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A3185 Pleuraphis mutica Lowland Desert Grassland Alliance

Type Concept Sentence: This lowland grassland alliance is characterized by a moderately dense to dense graminoid layer of perennial grasses that is typically dominated by Pleuraphis mutica. It occurs in the northern Chihuahuan Desert and adjacent Sky Islands and Sonoran Desert, extending into limited areas of the southwestern Great Plains, on alluvial flats, loamy plains, and basins sometimes extending up into lower piedmont slopes and on broad mesas.

Common (Translated Scientific) Name: Tobosa Grass Lowland Desert Grassland Alliance

Colloquial Name: Tobosa Grass Lowland Desert Grassland

Hierarchy Level:  Alliance

Type Concept: Vegetation is characterized by a moderately dense to dense graminoid layer of perennial grasses that is typically dominated by Pleuraphis mutica. Dense stands of Pleuraphis mutica can occur in mesic swales and depressions and along drainages (tobosa swales), sometimes with other mesic graminoids such as Panicum obtusum, Pascopyrum smithii, or Schizachyrium scoparium var. scoparium. Sporobolus airoides may be present in alkaline soils, but does not codominate. In degraded stands, Scleropogon brevifolius or Aristida spp. may codominate. Bouteloua gracilis may become important in northern stands transitioning into the Great Plains and on degraded desert stands. Scattered shrub or succulent species may be present, especially on degraded sites and along drainages and in depressions. This lowland grassland alliance occurs in the northern Chihuahuan Desert and adjacent Sky Islands and Sonoran Desert, extending into limited areas of the southwestern Great Plains. Stands occur on alluvial flats, loamy plains, and basins sometimes extending up into lower piedmont slopes and on broad mesas. Included in this alliance are mesic grasslands that occur in relatively small depressions or swales and along drainages that receive runoff from adjacent areas. Occupying low topographic positions, these sites generally have deep, fine-textured soils that are neutral to slightly or moderately saline/alkaline.

Diagnostic Characteristics: This grassland alliance occurs in relatively mesic lowland topographic positions and is characterized by the dominance of Pleuraphis mutica either alone or with Bouteloua gracilis, Bouteloua dactyloides, Panicum obtusum, or Scleropogon brevifolius present to codominant.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: Old Alliance V.A.5.N.c. Panicum obtusum Herbaceous Alliance (A.1238) is also floristically and ecologically similar to this alliance, but its associations were included in ~Sporobolus airoides - Sporobolus wrightii - Panicum obtusum Lowland Desert Grassland Alliance (A3186)$$. Both Panicum obtusum and Sporobolus airoides have wider distributions that extend well into the southern Great Plains and often co-occur. Many of these stands described by Bourgeron et al. (1993b) have low cover. More study is needed to determine if they are sparsely vegetated.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Vegetation included in this alliance has a sparse to moderately dense graminoid layer dominated by medium-tall, perennial bunchgrasses. The forb layer is typically sparse. Scattered cacti or shrubs may be present. Annual grasses and forbs are seasonally present to abundant.

Floristics: Vegetation is characterized by a moderately dense to dense graminoid layer of perennial grasses that is typically dominated by Pleuraphis mutica. Dense stands of Pleuraphis mutica can occur in mesic swales and depressions and along drainages (tobosa swales), sometimes with other mesic graminoids such as Panicum obtusum, Pascopyrum smithii, or Schizachyrium scoparium. Sporobolus airoides may be present in alkaline soils, but does not codominate. In degraded stands, Scleropogon brevifolius or Aristida spp. may codominate. Bouteloua gracilis or Bouteloua dactyloides (= Buchloe dactyloides) may become important in northern stands transitioning into the Great Plains and on degraded desert stands. Other grasses present may include Bothriochloa barbinodis, Chloris virgata, Dasyochloa pulchella (= Erioneuron pulchellum), Digitaria californica, Enneapogon desvauxii, Eragrostis intermedia, Eriochloa lemmonii, and Panicum hirticaule. The usually sparse perennial forbs may include Amaranthus palmeri, Chamaesyce albomarginata, Datura quercifolia, Hoffmannseggia glauca, Solanum elaeagnifolium, Solanum rostratum, and Phemeranthus aurantiacus (= Talinum aurantiacum). Scattered shrub or succulent species may be present, especially on degraded sites and along drainages and in depressions such as Flourensia cernua, Larrea tridentata, Nolina microcarpa, Cylindropuntia imbricata (= Opuntia imbricata), Opuntia phaeacantha, and Prosopis glandulosa, but generally have less than 10% cover.

