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A3186 Sporobolus airoides - Sporobolus wrightii - Panicum obtusum Lowland Desert Grassland Alliance
Type Concept Sentence: This lowland grassland alliance is characterized by a moderately dense to dense graminoid layer of perennial grasses dominated by Sporobolus wrightii, Sporobolus airoides, or Panicum obtusum. It is found in the northern Chihuahuan Desert and adjacent Sky Islands and Sonoran Desert, extending into the southern Great Plains. Stands occur along drainages and relatively small depressions or swales that receive runoff from adjacent areas.
Common (Translated Scientific) Name: Alkali Sacaton - Big Sacaton - Vine-mesquite Lowland Desert Grassland Alliance
Colloquial Name: Alkali Sacaton - Big Sacaton - Vine-mesquite Lowland Desert Grassland
Hierarchy Level: Alliance
Type Concept: This lowland grassland alliance is characterized by a moderately dense to dense graminoid layer of perennial grasses dominated by Sporobolus wrightii, Sporobolus airoides, or Panicum obtusum. Scattered shrub or succulent species may be present, especially on degraded sites and along drainages and in depressions. Other mesic graminoids such as Panicum hallii, Pascopyrum smithii, or Schizachyrium scoparium may be present to codominant. This alliance is found in the northern Chihuahuan Desert and adjacent Sky Islands and Sonoran Desert, extending into the southern 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 Sporobolus wrightii, Sporobolus airoides, or Panicum obtusum.
Rationale for Nominal Species or Physiognomic Features: No Data Available
Classification Comments: Old V.A.5.N.c. Panicum obtusum Herbaceous Alliance (A.1238) is floristically and ecologically similar to this alliance and its associations were included in this alliance (A3186). Both Panicum obtusum and Sporobolus airoides have wide distributions that extend well into the southern Great Plains. Muldavin et al. (1998c) described and classified Sporobolus airoides and Sporobolus wrightii grasslands together in the Sporobolus airoides and Sporobolus wrightii Series because both species occur sympatrically or in similar habitats in the Tularosa Basin. There is evidence of Sporobolus individuals hybridizing by the production of plants with intermediate characteristics of both species. Others have found that lowland Sporobolus airoides stands typically occurs on more saline/alkaline substrates than Sporobolus wrightii. Further review may suggest separating this alliance into two new alliances. More research needs to be done to resolve this.
Sporobolus airoides-dominated or -codominated grasslands are widespread outside the Chihuahuan Desert occurring in the interior western U.S. and Great Plains on a variety of substrates. Rangewide classification data analysis and review are needed to clarify distribution ranges and concepts of these other alliances. In past, NatureServe was conservative in creating new USNVC associations, which were largely based on dominant species. This is a problem when dominant/diagnostic species are nearly ubiquitous with a wide ecological amplitudes and distributions. We need to look at complete floristics of plots, which may have high fidelity, ecoregional and edaphic diagnostic species. See Similar NVC Types.
Sporobolus airoides-dominated or -codominated grasslands are widespread outside the Chihuahuan Desert occurring in the interior western U.S. and Great Plains on a variety of substrates. Rangewide classification data analysis and review are needed to clarify distribution ranges and concepts of these other alliances. In past, NatureServe was conservative in creating new USNVC associations, which were largely based on dominant species. This is a problem when dominant/diagnostic species are nearly ubiquitous with a wide ecological amplitudes and distributions. We need to look at complete floristics of plots, which may have high fidelity, ecoregional and edaphic diagnostic species. See Similar NVC Types.
Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Vegetation in this alliance has a moderately dense graminoid layer dominated by tall bunchgrasses. A sparse layer of medium-tall grasses may be also be present. Woody species are uncommon in stands of this alliance.
Floristics: This lowland grassland alliance is characterized by a moderately dense to dense graminoid layer of perennial grasses dominated by Sporobolus wrightii, Sporobolus airoides, or Panicum obtusum. Scattered shrub or succulent species may be present, especially on degraded sites and along drainages and in depressions. Other mesic graminoids such as Panicum hallii, Pascopyrum smithii, or Schizachyrium scoparium may be present to codominant. In more upland drier site species such as Bouteloua gracilis, Digitaria californica, Muhlenbergia porteri, Muhlenbergia richardsonis, Pleuraphis jamesii, and Scleropogon brevifolius may be prominent. Common forbs include Amaranthus palmeri, Datura quercifolia, Mentzelia pumila, Portulaca pilosa, Solanum elaeagnifolium, and Sphaeralcea hastulata. Scattered shrubs may be present with low cover such as Artemisia dracunculus, Atriplex spp., Chilopsis linearis, Ephedra spp., Ericameria nauseosa, Gutierrezia sarothrae, Mimosa aculeaticarpa var. biuncifera, or Prosopis spp. Near riparian woodlands, scattered trees such as Celtis laevigata var. reticulata (= Celtis reticulata), Fraxinus pennsylvanica, Juglans spp., and Populus fremontii may occasionally be present. Bourgeron et al. (1993b) described several stands of this alliance and recorded the canopy cover of graminoids to range from 30-70%. No other information is available about vegetation in this alliance.
