The High Plains
Land of Extremes
If you look beyond the apparent emptiness of the landscape, you will learn that the High Plains ecosystem, like all ecosystems, contains its own unique riches. Plants have evolved to be drought- and wind-resistant, and most have tough root systems to anchor the soil and to find and store water and nutrients underground. Many native animals live underground as a way to adapt to the harsh arid climate. Also found underground are valuable minerals and some of the largest coal seams in the world. This article and the accompanying foldout explore the unique characteristics of the High Plains ecosystem, primarily the northern portion, and what land managers and local communities are doing to improve and sustain the health and productivity of this vast grassland.
The eastern boundary of the High Plains is often cited as the 100th meridian or the 600-m contour or elevation line. But prairie vegetation boundaries are flexible, advancing or retreating in response to the weather. Located in the rain shadow of the Rocky Mountains, the High Plains is semi-arid, with precipitation averaging less than 50 cm per year. (By contrast, the tall-grass prairies of the Midwestern states receive as much as 100 cm of rain per year.)
During the winter, much of the annual precipitation in the High Plains occurs in the form of snow. Because of its location, the High Plains is subject to climatic extremes. Warm temperatures (above 21°C) one day can drop to below freezing the next.
Water is scarce in the High Plains. Rivers are few, and the water they contain is in high demand. Additional water can be found in several underground aquifers. The Ogallala Aquifer, North America's largest underground water source, lies beneath the western parts of Nebraska, Kansas, and Oklahoma, extending north into South Dakota, west into Wyoming, and south into New Mexico and Texas. These aquifers are like huge underground sponges made of porous sediments of sand and gravel eroded from the Rocky Mountains. Less-permeable sediments underneath the aquifers hold the water in place.
Grasses and Other Plants
The High Plains prairie is characterized by short and mid-mixed grasses that grow to less than 60 cm, responding to the reduced amount of water, cool temperatures, and resultant shorter growing season. These shorter grasses require less water and nutrients than the taller grasses found in the Midwest.
Soils are mostly deep, well drained, with loam and clay, supporting cool-season grasses, forbs, and shrubs. Dominant plant species of the High Plains include blue grama and green needle grass (bunch grasses), and buffalo grass and western wheatgrass (sod grasses). Their root systems make up 90 percent of the plant's mass.
A square meter of short-grass prairie can contain 12 or more plant species. In addition to grasses, the High Plains contain cushion plants, mat plants, and forbs. Cushion plants, like moss, also have large root systems that allow them to attach to rocky escarpments. Mat plants, such as sandwort, send their roots out in front of them. These compact plants have beautiful, fragile flowers that turn escarpments into natural rock gardens when they bloom. Forbs are herbaceous plants that grow less abundantly on the short-grass prairie, but have beautiful flowers that transform the prairie in times of adequate rainfall. Forbs are the dominant food sources for deer and pronghorn antelope.
Aster is one of many forbs preferred by wildlife on the High Plains.
Most prairie plants are dormant during the extremes of summer heat and winter cold, growing only in late spring or early summer and again in the fall. This plant survival mechanism allows the High Plains to support the many forms of wildlife and insects that eat, nest, or hide in the plants
Blue grama is a bunchgrass that grows in distinctive clumps. As many as 100 shoots can come up from a single plant. By contrast, buffalo grass is a sod grass, which produces horizontal stems called runners (stolons) and rhizomes. Runners inch along the ground surface and rhizomes go through the soil, extending their own roots and stems. (See illustration above)
Wyoming Game and Fish Department
The Prairie Dog Ecosystem
Early explorers of the High Plains referred to the dominant burrowing animal of the ecosystem as wild dogs of the prairie or the "prairy dog," because of the barking sound they make. These small rodents provide the anchor for vast plains ecosystems that are dependent on the complex systems of underground burrows the prairie dogs construct. This system of tunnels creates prairie dog "towns" or colonies teeming with a diversity of life. For example, prairie dogs churn up dirt, mixing topsoil with underlying soils, making it easier for forbs to propagate. Birds often congregate in and around the towns, attracted by the insects that are easily seen in the patches grazed by the prairie dogs. Larger animals such as deer and pronghorn antelope prefer to feed in prairie dog towns because they like the easily digested forbs and herbaceous plants that grow in the colonies. Some animal populations, such as burrowing owls and swift foxes, are actually declining in part because of the decline in prairie dog towns. The black-footed ferret, also dependent on prairie dog towns, declined to the point of near-extinction. For more information on the black-footed ferret and other animals that depend on the prairie dog ecosystem, see the Activity 1 & Activity 2 page.
|Black-tailed prairie dogs, once numerous on the High Plains, have suffered dramatic declines due to widespread eradication efforts.|
Wyoming Game and Fish Department
Energy Source for the Nation
The High Plains is a major source of coal, oil, gas, and uranium for the nation. For example, the Powder River Basin in northeastern Wyoming and southeastern Montana is home to the largest low-sulfur coal reserves in the United States. (Low-sulfur coal burns cleaner than the high-sulfur coal found in the eastern United States.) The coal in the Powder River Basin is found in thick seams—horizontal layers of solid coal running for kilometers beneath the Earth's surface. Some of these seams are 30 m thick and close to the surface, so the coal can be mined at the surface without going underground. As a result, huge quantities of low-cost, high-quality coal can be shipped by rail to 24 states to generate electricity. Over half of the electricity in the United States comes from coal-fired power plants. In 1995, 24 Powder River Basin mines produced 286 million tons of coal.
