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From the Desert to the Subalpine Forest

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Introduction 
Every day thousands of people experience a thrill while gazing down into the almost 9,000-foot drop of the Grand Canyon. Yet as my eyes scanned the cliffs for signs of vegetation and a light summer breeze brushed through my hair and tingled my senses, the thrill I felt was not only from the hues and shadows of the cliffs that vary with every passing second, but also from the diversity of the vegetation growing in the area. Through my binoculars I saw hundreds of Utah junipers (Juniperus osteosperma) polka-dotting the sheer cliffs as brittlebushes clung to existence in the unbearable heat near the Colorado River.

Grand Canyon

Grand Canyon


During the summer of 2006, I decided to take advantage of my family vacation to the Grand Canyon. I was reading the August 2006 issue of Kids Discover  magazine that featured the Grand Canyon to get some information about the place we would be visiting when one particular sentence struck me: "You could hike 3,000 miles from the Arctic Circle to Mexico to pass through nearly all the major environmental zones of the world. But it would be a lot easier  simply  to hike down the Grand Canyon!" (Soffer, 2006). I was amazed by this statement and decided to test this claim and take it a bit further.

The purpose of my research was to investigate the vegetation types of the Grand Canyon and the areas around it on a gradient of elevation with regards to the distribution of plant species, plant height, leaf size, plant density, and vegetation coverage, as well as environmental factors such as temperature and rainfall. I tested a proposed hypothesis: the higher the elevation, the greater the number of species of flora that would be present. However, above certain elevation (I gave an educated guess of about 7,000 feet), the number of species would fall because of the low temperatures and harsh climate.

 
A grove of quaking aspen in a mixed conifer forest at 8000-9500 feet.

A grove of quaking aspen in a mixed conifer forest at 8000-9500 feet.


Materials and Methods
Before leaving for our trip, I did some research in order to know what to expect in the diverse environment of the Grand Canyon, as well as what materials and methods I would need. I contacted a few researchers at the Grand Canyon Monitoring and Research Center of United State National Park Services in order to ensure that my proposed research topic would be practical, as well as to get some idea about the exact elevation differences I would experience. As for my materials, the primary technique I would implement in order to measure plant density and coverage would be different-sized plots.

Viola consults a booklet on flora identification.

Viola consults a booklet on flora identification.


Based upon Vegetation Description and Analysis: A Practical Approach (Kent & Coker, 1994), an ecology book I had read in order to prepare for my field trip, I decided that there would be three different plot sizes, each based on the type of flora found at that elevation zone. In elevations with no trees or shrubs, the plot size would be 4x4 m2. In elevations with shrubs but no trees, the plot size would be 10x10 m2, and for elevations with both trees and shrubs (or just trees), the plot size would be 20x20 m2. I approximated the size of the plot areas by walking out individual steps. I also designed a data sheet that I would use to record the data I would collect from the field for each plot. In order to ensure that the locations of the plots (which I would determine by random selection) were not affected by extreme outside factors that would skew the data, I chose to do three plots per site. From the information the researchers I had contacted had given me, there would be a roughly 9,000-foot change in elevation. I thus decided that I would record my data for each site at approximately 1,000-foot intervals.  

The other materials I needed were a Garmin eTrex Legend GPS (a global positioning system) to record the elevation and geographic location of each plot, a tape measure to measure plant height and leaf size, a camera, and several field guides to help me identify plant species.

Geological location of study sites.

Geological location of study sites.


Sample of field data collection sheet

Sample of field data collection sheet


After all this preparation, I was ready to conduct my research. My family and I arrived in Las Vegas by plane in the late August 2006. We rented a minivan and drove toward the Grand Canyon. Before arriving in Arizona, I had an image in my mind of a sea of sand with skeletons of bushes dotting the ground, with a few large cacti waving their prickly arms at me as we drove by, toward the Grand Canyon. However, a strikingly different sight met my eyes as I spotted Colorado piñon pines (Pinus edulis) littering the ground with their short needles, as well as an abundance of black sagebrushes (Artemisa nova) with lobed gray-green leaves.

