Washingtonia filifera

 Washingtonia filifera (California fan palm)( )

Arecaceae

• The California fan pal is the only palm native to California. It is thought to be an ancient species with a history dating back to the middle Tertiary when it occurred more broadly across coastal and Mojave Desert areas of the state. Today, the natural range of this species is highly localized at scattered desert sites where permanent water exists relatively close to the soil surface. There are approximately 100 palm oases in California, with populations ranging from only a few to hundreds of mature palms. The largest groups of palm oases occur around the Coachella Valley where geologic conditions along the San Andreas fault promote shallow groundwater tables. From this center of distribution, California fan palm extends to the north to Twentynine Palms and the Cottonwood Mountains and south into northern Baja California where it is replaced by the related Mexican fan palm (Washingtonia robusta). Although similar in appearance, the Mexican fan palm has bright green fronds compared to our California species with gray-green fronds, and reaches much greater heights with a narrow tapered trunk. Both are widely cultivated in southern California and other parts of the world. Mature California fan palms can reach to 70 feet in height, and up to 3 feet or more in diameter. However, where the trees have not been trimmed or burned, the diameters seem far greater as the old leaf bases and portions of dried leaves are maintained on the trunk surface. The highly flammable nature of this dead leaf material points to a key aspect of ecology of these palms. Palm seedlings require full sun for growth and survival but are easily overtopped and shaded where a dense shrub cover is present below the parent palms. Fire, an unexpected element of a desert environment, provides a means of reducing this shrub cover and allowing palm seedlings to become established. The thick and fibrous trunk of the palms makes them relatively impervious to the fire, while the biomass of woody shrubs below is consumed.
• Since California fan palms have a relatively long lifespan, extending perhaps to 200 years or more, occasional reproduction of seedlings is sufficient to maintain populations. Years with heavy desert rains have been associated with successful seedling establishment by the palms. Coyotes and other vertebrates eat the palm fruits and provide a means of transporting the seeds between oasis areas. Although there are exaggerated accounts of fan palms living for thousands of years, there is no scientific basis for such ages. In fact there is no direct way to date palms as their trunk structure does not produce annual growth rings. The best estimates of maximum age come from measured rates of leaf production along the trunk over several years, extrapolated to the full height of the palm.
• There are two primary topographic situations where California fan palm, and its associated oasis community, occurs. One of these is a wash-oasis habitat along canyons or arroyo bottoms where ground water collects. In the Coachella valley these are often positioned where movements along the San Andreas Fault force deep groundwater to the surface. These habitats are typically heterogeneous in the distribution of subsurface soil moisture and thus promote the localized presence of the palms and other associated species. Often there is a gradient from wetland sites with surface water to the fan palm areas with permanent groundwater pools at shallow soil depths, and then on to more typical wash communities with ephemeral groundwater. The second form of topographic sites are steep hillsides or small hanging canyons where spring or groundwater seeps provide a permanent water supply. While such sites seem to be unsuited for a long-lived species such as the fan palm, comparisons of century-old photographs with present stands of these seep oases suggest that they are stable. "California Desert Plants Philip W Rundel, Robert J Gustafson, Michael E Kauffmann."