Invalid Unit Specified
M053 Bouteloua gracilis - Bouteloua dactyloides Shortgrass Prairie Macrogroup

The U.S. National
Vegetation Classification
Type Concept Sentence: This macrogroup is composed of the matrix short grasslands in the western Great Plains, from southeastern Wyoming to the Texas panhandle, and is characterized the dominance of short grasses Bouteloua gracilis and Bouteloua dactyloides.
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Common (Translated Scientific) Name: Blue Grama - Buffalograss Shortgrass Prairie Macrogroup
Colloquial Name: Western Great Plains Shortgrass Prairie
Hierarchy Level: Macrogroup
Type Concept: This macrogroup forms the matrix grassland in the western half of the Western Great Plains Division east of the Rocky Mountains and ranges from southeastern Wyoming and the western Nebraska panhandle south into the panhandles of Oklahoma and Texas and eastern New Mexico. The vegetation is primarily dominated by Bouteloua gracilis and Bouteloua dactyloides throughout its range, with various associated graminoid species changing depending on latitude, precipitation, soils, and management. In the southern portion Prosopis glandulosa may form a sparse to moderately dense short-tree or shrub canopy in uplands over shortgrass understory. Associated graminoids may include Achnatherum hymenoides, Aristida purpurea, Bouteloua curtipendula, Bouteloua hirsuta, Carex filifolia, Carex inops ssp. heliophila, Eragrostis intermedia, Hesperostipa comata, Hesperostipa neomexicana, Koeleria macrantha, Muhlenbergia torreyi, Pascopyrum smithii, Pleuraphis jamesii, Sporobolus airoides, and Sporobolus cryptandrus. Although mid-height grass species may be present, especially on more mesic land positions and soils, they are secondary in importance to the sod-forming short grasses. Sandy soils have higher cover of Hesperostipa comata, Sporobolus cryptandrus, and Yucca glauca. Scattered shrub and dwarf-shrub species may also be present. Gutierrezia sarothrae is often present to codominant especially in disturbed areas. Cacti species such as cholla (Cylindropuntia imbricata) and prickly-pears (Opuntia polyacantha and Opuntia phaeacantha) can be abundant on some sites. Stands occur on primarily flat to rolling uplands. Soils typically are loamy and ustic but range from sandy to clayey. Climate is temperate, semi-arid continental with mean annual precipitation generally about 300 mm, ranging up to 500 mm in the warmer south extent where precipitation is less effective. Annual precipitation has a bimodal distribution, occurring mostly before the growing season in winter and early spring and then during summer as monsoon thunderstorms. Summer precipitation events are mostly <10 cm but occasionally larger. High variation in amount and timing of annual precipitation impacts the relative cover of cool- and warm-season herbaceous species.

Climate, fire and grazing constitute the primary processes impacting this macrogroup. In contrast to other prairie macrogroups, fire is less important, especially in the western range because the dry to xeric climate conditions produce less vegetation/fuel load. However, historically, fires that did occur were often very expansive, especially after a series of years with above-average precipitation when litter/fine fuels can build up. Currently, fire suppression and more extensive grazing in the region have likely decreased the fire frequency, and it is unlikely that these processes could occur at a natural scale. A large part of the range for this macrogroup (especially in the east and near rivers) has been converted to agriculture. Areas of the central and western range have been impacted by the unsuccessful attempts to develop dryland cultivation during the Dust Bowl of the 1930s. Historically, mesquite shrublands probably occurred as a natural component on more fertile soils and along drainages, but they have expanded their range into prairie uplands in recent decades.
Diagnostic Characteristics: This macrogroup is characterized by a short, often discontinuous graminoid layer typically dominated or codominated by Bouteloua gracilis and Bouteloua dactyloides. Many other graminoids of varying height may be associated; however, medium-tall and tall grasses will not dominate. Gutierrezia sarothrae is often present to codominant especially in disturbed areas. Woody plants may be present but typically have <10% cover. Cacti species such as Opuntia polyacantha and Cylindropuntia imbricata can be abundant on some sites.
Rationale for Nominal Species or Physiognomic Features: Nominal species Bouteloua gracilis and Bouteloua dactyloides were chosen because they are often dominant and diagnostic species for the herbaceous layer. Prosopis glandulosa was chosen to represent the dominant diagnostic species for ~Southern Great Plains Mesquite Shrub Prairie Group (G140)$$.
Classification Comments: The dominant grass in this macrogroup, Bouteloua gracilis, is tolerant of heavy grazing and drought, which favor it over other taller and less xeric grass species (Weaver and Albertson 1956). Some ecologists consider stands in this macrogroup to be disclimax grassland of mixedgrass prairie resulting from over-grazing by livestock (Weaver and Albertson 1956). Because this macrogroup classifies existing vegetation, it potentially could include both early-seral "disclimax" and late-seral "climax" stands. But in the northwest mixedgrass prairie region, where extended, heavy grazing may cause a shortgrass disclimax, it is not clear that the grassland per se is more similar to the shortgrass prairie described here or to a degraded form of mixedgrass prairie. So for now we extend this type from southeastern Wyoming into the Texas panhandle (as in Küchler 1985). In addition, in Montana and Alberta, in Great Plains Mixedgrass & Fescue Prairie Macrogroup (M051), there is Northern Great Plains Dry Mixedgrass Prairie Group (G331), which should be kept separate from this type. The Shortgrass Prairie grassland type in Sims et al. (1978) is closest conceptually to this macrogroup. Many others, such as Singh et al. (1983), Lauenroth and Milchunas (1992), Dick-Peddie (1993), Sims and Risser (2000), and Lauenroth and Burke (2008), recognize this macrogroup (limiting its northward distribution to southeastern Wyoming), though they may use climate or other environmental or geographic factors as well as typical shortgrass prairie composition. So, at least for now this macrogroup largely corresponds to the shortgrass steppe/prairie ecoregion and Western Great Plains Shortgrass Prairie (CES303.672), an ecological system. It may also be that western Great Plains juniper - oak scrub belongs here (M. Schiebout pers. comm. 2014), but more information is needed.

