Ecosystem Concepts and the Great Basin

Scale
Ecosystems within the Great Basin occur at different scales, with smaller systems nested within larger ones. The Great Basin is variously defined by hydrographers, physiographers, historians and biogeographers, although there is general agreement that the core includes the area from the Sierra Nevada on the west to the Wasatch Range on the east, and from south of the Snake River Plain on the north to the creosote bushes and black brushes that define the beginning of the Mojave Desert on the south. The Basin ecoregion includes the virtually lifeless sun-baked playas, alkaline flats that are home to salt-tolerant plants, salt lakes in which brine shrimp and flies reside, sand dunes teeming with various rodents, marshes that are crucial habitat for migratory waterfowl, vast expanses of sagebrush, the pinyon-juniper woodlands, the mountain islands isolating remnant plants, the aspen glens, and the sub-alpine forest that is home to the oldest living trees on Earth, 4,000-year-old bristlecone pines.

Connections
The living and nonliving components of Great Basin ecosystems are connected in an independent web, and some of these connections are very complex and difficult to perceive. This is illustrated by the subsurface water supply, referred to as the carbonate system, one of the two aquifers supporting plant, animal and human life in the Basin. To address Las Vegas's water needs, city water engineers are proposing to tap into the underground waters beneath remote valleys of eastern Nevada. The project would involve a system of 145 huge wells spread across nearly 20 percent of Nevada and connected by 1,600 km of pipeline. Preliminary environmental studies suggest that the effects of this proposed engineering effort could be widespread. Some critics maintain that groundwater pumping will lower the water table, destroying streams and marshes that support plant and animal life in the desert basins and possibly affecting Death Valley National Monument, some 160 km away.

Cycles and Change
Great Basin ecosystems are constantly cycling and changing over time and space. Some of these changes are the result of natural cycles, such as the water cycle, while others are the result of natural phenomena, such as climatic events or geological processes, or human-induced changes. Consider, for example, the environmental change recorded by the distribution of bristlecone pines. One specimen accidentally cut down by a researcher was more than 4,900 years old. Because bristlecone wood remains undecayed on the ground long after a tree has died, it has been possible to establish a tree-ring chronology for the species in excess of 9,000 years. Consistently, the dead specimens of bristlecone pine are found at a higher elevation than the living descendants, up to 150 m higher in one of the Great Basin's mountain ranges. Using tree-ring dates, we know that bristlecones were able to survive at a higher elevation during the Hypsithermal of 8,000 years ago, when summer temperatures were higher. Interestingly, over the last century Great Basin summer temperatures have once again been on the rise, and this has allowed seedlings of bristlecone pine to take root at higher elevations, just as they did during the Hypsithermal.

Diversity
Healthy ecosystems are characterized by biodiversity. In the Great Basin, scientists have found that particular plant species, such as shadscale and other saltbrushes (Atriplex species) have evolved a remarkable strategy for diversification. The plant has an increased number of chromosomes, a trait known as polyploidy. This variation allows Atriplex species to adapt to different environments and soil conditions. Fourwinged saltbrush (Atriplex Canescens) has the widest distribution of any perennial member of the genus, allowing it to grow from central Mexico to southern Canada and from Nebraska to the Pacific. (Trimble, S [1989]. The sagebrush ocean: A natural history of the Great Basin [p86]. Reno/Las Vegas: University of Nevada.)

Getting Prepared
Begin by checking the rules for collecting plant specimens from public lands or in parks, and ask for permission from owners of any private lands you'd like to explore. (As an alternative to actually collecting plants, you might bring along plant identification guides and photograph or sketch and measure specimens.) Next, contact a local agricultural or land management agency, a university botany department, or a museum to learn if there are any rare or endangered plants that students should not collect. With the children, discuss avoiding any such plants, as well as any poisonous or irritating plants, such as poison ivy and stinging needles (you might distribute photocopies of these plants for easier identification.)

