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F012 Temperate Grassland & Shrubland Formation

The U.S. National
Vegetation Classification
Type Concept Sentence: Temperate Grassland, Meadow & Shrubland is dominated by perennial grasses, forbs and shrubs typical of moderately dry to moist habitats and is found in the mid-latitude regions of all continents (23° to 55°N and S), varying from large open grassland landscapes to droughty hillside meadows in forested landscapes.
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Common (Translated Scientific) Name: Temperate Grassland & Shrubland Formation
Colloquial Name: Temperate Grassland & Shrubland
Hierarchy Level: Formation
Type Concept: Temperate Grassland, Meadow & Shrubland is dominated by mesomorphic perennial grasses and forbs and is found in the mid-latitude regions across the globe. It is associated with a moist to semi-arid climate and geographically occurs between temperate forests and deserts. The present plant assemblages were strongly affected by Pleistocene glaciations, though regions close to the equator may have retained vegetation back to the Tertiary.

Grasslands are a predominant type in this formation and each continent has its own popular name for its part of this formation. In North America, it is the prairie; in Eurasia, the steppe. South Americans usually refer to pampas and South Africans to the veld. The plants (and animals) of the North American and Eurasian sections of the biome are closely related, but have been impacted differently by Pleistocene and post-Pleistocene climate changes, human occupation and use, wildfires, and grazing pressures from both wild and domesticated large mammals. The origins of South America's pampas and southern Africa's veld are still poorly understood. Fire may be implicated, as it is a necessary management tool today in preventing the encroachment of woody plants.

In addition to the larger geographic areas of grasslands and associated shrublands, scattered grassland, shrub, and forb vegetation within temperate forest formations are included.

Although mesomorphic perennial grasses and shrubs are the most common growth forms in this formation, a large number of other herbaceous plants, primarily perennial forbs, are also found. Trees are not major components of the vegetation, except as a scattered layer (typically <10% cover).
Diagnostic Characteristics: Mesomorphic perennial grasses and shrubs are the most common growth forms in this formation, with a variable amount of perennial forbs. Trees are scattered to largely absent (typically <10% cover). Stands are found in the mid-latitude regions of all continents, typically associated with semi-arid climates or stressful sites in moist climates in the mid-latitudes (23° to 55°N and S).
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: No Data Available
Similar NVC Types:
F005 Temperate to Polar Scrub & Herb Coastal Vegetation, note: "2.B.2 ~Temperate Grassland & Shrubland Formation (F012)$$ has similarities to coastal vegetation, especially between coastal and inland dunes in terms of growth forms and even wind-driven processes."
F008 Cool Temperate Forest & Woodland, note: "Open woodlands or tree savannas, with grassy or shrubby understories, and with trees 10% cover or more, are placed here, but may have strong floristic similarities to grasslands."
F033 Cool Semi-Desert Scrub & Grassland, note: "Typically with small leaved, xerophytic shrubs (e.g., sage) and more open bare ground, sometimes with biological crust."
F016 Temperate to Polar Bog & Fen, note: "Upland transitions to wet-mesic or moist grasslands, such as wet-mesic prairies, can be hard to place."
F018 Warm Temperate Forest & Woodland, note: "Open woodlands or tree savannas, with grassy or shrubby understories, and with trees 10% cover or more, are placed here, but may have strong floristic similarities to grasslands."
F028 Boreal Grassland & Shrubland, note: "2.B.2 ~Temperate Grassland & Shrubland Formation (F012)$$ is currently separated based on geography and climate from boreal grassland (F028), but more specific vegetation criteria are needed."
F013 Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland, note: "2.B.2 ~Temperate Grassland & Shrubland Formation (F012)$$ transition, such as wet-mesic or moist grasslands and prairies, may be very similar to freshwater marshes and wet meadows (F013)."
F038 Mediterranean Scrub & Grassland, note: "The vegetation tends to produce highest biomass in the cool winters, and become dormant in the summer hot periods. Above-ground portions of perennial grasses dry and wither, or annuals set seed and die by late spring."
CFO05 Pasture & Hay Field Crop, note: "2.B.2 ~Temperate Grassland & Shrubland Formation (F012)$$ may overlap in composition with pasture grasslands (F045), particularly in grassland regions. And in regions where a pastoral tradition has existed from 100s to 1000s of years, recognition of native versus agricultural grasslands may be challenging."
Physiognomy and Structure: Mesomorphic perennial grasses and shrubs are the most common growth forms in this formation, with a variable amount of perennial forbs. Trees are scattered to largely absent (typically <10% cover). Grasses and forbs grow to different heights at maturity. Furthermore, some grasses and most forbs are erect, while others are recumbent, creeping along the ground. Thus a distinct layering of plant foliage occurs in some temperate grasslands. Forbs and grasses may grow and bloom at different times during the growing season, so temperate grasslands may have recognizable color phases, or aspects, depending on what plants are blooming. This is especially evident in the east European steppes. Grasses and perennial forbs are well-suited to withstand cold seasons and tolerate grazing and fire because of the position of their renewal buds near the ground surface. The plants are generally able to regenerate from these buds after seasonal die-downs, burns, or cropping by grazing animals (Woodward 2008). Among the grasses, both sod-forming and bunchgrasses are prominent throughout, but bunchgrasses become a much more frequent component of the vegetation in the drier short-grass regions.
Floristics:
Dynamics: Temperate grasslands around the world have been so heavily altered by human activities (especially grazing of livestock, plowing under and conversion to agriculture, increased fire frequency, or cessation of grass fires) that little survives that is truly natural. Fire may have been the first way people managed grasslands. Annual burning eliminated tree and shrub seedlings and stimulated the growth of new grass shoots. Deliberate burning may have occurred as soon as fire itself could be managed in order to attract the wild grazing animals upon which hunting and gathering peoples, and indeed, early agriculturalists, depended for protein. Repeated firing of the forest edge may have expanded grasslands into wetter climate regions, such as the Prairie Peninsula of the U.S. and the eastern pampas of Argentina and Uruguay. Later, farmers and townsfolk stopped all wildfires, and trees invaded the grasslands (Woodward 2008).

