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Wildlife, Animals, and Plants
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Introductory
SPECIES: Yucca brevifolia | Joshua Tree
ABBREVIATION :
YUCBRE
SYNONYMS :
Yucca brevifolia var. wolfei Jones
Yucca draconis var. arborescens Torr.
Yucca arborescens (Torr.) Trel.
SCS PLANT CODE :
YUBR
COMMON NAMES :
Joshua tree
Joshua-tree yucca
tree yucca
yucca-palm
TAXONOMY :
The currently accepted scientific name for Joshua tree is Yucca
brevifolia Engelm. The Yucca genus is both variable and unstable [44].
Natural hybridization is common, and numerous intermediate forms occur
[43]. This genus has received only limited attention [10], and many
taxonomic questions persist. Currently recognized varieties of Joshua
tree are as follows [28]:
Yucca brevifolia var. brevifolia
Yucca brevifolia var. jaegeriana McKelvey
Yucca brevifolia var. herbertii (J. M. Weber) Munz
Webber [43] first delineated the form herbertii on the basis of
morphological differences. Munz [28] found these differences to be
significant enough to distinguish this entity as a variety, var.
herbertii (J. M. Webber) Munz. Today, however, several researchers
question all of the varieties named by McKelvey [26], Munz [28], Webber
[43], and others. Cronquist and others [10] found little evidence to
delineate any varieties. This controversy points out the need for
additional research on this complex but fascinating group.
LIFE FORM :
Tree
FEDERAL LEGAL STATUS :
No special status
OTHER STATUS :
NO-ENTRY
COMPILED BY AND DATE :
D. Tirmenstein, March 1989.
LAST REVISED BY AND DATE :
NO-ENTRY
AUTHORSHIP AND CITATION :
Tirmenstein, D. 1989. Yucca brevifolia. In: Remainder of Citation
DISTRIBUTION AND OCCURRENCE
SPECIES: Yucca brevifolia | Joshua Tree
GENERAL DISTRIBUTION :
Joshua tree is one of the most characteristic plants of the Mohave
Desert [37] and extends southward to the Mohave-Sonoran Desert ecotone
[3]. This species grows from southern California, Mexico, and western
Arizona eastward into southern Nevada and southwestern Utah [23,46]. It
reaches its greatest abundance in the vicinity of Joshua Tree National
Monument, California [21]. Var. jaegeriana grows primarily in the
eastern portion of the Mohave; var. herbertii is restricted to parts of
the western Mohave Desert in California [25,28].
ECOSYSTEMS :
FRES30 Desert shrub
FRES35 Pinyon - juniper
FRES40 Desert grasslands
STATES :
AZ CA NV UT MEXICO
ADMINISTRATIVE UNITS :
DEVA GRCA JOTR LAME
BLM PHYSIOGRAPHIC REGIONS :
3 Southern Pacific Border
6 Upper Basin and Range
7 Lower Basin and Range
12 Colorado Plateau
KUCHLER PLANT ASSOCIATIONS :
K023 Juniper - pinyon woodland
K039 Blackbrush
K041 Creosotebush
SAF COVER TYPES :
239 Pinyon - juniper
SRM (RANGELAND) COVER TYPES :
NO-ENTRY
HABITAT TYPES AND PLANT COMMUNITIES :
Joshua tree is a climax dominant in unique woodlands of the Mohave
Desert. It also occurs with gramas (Bouteloua spp.) and galletas
(Hilaria spp.) in Joshua tree grasslands of the eastern Mohave [17], and
codominates in desert shrub communities with creosotebush (Larrea
tridentata), saltbush (Atriplex spp.), and bladder sage (Salazaria
mexicana) [29]. Joshua tree is listed as an indicator in the following
community type classifications (cts):
Area Classification Authority
CA: San Bernardino chaparral, woodland,
Mts. & forest cts Minnich 1976
Mohave Desert general veg. cts Thorne and others 1981
Mohave Desert desert scrub cts Vasek and Barbour 1977
San Gabriel general veg. cts Hanes 1976
----- general veg. cts Thorne 1976
s CA desert cts Johnson 1976
CA, NV: Mohave Desert desert scrub cts Brown 1982
VALUE AND USE
SPECIES: Yucca brevifolia | Joshua Tree
WOOD PRODUCTS VALUE :
Joshua tree wood is light, pliable, porous, durable, and has a unique
and attractive grain [26]. It is used in novelty products such as
picture frames, book covers, postcards, napkin rings, and boxes [26,43].
Joshua tree veneer, which is available in parts of southern California,
is attractive, provides good insulation, and improves acoustics [43].
IMPORTANCE TO LIVESTOCK AND WILDLIFE :
Joshua tree provides food and shelter for many animals of the Mohave
Desert. The foliage provides some browse for bighorn sheep [35] and
other wild ungulates. The Mexican woodrat, rabbits, and other small
mammals consume the young succulent leaves [25,26,43], as do domestic
sheep and goats in drier parts of the Mohave. Deer, squirrels, and
small birds consume the young blossoms and fruit [20,21]. Cattle,
burros, and wild horses also eat the fruit [10]. The antelope ground
squirrel, and presumably other rodents, cache dried Joshua tree seed for
winter use [20].
PALATABILITY :
The sweet blossoms and fleshy fruits of the Joshua tree are highly
palatable [20,21]. Dried seeds are particularly relished by the
antelope ground squirrel in winter [20,21]. Leaves are most palatable
to wild ungulates, small mammals, and domestic livestock when young and
succulent [25,26]. The palatability of Joshua tree to livestock and
wildlife in Utah has been rated as follows [11]:
UT
Cattle poor
Sheep poor
Horses poor
Pronghorn poor
Elk poor
Mule deer poor
Small mammals poor
Upland game birds ----
NUTRITIONAL VALUE :
Joshua tree is rated as poor in both energy and protein value [11].
