Wilderness Area, was about a 10-minute drive away, followed by a 2.5-mile uphill climb from the main campsite (Figures 3 and 4). Each morning, regardless of what day of the week it was or what the weather was like, we trudged up the mountain at nine in the morning and returned either at 4 pm or 6:30 pm, depending on the research conducted on that day. The sound of banging pots and pans roused us from our slumbers every morning no later than 7 am. Breakfast was always the same: oatmeal. While we tried to spice it up with brown sugar, raisins, or honey, it always had the same thick and bland taste. The first few days of our expedition were somewhat bleak; it rained every day. It was so cold that we went to sleep wearing multiple layers of clothes. The Scots were delayed in their arrival, and we were trying to comprehend the reality of eating oatmeal every day for the next three weeks. However, once the days became sunnier and everyone arrived so that we could begin our research, we began to enjoy the trip immensely. Everyone in my group joined in the excitement of actually holding a chipmunk prior to weighing it, or finally locating an unknown forb in a field guide. In the evenings, we all gathered around the campfire and shared our discoveries as well as our misfortunes.

A group of three photos. Top: vegetation with a small white flag in the center, bottom left: a lupine with purple flowers; bottom right: a sedge with its long grass-like stems.
Figure 6 (top) A white flag marking a 10m interval along the vegetation transect; Figure 7 (left) A lupine, one of the plants observed during our study; Figure 8 (right) A sedge, a common riparian species growing along Oliver Creek.

The first part of the Bio Group's research dealt with the vegetation of the Oliver Creek drainage basin (Figure 5). The study site consisted of meadowland and a recovering burn area on the north side of Oliver Creek, and forested land on the creek's south side. To determine how the vegetation changed with increasing distance from the stream, a straight-line transect was set up perpendicular to the eastwardly-flowing creek. This transect began at 4416'19"N, 10700'46"W on the north side of the stream and at 4416'19"N, 10700'45"W on the stream's south side. White flags were positioned every 10m from the stream along the transect, for 150m on the creek's north side and for 110m on the creek's south side (Figure 6). The meadow extended for a distance of about 60m, while the remaining land on the north side was an area experiencing regrowth after a 1988 burn event. Mature forest was found on the south side of the creek. At each white flag, we laid out a 1m2 vegetation sampling quadrat, using meter sticks. Within each quadrat, the percentage of cover was determined by means of the point-intercept method of using knitting needles on a meter stick frame (Elzinga). Vegetative species present were identified using guides such as Earl Jensen's Flowers of Wyoming's Big Horn Mountains and Big Horn Basin and Classification of Riparian Communities on the Bighorn National Forest, published by the USDA Forest Service. It was interesting to look at the Western vegetation, which differed from what I was used to seeing in Pennsylvania. Although I am well acquainted with many Eastern species of trees, shrubs, and plants, I encountered many plants, such as pussytoes (Antennaria), with which I was not familiar. Figures 7 and 8 show two of the plants that grew next to Oliver Creek, lupine (Lupinus) and sedge (Carex).

Three photos: A woman outdoors in gloves holds a chipmunk; a rectangular mammal trap; and a human hand holds a cord to weigh a small furry mammal.
Figure 9 (top) The author examining a chipmunk; Figure 10 (left) A typical small mammal trap setup; Figure 11 (right) Massing a small mammal

