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A3165 Flourensia cernua Upland Desert Scrub Alliance

Type Concept Sentence: This upland desert scrub has a Flourensia cernua-dominated shrub layer and occurs on broad desert gravelly plains extending up onto dissected gravelly alluvial fans and piedmonts (bajadas), and foothills in the Chihuahuan Desert. Substrates are typically coarse-textured loams on gravelly plains and slopes. Flourensia cernua-dominated stands on fine-textured (silty and clayey) soils are not included in this alliance.

Common (Translated Scientific) Name: American Tarwort Upland Desert Scrub Alliance

Colloquial Name: American Tarwort Upland Desert Scrub

Hierarchy Level:  Alliance

Type Concept: This upland desert scrub alliance occurs on broad desert plains extending up onto dissected gravelly alluvial fans and piedmonts (bajadas), and foothills in the Chihuahuan Desert (below the chaparral zone). The vegetation is composed of an open to moderately dense, short-shrub layer (<1 m tall) with Flourensia cernua as the dominant component, often forming extensive shrublands. If present, Larrea tridentata and Prosopis glandulosa have relatively low cover and do not codominate the shrub layer. Grasses are common but generally have lower cover than shrubs. Common associates include Bouteloua curtipendula and Achnatherum eminens. Other species present with lower cover may include shrubs such as Acacia constricta, Acacia greggii, Dasylirion spp., Haploesthes greggii, Isocoma pluriflora, Krameria erecta, Larrea tridentata, Cylindropuntia imbricata, Parthenium incanum, and herbaceous species such as Bouteloua ramosa, Bouteloua breviseta, and Chamaesaracha sordida. Substrates are typically coarse-textured loams on gravelly plains and slopes. Flourensia cernua-dominated stands on fine-textured (silty and clayey) soils are not included in this alliance.

Diagnostic Characteristics: This alliance occurs in upland landforms such as alluvial fans and piedmonts and foothills with coarse-textured soils in the Chihuahuan Desert and is characterized by dominance of Flourensia cernua in the shrub layer. If present, Larrea tridentata and Prosopis glandulosa have relatively low cover and do not codominate the shrub layer. Differential species that are characteristic of upland habitats such as Dasylirion leiophyllum are often present. Also characteristic is the lack of lowland, saline indicator species Distichlis spicata and Sporobolus airoides.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: There are two tarbush-dominated alliances: ~Flourensia cernua Lowland Basin Desert Scrub Alliance (A3152)$$ and ~Flourensia cernua Upland Desert Scrub Alliance (A3165)$$ that are distinguished by habitat (lowland fine-textured, often saline soils and upland coarse-textured, non-saline soils) and characteristic understory species that reflect the different habitats.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Vegetation included in this alliance has sparse to moderately dense cover of broad-leaved and microphyllous, evergreen shrub less the 1 m tall. The sparse to moderately dense herbaceous layer is dominated by perennial graminoids. Annual grasses and forbs are present seasonally.

Floristics: This Chihuahuan Desert alliance has a sparse to moderately dense woody layer that is generally less than 1 m tall. It consists of evergreen broad-leaved and microphyllous xeromorphic shrubs and is dominated by Flourensia cernua. Common woody associates include Acacia constricta, Acacia greggii, Atriplex canescens, Cylindropuntia imbricata (= Opuntia imbricata), Haploesthes greggii, Isocoma pluriflora, Koeberlinia spinosa, Krameria erecta (= Krameria glandulosa), Krameria lanceolata, Larrea tridentata, and Prosopis glandulosa. On rocky upland sites Aloysia wrightii, Dalea formosa, Dasylirion wheeleri, Parthenium incanum, Opuntia engelmannii, and Yucca baccata may also be present. The sparse to moderately dense herbaceous layer is dominated by grasses such as Achnatherum eminens (= Stipa eminens), Bouteloua curtipendula, Bouteloua gracilis, and Muhlenbergia porteri. Common forbs may include Croton texensis, Dyssodia spp., Eriogonum wrightii, Machaeranthera pinnatifida, and Zinnia spp. Muldavin et al. (1994a) described a rocky upland stand with 11 species of shrubs. Cover values of Flourensia cernua, Aloysia wrightii, total shrubs, Bouteloua curtipendula, Bouteloua eriopoda, and total perennial grasses were 8%, 2%, 13%, 7%, 5% and 16%, respectively.