Historically, mesquite shrublands probably occurred as a natural component on more fertile soils and along drainages, but where it has expanded its range into prairie uplands in recent decades, it is considered ruderal.
Similar NVC Types:
M052 Great Plains Sand Grassland & Shrubland, note:
M051 Great Plains Mixedgrass & Fescue Prairie, note: "includes mixedgrass groups ~Central Great Plains Mixedgrass Prairie Group (G133)$$ and ~Northern Great Plains Mixedgrass Prairie Group (G141)$$ that occur adjacent and may be transitional, and depending on past management may be overgrazed to resemble vegetation in this macrogroup."
M087 Chihuahuan Semi-Desert Grassland, note: includes mixedgrass groups ~Chihuahuan Desert Foothill-Piedmont & Lower Montane Grassland Group (G490)$$ and ~Chihuahuan Semi-Desert Lowland Grassland Group (G489)$$ that occur adjacent and may be transitional.
Physiognomy and Structure: This macrogroup is characterized by a short, often discontinuous herbaceous layer dominated by short perennial grasses. Woody vegetation is typically sparse or absent.
Floristics: This macrogroup spans a wide range and thus there can be some differences in the relative dominance of some species from north to south and from east to west. It is primarily dominated by Bouteloua gracilis and Bouteloua dactyloides (= Buchloe dactyloides) throughout its range with various associated graminoid species depending on precipitation, soils and management. In the southern extent Prosopis glandulosa may form a sparse to moderately dense short-tree or shrub canopy in uplands over shortgrass understory. Ziziphus obtusifolia and Atriplex canescens can codominate in some stands, especially in heavily grazed areas (Scifres 1980, Shiflet 1994). Associated graminoids may include Achnatherum hymenoides, Aristida purpurea, Bouteloua curtipendula, Bouteloua hirsuta, Bouteloua dactyloides, Carex filifolia, Eragrostis intermedia, Hesperostipa comata, Koeleria macrantha (= Koeleria cristata), Muhlenbergia torreyi, Pascopyrum smithii (= Agropyron smithii), Pleuraphis jamesii, Sporobolus airoides, and Sporobolus cryptandrus. Although mid-height grass species may be present, especially on more mesic land positions and soils, they are secondary in importance to the sod-forming short grasses. Sandy soils have higher cover of Hesperostipa comata, Sporobolus cryptandrus, and Yucca glauca. Scattered shrub and dwarf-shrub species such as Artemisia filifolia, Artemisia frigida, Artemisia tridentata, Atriplex canescens, Dalea formosa, Eriogonum effusum, Lycium pallidum, Mimosa borealis, and Rhus trilobata may also be present. Gutierrezia sarothrae is often present to codominant, especially in disturbed areas. Cacti species such as Cylindropuntia imbricata (= Opuntia imbricata), Opuntia polyacantha, and Opuntia phaeacantha can be abundant on some sites (Sims et al. 1978). Codominant forbs include Astragalus mollissimus, Erysimum asperum, Engelmannia peristenia (= Engelmannia pinnatifida), Gaura coccinea, Melampodium leucanthum, Machaeranthera tanacetifolia, Psoralidium tenuiflorum, and Thelesperma megapotamicum (M. Schiebout pers. comm. 2014). High annual variation in amount and timing of precipitation impacts relative cover of herbaceous species with cover of cool-season grasses more abundant when winter and early-spring precipitation is above average. Floristic information was compiled from Weaver and Albertson (1956), Sims et al. (1978), Brown et al. (1980, 1998), Barbour and Billings (1988), Milchunas et al. (1989), Lauenroth and Milchunas (1992), Dick-Peddie (1993), Ricketts et al. (1999), Sims and Risser (2000) Schiebout et al. (2008), and Lauenroth and Burke (2008).
Dynamics: Large-scale processes such as climate, fire and grazing constitute the primary processes impacting this macrogroup. The short grasses that dominate are extremely drought- and grazing-tolerant (Lauenroth and Milchunas 1992, Lauenroth et al. 1994a). These species evolved with large herbivores and drought (Milchunas and Lauenroth 2008) and adapted to historical heavy grazing with their low stature making them relatively resistant to overgrazing (Lauenroth et al. 1994a). The return intervals for grazing varied, with areas distant from water sources likely grazed less heavily as those near water. However, the shortgrass steppe probably has the highest intensity of grazing, historically (Lauenroth et al. 1994a, Milchunas 2006). This macrogroup is drought-tolerant, however, extended drought (over 3-4 years) will reduce cover (Landfire 2007a). Many shortgrass species are drought-tolerant and have root systems that extend up near the soil surface where they can utilize low precipitation events (Salas and Lauenroth 1982). If blue grama is eliminated from an area by extended drought (3-4 years) or disturbance such as plowing, regeneration is slow because of very slow tillering rates (Samuel 1985), low and variable seed production (Coffin and Lauenroth 1992), minimal seed storage in soil (Coffin and Lauenroth 1989), and limited seedling germination and establishment due to particular temperature and extended soil moisture requirements for successful seedling establishment (Hyder et al. 1971, Briske and Wilson 1978, 1980). Patterns and scales of heterogeneity related to historic natural grazing and fire regimes within the macrogroup are not well understood, but are assumed to be important to biodiversity (Fuhlendorf et al. 2006).