The second focus of our research efforts was a determination of the types and diversity of small mammals present in each habitat. This aspect of our studies was the most fun, since we got to hold the mammals in order to weigh and measure them (Figure 9). (Note that all of the mammals were safely released after trapping.) To conduct this part of the study, small-mammal trapping grids were set up in the same three habitats in which the vegetation transect was laid out. We did not place the trapping grids exactly along the vegetation transect, since our movements in assessing the vegetation could have distracted the mammals. Consequently, the mammal trapping grids were set up in different representative areas of the habitats. Each trapping grid consisted of 30 traps spaced 10m apart. The burn area and forest trapping grids were set up as 5x6 sampling rectangles, while the meadow was set up as a 4x7 trapping grid, with the two remaining traps positioned as extensions of the middle rows. Bait made of peanut butter and oats was placed in each of the aluminum traps; cotton wool was also added to keep the mammals warm in case of overnight capture. The traps were then covered with litter and brush to disguise them and to provide insulation against temperature extremes (Figure 10). The small mammals that we caught were carefully handled while they were measured for mass, total length, tail length, ear length, and hind foot length (Figure 11). Gender and reproductive condition were also noted. The animals that were captured were marked in case they were trapped again. We placed nail polish markings on their ears and also clipped a small amount of hair from a particular location that was noted on the data chart. We checked the traps twice daily -- at approximately 10 am and again at about 5 pm, each time resetting them for the next trapping session. The vegetation work was done in the afternoon between trap checks. Because of our long trapping day, the biology group stayed overnight at our high camp on the mountain in order to be able to check the traps on time in the morning on the five days that mammal counts were made.

Left, a woman in a hat stands in a field with equipment. Right, two women in a leafy environment examining something in their hands.
Figure 12 (left) Setting up the thermistor poles to record air temperatures; Figure 13 (right) Identifying macroinvertebrates in Oliver Creek

In addition to the main vegetation and small mammal studies, soil samples were collected in the three habitats, temperature variations of the air were monitored, and a macroinvertebrate sampling of the creek was performed. The purpose of the soil sampling was to provide a better idea of the conditions in which the vegetation grew. Soil sampling was performed at each of the vegetation quadrats. On-site measurements included soil moisture content, pH, and infiltration rates. Collected soil samples were sent for further analysis for conductivity and phosphorus, potassium, and magnesium content to Pennsylvania State University. The thermistor study was set up to provide hourly air-temperature monitoring of the valley. Five thermistor poles were set up on the north side of Oliver Creek at 30m intervals along the vegetation transect (Figure 12). Each pole had six probes, placed at 1m intervals, from ground level to a height of 5m. Temperature readings were recorded hourly over a three-day study period. Since we were working in a riparian zone, we identified the macroinvertebrates present at three stream locations -- a riffle, a run, and a pool just downstream of our vegetation transect -- and calculated the Pollution Tolerance Index (PTI) for each location (Figure 13). As the stream's substrate was made up of various-sized boulders and cobbles, 20 rocks were selected for examination at each location, and the number and type of macroinvertebrates present were recorded. The average rock circumferences and lengths were also measured.

Graph of forested area, showing percentage of foliage cover versus the distance from a stream.
Fig. 14A: Percent Coverage of Forested Area (Click to enlarge.)
Graph shows the coverage of meadow and burn areas relative to the distance from the stream.
Fig. 14B: Present Coverage of Meadow/Burn Area (Click to enlarge.)
A chart showing plant cover percentages of forested areas.
Fig. 15B: Plant Cover Percentage of Forested Area (Click to enlarge.)
A kite diagram titled, “Plant Cover Percentages of Meadow/Burn Area,” listing the plant types, their distance from the stream in miles, and their percentage of ground cover.
Fig. 15B: Plant Cover Percentage of Meadow/Burn Area (Click to enlarge.)

The data that we obtained during our expedition is presented in the accompanying graphs and tables. Figures 14A and 14B show the percent coverage of the three habitats by plants, litter, wood debris, rock, bare ground, and animal waste in relation to distance from Oliver Creek. Figures 15A and 15B are kite diagrams that break down the plant cover into forbs, grasses, sedges, shrubs, mosses and lichens, and conifers, while the specific types of plants found and their frequency of occurrence are listed in Table 1 (tables included at the end of the essay). Frequency of occurrence is obtained by dividing the number of quadrats that a plant occurs in by the total number of quadrats in a particular habitat -- seven in the meadow, nine in the burn area, and 12 in the forested area -- and then multiplying by 100%. Note that the vegetation quadrats did not include large-diameter trees in order to get a representative picture of the non-canopy vegetation in the forested and burn areas. An indication of the size of the trees in the wooded areas is given by Figure 16, which shows the mean circumference of the five closest trees within 3m of the vegetation quadrats. There were no notable trees in the meadow; although willows were found, they were so small that they were designated as shrubs. The burn area showed the greatest plant-species richness, with 80% of the observed types located there. The meadow had the lowest richness, with only 12 of the 30 observed types of plants. Plants common to all three areas included heartleaved arnica (Arnica cordifolia), fireweed (Epilobium angustifolium), grasses (Poa), and mosses. The majority of the quadrats on the north side of the stream (meadow/burn area) exhibited 50% or higher plant cover, while only five of the 12 studied quadrats on the forested south side showed a percentage plant cover greater than 50%.

