Common (Translated Scientific) Name: Big Bluestem - Western Wheatgrass - Blue Grama Grassland & Shrubland Division
Colloquial Name: Central North American Grassland & Shrubland
Hierarchy Level: Division
Type Concept: The division consists of grassland vegetation, which is often the regional matrix type, with interspersed shrublands. The occurrence and abundance of shrubs is a product of several factors, including geology and soils, natural and altered disturbance regimes, and land use. Species composition is also regulated by two major environmental gradients: an east-to-west precipitation gradient and a north-to-south temperature gradient. Plant height and stature vary with available moisture, with shortgrass prairie species (e.g., Bouteloua dactyloides and Bouteloua gracilis) dominating in the southwestern extent of the division, mixed grasses (e.g., Festuca altaica, Hesperostipa comata, Hesperostipa curtiseta, Koeleria macrantha, Muhlenbergia torreyi, Nassella leucotricha, Panicum virgatum, Pascopyrum smithii, Schizachyrium scoparium) in the central region and tallgrass prairie species (Andropogon gerardii, Panicum virgatum, and Sorghastrum nutans) in the east. The occurrence and prevalence of woody species is often a product of reduced fire frequency and enhanced grazing pressure. Woody species dominant in the shrublands can be either or both evergreen or deciduous, including Juniperus spp., Prunus spp., Quercus spp., Rhus spp., and Rosa spp. Associated graminoid and forb species in the shrublands are also found in the surrounding grasslands. Soils are predominantly Mollisols, that range from well-drained, sandy to loamy-sand, and clay loams. On sandy soils, Andropogon hallii, Sporobolus cryptandrus, and Artemisia filifolia predominate.
Diagnostic Characteristics: This division is represented by physiognomic types such as bunchgrasses, sod-forming grasses, and woody plants of dwarf or stunted stature. There is a wide suite of diagnostic species, that, though they are often shared with other divisions, are particularly dominant and widespread in this region. Diagnostic graminoids include Andropogon gerardii, Andropogon hallii, Aristida purpurea, Bouteloua curtipendula, Bouteloua gracilis, Bouteloua hirsuta, Bouteloua dactyloides, Calamagrostis canadensis, Festuca altaica, Festuca hallii, Panicum virgatum, Pascopyrum smithii, Pseudoroegneria spicata, Schizachyrium scoparium, Sorghastrum nutans, Spartina pectinata, Sporobolus cryptandrus, and Sporobolus heterolepis. Woody species include Artemisia filifolia, Artemisia frigida, Juniperus horizontalis, Juniperus virginiana, Cylindropuntia imbricata, Prosopis glandulosa, Prunus angustifolia, Prunus virginiana, Quercus havardii, and Rhus aromatica. Further work is needed to identify diagnostic forbs.
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: We refer to this division as Central North American rather than Great Plains, because the tallgrass prairie is not strictly Great Plains, and the prairie peninsula extends eastward to Illinois, Michigan, and even Ohio and southwestern Ontario. We largely use the term Great Plains in the narrower sense of encompassing shortgrass and mixedgrass prairies. We treat the "tree savannas" with forests and woodlands.
Overgrazing and fire suppression significantly impact the species composition of vegetation types in this division. Overgrazing may cause northern mixedgrass prairies to resemble shortgrass vegetation. Fire suppression typically leads to shrub and tree invasion.