In contrast to other prairie macrogroups, fire is less frequent, especially in the western extent where the often dry and xeric climate conditions decrease the fuel load and thus the relative fire frequency. However, historically, fires that did occur were often very extensive. Wright and Bailey (1982c) suggest that in semi-arid areas, big prairie fires usually occurred during drought years that followed one to three years of above-average precipitation, because of the abundant and continuous fuel. Consequently, these wildfires could travel far when the winds and air temperatures were high and relative humidity was low. There is debate as to the mean fire-return interval (MFRI) for this shortgrass macrogroup. However, there is no way to reconstruct a reliable historic fire-return interval because of the lack of long-lived trees, and trees that do exist are in relatively productive sites. All estimates of historic fire-return intervals must be based on those for surrounding vegetation types that do have means for reconstruction, and then extrapolated based on differences in primary production and herbivore removal of fuel loads. Therefore, there is no means to directly obtain the estimate, and the range is varied. It depends on many factors: portions will be drier, and portions will vary in frequency over time and there will be decadal variation. Anderson (2003) reports a broad mean fire-return interval (MFRI) of <35 years for shortgrass prairie. There is a wide variability of MFRI across this macrogroup, based on precipitation, fuel and ignition sources (Landfire 2007a). Because of the increasing precipitation gradient west to east in the shortgrass prairie, the shorter historic MFRI estimates (~5 years) are expected in the less xeric eastern extent.

Currently, fire suppression and more extensive grazing in the region have likely decreased the fire frequency even more, and it is unlikely that these processes could occur at a natural scale. A large part of the range for this macrogroup (especially in the east and near rivers) has been converted to agriculture. Areas of the central and western range have been impacted by the unsuccessful attempts to develop dryland cultivation during the Dust Bowl of the 1930s.
Environmental Description: This macrogroup forms the matrix grassland in the western half of the Western Great Plains Division and largely occurs in the rainshadow of the Rocky Mountains. Stands are located on primarily flat to rolling uplands. Soils typically are loamy and ustic and range from sandy to clayey (Scifres 1980, Shiflet 1994). This macrogroup is the driest of the Great Plains grasslands. In the southeastern-most expression of the grassland in Texas, it occurs on sites with soils providing relatively dry conditions such as Rough Breaks, Shallow Clay, Very Shallow, and Very Shallow Clay Ecological Sites (Elliott 2011).

Climate: The climate is temperate, semi-arid, and continental with mean annual precipitation generally about 300 mm, ranging up to 500 mm in the east. Annual precipitation has a bimodal distribution occurring mostly before the growing in winter and early spring and then during summer as monsoon thunderstorms (Sims et al. 1978). Summer precipitation events are mostly <10 cm with occasional larger events (Sala and Lauenroth 1982). High variation in amount and timing of annual precipitation impacts the relative cover of cool- and warm-season herbaceous species. Average daily temperature in July varies from 27°C in the southeast to 21°C in the northwest and along the foothills of the Rocky Mountains. Average daily temperature in January varies from 3°C in the south to -6°C in the northwest.

