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A3277 Larrea tridentata - Ambrosia dumosa Bajada & Valley Desert Scrub Alliance

Type Concept Sentence: This widespread alliance is characterized by an open, xeromorphic shrub layer codominated by Larrea tridentata and Ambrosia dumosa. Cover of either species does not exceed the other by more than twice, and no other species greatly exceeds the cover of both combined. Stands occur in the Mojave, Sonoran and Colorado deserts on alluvial fans, bajadas, upland slopes and minor washes on well-drained, sandy soils derived from colluvium or alluvium.

Common (Translated Scientific) Name: Creosotebush - Burrobush Bajada & Valley Desert Scrub Alliance

Colloquial Name: Creosotebush - Burrobush Bajada & Valley Desert Scrub

Hierarchy Level:  Alliance

Type Concept: This widespread alliance occurs in the Mojave, Sonoran and Colorado deserts and extends north into the transition zone with the Great Basin. The vegetation is characterized by an open, xeromorphic shrub layer codominated by Larrea tridentata and Ambrosia dumosa. Cover of either species does not exceed the other by more than twice, and no other species greatly exceeds the cover of both combined. Other desert shrubs and dwarf-shrubs may be present to codominant, including Atriplex confertifolia, Atriplex hymenelytra, Ephedra funerea, Ephedra nevadensis, Hymenoclea salsola, Krameria grayi, Krameria erecta, Lycium andersonii, Cylindropuntia ramosissima, Psorothamnus arborescens, Psorothamnus fremontii, Salazaria mexicana, Senna armata, and many others. If Encelia farinosa or Yucca schidigera is present, cover is low (<1-2% cover). Occasional emergent Fouquieria splendens or Yucca brevifolia and herbaceous species such as Croton californicus, Eriogonum inflatum, Echinocactus polycephalus, Galium angustifolium, or Pleuraphis rigida may also be present. Abundant annuals may be seasonally present. Stands occur on alluvial fans, bajadas, upland slopes, piedmonts and minor washes. Sites are gentle to moderately sloping. Substrates are typically well-drained, sandy soils derived from colluvium or alluvium. A pebbly pavement may form on the soil surface. Substrates are rarely calcareous with a caliche hardpan because caliche tends to restrict rooting of the shallow-rooted Ambrosia dumosa. This vegetation is very common and dominates much of the desert landscape in the southwestern U.S.

Diagnostic Characteristics: This alliance is characterized by an open, xeromorphic shrub layer codominated by Larrea tridentata and Ambrosia dumosa with at least 2% total cover. Cover of either species does not exceed the other by more than twice, and no other species greatly exceeds the cover of both combined. If Encelia farinosa or Yucca schidigera is present, cover is low (<1-2% cover).

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: The alliance concept is based on classification work done by Thomas et al. (2004) on the Mojave Ecosystem Mapping Project, Keeler-Wolf (2007) and Sawyer et al. (2009). Many associations will be added following publication of the recent National Park Service work in the Mojave (Evens et al. 2014).

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Vegetation included in this alliance has a sparse woody layer dominated by facultative deciduous dwarf-shrubs often with microphyllous evergreen desert shrubs. Cacti and rosette succulents may be also present. The sparse herbaceous layer is dominated by a suffrutescent grass with a few perennial forbs. Annual grasses and forbs are present seasonally.

Floristics: The vegetation is characterized by an open, xeromorphic shrub layer codominated by Larrea tridentata and Ambrosia dumosa. Cover of either species does not exceed the other by more than twice, and no other species greatly exceeds the cover of both combined. Other desert shrubs and dwarf-shrubs may be present to codominant, including Atriplex confertifolia, Atriplex hymenelytra, Ephedra funerea, Ephedra nevadensis, Hymenoclea salsola, Krameria grayi, Krameria erecta, Lycium andersonii, Cylindropuntia ramosissima (= Opuntia ramosissima), Psorothamnus arborescens, Psorothamnus fremontii, Salazaria mexicana, Senna armata, and many others. If Encelia farinosa or Yucca schidigera is present, cover is low (<1-2% cover). Occasional emergent Fouquieria splendens or Yucca brevifolia and herbaceous species such as Croton californicus, Eriogonum inflatum, Echinocactus polycephalus, Galium angustifolium, or Pleuraphis rigida may also be present. Abundant annuals may be seasonally present (Thomas et al. 2004).