Dynamics:  Flourensia cernua has increased in this century (Muldavin et al. 1998c). Livestock grazing favors Flourensia cernua over grasses because the shrub is unpalatable to livestock and relatively shallow-rooted, and therefore competes strongly with grasses for soil moisture (Muldavin et al. 1998c). Severe droughts and overgrazing early in this century have likely contributed to these changes in the vegetation. Buffington and Herbel (1965) report that Larrea tridentata has displaced many stands of Flourensia cernua and cite that it may be because Larrea tridentata only competes with grasses during the shrub''s seedling stage. Muldavin et al. (1998c) state that stands with no graminoid layer are unlikely to develop one, but stands with a graminoid layer are likely to maintain it if not overgrazed. Impermeable caliche and argillic horizons are not uncommon on these sites. These layers restrict deep percolation of soil-water and may favor the shallower root grasses and shrubs such as Flourensia cernua over more deeply rooted shrubs like Larrea tridentata and Prosopis spp. (McAuliffe 1995).
Environmental Description:  Shrublands in this Chihuahuan Desert alliance occur on broad gravelly desert plains extending up upland sites on dissected gravelly alluvial fans and piedmonts (bajadas), foothills, and rarely, on steep mountains slopes. Elevations range from 1300-1650 m. Climate is semi-arid with hot summers. Mean annual precipitation is approximately 22 cm, but is highly variable with drought not uncommon. Annual precipitation is distributed bimodally with about one-third occurring in late winter and two-thirds in July through October often as high-intensity convective storms. Most stands occur on gently sloping sites on all aspects. Substrates are typically coarse-textured loams on gravelly plains and slopes. On steeper slopes, soils may be very stony. Ground cover is relatively low. Johnson (1961c) described stands where mean cover of bare soil, rock and litter was 61%, 20%, and 7%, respectively.
Geographic Range: This desert scrub alliance occurs in the Chihuahuan Desert and ranges from western Texas, across southern New Mexico and southeastern Arizona, south into Coahuila and Chihuahua, Mexico.

Nations: MX,US

States/Provinces:  AZ, MXCHH, MXCOA, 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.2 Creosotebush - American Tarwort - Mesquite species Chihuahuan Desert Scrub Macrogroup M086 3.A.2.Na.2
Group 3.A.2.Na.2.a Creosotebush - American Tarwort - Viscid Acacia Chihuahuan Mixed Desert Scrub Group G288 3.A.2.Na.2.a
Alliance A3165 American Tarwort Upland Desert Scrub Alliance A3165 3.A.2.Na.2.a
Association CEGL001336 American Tarwort / Sideoats Grama Shrubland CEGL001336 3.A.2.Na.2.a
Association CEGL001338 American Tarwort / Southwestern Needlegrass Shrubland CEGL001338 3.A.2.Na.2.a
Concept Lineage: Old Alliance III.A.5.N.a. Flourensia cernua Shrubland Alliance (A.861), in part, 2 upland associations

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: No Data Available
Concept Author(s): K.A. Schulz, in Faber-Langendoen et al. (2013)

Author of Description: K.A. Schulz

Acknowledgements: No Data Available

Version Date: 01-08-14
  • Brown, D. E., editor. 1982a. Biotic communities of the American Southwest-United States and Mexico. Desert Plants Special Issue 4(1-4):1-342.
  • Buffington, L. C., and C. H. Herbel. 1965. Vegetational changes on a semidesert grassland range from 1858 to 1963. Ecological Monographs 35(2):139-164.
  • Dick-Peddie, W. A. 1993. New Mexico vegetation: Past, present, and future. University of New Mexico Press, Albuquerque. 244 pp.
  • Donart, G. B., D. Sylvester, and W. Hickey. 1978a. A vegetation classification system for New Mexico, USA. Pages 488-490 in: Rangeland Congress, Denver, CO, 14-18 August 1978. Society for Range Management, Denver.
  • Faber-Langendoen, D., J. Drake, M. Hall, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, M. Russo, K. Schulz, L. Sneddon, K. Snow, and J. Teague. 2013-2019b. Screening alliances for induction into the U.S. National Vegetation Classification: Part 1 - Alliance concept review. NatureServe, Arlington, VA.
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  • Leopold, B. D., and P. R. Krausman. 1988. Plant associations of the lower desert shrubland in Big Bend National Park, Texas. Contributed paper second symposium on the Resources of the Chihuahuan Desert. Chihuahuan Desert Research Institute, Alpine, TX. 47 pp.
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  • McMahan, C. A., R. G. Frye, and K. L. Brown. 1984. The vegetation types of Texas including cropland. Texas Parks and Wildlife Department, Austin. 40 pp. plus map.
  • Muldavin, E., P. Mehlhop, and E. DeBruin. 1994a. A survey of sensitive species and vegetation communities in the Organ Mountains of Fort Bliss. Volume III: Vegetation communities. Report prepared for Fort Bliss, Texas, by New Mexico Natural Heritage Program, Albuquerque.
  • Muldavin, E., Y. Chauvin, and G. Harper. 2000b. The vegetation of White Sands Missile Range, New Mexico: Volume I. Handbook of vegetation communities. Final report to Environmental Directorate, White Sands Missile Range. New Mexico Natural Heritage Program, University of New Mexico, Albuquerque. 195 pp. plus appendices
  • Muldavin, E., and P. Mehlhop. 1992. A preliminary classification and test vegetation map for White Sands Missile Range and San Andreas National Wildlife Refuge, New Mexico. University of New Mexico, New Mexico Natural Heritage Program.
  • Muldavin, E., et al. 1998c. Plant community inventory for Fort Bliss. Unpublished report in preparation by the New Mexico Natural Heritage Program, Albuquerque, NM.
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