Explain to the students the proper procedures for collecting plant specimens: take care not to trample vegetation, and take only the minimum necessary to make an identification (one sprig with leaves and flower for woody plants; for others you might need the whole plant, but uproot a plant only if there are at least 20 others nearby). Once the children clearly understand the rules, they are ready to collect.

To the Field and Back
Have each student collect up to six different plant specimens during their walk. Back in the classroom, the children should press the plants between layers of newspaper (either in a press or beneath a heavy book). When the plants are dry, they can be mounted onto card stock with diluted white glue. Students should then refer to plant guides and other references to label each plant with its common and scientific names.
After everyone has dried, mounted, and labeled their specimens, the children should begin to conduct research on their plants, referring to accounts of local history as well as plant guides. If the species is native, students should try to discover the following:

• What is the plant's place in a food web?
• What animals use the plant for food or shelter?
• What do humans do with the plant? What might they do with it in the future?
• Is the plant species increasing or decreasing in number in your area?
• Are there threats to the plant's existence?
• What can people do to ensure that this plant thrives?

If the plant is nonnative, students should investigate the following questions:

• When, why, and how was the species introduced locally?
• What are the drawbacks of its presence?
• What are the benefits of its presence?
• What animals use the plant for food and shelter? Are these animals native or introduced species?
• What natural balancing mechanisms keep the plant in check in its place of origin?
• Does this plant threaten native plant communities? If so, how?
• What can people do to ensure that this plant does not damage native plant communities?

To conclude the activity, have students summarize their findings on a card attached to the mounted plant specimen and create a class display of their work.

Extensive Learning
To extend this lesson, consider visiting an arboretum or herbarium at your local college, museum, land management agency, or university. Botanists there can discuss native and nonnative plants with your class. Alternatively, you might invite to your class a botanist, wildlife biologist, member of a garden club or native plant society, local agricultural extension service agent, or coordinator of your state's department of weed and pest control. These people can also be sources of information to students as they do their research. Finally, telephone the "Wild Hot Line," at 800-354-4595 from April through July, to learn about events celebrating wildflowers on the nation's public lands.

Information about beavers
When beavers are removed from the ecosystem, several things can happen, depending on the vegetation present. In areas where woody plants grow, vegetation once harvested by beavers for food, dams, and shelter increases in size and density until sunlight no longer reaches the stream. When this happens, the stream loses its capacity to support various life forms (for example, the insects that fish eat). Thus, the stream becomes less and less productive.
In areas where woody vegetation does not grow, the removal of beavers means that their old dams are not maintained. Flood water will breach the dams, causing accelerated erosion and bank cutting. Water cascading through the old dams increases stream velocity, allowing it to scour once-stable channels and streambanks. The eroded sediments and soils are then carried away by the turbulent water. Raw, open streambanks can no longer support vegetation that reduces stream flow velocities, and the degradation cycle continues until positive events cause the aggregation cycle to start over.

The Marys River ecosystem in Elko County, Nevada, is a 290 km-long ribbon of life in the desert. Its broad wildlife-rich medowlands were enhanced through centuries of beaver activity. Because beaver dams slowed the river's flow, wide curves and deep pools could be maintained. Slower water drops its settlement load, and over the centuries, valleys filled in and meadows were created that contained a wide diversity of plants and animals. The waters were rich with Lahontan cutthroat trout, and a great number of mammals, birds, reptiles lived here, including river otters, antelopes, bobcats, and cranes. The mobile Shoshone tribe lived here, moving where plants and animals were seasonably available. In the 1820's Anglo-American beaver trappers arrived, killing the animals for their skins, which were exported to the eastern United States and Europe to be made into hats. As a result, the animals were nearly exterminated from the area.
Brainstorm all the ways the Marys River ecosystem would have changed with the disappearance of beavers.

