Print Report

A3279 Ambrosia dumosa Desert Dwarf Scrub Alliance

Type Concept Sentence: This desert scrub alliance is characterized by an open dwarf-shrub layer dominated by Ambrosia dumosa occurring on dry rocky sites that are too harsh for Larrea tridentata to be abundant and on sites where Larrea tridentata has been removed by disturbance.

Common (Translated Scientific) Name: Burrobush Desert Dwarf Scrub Alliance

Colloquial Name: Burrobush Desert Dwarf Scrub

Hierarchy Level:  Alliance

Type Concept: This desert scrub alliance is characterized by an open dwarf-shrub layer dominated by Ambrosia dumosa. Other characteristic species include Encelia farinosa, Eriogonum fasciculatum, and Ephedra nevadensis. Rocky slope sites tend to contain Echinocactus polycephalus, Ferocactus cylindraceus, Mammillaria sp., and other cacti. Lower bajada slopes in the northern and western Mojave tend to have Ericameria cooperi, Grayia spinosa, Lycium cooperi, and Tetradymia stenolepis. This alliance is found in the Mojave, Sonoran and Colorado deserts. Sites occur on dry rocky sites that are too harsh for Larrea tridentata to be abundant and on sites where Larrea tridentata has been removed by disturbance. It also may occur in areas which sustain slightly cooler winter temperature than Larrea tridentata-dominated areas such as edges of mid-elevation basins in the northern and western Mojave Desert.

Diagnostic Characteristics: This dwarf-shrub alliance is dominated by diagnostic species Ambrosia dumosa without significant cover of Larrea tridentata. Other characteristic species present to codominant include Encelia farinosa, Eriogonum fasciculatum, and Ephedra nevadensis. Ambrosia dumosa >1% absolute cover when Larrea tridentata <1% absolute cover (Thomas et al. 2004); Ambrosia dumosa >1% absolute cover, and other species with less cover in the shrub canopy (Keeler-Wolf et al. 2005); or Ambrosia dumosa >2 times as much absolute cover as Larrea tridentata; Ambrosia dumosa exceeds the cover of other subshrubs (Keeler-Wolf et al. 1998a, Evens and Hartman 2007).

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: Ambrosia dumosa-dominated communities occurring on sand deposits are included in ~Pleuraphis rigida Desert Grassland Alliance (A3170)$$ rather than this alliance.

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 perennial grass with a few perennial forbs. Annual grasses and forbs are present seasonally.

Floristics: This alliance is characterized by an open dwarf-shrub layer is dominated by Ambrosia dumosa. Other characteristic species include Encelia farinosa, Eriogonum fasciculatum, and Ephedra nevadensis. Rocky slope sites tend to contain Echinocactus polycephalus, Ferocactus cylindraceus, Mammillaria sp., and other cacti. Lower bajada slopes in the northern and western Mojave tend to have Ericameria cooperi, Grayia spinosa, Lycium cooperi, and Tetradymia stenolepis. Other characteristic species include Acacia greggii, Agave utahensis, Gutierrezia sarothrae, Opuntia phaeacantha, Pleuraphis rigida, and Sphaeralcea ambigua (Warren et al. 1982). This alliance typically lacks psammophytes.

Dynamics:  Fire and long-term intensive grazing exclude Ambrosia dumosa from stands. Typical small-scale disturbances, such as blading, excavation, and spot fires, initiate small stands. Ambrosia dumosa is not well-adapted to fire because of its limited ability to sprout. Natural disturbance processes probably did not involve periodic fire until non-native grasses became important. Ambrosia dumosa primarily re-establishes from seed from off-site sources after fire (Vasek 1979, 1983, McAuliffe 1988, Hunter 1989).
Environmental Description:  Vegetation included in this alliance occurs on rocky canyon and upland slopes, bajadas, and sandy plains in western Arizona and southeastern California, below 1200 m elevation. 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. There are two very different habitats reported for this vegetation type. In the Grand Canyon, stands occur on moderate to steep, rocky slopes with south aspects in the inner gorge, from 610 to 1190 m in elevation. Substrates are derived from limestone, shale and colluvium, and the soils are thin, coarse-textured and rocky (Warren et al. 1982). Sites occur on dry rocky sites that are too harsh for Larrea tridentata to be abundant and on sites where Larrea tridentata has been removed by disturbance. It also may occur in areas which sustain slightly cooler winter temperature than Larrea tridentata-dominated areas such as edges of mid-elevation basins in the northern and western Mojave Desert (Sawyer et al. 2009).
Geographic Range: This alliance is found in the Mojave, Sonoran and Colorado deserts.

Nations: MX,US

States/Provinces:  AZ, CA, MXSON, NM, NV


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.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 A3279 Burrobush Desert Dwarf Scrub Alliance A3279 3.A.2.Na.4.b
Association CEGL000954 Burrobush - (Rough Joint-fir, Nevada Joint-fir) Dwarf-shrubland CEGL000954 3.A.2.Na.4.b
Association CEGL005074 Burrobush Dwarf-shrubland CEGL005074 3.A.2.Na.4.b
Concept Lineage: This alliance includes old alliance 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: = Ambrosia dumosa (White bursage scrub) Alliance (Sawyer et al. 2009) [33.060.00]
= Ambrosia dumosa Shrubland Alliance (Evens et al. 2014)
= Ambrosia dumosa Shrubland Alliance (Evens et al. 2012)
= Ambrosia dumosa Shrubland Alliance (CNPS 2017) [33.060.00]
>< Brittlebush-White Bursage Series (Sawyer and Keeler-Wolf 1995)
>< 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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