Before setting up my first plot, I visited the Grand Canyon National Park Visitor Center to let the officers know about my research and what I intended to do. They were quite helpful in their explanations of where I was allowed to go and not go, as well as the best places to set up my plots so that I would find diverse species of flora. They even supplied me with pamphlets and booklets that would give me further information on the different flora species in each area, as I was not allowed to collect and bring home samples of any unidentified plant species.

 
Viola measuring plant height in the mixed conifer forest.

Viola measuring plant height in the mixed conifer forest.


Fieldwork
On the beautiful morning on August 26, 2006, I started my fieldwork and randomly chose the location of my first plot at an elevation of 6,940 feet, not too far from our campsite inside the Grand Canyon National Park on the South Rim. I recorded the elevation and location (longitude and latitude) first. The area had many large, tall trees that I identified as ponderosa pines (Pinus ponderosa) because of their brightly patterned brown bark and their mint-like smell; their decaying needles created a brown carpet beneath my feet. The area also had small patches of grass emerging through the needle bed and many gray-green bushes with small, three-lobed leaves. Because there were several large trees and a profusion of bushes, the area of this first plot was 20x20 m 2 . I chose one of the largest ponderosa pines in the area and used it as one of the corners of my plot. After setting up the barriers of my plot, I then proceeded to count the number of different species present and the number of each species within the plot.

For plants such as grass species, I recorded only the percentage of coverage because counting each individual plant would have been extremely difficult. I estimated the plant coverage for the plot, which was around 40%-45%. For every plant species I found, I chose a mature sample and measured it. I used my measuring tape for the height of shrubs and smaller plants, but for trees I used my father as an estimating device and estimated how many versions of my father it took, stacked on top of each other, to reach the tree's height. I was amazed at the diversity of species present in the area of my first plot. The species ranged from blue grama grass (Boutelou gracilis) that were 5-11 centimeters tall, to one lone pancake prickly pear (Opuntia chlorotica), with spikes that were 8-10 centimeters long. The entire procedure took approximately one hour because of the many species I was unfamiliar with, and I was thus forced to consult the  National Audubon Society Field Guide to the Southwestern States (Alden et al., 2005) and A Field Guide to the Plants of Arizona (Epple, 1995). I continued this procedure for my next two plots, which were randomly chosen at a similar elevation range, but the time I spent per plot was less as I became more familiar with the species present.

Portion of master sheet. (Click to Enlarge)


My expedition continued over four days, from August 26 to August 29. Because of physical and time limitations, my family and I were unable to hike down to the Colorado River. Instead, as suggested by National Park officers, we drove to different areas around Grand Canyon National Park, including the San Francisco Peaks area, to reach my planned elevation intervals. I was able to get an elevation range from 1,749 feet to 10,371 feet and collected data from 24 plots at eight different elevation sites. The map shows the locations of my field sites.

After the completion of my fieldwork, I compiled my data into a master sheet. I started to analyze the data I collected.

 
The effect of elevation on total number of species

The effect of elevation on total number of species


Results and Discussion
The graph shows the effect of elevation on the total number of species found at each elevation site. My data supports my hypothesis that the total number of species increases as the elevation increases, with the greatest number of species being at an elevation of around 8,000 feet; the number of species declines from that point. To my surprise, while the number of shrub species and tree species generally peaks at around 6,000 to 7,000 feet, the number of "other" species (mainly small flowering plants and different types of grasses) steadily increases to the highest elevation range I was able to visit, with 11 different species being the greatest number. This is most likely due to the increase in rainfall and the cooler temperatures at higher elevations. At the highest elevation I visited, 10,371 feet, the annual rainfall is around 35 inches per year, which supports a larger and more diverse group of plant species. However, the low average daytime temperature, around 55°F, could be a major limiting factor that causes a reduction in the number of tree and shrub species. Temperature can be seen as the major controlling factor in tree distribution (Jeffree, 1960). The inability of tree seeds to germinate or become established may also limit the northern distribution of trees, as indicated by Black and Bliss (1980). However, species with relatively short life spans have adapted to have rapid growth as soon as environmental conditions become favorable.  