Dynamics:  Substrates are typically not calcareous with a caliche hardpan as the caliche tends to restrict rooting of the shallow-rooted Ambrosia dumosa.
Environmental Description:  This widespread alliance occurs in the Mojave, Sonoran and Colorado deserts and extends north into the transition zone with the Great Basin. Elevation ranges from -75 to 1200 m. Climate is arid to semi-arid, with hot summers. The amount of winter freezing depends on latitude and elevation. Mean annual precipitation ranges from 22 cm to less than 15 cm. Stands occur on alluvial fans, bajadas, upland slopes, piedmonts and minor washes. Sites are gentle to moderately sloping. Substrates are typically well-drained, sandy soils derived from colluvium or alluvium. A pebbly pavement may form on the soil surface. Substrates are rarely calcareous with a caliche hardpan because caliche tends to restrict rooting of the shallow-rooted Ambrosia dumosa (Thomas et al. 2004, Sawyer et al. 2009).
Geographic Range: This alliance is found in the Mojave, Sonoran and Colorado deserts and extends into the transition zone with the Great Basin in southern Nevada.

Nations: MX,US

States/Provinces:  AZ, CA, MXSON, NV


Confidence Level: Low

Confidence Level Comments: No Data Available
Grank: G5

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.4 Saguaro - Organ Pipe Cactus - Burrobush Mojave-Sonoran Semi-Desert Scrub Macrogroup M088 3.A.2.Na.4
Group 3.A.2.Na.4.b Creosotebush - Burrobush - Brittlebush Desert Scrub Group G295 3.A.2.Na.4.b
Alliance A3277 Creosotebush - Burrobush Bajada & Valley Desert Scrub Alliance A3277 3.A.2.Na.4.b
Association CEGL000956 Burrobush - Creosotebush Dwarf-shrubland CEGL000956 3.A.2.Na.4.b
Association CEGL001261 Creosotebush Monotype Shrubland CEGL001261 3.A.2.Na.4.b
Association CEGL002954 Creosotebush - Burrobush Shrubland CEGL002954 3.A.2.Na.4.b
Association CEGL005136 Creosotebush - Burrobush - Ocotillo Shrubland CEGL005136 3.A.2.Na.4.b
Association CEGL005137 Creosotebush - Burrobush - (Littleleaf Ratany, White Ratany) Shrubland CEGL005137 3.A.2.Na.4.b
Association CEGL005755 Creosotebush - Burrobush - (Nevada Joint-fir, Water Jacket) Desert Shrubland CEGL005755 3.A.2.Na.4.b
Association CEGL005756 Creosotebush - Burrobush - Fremont''s Chaffbush Desert Shrubland CEGL005756 3.A.2.Na.4.b
Association CEGL005757 Creosotebush - Burrobush - Shadscale Saltbush Desert Shrubland CEGL005757 3.A.2.Na.4.b
Association CEGL005758 Creosotebush - Burrobush - Desert-holly Desert Shrubland CEGL005758 3.A.2.Na.4.b
Association CEGL005759 Creosotebush - Burrobush - Death Valley Joint-fir Desert Shrubland CEGL005759 3.A.2.Na.4.b
Association CEGL005760 Creosotebush - Burrobush - Eastern Mojave Buckwheat Desert Shrubland CEGL005760 3.A.2.Na.4.b
Association CEGL005761 Creosotebush - Burrobush - Burrobrush Desert Shrubland CEGL005761 3.A.2.Na.4.b
Association CEGL005762 Creosotebush - Burrobush - Mojave Yucca Desert Shrubland CEGL005762 3.A.2.Na.4.b
Association CEGL005763 Creosotebush - Burrobush / Cryptogamic Crust Desert Shrubland CEGL005763 3.A.2.Na.4.b
Association CEGL005764 Creosotebush - Burrobush / Big Galleta Desert Shrubland CEGL005764 3.A.2.Na.4.b
Association CEGL005765 Creosotebush - Cattle Saltbush Desert Shrubland CEGL005765 3.A.2.Na.4.b
Concept Lineage: This alliance includes old alliances III.A.5.N.a. Larrea tridentata - Ambrosia dumosa Shrubland Alliance (A.2532) and IV.A.2.N.a. Ambrosia (dumosa, eriocentra) Dwarf-shrubland Alliance (A.1102), in part.

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: = Larrea tridentata - Ambrosia dumosa (Creosote bush - white burr sage scrub) Alliance (Sawyer et al. 2009) [33.140.00]
= Larrea tridentata - Ambrosia dumosa Shrubland Alliance (Evens et al. 2012)
= Larrea tridentata-Ambrosia dumosa Shrubland Alliance (Evens et al. 2014)
>< Mojave Creosote Bush Scrub (#34100) (Holland 1986b)
? Mormon Tea Series: Ambrosia dumosa - Ephedra nevadensis - Ferocactus acanthodes Association (Warren et al. 1982)
>< Sonoran Creosote Bush Scrub (#33100) (Holland 1986b)
>< White Bursage Series (Sawyer and Keeler-Wolf 1995)
Concept Author(s): J.O. Sawyer and T. Keeler-Wolf (1995)

Author of Description: K.A. Schulz

Acknowledgements: No Data Available

Version Date: 12-18-14
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