BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Yucca schidigera | Mojave Yucca 



GENERAL BOTANICAL CHARACTERISTICS : 
Mojave yucca can be arborescent or shrublike, with single or clumped
erect stems [39].  This highly variable, long-lived, slow-growing
species is simple-stemmed or sparingly branched, with the first branches
occurring a few feet off the ground [20].  Mojave yucca generally grows
from 9.2 to 14.8 feet (2.8-4.5 m) tall, although specimens as tall as 30
feet (9 m) have been reported [20,21].  Individual plants may live for
hundreds of years [27].  The gray-brown bark is rough and ridged [20].

Linear to linear-lanceolate, yellow-green or blue-green leaves 1 to 4.9
feet (3-15 dm) in length occur in clusters at the end of branches
[20,22,40].  Dead leaves along the stems often extend nearly to the
ground [20].  The densely crowded, glabrous to slightly scabrous,
fragile inflorescence is 2 to 4 feet (0.65-1.30 m) long and pale
yellow-green with a red or purple tinge [20].  Small globose flowers are
white or cream-colored and often tinged with purple [20,37].  The plump,
fleshy fruit is tapered and cylindrical and contains numerous thick,
dull black, wingless, ovoid seeds [20,22,37].


RAUNKIAER LIFE FORM : 
   Phanerophyte
   Geophyte


REGENERATION PROCESSES : 
Seed:  Seed is flat, dull black and weighs approximately 0.005 ounce
(139 mg) [2,15,37].  The seed is contained in large, plump, indehiscent,
baccate fruits which frequently remain on the tree until early winter
[14,20].  These sweet, fleshy fruits are eaten by many vertebrates,
which are the primary dispersal agents [40].  Plants may not produce
fruit in poor years [36].

Pollination:  One of the most interesting and well-studied aspects of
yucca ecology is the symbiotic relationship between yuccas and their
yucca moth pollinators.  Mojave yucca relies solely on the yucca moth
(Tegeticula yuccasella) for pollination [41,42,43].  Seed production is
thus entirely dependent on the availability of this pollinator, which
while in the larval stage, feeds on a small number of seeds (generally
around 3 percent) [14].  In years of extremely low pollinator
availability, sexual reproduction may not occur.

Germination:  The seeds of most yuccas germinate well when planted under
favorable temperature and moisture regimes [15].  Seed viability
approaches 80 percent [2].  Germination can occur within only 6 days if
seed is first soaked in water for 24 hours [37].  Germination capacity
is reduced when seeds are subjected to high temperatures for even brief
periods of time [15].  Percent germination of seed exposed to different
temperatures for varying lengths of time was as follows [15]:

                        Percent Germination
              2 hours                     5 minutes
           -------------       ------------------------------
 Control   80 C     90 C       90 C    100 C    110 C   120 C
--------------------------------------------------------------
    69     16        0         83       54       11       0

Vegetative regeneration:  Very few seedlings have been observed on many
of the harsh sites on which Mojave yucca grows [40].  Reproduction by
seed may have been much more important during more favorable climatic
regimes.  Most regeneration now probably occurs through root-sprouting,
which has been noted after fire or mechanical removal [7,30].


SITE CHARACTERISTICS : 
Mojave yucca grows on dry rocky slopes, mesas, sandy desert washes, and
bajadas [22,29].  Dense concentrations of this species are rare in
southern California but do occur in Arizona and Nevada [37].  

Soils and climate:  Mojave yucca generally occurs on gravelly soils
[37], and has been reported on alkaline and saline soils [28,36].  It is
well adapted to xeric conditions and can grow in areas receiving only 6
inches (150 mm) of precipitation annually [28].  Coastal sage sites of
southern California in which this yucca grows are characterized by
winter rains but very little summer precipitation [3].

Elevation:  Generalized elevational ranges of Mojave yucca are as
follows [20,21,39,36]:
        
        from less than 5,000 feet to (rarely) 7,800 feet (1,524-2,377 m) in CA
        from 2,198 to 2,952 feet (670-900 m) in se NV
        from 2,952 to 3,650 feet (900-1,100 m) in s NV   
        from 2,952 to 4,920 feet (900-1,500 m) in UT


SUCCESSIONAL STATUS : 
Mojave yucca is a slow-growing and long-lived species [37].  It is a
constituent of certain climax desert shrub communities [33].  This yucca
is susceptible to deep-soil disturbance and reestablishes a site slowly
and gradually [33].  It is generally not well represented in early seral
communities.


SEASONAL DEVELOPMENT : 
Mojave yucca flowers during the early spring [1].  Fruit develops in
late spring to early summer [1] and sometimes remains on the plant into
early winter [20].

Evidence suggests that the timing of flowering is primarily controlled
by daylength [1].  Temperature is also an important influence, and
flowering is often delayed at higher elevation sites [20].  Generalized
flowering and fruiting dates are as follows [1,20,22,28]:

Location        Beginning of flowering   End of flowering   Fruiting
  CA                  April                   May              April
  NV                  March                   May              May

Significant annual variation in seasonal development has been noted;
climatic factors may account for this variation.  Specific phenological
development at a Nevada site over a 3-year period was as follows [1]:

Phenological stage       1971            1972            1973
Bud                      March           ----            April
Flower                   March           March           April
Fruit                    May-July        April-July      May-June

Related categories for Species: Yucca schidigera | Mojave Yucca