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A3163 Prosopis velutina Ruderal Desert Scrub Alliance

Type Concept Sentence: This widespread ruderal alliance occurs as invasive upland shrublands found in former semi-desert grasslands in the foothills and piedmonts in the Sky Island region of southern Arizona and adjacent Mexico, and north into the lower Mogollon Rim foothills. The open to dense, tall (2-5 m) to short (<2 m) shrub layer is dominated by Prosopis velutina with typically low cover of desert grasses.

Common (Translated Scientific) Name: Velvet Mesquite Ruderal Desert Scrub Alliance

Colloquial Name: Ruderal Velvet Mesquite Desert Scrub

Hierarchy Level:  Alliance

Type Concept: This ruderal alliance occurs as the common invasive upland shrublands found in former semi-desert grasslands in the foothills and piedmonts in the Sky Island region of southern Arizona and adjacent Mexico, and north into the lower Mogollon Rim foothills. The open to dense, tall (2-5 m) to short (<2 m) shrub layer dominated by Prosopis velutina. Associated species that may codominate or form a short-shrub layer include Acacia greggii, Atriplex canescens, Calliandra eriophylla, Fouquieria splendens, and Mimosa dysocarpa. Grass cover is generally low and composed of desert grasses such as Dasyochloa pulchella, Muhlenbergia porteri, and Pleuraphis mutica. Scattered juniper trees may be present. Larrea tridentata is absent or has low cover. Substrates are typically derived from alluvium. During the last century, the area occupied by this vegetation has increased through conversion of desert grasslands as a result of drought, overgrazing by livestock, and/or decreases in fire frequency.

Diagnostic Characteristics: Shrub layer is dominated by Prosopis velutina and occurs on upland sites with alluvial or colluvial substrates, not eolian sand deposits or alkaline/saline bottomland sites.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: This alliance is considered to be a native ruderal invasive alliance that historically did not occur naturally. Whether or not upland mesquite shrublands ever occurred naturally or not, they have unnaturally greatly expanded their range and now dominate vast areas of former semi-desert grassland in foothills and piedmonts of the Chihuahuan Desert, extending west into the Sky Island region southern Arizona and adjacent Mexico, and north into the lower Mogollon Rim foothills. Upland Prosopis glandulosa-dominated scrub has similarly expanded its range and occurs further west. In addition, because Prosopis velutina can have both shrub and tree growth forms, there may be confusion classifying a given stand. In general, desert upland stands are considered shrublands. Prosopis velutina-dominated stands are considered natural along drainages and in lowland areas.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Vegetation included in this alliance has a moderate to dense layer of xeromorphic deciduous shrubs that is less than 5 m tall. The herbaceous layer may be sparse to moderately dense and is dominated by graminoids, with annual forbs present seasonally. Succulents may also be present.

Floristics: This alliance occurs as the common invasive upland shrublands that are characterized by an open to dense, tall (2-5 m) to short (<2 m) shrub layer dominated by Prosopis velutina. Associated species that may codominate or form a short-shrub layer include Acacia constricta, Acacia greggii, Atriplex canescens, Calliandra eriophylla, Ericameria laricifolia, Fouquieria splendens, Gutierrezia sarothrae, Isocoma tenuisecta, Lycium spp., Mimosa aculeaticarpa var. biuncifera, Mimosa dysocarpa, and Cylindropuntia versicolor (= Opuntia versicolor). The herbaceous layer is sparse to moderately dense (<10-50% cover). Grass cover is generally low and composed of desert grasses such as Dasyochloa pulchella (= Erioneuron pulchellum), Muhlenbergia porteri, and Pleuraphis mutica. Common herbaceous species include Abutilon incanum, Aristida ternipes, Bouteloua chondrosioides, Bouteloua curtipendula, Bouteloua repens, Bouteloua rothrockii, Croton pottsii, Digitaria californica, Gutierrezia microcephala, Kallstroemia grandiflora, Portulaca oleracea (= Portulaca retusa), and Phemeranthus aurantiacus (= Talinum aurantiacum). Forbs often have high species richness but with typically relatively low cover. Exotic perennial grass Eragrostis lehmanniana may be present to dominant. Scattered juniper trees may be present. Larrea tridentata is absent or has low cover.