A table with plant names and other data, titled: "Table 1: Frequency of Occurrence of Vegetation In the Habitat Quadrats (Expressed as a Percentage)."
Table 1 (Click to enlarge.)
A bar chart titled: "Figure 16: Mean Circumference of 5 Closest Trees Within 3 meters of Numbered Quadrats."
Fig. 16 Mean Circumference of 5 Closest Trees Within 3m of Numbered Quadrants (Click to enlarge.)
A bar chart titled: "Figure 17: Number of Small Mammal New Captures for 5 Trap Days and Nights."
Figure 17: Number of Small Mammal New Captures for 5 Trap Days and Nights (Click to enlarge.)
A scatter chart plotting the relationship between plant and small mammal species richness.
Fig. 18: Relationship Between Plant and Small Mammal Species Richness (Click to enlarge.)

Seven different species of mammals were captured during a five-day study period, as shown in Figure 17. Least chipmunks (Tamius minimus confines) were the dominant species in the burn area and forest, while meadow voles (Microtus pennsylvanicus insperatus) were the most frequently caught species in the meadow. Table 2 lists the number of small mammal captures that occurred overnight and during the day in each of the three habitats. Both new captures (bold type) and recaptures (parentheses) are listed. The burn area had the highest number of small mammals caught, but the lowest richness, since only chipmunks were captured. The forest showed the greatest species richness, with five types of mammals captured. There appears to be no direct correlation between plant and small-mammal species richness, as indicated in Figure 18. The burn area, which exhibited the greatest plant-species richness, also had the lowest small-mammal species richness. Only two small mammal species were captured in more than one habitat; least chipmunks in all three habitats and the red squirrel (Tamusciurus hudsonicus baileyi) in the forest and the meadow. Five of the seven observed species limited themselves to one environment. Use of the Simpson diversity index, Ds =1-Spi2, where pi is the relative species abundance, to compare the small mammal communities in the three habitats yielded values of Ds(burn)=0, Ds(meadow)=0.66, and Ds(forest)=0.65. The diversity indices of the meadow and forest are very comparable and are greater than that of the burn area, in which only one small mammal species was found.

A table with data, titled: "Table 2: Overall Number of Small Mammal Captures by Day/Time of Day."
Table 2 (Click to enlarge.)
A table titled: "Table 3A: Soil Nutrient Levels for Forested Area."
Table 3A (Click to enlarge)
A table titled: "Table 3B: Soil Nutrient Levels for Meadow/Burn Area."
Table 3B (Click to enlarge.)
Soil ph is measured on the y-axis (vertical). Distance from stream is measured on the x-axis (horizontal).
Fig. 19: Variation of Soil pH Across the 3 Habitats (Click to enlarge.)

The soil was acidic throughout the entire riparian zone, as indicated by the graph in Figure 19, with the least acidic soil found in the burn area. Mean values of pH increased from 4.8 in the forested area to 5.0 in the meadow to 5.7 in the burn area. As shown in Tables 3A and 3B, the soil analysis by the Agricultural Analytical Services Laboratory at Pennsylvania State University indicated that the meadow had the lowest soil-nutrient levels, with only magnesium in the optimum plant-growth zone. Highest nutrient levels were found in the burn area, with the amounts of potassium and magnesium present increasing significantly at the meadow/burn area transition.

