The dominant plants of grasslands are, no surprise, grasses. Most grasslands are composed of several genera and numerous species so that the associations are defined not by species composition (as in the association of the temperate deciduous forest in eastern North America), but the nature of the grasses as a unit. Thus, the Great Plains are divided into short, mid and tall grass prairies based on the height of the grasses and the nature of individual plants rather than the presence of individual species or genera of grasses.
Fire is an essential factor of the grassland biome. Localized lightening storms rumble across the biome almost daily during the warm to hot, and dry, summer months setting hundreds of fires. Most of these convection storms are accompanied by high winds which mean that lightening-caused fires usually burn large areas in an exceedingly brief period of time. Even today, grass fires can cover tens of square miles in a single day. Early humans often utilized fire as an aid in hunting fleet-footed grazing animals. Fires were set to force animals over cliffs or into narrow drainages where they could be killed. Native Americans used fire to promote new growth of grass to attract animals to a particular place and to encourage certain species that were used for food.
Fueled by dry grass and low shrubs, grassland fires rarely generate sufficient heat to alter soil chemistry or even to kill the grasses or shrubs. With the growth tips of grasses and many shrubs (and some herbaceous perennials as well) located at or just below ground-level, re-establishment of the vegetation is often rather rapid. The thin coating of ash promotes seedling establishment, acting as a natural fertilizer.
Another important aspect of grasses is that the bulk of its biomass is located in the root system. These massive root systems not only allow growth points to be scattered over a larger area, but are an effective adaptation to the low-moisture soil levels of most grasslands. Rhizome (underground stems) of a single plant often spread over a wide area, and if broken from the parental plant can serve as an asexual form of reproduction. Wind pollination, and thus outcrossing as a form of sexual reproduction is readily accomplished as grasslands tend to be constantly windy, and insect pollinators limited.
The combination of fire and grazing pressure imposed by numerous large mammals have undoubtedly shaped the evolutionary adaptations of grasses. Even the small seeds, easily carried by birds and small animals (such as mice and ants) are effective adaptations to its environment
B. General features:
1. Dominant plants are members of the grass family (Poaceae), several genera and species common but usually with one or two dominate.
2. Most grasses are rhizomatous (possessing rhizomes) and are wind pollinated.
3. Moderate temperature but notable extremes: -20° F to 110° F common, and even colder temperatures in the north.
4. Variable precipitation: 6-40 in (15-100 cm).
5. Soils generally fertile, deep and rich; variable
6. Growing season of 120-200 days.
7. Generally flat to rolling topography cut by stream drainages where there is a riparian or river-bank habitat.
8. Scattered rain and lightening common in summer months ("convection storms") with more general rains and snows in winter months.
9. Fire a major factor in maintaining biome.
STEPPE (GRASSLAND)
CLIMATE. Grasslands are temperate environments, with warm to hot summers and cool to very cold winters; temperatures are often extreme in these midcontinental areas. They are often located between temperate forests and deserts, and annual precipitation falls between the amounts characteristic of those zones. Winds play an important role in these very open environments. Precipitation varies from highly seasonal to spread throughout the year. There is a substantial snow buildup in the northern part of the zone, which diminishes greatly to the south.
SOILS. Grasslands are typically underlain by chernozems, soils that are alkaline because net water movement within them has been upward, carrying calcium with it which precipitates as calcium carbonate. Prairie chernozems are blackish in their upper horizons because of the constant decay of grasses into dark humus. Taller-grass prairies have browner soils, richer in humus and loamy in structure.
VEGETATION. Grassland is largely dominated by grasses, but with annual and perennial forbs intermixed in different proportions in different areas. The average height of the grass is correlated with rainfall, so there are tall-, medium-, and short-grass prairie zones across a longitudinal gradient from east to west in North America. The aspect changes considerably between spring, when the grasses are green and the forbs are in bloom, and midsummer, when brown, seeding, and dying plants predominate. Some steppes, especially in more arid areas, are dominated by shrubs and differ from deserts primarily in their higher latitudes, lower mean temperatures, and lower diversity.