The Powder River Basin supplies over one quarter of the nation's coal. Black Thunder Mine, the largest coal mine in North America, is located in the High Plains.
The reddish siltstone rock that caps many ridges and buttes in the Powder River Basin is called "clinker" or "scoria." Clinker is rock that has been fused by the natural burning of underlying coal beds. Its red color is due to the oxidation, or rusting, of iron in the rock. The clinker, which covers about 4,200 km2 of the basin, was formed by the burning of some 27 to 54 billion metric tons of coal within the past three million years. Some coal still burns today, sparked by range fires or spontaneous combustion.
Clinker, the reddish rock, formed when coal beds burn naturally, caps the Rochelle Hills escarpment in Wyoming. Clinker traps water, which attracts plants and wildlife. It forms unique landscapes and ecosystems of its own in the northern High Plains.
Ed Heffern, BLM
Clinker forms a distinct part of the ecosystem in the basin. Because soils formed from clinker are very permeable, they absorb rain and melting snow like a sponge and protect it from evaporation. Plants such as ponderosa pine and skunkbush sumac grow on clinker because of this stored water. Deer and elk herds graze over it, and some springs that emerge at the base of the clinker have water quality good enough to support trout.
In addition to the challenges inherent in living in a harsh environment, the people of the High Plains face a number of management challenges to keep the land healthy and productive. Water is scarce; many riparian (streamside) areas are becoming depleted; and in some areas, native grasses are being crowded out by invasive weeds. Local communities are changing farming and ranching practices to address these challenges. For example, ranchers and other land managers are turning to new rotational or seasonal grazing practices to help protect sensitive riparian areas. They are stepping up efforts to control invasive weed species, and they are using carefully controlled fires to replace the natural cycles of disturbance once provided by natural fire and bison. (Fire and bison both keep the grasses clipped, lowering vegetative buildup. In addition, fire and bison manure add nitrogen to the soils, producing nitrogen-rich grasses.)
Prairie dog towns support many plants and animals of the High Plains, including the burrowing owl, which depends on the good burrow habitat provided by the prairie dog.
Wyoming Game and Fish Department
Water, the lifeblood of the land, has always been a limiting factor in the settlement of the High Plains. The early farmer had a hard time coaxing crops from the plains until the windmill was used to harvest water from aquifers below the ground's surface. Approximately 90 percent of the water pumped from the Ogallala Aquifer is used for irrigation. Precipitation and surface streams replenish the aquifer, but surface streams in the arid High Plains are sparse and many are ephemeral, wet only at certain times of the year. Because of the heavy demand for water and the slow replenishment rate, the average water level of the aquifer declined nearly 3 m between 1940 and 1980, then another 30 cm in the 1980s. Better water management and new technologies have helped to slow this depletion. However, greater efforts will be needed to ensure that the water levels in the aquifer stabilize.
Before the High Plains were settled, bison and other wild herbivores grazed the prairies. Eventually, as settlers moved in, these native roamers had to compete with cattle and sheep. Early settlers often grazed too many sheep or cattle for too long a period in one place. Thus, overgrazing was very common at the turn of the century. Although management practices have steadily improved since then, overgrazing still causes serious problems in many areas. Where public rangelands are involved, Resource Advisory Councils provide opportunities for a wide range of interests at the state and community level to have a voice in the management of grazing practices. Through a collaborative decision-making process, these councils are playing a critical role in developing guidelines for ecological grazing on public rangelands.
Riparian areas are the green, vegetated areas that border streams and rivers in the otherwise arid and semi-arid West. The condition of these critical areas in much of the western United States has been poor throughout much of this century. In the High Plains, rivers and streams are not abundant, and the productive areas surrounding them are often fragile and extremely important to sustaining healthy populations of fish, wildlife, and plants. Yet, concentrations of cattle and sheep in riparian areas and lower water levels have put stress on the ecological integrity of these streams. Declining conditions in riparian areas in some parts of the High Plains also have contributed to the decline of rare moisture-loving plants such as the Ute Lady's Tresses, a threatened orchid found along streams or where mountains begin at the western edge of the plains. This delicate plant requires specific moisture, sunlight, and temperature levels to thrive. Public and private land managers are beginning to assess and improve the condition of riparian areas and are implementing conservation measures through cooperative efforts with local ranchers and others.