Linear graph of daily rainfall from June 26 to July 7, 2000, in area of Wyoming, part of student project.
Fig 20: Daily Precipitation in mm from June 26 to July 7 (Click to enlarge.)
A bar chart titled: "Figure 21: Variation in Air Temperature in Burn Area and Meadow at 0 and 5 meter Heights."
Fig. 21: Variation of Air Temperature in Burn Area and Meadow at 0 and 5m Heights (Click to enlarge.)

As is seen in Figure 20, the region experienced measurable levels of precipitation only during the first part of the study; there was negligible precipitation after June 30. Since the small mammal study began on June 29, on which only 0.3 mm of rain fell, rainfall was not a factor in the capture rate. Figure 21 gives the air temperature results at ground level and at 5m from two thermistor poles located 120m apart, one placed in the meadow and the other in the burn area. The results indicate that the air at ground level in the meadow exhibited greater variations in temperature than did the air next to the ground in the burn area. At higher air column levels,both the meadow and the burn area showed comparable fluctuations in air temperature over a 24-hour time period as well as a smaller level of variation than that which occurred in the air closer to the ground.

A table with data for various aquatic organisms, titled: "Table 4: Macroinvertebrate Data from Oliver Creek."
Table 4 (Click to enlarge.)

The quality of the water in Oliver Creek was assessed using the 22 specific-indicator organisms of the Pollution Tolerance Index (PTI). Table 4 lists the indicator macroinvertebrates that were found in the three study areas. Classification of the macroinvertebrates present in a riffle, run, and pool yielded cumulative index values of 20, 15, and 15, respectively. PTI values between 17 and 22 indicate good water quality, while numbers in the range 1116 suggest fair water quality.

Much still remains to be done in order to finish the analysis of the data that were collected on the expedition, and not all of it, such as the data on the small mammals' weight and size and soil infiltration rates, have been included in this essay. Additional statistical relationships need to be determined, comparisons between data acquired on this expedition and that obtained on any previous studies of the area and cited in the literature must be made, and study techniques and methods must be examined for deficiencies. A follow-up expedition to the area would be especially useful, particularly to see how the regrowth in the burn area has progressed.

A collection of supplies beneath a banner that reads: "Aunt Bea's Chuckwagon."
Figure 22. Aunt Bea's Chuckwagon - The place to be on the Fourth of July

Even if my research efforts do not produce a significant scientific contribution, my Wyoming expedition was a success. It provided me with an amazing opportunity to learn how fieldwork is actually conducted, to spend time in the wilderness examining and marveling at the natural world, and to interact with people from another continent whom I had never met before but who had the common bond of a love of science. This trip held a lot of "firsts" for me: my first time camping, my first time holding a chipmunk, my first time going to the bathroom in the woods. I had to carefully measure distances for the vegetation quadrats, set up the 5m thermistor poles,carry traps up the side of a mountain, and make sure that I correctly recorded my findings. Although the trip was serious while we were working, we also had time to have fun. I am left with many memories of the expedition. I remember the first day we spent with the Scots, and how we marveled over how they supposedly spoke the same language as we did yet used so many foreign words. Their use of "trainers" for sneakers, "minging" for disgusting, and "Philadelphia" for any type of cream cheese, prompted us to put together a Scottish-American dictionary. I remember spending the Fourth of July at an artists' residency, playing volleyball, eating at "Aunt Bea's Chuckwagon" (Figure 22), and watching fireworks light up the night sky. I remember stumbling out of the tent at high camp at four in the morning to take a thermistor reading and sitting in the hot afternoon sun determining sedge cover. I remember my first sighting of a moose along Oliver Creek and looking up into the clear Wyoming night sky to find Cassiopeia and Cygnus. I remember 34 students sitting around a campfire making s'mores and the way we slowly dismantled the camp on our last day in Wyoming. The three weeks that I spent in the mountains of Wyoming doing research as part of a scientific expedition allowed me to learn more about our wilderness areas while interacting with a diverse group of people. This experience led me to the realization that I want to discover more about the natural world and go on many more scientific expeditions.



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