Similar NVC Types:
D008 Eastern North American Forest & Woodland, note:
D024 Eastern North American Grassland & Shrubland, note:
D022 Western North American Grassland & Shrubland, note:
D102 Southeastern North American Grassland & Shrubland, note:
D323 Eastern North American Temperate & Boreal Freshwater Marsh, Wet Meadow & Shrubland, note:
D326 North American Great Plains Forest & Woodland, note:
Physiognomy and Structure: In open grasslands, physiognomy ranges for from short-statured grasses (Buchloe dactyloides and Bouteloua gracilis) in the west to mixed grasses (e.g., Festuca altaica, Hesperostipa comata, Hesperostipa curtiseta, Koeleria macrantha, Muhlenbergia torreyi, Nassella leucotricha, Panicum virgatum, Pascopyrum smithii, Schizachyrium scoparium) in the central region and tall grasses (Andropogon gerardii and Sorghastrum nutans) in the east. Dominant grasses may exhibit either bunch or sod-forming tendencies, which may be widely dispersed or growing densely. The height of grasses is influenced by slope, soils, and aspect. The species composition and dominance of native grasses is a function of latitude, with C3 grass species predominating at higher latitudes and C4 at lower latitudes. Regionally, species composition is a product of soil texture. For example, Bouteloua curtipendula and Bouteloua hirsuta predominate on coarse soils, whereas Buchloe dactyloides is more abundant on clay soils. On deep, sandy soils, for example, grass cover might be sparse and shrubs such as Artemisia filifolia, Prunus angustifolia, and Rhus aromatica predominate. The proportion of shrubs to graminoids is a product of land use and/or substrate. Woody species are typically short-statured or stunted individuals, ranging in height from 0.3 to 3 m. Predominant woody taxa can be either evergreen or deciduous.
Floristics: The families Asteraceae, Fabaceae, and Poaceae predominate in this division. Common and predominant grasses include Achnatherum hymenoides, Andropogon gerardii, Andropogon hallii, Aristida purpurea, Bouteloua curtipendula, Bouteloua gracilis, Bouteloua hirsuta, Bothriochloa laguroides ssp. torreyana, Bouteloua dactyloides, Calamagrostis canadensis, Calamagrostis stricta, Calamovilfa gigantea, Calamovilfa longifolia, Festuca altaica, Festuca hallii, Hesperostipa comata, Hesperostipa curtiseta, Koeleria macrantha, Muhlenbergia torreyi, Nassella leucotricha, Panicum virgatum, Pascopyrum smithii, Paspalum plicatulum, Pleuraphis jamesii, Pleuraphis mutica, Poa pratensis, Pseudoroegneria spicata, Schizachyrium scoparium, Sorghastrum nutans, Spartina pectinata, Sporobolus airoides, Sporobolus compositus, Sporobolus cryptandrus, Sporobolus heterolepis, and Tripsacum dactyloides. Other graminoids include Carex filifolia, Carex inops ssp. heliophila, and Carex meadii.
Forb species richness is high in this division and includes, but is not limited to, species such as Ambrosia psilostachya, Amphiachyris dracunculoides, Artemisia frigida, Astragalus mollissimus, Comandra umbellata, Dalea purpurea, Echinacea angustifolia, Engelmannia peristenia, Eryngium yuccifolium, Erysimum capitatum, Euphorbia corollata, Fragaria virginiana, Gaura coccinea, Helianthus grosseserratus, Helianthus pauciflorus, Liatris pycnostachya, Liatris spicata, Lygodesmia juncea, Melampodium leucanthum, Machaeranthera tanacetifolia, Oligoneuron rigidum, Parthenium integrifolium, Phlox pilosa, Ratibida pinnata, Silphium laciniatum, Silphium integrifolium, Silphium terebinthinaceum, Sphaeralcea coccinea, Symphyotrichum ericoides, and Thelesperma megapotamicum.
Woody plant species include Amelanchier alnifolia, Amorpha canescens, Artemisia cana, Artemisia filifolia, Artemisia frigida, Artemisia tridentata, Atriplex canescens, Ceanothus americanus, Dalea formosa, Dasiphora fruticosa ssp. floribunda, Juniperus ashei, Juniperus horizontalis, Juniperus pinchotii, Juniperus virginiana, Juniperus horizontalis, Mimosa borealis, Cylindropuntia imbricata (= Opuntia imbricata), Opuntia polyacantha, Opuntia phaeacantha, Prosopis glandulosa, Prunus angustifolia, Prunus virginiana, Quercus havardii, Rhus aromatica, Rosa arkansana, Rosa carolina, Symphoricarpos orbiculatus, Symphoricarpos occidentalis, and Yucca glauca.