DIVERSITY. Plant and animal diversity is rather low in this structurally simple, temperate-climate, zone. For example, usually no more than two or three species of large grazing mammals occur in a typical temperate grassland, as compared with a dozen or more in some tropical (savanna) grasslands. Birds are diverse only in wetlands and in riparian vegetation along rivers. Southern-hemisphere grasslands adjacent to tropical forests and savannas may have a higher animal diversity than those in the northern hemisphere. The only major vertebrate groups especially characteristic of grasslands are passerine birds--larks, pipits, and buntings. The grass family is one of the largest in world, and grasses as individual plants are probably the most abundant plants in the world.
PLANT ADAPTATIONS. Grasses are superbly adapted to cover open ground, relatively resistant to both fire and grazing because their leaves grow from the base, unlike most plants, in which new leaves continually grow from the branch tips. Thus as the productive part of a grass plant is burned or eaten away, as long as its base remains intact, new growth follows immediately. Grass leaves are also heavily endowed with silica, which wears down the teeth of grazing animals, and some forbs of this zone (locoweeds, for example) are highly toxic to grazers. Most grasses proliferate by means of rhizomes, stems that travel along just underground and send up new leaves at regular intervals. Others, especially in drier areas, grow as bunch grasses, plants that resist wind desiccation by the denseness of their growth form; many forbs of this zone are similarly structured. Grasses are wind pollinated, very effective in this open environment.
ANIMAL ADAPTATIONS. Burrowing is an important adaptation for small animals to avoid predation in this open environment. Some of the burrowers are colonial, probably also an adaptation for early predator detection. Some mid-sized carnivores are highly adapted to dig out the smaller burrowers. Because of its openness and thus the ease of moving about, this environment supports large populations of grazing mammals, which form herds for defense against the large predators that follow them. Ground-nesting and -feeding birds are very subject to predation, and almost all are cryptic, brown-streaked above, with well-developed distraction displays; with no elevated perches available, most sing from the air.
HUMAN EFFECTS. As grain crops are all grasses, this environment is well-suited for them; thus huge regions of temperate grasslands have been altered for grain-growing. The grazing of livestock brings more intense pressure on many areas than native ungulates did, changing species representation in plant communities because some are more susceptible to grazing than others. Many plants of this environment are adapted to early succession and, when introduced to other continents, become invasive weeds; they colonize disturbed sites rapidly and often outcompete native species. Together with grazing, this has changed the makeup of grasslands everywhere, especially in North America, so that "natural" grasslands are rare.
The prairie blazingstar is one of the most beautiful flowers on the tallgrass prairie. It has magenta colored flowers arranged along a spike at the top of a long stalk up to 5 feet high. Many kinds of butterflies are attracted to this flower.
Prairies are maintained by fire and grazing animals. Another way to manage a prairie is to mow it in the middle of July and bale the hay. Haying removes much of the thick vegetation that accumulates, and it allows the prairie to grow in a healthy way.
Sure! This stinging nettle plant is very attractive when it's in flower like this - but be careful! This plant causes a painful sting when it touches your bare skin. It grows to 3 feet tall in moist shady woods. This adaptation helps the plant protect itself from grazers and people, too!
Well, for one thing, much of the North American prairie land was turned into farms in the early 1900's so that people could make a good living growing and selling crops. Bison, which are often mistakenly called buffalo, were hunted to near extinction because their meat and hides were so valuable. Deer and antelope are still found in places like Wyoming, but the herds are dwindling.
Prairies are famous for their beautiful flowers and grasses that bloom in the springtime. In Autumn the prairie takes on a different kind of beauty. Leaves of the tall grasses turn beautiful shades of yellow, orange, and tan.
About one quarter of the earth's land is grasslands. The wild prairie has disappeared, for the most part, from the United States. Only a few spots of wild prairie remain. Because the soil is so productive and rich in nutrients, nearly all of the wild grasslands have been converted into commercial farms. Now the prairie feeds the nation and the world. Why do you think prairies are often called the "breadbaskets of the world?"