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A0485 Washingtonia filifera Wet Woodland Alliance

Type Concept Sentence: This woodland alliance of the desert Southwest is found along canyon waterways and faultlines on intermittently flooded sites below 900 m in elevation. Permanent subsurface water is required to maintain Washingtonia filifera, a relict species. Only 24 sites are known to support oases in the Colorado and Sonoran deserts, one of the most arid regions in North America.

Common (Translated Scientific) Name: California Fan Palm Wet Woodland Alliance

Colloquial Name: California Fan Palm Oasis

Hierarchy Level:  Alliance

Type Concept: This alliance of the oases of the Colorado and Sonoran deserts is recognized by the presence of Washingtonia filifera as the sole or dominant tree in the canopy. There is great floristic diversity among oases, and this palm is the only species that does not differ in its relative importance. The vegetation of oases along waterways differs consistently from those along faultlines. Other trees that may be present include Fraxinus velutina, Platanus racemosa, Populus fremontii, and Quercus chrysolepis. A subcanopy is often present and may be composed of Prosopis glandulosa, Salix exigua, Salix gooddingii, and Salix lasiolepis. This woodland alliance of the desert Southwest is found along canyon waterways and faultlines on intermittently flooded sites below 900 m in elevation. Permanent subsurface water is required to maintain Washingtonia filifera, a relict species. Only 24 sites are known to support oases in the Colorado and Sonoran deserts, one of the most arid regions in North America. The mean 24-hour maximum temperature may exceed 38°C for several weeks a year. Annual precipitation totals between 90 and 168 mm. Salinity is low in the root zone, but increases near the surface where evaporation leaves salt accumulations. Reproduction of Washingtonia filifera is limited by water supply, surface salinity, rainfall, and fire. Oases are the only desert community in which fire is an important abiotic factor. Fan palms are fire-tolerant, while the understory species are not. Fires open up the understory allowing palm seedlings to establish. Removal of the understory also decreases competition for water.

Diagnostic Characteristics: Washingtonia filifera >3% absolute cover in the tree canopy (Keeler-Wolf et al. 1998a).

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: There is great floristic variation among oases; however, canyon waterway oases differ consistently from those along faultlines in the importance of plants other than fan palms.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: This seasonally flooded, temperate, broad-leaved evergreen palm woodland of desert streams and seeps has an open to continuous canopy of emergent trees less than 30 m in height. Occasional, medium to tall shrubs may be present. The herbaceous layer is sparse.

Floristics: This alliance of the oases of the Colorado and Sonoran deserts is recognized by the presence of Washingtonia filifera as the sole or dominant tree in the canopy. There is great floristic diversity among oases, and this palm is the only species that doesn''t differ in its relative importance. Oases along waterways differ consistently from those along faultlines. Other trees that may be present include Fraxinus velutina, Platanus racemosa, Populus fremontii, and Quercus chrysolepis. A subcanopy is often present and may be composed of Prosopis glandulosa, Salix exigua, Salix gooddingii, and Salix lasiolepis.

Dynamics:  Seasonal flooding and fire are the dynamic processes required to maintain this alliance. Seasonal flooding reduces salinity in the surface soils and moistens the substrate for germination of Washingtonia filifera. This species also requires full sun to germinate and thrive. The oases where these trees grow form one of the few desert communities which can carry fire. Washingtonia is fire-resistant, while the other species in this community are not. Periodic fires clear the understory and reduce competition for water. The most favorable conditions for reproduction of Washingtonia occur when a late-season fire opens the understory before a moist winter. Once established, the palms require permanent soil moisture.
Environmental Description:  This woodland alliance of the desert Southwest is found along canyon waterways and faultlines on intermittently flooded sites below 900 m in elevation. Permanent subsurface water is required to maintain Washingtonia filifera, a relict species. Only 24 sites are known to support oases in the Colorado and Sonoran deserts, one of the most arid regions in North America. The mean 24-hour maximum temperature may exceed 38°C for several weeks a year. Annual precipitation totals between 90 and 168 mm. Salinity is low in the root zone, but increases near the surface where evaporation leaves salt accumulations. Reproduction of Washingtonia filifera is limited by water supply, surface salinity, rainfall, and fire. Oases are the only desert community in which fire is an important abiotic factor. Fan palms are fire-tolerant, while the understory species are not. Fires open up the understory allowing palm seedlings to establish. Removal of the understory also decreases competition for water.
Geographic Range: This woodland alliance occurs on faultlines and canyon waterways which flood seasonally in the arid deserts of the American Southwest and western Mexico. There are currently 24 known examples of this alliance in Arizona, Nevada, and California.

Nations: MX,US

States/Provinces:  AZ, CA, NV


Confidence Level: Low

Confidence Level Comments: No Data Available
Grank: GNR

Greasons: No Data Available
Type Name Database Code Classification Code
Class 1 Forest & Woodland Class C01 1
Subclass 1.B Temperate & Boreal Forest & Woodland Subclass S15 1.B
Formation 1.B.3 Temperate Flooded & Swamp Forest Formation F026 1.B.3
Division 1.B.3.Nd Western North American Interior Flooded Forest Division D013 1.B.3.Nd
Macrogroup 1.B.3.Nd.2 Interior Warm & Cool Desert Riparian Forest Macrogroup M036 1.B.3.Nd.2
Group 1.B.3.Nd.2.b Western Interior Riparian Forest & Woodland Group G797 1.B.3.Nd.2.b
Alliance A0485 California Fan Palm Wet Woodland Alliance A0485 1.B.3.Nd.2.b
Association CEGL000001 California Fan Palm Flooded Woodland CEGL000001 1.B.3.Nd.2.b
Concept Lineage: No Data Available

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: = Washingtonia filifera (California fan palm oasis) Alliance (Sawyer et al. 2009) [61.520.00]
= Washingtonia filifera Woodland Alliance (Evens et al. 2012)
= Washingtonia filifera Woodland Alliance (CNPS 2017) [61.520.00]
= Desert Fan Palm Oasis Woodland (#62300) (Holland 1986b)
= Fan palm series (Sawyer and Keeler-Wolf 1995)
Concept Author(s): M. Schindel, in Faber-Langendoen et al. (2013)

Author of Description: G. Kittel

Acknowledgements: No Data Available

Version Date: 12-18-14
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