Dynamics: Historically, vegetation dynamics were driven by fire, grazing and drought. The importance of these factors differs from east to west. For example, fire is considered more important in the humid eastern portion of the division where high levels of precipitation result in the accumulation of biomass. In the absence of fire, thatch build-up can suppress species richness and favor predominant grasses. In the semi-arid west, however, biomass accumulation is limited by low annual precipitation. Fire and grazing have been substantially altered since Euro-American settlement. These factors, in concert, affect the proportion of woody species relative to grasses in given locales. Bison, historically the large herbivore in grasslands, has been replaced by domesticated cattle, and fire frequencies have been greatly altered. This and the replacement of native grasses with non-native pasture grasses have contributed to the increased abundance of woody plants in much of the region.
Environmental Description: Climate: The division occurs within three climate types (sensu Trewartha): Temperate Continental, Dry Steppe (semi-arid), and Subtropical humid. As a result, there are distinct gradients of precipitation and temperate within the division. The precipitation gradient extends along an east-to-west axis, with an average annual precipitation of 1425 mm at Columbus, Ohio, 1083 mm in Columbia, Missouri, to a low of 477.5 mm at Boise City, Oklahoma. The western extent of the region is subject to periodic, often severe, droughts. The temperature gradient is strongest south-north. The annual average temperature in the southern extent of the division is 18.6°C (mean high of 25.7°C and a mean low 11.6°F) at San Angelo, Texas, to 3.1°C in Regina, Saskatchewan (a mean high of 18.9°C in July and a mean low of -14.7°C). The temperature gradient affects the ratio of species exhibiting the C3 to C4 photosynthetic syndromes in the flora, with a shift to C3 from south to north.
Soils/substrate: Although Mollisols predominate under grassland ecosystems, Entisols are common in much of the region, such as the Nebraska Sandhills. Alfisols, Vertisols and Inceptisols are present to a lesser extent. There is considerable variation in soil associations within these orders. Soil texture runs the gamut from fine-textured loams, clay loams, silty clays, and clays to coarse sandy and gravelly soils. Soil depth also ranges from deep, well-developed soils to shallow soils on rock outcrops. In the semi-arid western extent of the division, caliche is common as are gypsum-derived soils.
In the northern portion of division, glaciation during the Pleistocene and glacial till is a key component to soil development. In the High Plains, Ogallala Outwash, sediments and gravels deposited as a result of the Laramide Orogeny, contribute to the surface geology and soil development.
Topography ranges from gentle rolling to rugged, depending upon surface geology. Sandstone and limestone surface formations are common to the east of the High Plains. For example, red stone formations of Permian age are common in much of the region. These give way to Pennsylvanian sandstones in the east.
Geographic Range: This division extends on its western edge from the Rocky Mountains, from New Mexico to Alberta. Eastward, the core of the division occurs from Texas north to Manitoba, but its eastern extent forms a complex pattern with eastern deciduous forests, woodlands and savannas, particularly in the Midwest "prairie peninsula," where tallgrass prairie outliers extend as far east as Michigan, Ohio and extreme southwestern Ontario.
Nations: CA, MX, US
States/Provinces: AB, AR, CO, IA, IL, IN, KS, LA, MB, MI, MN, MO, MT, MXCH?, MXCO?, ND, NE, NM, OH, OK, ON, SD, SK, TX, UT, WI, WY
|US Forest Service Ecoregions (2007)|
Confidence Level: High
Confidence Level Comments:
Synonomy: = Plains Grassland (Brown et al. 1998)
Concept Author(s): Faber-Langendoen et al. (2015)
Author of Description: B. Hoagland and D. Faber-Langendoen
Version Date: 08Jan2016
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