Dynamics:  Impermeable caliche and argillic horizons are not uncommon on these sites. These layers restrict deep percolation of soil-water and may favor the shallower rooted grasses over more deeply rooted shrubs such as Larrea tridentata and Prosopis spp. (McAuliffe 1995). Pleuraphis mutica is relatively tolerant of livestock grazing. In west-central Arizona, livestock have nearly eliminated all native grasses except Pleuraphis mutica from semi-desert grassland (Brown 1982a). Exotic plants invaded, especially exotic annual grasses, such as Bromus rubens, and now dominate the landscape. These Pleuraphis mutica grasslands are the result of livestock disturbance and exotic plant invasion and should not be classified as natural. Stands codominated by Scleropogon brevifolius are characteristic of sites with past heavy grazing by livestock (Whitfield and Anderson 1938).
Environmental Description:  This lowland grassland alliance occurs in the northern Chihuahuan Desert and adjacent Sky Islands and Sonoran Desert, extending into limited areas of the southwestern Great Plains. Climate is arid to semi-arid with hot summers. Freezing temperatures may occur during winter. Mean annual precipitation is approximately 22 cm at the Jornada Experimental Range, but is highly variable annually with drought not uncommon. Annual precipitation is distributed bimodally with about a third of precipitation occurring in late winter and two-thirds in July through October often as high-intensity convective storms. The most arid season is late spring and early summer. Sites are generally flat to gently sloping alluvial flats and plains with more densely vegetated stands occurring in depression in basin and plains (playas), and in the floodplains along the drainages that dissect the mesas and piedmonts. These sites often receive excess runoff from the surrounding landscape and some may be intermittently flooded. The flooding is typically caused by locally occurring, summer thunderstorms. Elevations range from 1300-1650 m. Soils are shallow to deep, silt or clay loams, or clays, alkaline, often calcareous and sometimes with caliche or argillic horizons. These soils are non-saline to slightly saline and derived from gravelly or silty alluvium. Ground cover is variable. Johnson (1961c) and Bourgeron et al. (1993b) describe stands where mean cover of bare soil, gravel, and litter ranged from 10-70%, 0-15% and 20-85%, respectively. The high grass and litter cover help maintain the habitat by promoting water infiltration and reducing evaporation (Muldavin et al. 1998c). On moderately steep slopes soils may be very stony with higher cover of rock and lower cover of litter. Soils are derived from gravelly or silty alluvium, or basalt.
Geographic Range: This lowland grassland alliance is found from the northern to central Chihuahuan Desert from the Trans-Pecos in western Texas, southern New Mexico and southeastern Arizona south to central Chihuahua and Coahuila, Mexico. Stands also occur in the transition zone with the southwestern Great Plains.

Nations: MX,US

States/Provinces:  AZ, MXCHH?, MXCOA?, MXSON?, NM, TX


Confidence Level: Low

Confidence Level Comments: No Data Available
Grank: GNR

Greasons: No Data Available
Type Name Database Code Classification Code
Class 3 Desert & Semi-Desert Class C03 3
Subclass 3.A Warm Desert & Semi-Desert Woodland, Scrub & Grassland Subclass S06 3.A
Formation 3.A.2 Warm Desert & Semi-Desert Scrub & Grassland Formation F015 3.A.2
Division 3.A.2.Na North American Warm Desert Scrub & Grassland Division D039 3.A.2.Na
Macrogroup 3.A.2.Na.3 Black Grama - Bullgrass - Tobosa Grass Chihuahuan Semi-Desert Grassland Macrogroup M087 3.A.2.Na.3
Group 3.A.2.Na.3.d Tobosa Grass - Alkali Sacaton - Vine-mesquite Semi-Desert Lowland Grassland Group G489 3.A.2.Na.3.d
Alliance A3185 Tobosa Grass Lowland Desert Grassland Alliance A3185 3.A.2.Na.3.d
Association CEGL001542 Creosotebush / Tobosa Grass Shrub Grassland CEGL001542 3.A.2.Na.3.d
Association CEGL001637 Tobosa Grass Monotype Grassland CEGL001637 3.A.2.Na.3.d
Association CEGL001638 Tobosa Grass - Blue Grama Grassland CEGL001638 3.A.2.Na.3.d
Association CEGL001639 Tobosa Grass - Vine-mesquite Grassland CEGL001639 3.A.2.Na.3.d
Association CEGL001640 Tobosa Grass - Burrograss Grassland CEGL001640 3.A.2.Na.3.d
Association CEGL002272 Tobosa Grass - Buffalograss Grassland CEGL002272 3.A.2.Na.3.d
Concept Lineage: Old Alliances included in the new alliance: Old Alliance: V.A.5.N.d. Pleuraphis mutica Herbaceous Alliance (A.1249) and Old Alliance: V.A.5.N.i. Pleuraphis mutica Intermittently Flooded Herbaceous Alliance (A.1330).

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: = Hilaria mutica Association (143.121) (Brown 1982a) [within Tobosa Grass-Scrub Series]
= Hilaria mutica Herbaceous Alliance (Muldavin et al. 2000b)
? Hilaria mutica Series (Muldavin et al. 1998c)
= Tobosa Series (Diamond 1993)
= Tobosa Series (Swales) (Dick-Peddie 1993) [included within the Plains-Mesa Grassland]
Concept Author(s): D.E. Brown (1982a)

Author of Description: K.A. Schulz

Acknowledgements: No Data Available

Version Date: 12-18-14
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