Dynamics: Enhanced soil moisture from the slope position and the high water-holding capacity of the fine-textured soil promote abundant grass growth. The high grass cover further enhances soil moisture by reducing evaporation from the soil and increasing water infiltration. These conditions promote well-developed soils (Muldavin et al. 1998c). These once extensive grasslands of the Chihuahuan Desert have experienced significant declines throughout their range. Livestock grazing and manipulations by land managers have resulted in fragmentation of habitat and loss of biodiversity within stands.
Environmental Description: This lowland grassland alliance occurs in the northern Chihuahuan Desert and adjacent Sky Islands and Sonoran Desert, extending into the southern Great Plains. Climate is semi-arid with most of the 20-43 cm of annual precipitation falling during the late-summer and early-fall monsoon period. Precipitation may concentrate in these lowland sites from upland runoff during the typically high-intensity convection storms common during the monsoon season. Stands occur on alluvial flats, loamy plains, and basins, sometimes extending up into lower piedmont slopes and on broad mesas. Elevation ranges from 1185-2730 m. Stromberg (1993c) reported these grasslands occur on a variety of sites, from riverbanks, sandy washes and floodplains to upland areas "where microtopography or edaphic conditions allowed for accumulation of water." They may also be found in lower salinity sites within depressional wetlands such as bolsons and playas. Included in this alliance are mesic grasslands that occur in relatively small depressions or swales and along drainages that receive runoff from adjacent areas. Stands of this vegetation also occur at the base of many clay dunes (lomas) in the lower Rio Grande valley of Texas and extend as far west as Arivaca Cienega, Buenos Aires National Wildlife Refuge, Arizona, where they may also form a continuous cover on low-elevation lomas. Stands occur in a playa in the Tularosa Basin (Muldavin et al. 1992). Occupying low topographic positions, these sites generally have deep, fine-textured soils that are neutral to slightly or moderately saline/alkaline. These soils are derived from clay alluvium and range in texture from silty clay loams to clays. They are derived from alluvium and have a high moisture-holding capacity. The sandy wash sites presumably have coarser substrates. These grasslands often occur on sites that have a high water table or are subject to periodic flooding. The wetland/upland boundary and the hydrology are unclear.
Geographic Range: This grassland alliance occurs in the Chihuahuan Desert ranging from the Trans-Pecos in western Texas, southern New Mexico and southeastern Arizona south to central Chihuahua and Coahuila, Mexico. Stands also extends north and east into the southwestern Great Plains.
Nations: MX,US
States/Provinces: AZ, CO, MXCHH, MXCOA, MXSON?, MXTAM, NM, TX
Plot Analysis Summary:
http://vegbank.org/natureserve/ELEMENT_GLOBAL.2.899311
Confidence Level: Low
Confidence Level Comments: No Data Available
Grank: GNR
Greasons: No Data Available
Concept Lineage: Old Alliances included in new alliance V.A.5.N.c. Panicum obtusum Herbaceous Alliance (A.1238), V.A.5.N.c. Sporobolus airoides Sod Herbaceous Alliance (A.1241), V.A.5.N.d. Sporobolus airoides Herbaceous Alliance (A.1267), V.A.5.N.b. Sporobolus wrightii Herbaceous Alliance (A.1205), V.A.5.N.m. Sporobolus wrightii Saturated Herbaceous Alliance (A.1435)
Predecessors: No Data Available
Obsolete Names: No Data Available
Obsolete Parents: No Data Available
Synonomy: < Bouteloua gracilis Super Alliance (Muldavin et al. 2000b)
> Sporobolus airoides Herbaceous Alliance (Muldavin et al. 2000b)
>< Sporobolus airoides and S. wrightii Series (Muldavin et al. 1998c)
< Sacaton Series (Dick-Peddie 1993)
= Sacaton Series (142.24) (Brown 1982a) [within Great Basin Shrub-Grassland.]
> Sporobolus airoides Herbaceous Alliance (Muldavin et al. 2000b)
>< Sporobolus airoides and S. wrightii Series (Muldavin et al. 1998c)
< Sacaton Series (Dick-Peddie 1993)
= Sacaton Series (142.24) (Brown 1982a) [within Great Basin Shrub-Grassland.]
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