Historically, fires were often very expansive, especially after a series of years with above-average precipitation when litter/fine fuels can build up. Currently, fire suppression and more extensive grazing in the region have likely decreased the fire frequency even more, and it is unlikely that these processes could occur at a natural scale. A large part of the range for this macrogroup (especially in the east and near rivers) has been converted to agriculture. Areas of the central and western range have been impacted by the unsuccessful attempts to develop dryland cultivation during the Dust Bowl of the 1930s.
Geographic Range: This macrogroup forms the matrix grassland in the western half of the Western Great Plains Division east of the Rocky Mountains and ranges from the Nebraska panhandle and southeastern Wyoming south into the panhandles of Oklahoma and Texas and eastern New Mexico, although some smaller patch examples may reach as far north as southern Canada.
Nations: CA, MX?, US
States/Provinces: CO, KS, NE, NM, OK, TX, WY
US Forest Service Ecoregions (2007)
Domain Name:
Division Name:
Province Name: Southwest Plateau and Plains Dry Steppe and Shrub Province
Province Code: 315    Occurrence Status: Confident or certain
Section Name: Western Great Plains Section
Section Code: 331F     Occurrence Status: Confident or certain
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: High
Confidence Level Comments:
Grank: GNR
Greasons:
Name:Database Code:Classification Code:
Class 2 Shrub & Herb Vegetation C02 2
Subclass 2.B Temperate & Boreal Grassland & Shrubland S18 2.B
Formation 2.B.2 Temperate Grassland & Shrubland F012 2.B.2
Division 2.B.2.Nb Central North American Grassland & Shrubland D023 2.B.2.Nb
Macrogroup M053 Western Great Plains Shortgrass Prairie M053 2.B.2.Nb.3
Group G144 Great Plains Shortgrass Prairie G144 2.B.2.Nb.3.a
Concept Lineage:
Predecessors:
Obsolete Names:
Bouteloua gracilis - Buchloe dactyloides Great Plains Shortgrass Prairie Macrogroup
Bouteloua gracilis - Buchloe dactyloides Shortgrass Prairie Macrogroup
Great Plains Shortgrass Prairie
Obsolete Parents:
Synonomy: = Bouteloua-Buchloë (Küchler 1964) [This potential natural vegetation type is approximately equivalent to the NVC macrogroup existing vegetation.]
> Black Grama - Alkali Sacaton (702) (Shiflet 1994)
> Black Grama - Sideoats Grama (703) (Shiflet 1994)
> Blue Grama - Buffalograss (611) (Shiflet 1994)
> Blue Grama - Galleta (705) (Shiflet 1994)
> Blue Grama - Sideoats Grama (706) (Shiflet 1994)
> Blue Grama - Sideoats Grama - Black Grama (707) (Shiflet 1994)
> Blue Grama - Western Wheatgrass (704) (Shiflet 1994)
> Buffalo-grass Series - 142.13 (Brown et al. 1980)
> Galleta -Alkali Sacaton (712) (Shiflet 1994)
= Grama "Shortgrass" Series - 142.12 (Brown et al. 1998)
> Grama "Shortgrass" Series - 142.12 (Brown et al. 1980)
= Grama - Buffalo Grass Section (3113) (Bailey 1980)
> Grama - Buffalograss (715) (Shiflet 1994)
> Grama - Feathergrass (716) (Shiflet 1994)
>< Grama - Needlegrass - Wheatgrass Section (3111) (Bailey 1980) [Includes western portion of this section.]
< Great Plains-Shortgrass Prairie Province (3110) (Bailey 1980) [Does not include Wheatgrass - Needlegrass Section (3112).]
>< Mixed "Shortgrass" Series - 142.13 (Brown et al. 1998)
> Mixed "Shortgrass" Series - 142.14 (Brown et al. 1980)
< Mixed Prairie (Weaver and Albertson 1956)
< Northern Mixed Prairie (Singh et al. 1983)
> Plains and Mesas Grasslands (Dick-Peddie 1993)
= Shortgrass Prairie (Sims et al. 1978)
> Shortgrass Steppe (Singh et al. 1983)
> Shrub-Grass Disclimax Series - 142.15 (Brown et al. 1980)
< Southern Mixed Prairie (Singh et al. 1983)
>< Vine Mesquite - Alkali Sacaton (725) (Shiflet 1994)
>< Wheatgrass - Saltgrass - Grama (615) (Shiflet 1994)
Concept Author(s): P.L. Sims, J.S. Singh, and W.K. Lauenroth (1978)
Author of Description: K.A. Schulz and B. Hoagland
Acknowledgements:
Version Date: 10Nov2015
References:
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