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Grazing’s role in grassland ecosystems

Robert Fears for Progressive Forage Published on 30 August 2016
Grasses, livestock and mosaic burns are all components of one system

Our creator designed this world to operate through interwoven functions of biological components, which collectively form an ecosystem. Ecosystems function more efficiently when organism populations remain in balance with each other.

Balanced or near balanced ecosystems thrive through symbiotic relationships among the various organisms. “Sym” means together and “bio” means life; so symbiosis is defined as “living together.” Symbiosis occurs when species within a community develop close interactions and at least one involved organism benefits from the relation.

Humans were part of the original ecosystem in the Garden of Eden and still function within biotic systems. The problem is that many people do not understand the true concept of ecosystems and they try to manage one component without considering how their actions will affect the other organisms.

One example of failing to look at the total picture is the effort by several groups to eliminate the livestock industry and grazing animals. Grazing, as well as fire, are very important functions in healthy ecosystems, as history shows.

Plant-animal relationships

A review of grazing history in the U.S. reveals the relationships between plants and animals and how grazing enhances these associations. Grassland grazing history was addressed by Steve Clubine, a grassland management consultant, at a Restore the Land Conference in Bastrop, Texas. Clubine explained that thousands of years ago, large herbivores (plant eaters) such as big-horned bison and mammoth were replaced by bison and elk.

Eastern bison were found in small herds of a few hundred, whereas plains bison roamed the prairies in large herds of several thousand animals. Populations of plains bison may have grown as a result of Native Americans dying from diseases brought into the country by European explorers.

“In contrast to common belief, bison were largely resident animals, not migratory,” said Clubine. “They followed fire that was either started by lightning or the Indians. Bison heavily grazed fresh burns and lightly grazed other areas during warm weather and made greater use of riparian and unburned areas in the winter."

A patchwork of burned and unburned prairie provided intermingled brood and nesting cover for the greater prairie chicken, bobwhite quail and other grassland biota including rabbits, rodents, insects and soil microorganisms.

“Prior to widespread use of the steel plow, tallgrass prairies extended throughout the American Midwest and smaller portions of southern central Canada. They formed the transition zone between the eastern North American forests west to the shortgrass prairies and extended south into parts of Oklahoma and Texas."

“The most obvious features of prairie ecosystems are the tall grasses such as indiangrass, big bluestem, little bluestem and switchgrass,” Clubine said. “These grasses average between 4.9 and 6.6 feet tall with occasional stalks as high as 8.2 to 9.8 feet. Prairies also include a large percentage of forbs (herbaceous broadleaf plants), such as prairie rosinweed, gay feathers, sunflowers, asters, coneflowers and many other species.

“Prairies were rarely without grazing animals. Areas recovered from a burn were severely grazed, but lightly grazed when not burned. The recovery period is often more productive for grassland birds and plants than any static condition. Burned but ungrazed prairie is a recent perception of preservation to which neither native plants nor animals may be adapted.

“Cattle began replacing bison as early as the 1500s in many areas and by the 1700s in Illinois,” Clubine said. “After the Civil War, the cattle industry shifted westward to the Great Plains and Illinois ranches were eventually converted to cropland. Wildlife thrived after settlers began farming as long as quality grassland remained. Draft animals that included oxen, horses and mules required 2 acres of grass for each acre farmed.

“Euro-Americans continued the mosaic burn practice initiated by the Indians. There was too much grass for their livestock and new patches had to be burned each year for new palatable forage. The patchwork of burned and variably grazed grasslands contributed more to the abundance of small game after Euro-American settlement than grain crops to which credit is erroneously given.

“When tractors replaced draft animals in the 1900s, 50 million acres of grasslands were converted to crops,” Clubine said. “To use surplus production, cattle began to be finished on grain instead of grass. Grassland wildlife populations, including ground nesting birds, plummeted."

Grain prices fell during and after the Depression, fostering a New Deal Era cropland retirement program. Cropland was planted to grasses and annual lespedeza, causing grassland wildlife to again flourish.

“World War II brought high demand for grain and when grassland was put back into tillable crops, prairie chickens and other grassland wildlife populations once again plummeted. During the 1950s, when drought brought fears of another Dust Bowl, cropland was planted back to grass and wildlife rebounded.”

History shows that grass and grazing are very important to wildlife, including large and small mammals, birds, insects and soil microorganisms.

Soil-plant relationships

Soil is the foundation of all ecosystems and the degree of soil health governs their ability to function. Soil health, also referred to as soil quality, is the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals and humans.

Plants and soil have a symbiotic relationship. As part of the ecosystem, plants depend upon soil for anchorage, oxygen, water, temperature moderation and nutrients. In turn, soil depends upon plants to maintain health.

Dr. David Weindorf, with Texas Tech University, discussed soils and their contributions to the environment at a recent Sustainable Rangeland Symposium in Lubbock, Texas. He stated that through photosynthesis, plants convert carbon from carbon dioxide (CO2) into organic matter in the form of roots, stems and leaves.

Grasses, due to fibrous root systems, create a tremendous amount of soil organic matter (SOM) as their root materials die and slowly degrade. Organic matter is slowly decomposed by soil microorganisms (such as nematodes, algae, amoebae, fungi, actinomycetes and bacteria) from which humic and fulvic acids are formed. These two acids are important for promotion of plant growth.

“Within soil, organic matter serves as a nutrient reservoir, a source of energy for microorganisms, improves soil structure and increases water infiltration and holding capacity,” Weindorf said.

“Organic matter also buffers soil against rapid changes in pH and salinity. Modification of the land surface to row crop agriculture stifles many of these natural processes. Inputs of organic matter are dramatically reduced as crop vegetation is harvested and removed from the land surface."

"Furthermore, plowing of the land surface destroys soil structure and promotes erosion. Plowing aerates soil, causing oxidation of organic matter that releases carbon back to the atmosphere as carbon dioxide.”

Negative effects of row crop production on soil health are not reasons for banning farming; however, farmers should be aware of these effects and use farming methods that reduce the imprint. Progressive farmers have used soil conservation practices in their operations for a long time.

These practices include terracing, no-till or minimum tillage, judicious use of fertilizers and pesticides, proper maintenance of riparian areas and cover crops. Most farmers understand they must keep soil covered with vegetation on a continual basis. The take-home message is livestock grazing rangeland is a natural process and, when managed properly, the system requires few inputs.

Soil-plant-animal-human relationships

Humans require resources from ecosystems for life. These resources include land, water, energy, food, housing and infrastructure. If done correctly, land, water and energy can be obtained with very little impact on the ecosystem. Housing is not a problem on large acreage; however, ranchettes and subdivisions remove considerable land from ecosystems.

Infrastructures such as utility rights-of-way, highways, roads and cities are continually consuming land that will no longer be able to function as a natural ecosystem. Therefore we must make a greater effort to manage the remaining rural land in a manner to balance our activities with functions of other ecosystem components. This is vital for human survival.

“Proper land use management needs to be undertaken seriously and by those with a working knowledge of ecosystem dynamics so that disruptions to natural cycles can be minimized in some cases and avoided altogether in others,” Weindorf said.

“Individuals with a working knowledge of natural resource management have an obligation to educate others in proper use and stewardship of land. Effectiveness of our efforts is for long-term survival and vigor of humanity on this earth.”  end mark

PHOTO: Grasses, livestock and mosaic burns are all components of one system; understanding their interplay can increase the effectiveness of management efforts. Photo courtesy of Robert Fears.

Robert Fears
  • Robert Fears

  • Freelance Writer
  • Georgetown, Texas