"Looking Back, Looking Ahead"
The Indian ricegrass (Oryzopsis hymenoides) is the highly preferred forage of many domestic and non-domestic animals in the southwestern states. Because of this, the land is being heavily grazed in most areas. Arizona in particular is suffering from overgrazed land.
Glen Canyon National Recreation Area is located in northern Arizona and southern Utah. The Bureau of Land Management monitors and manages grazing. It currently determines the utilization of a plant by height. Is there a better way to determine utilization?
I took samples from three areas: no grazing, deferred grazing, and yearlong grazing. To identify the classes the plants belong to, I measured the diameter of 100 plants from each site. Then I collected 40 plants from no grazing (site 1), 10 plants from deferred grazing (site 2), and 10 plants from yearlong grazing (site 3). After the Indian ricegrass was collected, I measured two centimeters, cut the plant, and then weighed each section to develop height/weight relationships.
The results showed that height alone cannot be used to determine utilization. The diameter of a plant plays an important role in finding the utilization of plants. A plant that is 25 centimeters high with a 10-centimeter diameter does not have the same utilization as a plant that is 25 centimeters high with a diameter of two centimeters.
The Bureau of Land Management states that 50 percent utilization of a plant allows it to re-grow after it is grazed. If height and diameter are both used, the accuracy of 50 percent utilization will increase, which will improve the rangeland.
The Indian ricegrass is the most common vegetation that domestic animals in Arizona graze. Indian ricegrass is found throughout the western states. They grow in a variety of places, from sandy to clay soil. Over the course of the twentieth century, Indian ricegrass began to disappear because of overgrazing. How will the land look in the future? Will it become like the deserts in the Middle East due to overgrazing? Or can we save the land and keep it as our elders remember?
Before the Glen Canyon Dam was built and Lake Powell formed, and before the city of Page, Arizona, was developed, the land was home to Native Americans (Navajos) in the surrounding area. Elders told me that the land had a lot of vegetation. The grass would grow up to their knees and waists. When the wind blew, the land looked like a yellow ocean. Today there is little vegetation holding the soil down; water and wind are eroding the land. What can we do to improve our land? I conducted a study on Indian ricegrass to determine 50 percent utilization. Scientists know that 50 percent utilization of a plant allows full outgrowth the next year. Currently, the Bureau of Land Management uses height alone to determine 50 percent utilization. I found that the diameter of a plant affects utilization. I did my research in three different areas: no grazing (site 1), deferred grazing (site 2), and yearlong grazing (site 3).
First, I took 100 random samples of the Indian ricegrass from each site. To make an unbiased sample, I dropped a pencil and walked in the direction to which it pointed. Every three steps I stopped and measured the basal diameter and the height of the plant. After 300 plants were measured, I grouped the Indian ricegrass into six basal-diameter classes: Class I = .1 to 5 centimeters, Class II =5.1 to 10 centimeters, Class III = 10.1 to 15 centimeters, Class IV = 15.1 to 20 centimeters, Class V = 20.1 to 25 centimeters, and Class VI = 25.1 to 30 centimeters. I grouped them into classes to get a closer look at the differences between each plant.
Site 1 has not been grazed for over 30 years. It represents the past, when there was very little overgrazing. When my classification was completed, I collected 40 plants. I collected plants having a diameter of between .1 and 20 centimeters. I used string and paper bags to hold the plants. The string was tied in various places along the plant. I then cut the plants at ground level. I put them in the paper bags to transfer them to the laboratory where measurements could be taken. When all 40 plants were collected, I dried them in an incubator at 70º Celsius for 48 hours. After each plant was dry, I cut and weighed 2-centimeter sections, starting from the bottom until I reached the seeds. The weights of the 2-centimeter sections were added together to find the height/weight relationship. I found the percentage utilization of the Indian ricegrass by dividing a weight by the total weight, then multiplying by 100. For example:
Plant sections taken|
from one plant (cm)
Individual section |
Cumulative ||Utilization weight (g)|
When everything was completed, I transferred all the information to an Excel program and then graphed my results.
Sites 2 and 3 show how the land is being used today. I used the same methods as I did for site 1. I collected 10 plants from site 2 and 10 plants from site 3. They show the difference between a deferred-grazing area and a yearlong grazing area. Just by visual observation, the sites were different. There was more vegetation in site 2 (deferred) than site 3 (yearlong). Site 2 had a fairly steady height while site 3's height varied from one plant to another. Erosion was occurring in both sites, but more severely in site 3. When sites were compared with diameters, site 3 had larger diameters but site 2 had more plant mass. Because both sites represent the present, I compared them to site 1, the past.
Site 1 had more plants and plant mass and the height was greater than in sites 2 and 3. No visual erosion occurred in site 1 and there was more vegetation when compared to deferred grazing and yearlong grazing areas. Sites 2 and 3 had other plants growing because there was less Indian ricegrass. Since the Indian ricegrass is a winter plant and is grazed in the winter, more summer and annual plants are present. Two plants that are present in these two areas are the summer plant (Sporobolus spp.) and snakeweed (Gutierrezia spp.). The occurrence of the summer plant is increasing because there is less Indian ricegrass and it is not as heavily grazed. Snakeweed grows when overgrazing or disturbance occurs in an area of open space and less vegetation. Livestock do not eat the snakeweed. At the end of my study, I found that 50 percent utilization is different when diameter and weight are both used.
If nothing is done about overgrazing, I think that the land will eventually look like the Middle East. The Middle East is an example to us of what can happen to land if it is overgrazed. If action is taken, the land can improve slowly. Everyone is willing to help but they don't know where or how to begin. This study is a small step toward progress in land management and conservation. My question is, will the surrounding organizations use the data I¹ve collected to determine grazing or will they stick with their methods?
I hope that my research will change how the land is grazed and that people will use this information to make the land thrive once again, especially on my reservation. The Navajo Reservation is being heavily overgrazed and erosion is occurring. The Navajos are ruining their land but do not know how to stop. In the future I plan to help my people by educating them about overgrazing and the tragedy of the commons: Everyone is out for themselves. They have more animals for more food and money. They don¹t know that they are really hurting themselves and others in the long run. My goal is to make this land a yellow ocean once again. The future of our land depends on how we use it today.
Alston, J.F., B.R. Bobowski, C. Goctzc, K. McMullen, L. Newcomb, J.P. Ritenour, and J. R. Spence (listed alphabetically). Grazing Management Plan for Glen Canyon National Recreation Area, prepared by members of the Department of the Interior, National Park Service, GCNRA, 1999.
Bobowski, Benny. (National Park Service, Range Ecologist). Personal Interview, November 1999.
Interagency Technical Team. Utilization Studies and Residual Measurements. U.S. Department of the Interior, Bureau of Land Management - National Applied Resources Sciences Center, (BLM/RS/ST-96/004+1730), 1996.
Jones, T. A. "A Viewpoint on Indian Ricegrass Research: Its Present Status and Future Prospects." Journal of Range Management 43(5), 1990.
United States Department of Agriculture Forest Service. "Indian Ricegrass," Range Plant Handbook, 1988.
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Supplement a study of biology with an activity drawn from this winning student essay.