Pastoralism in all likelihood first developed in the temperate grasslands of the Old World. Shifts in plant species abundance no doubt accompanied the spread of pastoral societies, since livestock select the most palatable plants. Weedy grasses and forbs evolved in response to the trampling and cropping of the vegetation by cattle, sheep and other hoofed grazers. Tolerant of disturbance and preferring open habitat, weeds typically germinate rapidly in full sun, have short lifespans, produce large numbers of easily dispersed seeds, and thus spread quickly to new disturbed sites. Not surprisingly, Old World weeds followed cattle, sheep, and goats when the animals were transported to other parts of the world (Woodward 2008).
Environmental Description: Gradation in precipitation amounts occurs in most regional expressions of the biome and is mirrored in the zonation pattern of the vegetation and animal life in each. In some instances, such as in North America, longitudinal zones dominate and replace each other in an east-west direction across the mid-continent. In other areas, latitudinal zonation is prominent and plant and animal communities change in a north-south direction. Still other natural grasslands are a consequence of rainshadows on the lee sides of major mountain ranges or of high elevation, as is the case in southern Africa (Woodward 2008).

Climate: Temperate grasslands have developed in regions having a semi-arid climate (mostly BSk in the Köppen climate classification). Mid-latitude semi-arid climate regions receive 25-75 cm (10-20 inches) of precipitation a year. In some areas (most notably the mid-continental prairie of North America and the East European steppes of Eurasia), a significant amount falls as snow during the winter months, such that snowmelt contributes importantly to soil moisture in early spring. The interior position of grasslands on the large North American and Eurasian continents results in the wide annual range in temperatures, a temperature pattern that is considered typical for the biome. Winters see temperatures well below freezing, whereas summers can be scorchingly hot. Such a temperature pattern is described by climatologists as continental. Similar temperature conditions often occur in humid forested regions at the same latitudes (Woodward 2008).

North American and Eurasian grasslands owe their existence to their positions in the middle of large continents, where precipitation is reduced and temperature extremes are pronounced. The South American grasslands lie in the rainshadow east of the Andes Mountains. In Africa, elevation is a factor. According to latitude alone, these African grasslands are subtropical, but the elevated surface at the southern end of the African Plateau creates regional temperature patterns similar to middle latitude conditions (Woodward 2008).

In all regions of the formation, gradual changes in climate occur across great distances. In Eurasia, the variation occurs in a north-south direction. The wetter (subhumid) northern regions of the Temperate Grassland border the Cool Temperate Forest & Woodland and Boreal Forest & Woodland formations, and the drier (arid) southern margins grade into the Desert formations. In the Americas, the gradation from subhumid to arid runs in an east-west direction, with progressively less precipitation the farther west one goes. In all areas a change in vegetation coincides with the change in total precipitation. Wetter areas contain taller grass species and usually a greater variety of plants and animals than do the shorter grass areas in the driest parts of the biome (Woodward 2008).

