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A3147 Yucca schidigera Scrub Alliance

Type Concept Sentence: Stands of this shrubland alliance have a sparse, emergent tree layer of Yucca schidigera with 3-5% total cover over a shrub canopy. It occurs throughout the Mojave and Colorado deserts, and southern Great Basin on alluvial fans, rocky slopes and upper bajadas.

Common (Translated Scientific) Name: Mojave Yucca Scrub Alliance

Colloquial Name: Mojave Yucca Scrub

Hierarchy Level:  Alliance

Type Concept: Stands of this desert alliance are found throughout the Mojave and Colorado deserts and southern Great Basin. The vegetation is characterized by a sparse, emergent woody layer of Yucca schidigera (2-5 m tall) with 3-5% total cover over an open to moderately dense short-shrub layer. Short shrubs present may include Ambrosia dumosa, Agave deserti, Coleogyne ramosissima, Echinocactus polycephalus, Echinocereus engelmannii, Encelia farinosa, Ephedra nevadensis, Eriogonum fasciculatum, Ferocactus cylindraceus, Larrea tridentata, Cylindropuntia acanthocarpa, Opuntia spp., Peucephyllum schottii, Salazaria mexicana, Simmondsia chinensis, and Viguiera parishii. The herbaceous layer is open or patchy to sparse and often dominated by Pleuraphis rigida with annuals seasonally present. Stands occur on alluvial fans, rocky slopes and upper bajadas. Sites are rocky, well-drained slopes between 50 and 2500 m elevation, but stands regularly occur above 900 m in the Mojave Desert. Substrates are well-drained sandy loams.

Diagnostic Characteristics: Stands of this alliance have Yucca schidigera with >2% cover in the emergent small tree layer or shrub layer over a short-shrub canopy; other species, including Ambrosia dumosa and Larrea tridentata, may be equal or higher cover (Thomas et al. 2004). Yucca schidigera may not be dominant, but is regarded as an indicator species with other desert scrub species often dominating the vegetation (Sawyer et al. 2009).

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: Yucca schidigera is one of the characteristic shrubs at mid elevations in the eastern and central Mojave Desert and of the desert slopes of the Peninsular and Transverse ranges. In these areas, Yucca schidigera rarely dominates but acts as an indicator species at low cover in stands at slightly lower elevations and on shallower soils than those of ~Yucca brevifolia Wooded Scrub Alliance (A3148)$$. Some stands attain the highest shrub diversities, up to 30 species, found in hot deserts of California. Stands grade into those of ~Larrea tridentata - Ambrosia dumosa Bajada & Valley Desert Scrub Alliance (A3277)$$ at lower elevations and at mid elevations into ~Coleogyne ramosissima Mojave Desert Scrub Alliance (A3144)$$, ~Eriogonum fasciculatum - Viguiera parishii Desert Scrub Alliance (A3150)$$, ~Grayia spinosa Scrub Alliance (A3171)$$, ~Ephedra nevadensis - Lycium andersonii - Grayia spinosa Scrub Alliance (A4245)$$, and ~Prunus fasciculata - Salazaria mexicana Northern Mojave Desert Wash Scrub Alliance (A4185)$$.

There are several new proposed associations from California which do not have descriptions, but are identified in Sawyer et al. (2009). Therefore, this alliance description will require revision when they are authored and included in the USNVC.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: This succulent, extremely xeromorphic, evergreen shrubland has emergent trees (<2-5 m tall) over an open desert scrub canopy. Yucca schidigera is very low in total cover but dominates the tree layer. The herbaceous layer is often dominated by graminoids.

Floristics: Stands of this shrubland of the Mojave and Colorado deserts are characterized by a sparse, emergent woody layer of Yucca schidigera with 3-5% total cover over a short-shrub canopy. Yucca schidigera range from 2-9 m tall, but are usually <5 m tall. Short shrubs present may include Ambrosia dumosa, Agave deserti, Coleogyne ramosissima, Echinocactus polycephalus, Echinocereus engelmannii, Encelia farinosa, Ephedra nevadensis, Eriogonum fasciculatum, Ferocactus cylindraceus, Larrea tridentata, Cylindropuntia acanthocarpa, Opuntia spp., Peucephyllum schottii, Salazaria mexicana, Simmondsia chinensis, and Viguiera parishii. The herbaceous layer is open or patchy to sparse and often dominated by Pleuraphis rigida with annuals seasonally present.