Dynamics:  Shrublands dominated by Prosopis spp. have replaced large areas of desert grasslands, especially those formerly dominated by Bouteloua eriopoda in Trans-Pecos Texas, southern New Mexico and southeastern Arizona (York and Dick-Peddie 1969, Hennessy et al. 1983). Studies of related species Prosopis glandulosa on the Jornada Experimental Range suggest that combinations of drought, overgrazing by livestock, wind and water erosion, seed dispersal by livestock, fire suppression, shifting dunes and changes in the seasonal distribution of precipitation have caused this recent, dramatic shift in vegetation physiognomy (Buffington and Herbel 1965, Herbel et al. 1972, Humphrey 1974, McLaughlin and Bowers 1982, Gibbens et al. 1983, Hennessy et al. 1983, Schlesinger et al. 1990, McPherson 1995).

Prosopis and other shrubs have extensive root systems that allow them to exploit deep soil water that is unavailable to shallower rooted grasses and cacti (Burgess 1995). This strategy works well except on sites that have well-developed argillic or calcic soil horizons that limit infiltration and storage of winter moisture in the deeper soil layers (McAuliffe 1995). McAuliffe found Prosopis velutina invasion on these sites limited to a few, small individuals. This has implications in plant geography and grassland revegetation work in the southwestern U.S.
Environmental Description:  This ruderal alliance occurs as the common invasive upland shrublands found in former semi-desert grasslands in the foothills and piedmonts in the Sky Island region of southern Arizona and adjacent Mexico, and north into the lower Mogollon Rim foothills. As described from the foothills of Buenos Aires National Wildlife Refuge in southern Arizona, stands are found on valley floors, swales and ridges at an elevational range of 915-1170 m. Sites are flat to moderately steep slopes on foothills, alluvial fans and outwash plains of all aspects. Substrates are typically well-drained sandy loam but include silt loam and clayey soils. Bare ground or small rocks frequently dominate the ground cover. During the last century, the area occupied by this vegetation has increased through conversion of desert grasslands as a result of drought, overgrazing by livestock, and/or decreases in fire frequency.
Geographic Range: This upland ruderal thornscrub alliance is found on foothills and piedmonts in the Sky Island region of southern Arizona and adjacent Mexico extending north into the lower Mogollon Rim foothills. Stands may occur in extreme southwestern New Mexico.

Nations: MX,US

States/Provinces:  AZ, CA, MXSON, NM


Confidence Level: Low

Confidence Level Comments: No Data Available
Grank: GNA

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.90 Honey Mesquite / Red Brome - Lehmann''s Lovegrass Desert Ruderal Scrub & Grassland Macrogroup M512 3.A.2.Na.90
Group 3.A.2.Na.90.b Honey Mesquite - Velvet Mesquite Warm Desert Ruderal Scrub Group G819 3.A.2.Na.90.b
Alliance A3163 Velvet Mesquite Ruderal Desert Scrub Alliance A3163 3.A.2.Na.90.b
Association CEGL001388 Velvet Mesquite - Catclaw Acacia Ruderal Shrubland CEGL001388 3.A.2.Na.90.b
Association CEGL001391 Velvet Mesquite / Bush Muhly Ruderal Shrubland CEGL001391 3.A.2.Na.90.b
Association CEGL005343 Velvet Mesquite / Lehmann''s Lovegrass Ruderal Shrubland CEGL005343 3.A.2.Na.90.b
Association CEGL005344 Velvet Mesquite / Fourwing Saltbush / Mixed Grasses Ruderal Shrubland CEGL005344 3.A.2.Na.90.b
Association CEGL005345 Velvet Mesquite / Fairy Duster Ruderal Shrubland CEGL005345 3.A.2.Na.90.b
Association CEGL005346 Velvet Mesquite / Velvetpod Mimosa Ruderal Shrubland CEGL005346 3.A.2.Na.90.b
Association CEGL005347 Velvet Mesquite Ruderal Foothill Shrubland CEGL005347 3.A.2.Na.90.b
Association CEGL005348 Velvet Mesquite / Mixed Grasses Ruderal Shrubland CEGL005348 3.A.2.Na.90.b
Concept Lineage: Old Alliance III.A.5.N.a. Fouquieria splendens Shrubland Alliance (A.863), in part, one association. Old Alliance III.B.3.N.a. Prosopis velutina Shrubland Alliance (A.1043), in part, eight associations

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: >< Mesquite Series (Sawyer and Keeler-Wolf 1995)
Concept Author(s): K.A. Schulz, in Faber-Langendoen et al. (2013)

Author of Description: K.A. Schulz

Acknowledgements: No Data Available

Version Date: 12-21-15
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