Soil/substrate/hydrology: The soils beneath prairies, steppes, pampas, and high veld are among the most fertile on Earth. Once the technology was available to break through the thick sod, many grasslands were converted to agriculture. Wheat and corn replaced native grasses, and the temperate grasslands became the breadbaskets of their respective countries (Woodward 2008).

Formation of Temperate Grassland soils: The underground portion of the grass plant is equally, if not more, important to the functioning of the ecosystem and formation of soil. Grasses develop a dense, intricate system of fine roots that not only acts to hold the plant in place but absorbs water and nutrients from the soil and stores some of the carbohydrates that the plant manufactures during photosynthesis for later use. In fact, more living plant matter (biomass) exists below ground in the temperate grasslands than above. Roots continually grow, die, and decay and thus contribute organic matter in the form of humus to the soil. The fine roots create a crumbly texture to the soil that allows water and air to penetrate to depths up to 3.5 m (12 feet) in the wetter parts of the biome, further enhancing the soil environment for plant growth. Those soluble compounds (e.g., calcium carbonate and magnesium carbonate) that might be leached to depth after rainstorms or snowmelt can be returned to the root zone during dry periods by capillary action along the tiny tunnels left by dead roots. The carbonates precipitate out near the top of the subsoil (B horizon) when the soil moisture evaporates. The concentration of carbonates in this manner is the main feature of the soil-forming process known as calcification, which is characteristic of semi-arid and arid climate regions. The carbonate-rich layer forms closer to the surface the drier the climatic conditions (Woodward 2008).

Soil types: Grassland soils of temperate regions are classified in U.S. Soil Taxonomy as Mollisols. The prefix "moll" means soft and describes the friable or crumbly texture of these soils that persists even when the top layers dry out. Other parts of the world and the United Nations Food and Agriculture Organization use other names. In Canada they are called chernozemic soils; in Russia they are chernozems. Mollisols are brown in color due to the abundance of humus in both the topsoil and subsoil (A and B horizons). Color varies from dark brown and even black to chestnut brown and light brown as climate changes from subhumid to dry and grasses change from tall with deep roots to short with shallow roots. For the darkest of all, the truly black soils, the Russian name Chernozem (meaning black soil) is used, even in the United States. Chernozems have especially deep A and B horizons (each up to 1 m [3 feet] deep), both of which are dark with humus and humic acid stains. They have formed where semi-arid regions receive the most precipitation and where the parent material is a fine, windblown material known as loess. Loess originated as tiny particles on the newly exposed bare ground at the edge of continental glaciers when ice sheets retreated at the end of the Pleistocene ice age. Winds coming off the ice picked the dust-like material up and carried it to more humid, vegetated regions, where it accumulated. Thick deposits of loess occur in the Central Lowlands of North America, across much of semi-arid Eurasia, and in Uruguay and eastern parts of Argentina. Loess is often rich in carbonates. The soils developed on it are among the most fertile in the world, and today they produce much of the world's wheat and corn (both of which are domesticated grasses) (Woodward 2008).
Geographic Range: Temperate grasslands and shrublands occur in the middle latitudes (25-55°) of both hemispheres. Specific latitudes depend upon the continent on which they are located. The largest areas of this formation are found in the Northern Hemisphere on the North American and Eurasian continents. Smaller but still major segments of the formation are found in the Southern Hemisphere in South America and southern Africa (Woodward 2008).
Nations: AR, BR, CA, CL, CN, LS, MN, MX, RU, US, UY, ZA
States/Provinces:
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: Moderate
Confidence Level Comments:
Grank: GNR
Greasons:
Concept Lineage:
Predecessors:
Obsolete Names:
Obsolete Parents:
Synonomy: = Temperate Grassland (Woodward 2008) [Despite the name, shrublands found within the grassland regions are included in Woodward's concept.]
Concept Author(s): Hierarchy Revisions Working Group, Federal Geographic Data Committee (Faber-Langendoen et al. 2014) after S. Woodward (2008)
Author of Description: D. Faber-Langendoen and J. Messick
Acknowledgements:
Version Date: 17Oct2014
References:
  • Faber-Langendoen, D., T. Keeler-Wolf, D. Meidinger, C. Josse, A. Weakley, D. Tart, G. Navarro, B. Hoagland, S. Ponomarenko, J.-P. Saucier, G. Fults, and E. Helmer. 2015c. Classification and description of world formation types. General Technical Report RMRS-GTR-000. USDA Forest Service, Rocky Mountain Research Station, Fort Collins, CO.
  • Woodward, S. 2008. Grassland biomes. Greenwood Press, Westport, CT.