Dynamics:  This alliance occurs in extremely xeric sites and is well-adapted to prolonged drought and heat stress. Growth slows or stops in winter due to cold and is inhibited at other times by heat. Winter rains are sometimes sufficient to allow ephemeral herbs to flower in the spring. Late summer thunderstorms also contribute moisture.

Yucca schidigera sprouts from roots after fire or mechanical disturbance (Tirmenstein 1990). Sprouting is less vigorous when the plants are severely injured (Vasek et al. 1975). A high percentage of individuals can survive recurrent fire (Tratz 1978), most likely the result of patchy fires and strong sprouting abilities. However, plant response varies in different regions. For example, plants in the Mojave Desert took up to 6 years to attain pre-burn cover with many more years to recover stature and biomass, whereas plants in southern California chaparral responded more readily in 2 years with an increase in stem number (Tirmenstein 1990). The fire characteristics are little known for this alliance.
Environmental Description:  Stands of this desert alliance are found throughout the Mojave and Colorado deserts and southern Great Basin on alluvial fans, rocky slopes and upper bajadas. The climate is semi-arid with yearly precipitation totals are quite low, averaging between 10 and 25 cm. Year-to-year precipitation variability can be quite large. Sites are rocky, well-drained slopes between 50 and 2500 m elevation, but stands regularly occurs above 900 m in the Mojave Desert. Substrates are well-drained sandy loams.(Sawyer et al. 2009).
Geographic Range: Stands of this desert alliance occur throughout the Mojave and Colorado deserts, and southern Great Basin.

Nations: US

States/Provinces:  AZ, CA, NV


Confidence Level: Moderate

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.B Cool Semi-Desert Scrub & Grassland Subclass S11 3.B
Formation 3.B.1 Cool Semi-Desert Scrub & Grassland Formation F033 3.B.1
Division 3.B.1.Ne Western North American Cool Semi-Desert Scrub & Grassland Division D040 3.B.1.Ne
Macrogroup 3.B.1.Ne.1 Yellow Rabbitbrush - Blackbrush / Indian Ricegrass Dry Shrubland & Grassland Macrogroup M171 3.B.1.Ne.1
Group 3.B.1.Ne.1.a Joshua Tree - Eastern Mojave Buckwheat - Rough Joint-fir Mixed Desert Scrub Group G296 3.B.1.Ne.1.a
Alliance A3147 Mojave Yucca Scrub Alliance A3147 3.B.1.Ne.1.a
Association CEGL003117 Mojave Yucca / Big Galleta Shrubland CEGL003117 3.B.1.Ne.1.a
Association CEGL005295 Mojave Yucca - Creosotebush - Burrobush Shrubland CEGL005295 3.B.1.Ne.1.a
Association CEGL005780 Mojave Yucca - Blackbrush Shrubland CEGL005780 3.B.1.Ne.1.a
Association CEGL005781 Mojave Yucca - Eastern Mojave Buckwheat Shrubland CEGL005781 3.B.1.Ne.1.a
Association CEGL005782 Mojave Yucca - Creosotebush - Nevada Joint-fir Shrubland CEGL005782 3.B.1.Ne.1.a
Association CEGL005783 Mojave Yucca - Buckhorn Cholla Shrubland CEGL005783 3.B.1.Ne.1.a
Concept Lineage: A.881

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: = Yucca schidigera (Mojave yucca scrub) Alliance (Sawyer et al. 2009) [33.070.00]
= Yucca schidigera Shrubland Alliance (Evens et al. 2012)
= Yucca schidigera Shrubland Alliance (Evens et al. 2014)
= Yucca schidigera Shrubland Alliance (CNPS 2017) [33.070.00]
>< Mojave Mixed Steppe (#34220) (Holland 1986b)
>< Mojave Yucca Scrub and Steppe (#34230) (Holland 1986b)
= Mojave yucca series (Sawyer and Keeler-Wolf 1995)
Concept Author(s): J.O. Sawyer, T. Keeler-Wolf, and J. Evens (2009)

Author of Description: K.A. Schulz

Acknowledgements: We have incorporated significant descriptive information previously compiled by M. Schindel.

Version Date: 12-18-14
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