Information about cattle
When cows gather in an area, vegetation is eaten or trampled and the cows defecate and urinate into streams. As cattle drink and trample vegetation, they cause the banks to erode and vegetation there to die. Once the plants along the banks disappear, there is less shade, so water temperature rises. Erosion increases, causing more sediment to be carried by the stream. Because the stream banks are not stabilized by vegetation, the current starts to cut a straighter stream course, resulting in the loss of stream pools. Overall, water quality decreases, and higher water temperatures, more sediment, and fewer pools threaten the stream's fish population. Other wildlife that live in the area have difficulty finding food and shelter, so those animals move to another area or die off, reducing the diversity of the local ecosystem. Such damage can be prevented by good management practices -a different season of use, a shorter grazing period near the stream, fencing off the stream, or developing water away from the stream.

Ranching became a way of life along the Marys River, beginning in the 1870's. Prior to the passage of the Taylor Grazing Act in 1934, cattle, sheep, and domestic horse grazing was uncontrolled and in some cases extremely heavy throughout the area. Most of the area was federally acquired in the Treaty of Guadaloupe-Hidalgo of 1848. Some of the land (particularly land attached to water) became privately owned homesteads, while the rest remained in public ownership but used for cattle grazing. Today, ranching is still a major occupation in Elko County. Cattle stay near water and shade, and large numbers of them will congregate in and around riparian areas during the hot summer months.
Brainstorm all of the ways that cattle grazing could change the Marys River ecosystem.

Information about restoration
BLM continues to try to acquire additional lands in the Marys River ecosystem. Ecosystem health is improving, and all of the streams on BLM lands have been closed to cattle grazing (more than 8,400 hectares). BLM monitors the health of habitat, vegetation, streams, and archaeological and historic sites to assure that their condition is improving. Fences, riparian planting, conservation easements across private lands, spring exclosures to keep cattle out, pipelines to move cattle watering holes to less sensitive areas, and fires to burn off less desirable vegetation so that plants useful to wildlife can grow are all projects BLM has accomplished with various partners in the past four years.
To address ranchers' concerns about the loss of available grazing lands and the county government's concern about the loss of property tax revenue, the BLM worked with Olympic Management Inc., to make additional land available to ranchers in Elko County. This time the BLM exchanged 18,800 hectares of difficult to manage federal lands in Elko County, but not along streams, for other lands in southern Nevada owned by Olympic Management, Inc., which provide important habitat for the threatened desert tortoise. Olympic then sold the lands in Elko County to ranchers. The property tax base was restored to Elko County because BLM lands became privately owned and subject to property tax. The increase in hunting and fishing, because of improved access to public lands, resulted in recreationists spending an additional $600,000 a year in taxable recreation-related activities.
At one time the Bureau of Land Management (BLM) managed 35 percent of the Marys River ecosystem. In 1975, the Lahotan cutthroat trout was listed as a endangered species under the Endangered Species Act. Once a species is listed, the BLM is required to coordinate management with the U.S. Fish and Wildlife Service to ensure that actions taken will not jeopardize that species's survival. The BLM wanted to improve the condition of the Marys River ecosystem, in part to help the habitat of the endangered fish and also to address problems in surrounding streams that had been caused by overgrazing of cattle. BLM was concerned, however, that any measures implemented in their lands would not be effective because 65 percent of the waterways still would be used by ranchers for cattle grazing.
The solution to the dilemma came from Las Vegas, Nevada, where BLM owned additional lands. BLM had found it difficult to manage their lands in this urban setting and had earmarked them for disposal in their land-use plans. Olympic Management, Inc., a development company, wanted the high-value Las Vegas land for housing and shopping malls. Olympic offered to buy private land from ranchers along the Marys River and then trade the land to BLM in exchange for the Las Vegas lands.
In 1991, BLM traded 264 hectares in Las Vegas to Olympic for about 18,800 hectares of Marys River, thus transferring 104 additional km of the ecosystem's streams to federal ownership (BLM originally managed 100 km along the Marys River.) BLM now managed 65 percent of the Marys River ecosystem streams, and both parties could more easily manage their own land.
Brainstorm all the actions BLM biologists might take to restore health to the Marys River ecosystem.