Haughian Ranch: At the local level, riparian areas in many places are begining to rebound in response to new intensive management techniques. For example, owners of the Haughian ranch in eastern Montana are working with federal, state and local cooperators to imporve the health of the riparian areas along historic Custer Creek. This ephemeral creek flows through the ranch, which is made up of 80,000 acres of private and public High Plains rangeland along the Yellowstone River. For 50 years, wild horses, cattle, and sheep had degraded the range and riparian areas by overgrazing and trampling streambanks, causing erosion and destroying fragile riparian plants. By staggering the grazing season of each pasture, keeping pasture sizes small, and varying the number of animals grazing each pasture, the Haughians were able to increase streambank vegetation, improve wildlife habitat, reduce erosion, and improve water quality.
Scott Kaiser, Montana Department of Natural Resources and Conservation
Fire has played a part in the prairie ecosystem for thousands ofyears. Fires are ignited naturally by lightning. Native Americans also learned to set fires to promote new growth of grasses or to drive wildlife for hunting purposes. Grassland ecosystems depend on fire to recycle carbon and nutrients into the soil and to influence plant composition. But fire suppression efforts since the early 1900s have changed the composition of many grassland communities, an example of how single-purpose management techniques, however well intentioned, can degrade natural systems. Controlled fires can improve the quality of grasslands by removing buildup of vegetative litter, warming soil temperatures, and assisting seed germination.
Some fires that were once suppressed are now allowed to burn as part of a natural cycle within forest and grassland ecosystems. In remote areas, some agencies allow wild land fires to burn where there is an approved plan, as long as the fires remain within "prescribed" limits. However, wildfires are still aggressively fought near populated areas.
As more and more communities recognize the importance of fire to a healthy grassland ecosystem, prescribed fires are used increasingly as a management tool. Prescribed burns are planned and initiated by qualified professionals who are trained in using fire for resource management. Before any prescribed fires, burn plans must be approved. These plans must specify the objectives of the fire; location, size, and type of fire; how the fire will be started and controlled; how the smoke from the fire will be managed; and how the fire will be monitored and evaluated.
Invasive weeds pose another threat to the High Plains ecosystem. These harmful and aggressive plants form monocultures (where one species replaces a diversity of species), reduce wildlife habitat, and degrade streams and ponds by displacing native grasses and plants that protect and hold the soil in place.
Weeds also greatly reduce the productivity of rangelands, affecting local economies throughout the High Plains. For example, leafy spurge, a very aggressive invasive weed, costs North Dakota about $75 million a year in damages due to lost livestock and agricultural production. Leafy spurge takes over rangelands and croplands. It reduces available forage and also is an irritant to the mouth and digestive tract, making some cattle sick.
|Leafy Spurge, a pesky weed common in the high plains, takes over large areas, causing economic and ecological damage. It can have a root system that extends for 6m or more.|
Photo: Steve Dewey
Illustration: Robert Allen, BLM
Efforts are under way to attack problem weeds in the High Plains such as musk thistle, Canada thistle, field bindweed, leafy spurge, Russian knapweed, and salt cedar (also known as tamarisk).
Methods of controlling weeds include biological (introducing a natural predator, typically a species-specific insect), chemical (spraying with herbicides), cultural (controlled grazing), and manual (hand pulling). But weed scientists and land managers agree that early detection and quick control of small weed infestations are the most effective approaches.
The Powder River Basin is home to North America's largest coal mines. Mining this extensive brings concerns about the effects on the long-term health of the ecosystem, including erosion, groundwater quality, and wildlife habitat. The challenge is to ensure that permitted mining activities are environmentally acceptable. Years of environmental studies are providing new information on how to design mines in order to minimize ecological damage. Tougher coal mining and environmental regulations over the past two decades now require mining companies to address ecological concerns by developing comprehensive plans, which are reviewed through public hearings and other forums. As a result, some mining activities are altered during certain wildlife migration, breeding, or nesting periods to protect wildlife such as deer, elk, and waterfowl. Reclamation, the process of restoring the land after mining, is also a required part of the process. Before and during mining, the topsoil is stockpiled. After mining is completed, the land is graded to approximate the original contour. Topsoil is then spread and native vegetation planted.
Even though the High Plains contains many unique ecological systems, it shares common components with every other ecosystem—variations in size and scale, connections between the living and nonliving components, a diversity of living things, mechanisms to achieve a balance, and cycles and change over time. When students begin to understand these elements, they will be better prepared as adult citizens to make decisions that will sustain the integrity of ecological systems over the long term, whether they live in the city or in the vast grasslands of the High Plains.
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