1
What is a grassland? What kinds of grasslands are there, and where are they found?
INFOGRAPHIC 27.1
Which of the following statements describes a grassland biome?
Grasslands are biomes with biotic and abiotic conditions that support the growth of grass and herbaceous plants but not trees.
Grassland biomes are found exclusively in semi-arid areas with very low levels of rainfall, most of which falls in the winter season.
Grasslands have thick soils that develop due to the long, warm growing season characteristic of their tropical environment.
Grasslands are only found in temperate regions that experience hot summers and cold winters, conditions that make it impossible to support tree growth.
A
Temperate grasslands:
occur in places that have both rainy and dry seasons but are warm year-round.
have a seasonal climate with cold winters and hot summers.
are cold most of the year and are characterized by very short growing seasons.
are high-altitude grasslands that get all their precipitation in the form of snow.
B
Why do grasslands exist in areas that receive enough rainfall to support forests?
These areas may have been intentionally cleared and maintained as pastures, they may be habitat for grazers that prevent young tree saplings from growing, or fire may periodically come through, preventing the establishment of forests.
2
Why are grasslands important?
INFOGRAPHIC 27.2
The most widespread use of grasslands worldwide is for:
growing crops like wheat and corn.
conversion to orchards or tree farms.
grazing domestic livestock.
harvesting wild crops.
C
Pastoralists:
are herders who graze their livestock in tight herds, moving them constantly across vast swaths of rangeland.
are landowners who plant fast-growing, nutrient-dense grasses to maximize livestock production in small pastures.
partition their land into separate fenced-in pastures and divide their livestock between these fenced areas so as to control them more easily.
are livestock owners who are paid to remove sensitive grassland areas from production.
A
Identify the ecosystem services that grasslands provide, dividing them into the three categories identified in Infographic 12.2: cultural benefits, human provisions, and ecosystem regulation and support.
Cultural benefits: areas for recreation, educational programs to teach students about grasslands or natural habitats in general, reconnecting with traditional or historical ways of life, etc.
Human provisions: Conversion to farm and ranchland
Ecosystem regulation and support: nutrient cycling, soil formation and protection, carbon sequestration, protection of surface water and refilling of ground water, wildlife habitat; storehouses of genetic diversity for our major cereal crops.
3
What threats do grasslands face?
INFOGRAPHICS 27.3, 27.5, AND 27.6
The conversion of a grassland into a desert is a process known as _____________.
Desertification
Which of the following is not a current cause of desertification of rangeland?
Climate change, especially shifting rainfall patterns that will result in less precipitation
Conversion of rangeland to urban and suburban development
Irrigation of farmland
Overgrazing by domesticated livestock
C
In what way are grasses adapted to normal levels of grazing?
They are unpalatable, so grazers eat very little of any one plant.
The saliva of grazers acts like a growth hormone, stimulating the grasses they are biting to grow.
Grasses can grow faster than grazers can eat them.
The growth area of a grass is at its base not its tip, and cropping the grass stimulates it to grow.
D
What is overgrazing, and how can it damage a grassland? Why is undergrazing just as problematic as overgrazing?
Overgrazing can harm grasslands by killing the grasses (when grass is overgrazed, animals start running out of food and graze the grass down to its roots; the blade can no longer regenerate, and the plant eventually dies) and making it harder for grasses to regrow (increased soil erosion because there are not enough plant roots to hold the soil in place and compacted soil from the trampling of so many grazers).
Undergrazing presents another set of problems. When there are not enough grazers, grasses grow tall; these tall grasses and the plant detritus from dead grass prevent sunlight from reaching the buds. Undergrazing also increases the proportion of unpalatable plant species since grazers can avoid these and only eat the tasty grasses; over time this degrades the usefulness of the grassland as a good source of food for grazers.
4
What is involved in the formation of soil, and how does land use affect it?
INFOGRAPHIC 27.4
True or False: Soil formation is a slow process, taking a year or more to form just 1 mm of soil.
TRUE
12. In desertification, it is the _____________ and _____________ soil horizons that are lost.
O and A
13. The soil type that is best for growing plants, in terms of water penetration and root support, is:
sand.
silt.
clay.
All of these are equally suitable for plant growth.
B
What caused the Great Dust Bowl of the early 1900s in the United States, and what lessons can we learn from that experience?
Overgrazing and over-farming the prairies of the American west — use beyond what those land areas could support — led to soil erosion so expansive that dust storms would blacken the skies for miles. This massive erosion rendered these areas unusable for years. Careful management of the land should be of primary importance to minimize soil erosion — this means not overgrazing rangeland and not over-plowing farmland (or leaving plowed or recently harvested land without plants growing on it).
5
How can we manage grasslands to reduce the threats they face while still using them productively?
INFOGRAPHIC 27.7 AND TABLE 27.1
Shelterbelts are:
trees planted at the edge of a farm or grassland that protect crops or grasses from wind and prevent encroachment of nearby deserts.
planned grazing systems where animals are allowed to graze on a small section of pasture for a few days before being moved to another section so as to prevent overgrazing.
legal agreements, including tax breaks, that restrict how a landowner can develop and use land so that the land will be protected in perpetuity.
areas managed in ways that protect the habitat but allow recreational use so as to benefit both nature and people.
A
How does grazing by native herbivores impact grassland ecosystems? What techniques are used in Allan Savory’s holistic planned grazing method to mimic the impact of natural grazers?
Contrary to what one might expect, grazing by wild ungulates is good for grasslands. Because wild herbivores evolved to survive on grasslands, both grazers and grasses are well adapted to each other. As grasses grow from the base rather than the tip, clipping off the top of the blade does not kill the plant. Rather, herbivores expose new growth shoots to the sunlight, thus stimulating the plants’ growth. Furthermore, by breaking up the soil with their hooves, they allow water to penetrate the ground and enable seeds to germinate and take root. And their waste returns nutrients such as nitrogen and phosphorus to the soil in a form that plants can easily use. Wild herds graze in tightly bunched packs (as a form of protection from predators), and move quickly from one patch of land to the next. Thus, while grasses are eaten down completely in a short time, the land is left alone for a long time to recover. The result: Animals are fed and grasses regenerated in a mutually beneficial cycle.
Allan Savory’s holistic planned grazing method seeks to mimic the high densities and patterns of movement of wild grazers. Cattle are kept in a small part of the areas to be grazed in sufficient numbers to completely graze down the area. When all the grasses (palatable and unpalatable) are grazed, the cattle are moved to the next area and are not allowed to return to the previous grazed area until it has fully recovered.