Chart 4: The effect of elevation on temperature (August) (Click to Enlarge)


Chart 5: The effect of elevation on vegetation coverage (%) (Click to enlarge)


Chart 6: The main species found in each Merriam's Life Zone (Click to enlarge)


The site at the lowest elevation range had the fewest plant species, without any trees. This is explained by the very little rainfall and average daytime temperatures higher than 90°F, which make the environment a very difficult and challenging place in which to survive. Indeed, the landscape at 1,749 feet is a desert, with few plants and mostly sand as the soil type. Another trend I found from my results is that as elevation increases, the percentage of plant coverage also increases, with species other than trees contributing the most. The bar graph shows this trend clearly. This pattern could be explained by leaf size, as the larger and broader leaves of many species were found in higher elevation zones, whereas the smaller and thinner leaves were found mainly at lower elevations.

The vegetation types in the different elevation zones have been studied by many researchers. In 1890, C. Hart Merriam developed the "life zones" concept, based on his studies in the San Francisco Peaks region of Arizona. Modern ecologists still consider his life zones as the major biomes of North America. The defining species of each elevation range in my research matched up quite well with that of Merriam (1890). The chart shows the dominant species I found, combined with the data from Merriam's life zones.

White bursage (Ambrosia dumosa) dominated the desert landscape.

White bursage (Ambrosia dumosa) dominated the desert landscape.


 

Conclusion
My research data supports my original hypothesis: the higher the elevation, the greater the number of flora species present. However, the decline in the number of different species was at 9,000 feet, not at 7,000 feet as I predicted. The data I collected are consistent with the research of C. Hart Merriam (1890) and  Kids Discover  magazine (2006). There are indeed several key species that seem to define different elevation zones and, as my hypothesis stated, there is a certain point at which the total number of distinct species within an elevation range declines because of the harsh climate. This study made me realize the challenges faced by field biologists, and it gave me the opportunity to explore the field research process. If given more time at the Grand Canyon, I would have traveled to an elevation above 10,500 feet (the artic-alpine zone) to complete my research. It would have been interesting to see if this last elevation zone would have confirmed my hypothesis, with fewer species than in the 10,000-foot elevation zone. However, the most rewarding experience of my research was being able to see a 9,000-foot elevation change in a span of only four days.

I would like to express my appreciation to Barbara Ralston at the Grand Canyon Monitoring and Research Center for her support and suggestions for my research. I thank my parents for driving me through a 9,000-foot elevation change, as well as for helping me in the field.

 

Bibliography

Alden, Peter, et al.  National Audobon Society, Field Guide to the Southwestern States. New York: Alfred A. Knopf, 2005.

Biotic Communities of the Colorado Plateau: C. Hart Merriam and the Life Zones Concept.  Land Use History of the North America Colorado Plateau. Retrieved from the World Wide Web on 1 February 2007. http://www.cpluhna.nau.edu/Biota/merriam.htm.

Black, R.A., and L.C. Bliss. "Reproductive ecology of  Picea mariana  (Mill) BSP at tree line near Inuvik, Northwest Territories, Canada." Ecological Monographs 50 (1980): 331-354.

Epple, Anne.  A Field Guide to the Plants of Arizona. Guilford: Globe Pequot Press, 1995.

Jeffree, E.P. "A climatic pattern between latitudes 40° and 70° N and its probable influence on biological distributions."  Proceedings of the Linnaean Society,  London  171, 89-121.

Kent, Martin, and Paddy Coker.  Vegetation Description and Analysis: A Practical Approach. Chichester: John Wiley & Sons, 1994.

Martin, Ronald.  Cedar Breaks National Monument Wild Flower Guide. Springdale: Zion Natural History Association, 2000.

Merriam, C.H., and L. Steineger. "Results of a biological survey of the San Francisco mountain region and the desert of the Little Colorado, Arizona." U.S. Department of Agriculture, Division of Ornithology and Mammalia, Washington, D.C.  North American Fauna Report 3 (1890).

Rainfall and Temperature Data. Weather Underground. Retrieved from the World Wide Web on 20 January 2007. http://www.wunderground.com.

Soffer, Jessica. "Grand Canyon."  Kids Discover  August 2006: 16-18.

 

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