Specific food values of various parts of Joshua tree (var. jaegeriana)
are as follows [43]:
oil water n-free crude fat fiber ash
extract protein
see 34.4% 5.9% 34.8% 10.2% 3.2% 9.9% 1.6%
pods ---- 7.6% 60.0% 6.7% 2.0% 16.8% 6.9%
seed meal ---- 9% 53% 15.5% 5% ---- 2.5%
COVER VALUE :
Joshua tree provides much-needed shade and cover for numerous
desert-dwelling animals. Arborescent plants are rare in the Mohave
Desert, and the branches of this tall yucca provide perching sites for
predatory birds such as the sparrow hawk and loggerhead shrike [21].
This tall, shaggy, irregularly shaped yucca lends itself to favorable
nesting or resting sites for many small birds and reptiles. Studies
have shown that at least 25 species of birds nest in the Joshua tree.
Some, such as the Scott's oriole, nest in shady leaf clusters, while
others, such as the flicker and ladder-backed woodpecker, excavate nest
holes in the corky trunks [20,21]. The yucca night lizard usually
exists in close proximity to Joshua trees, inhabiting dark rotting
hollows where available [21] and feeding on the abundance of insects
associated with this tree [25]. Woodrats frequently build nests in the
fallen trunks of Joshua trees [25]. The Mexican woodrat often uses the
leaves as nesting material [26].
Domestic livestock seek out shade provided by Joshua trees [16]. The
degree to which Joshua tree provides environmental protection during one
or more seasons for wildlife in Utah has been rated as follows [11]:
UT
Pronghorn poor
Elk poor
Mule deer poor
Small mammals fair
Small nongame birds fair
Upland game birds good
Waterfowl poor
VALUE FOR REHABILITATION OF DISTURBED SITES :
Joshua tree woodlands are extremely fragile and can take centuries to
recover from disturbance [41]. Joshua tree can be used in
rehabilitation, although its potential value for both long- and
short-term revegetation is rated as low. It has moderate value for
erosion control [11]. Seedlings can be transplanted onto disturbed
sites, but it is is important not to overwater young plants [43].
OTHER USES AND VALUES :
Historical uses: Wood - Ancient Cliff Dwellers of the Southwest often
incorporated Joshua tree beams into their living structures [43]. Early
ranchers built fences from the cork trunks [20,21]. The pulp was made
into fine paper and for a time a London newspaper was printed on
newsprint made from Joshua tree pulp [26]. High processing and
transportation costs eventually put an end to its use in the paper
industry. Other - Native Americans used the rootlets to make a red dye,
and made rope, sandals, mats, and baskets from fibers obtained from the
leaves [20,21,25]. They roasted and ate the flower buds, and used the
ground seeds to make meal and mush [25,26]. They produced an alcoholic
beverage from the fermented buds and flowers [25].
Modern uses: The clear, tasteless, and nearly odorless oil obtained
from seeds and pods, and sapogenins derived mainly from Joshua tree
roots, may someday have commercial value [34,43]. Chemicals obtained
from the Joshua tree have been used in the synthesis of vanillin, as a
fertilizer, and as a carbon dioxide stabilizer used in controlling oil
fires [43]. The Joshua tree's unique appearance makes it well suited
for use as an ornamental [35]. It has been transplanted successfully
outside of its natural range in Nevada and Utah [10].
MANAGEMENT CONSIDERATIONS :
Grazing: Many Joshua tree woodlands have been heavily grazed by
livestock in the past. Grazing systems have little or no effect on
improving range conditions because of the extreme aridity and harshness
of these areas. Efforts to improve these ranges tend to be expensive
and yield few beneficial results [15].
Biomass: Joshua biomass is difficult to determine accurately. Bostick
and Tueller [5] reported that biomass ranged from 449 pounds per acre
(504 kg/ha) on poor sites to 2,483 pounds per acre (2,790 kg/ha) on
excellent sites; biomass averaged 1,369 pounds per acre (1,538 kg/ha).
Damage: Extensive vandalism has occurred in many Joshua tree woodlands
in California [43]. Larger trees have been burned or defaced, and many
trees have been dug up for planting in urban or residential areas.
Survival of trees removed in this manner is believed to be extremely
rare.
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Yucca brevifolia | Joshua Tree
GENERAL BOTANICAL CHARACTERISTICS :
Joshua tree is a large, erect, evergreen, arborescent monocot
[10,26,34,43]. It is generally single-stemmed, but plants with two or
three stems also occur [26,43]. Joshua tree is the largest nonriparian
plant of the Mohave Desert, reaching heights of 16 to 49 feet (5-15 m);
the huge reddish-brown to gray trunks can grow to 2 or 4 feet (0.6-1.2
m) in diameter [10,21,28,34]. Erratic branching generally begins 3 to
10 feet (1-3 m) above the ground [10,26] and is often caused by the
yucca-boring weevil which destroys the growing tips [21]. Branches are
erect, ascending or spreading, and form a dense, compact, rounded top
[10,26]. The soft, corklike bark is rough and fissured [21,26]. The
inflorescence is a crowded, brittle often glabrous panicle [26].
Globose flowers are greenish-white or gray and papery at maturity, with
an odor described as "unpleasantly mushroom-like" [26,43].
The exact age of Joshua trees may be difficult to determine since
annuanl rings are not produced [21]. The overall shape, however, can
provide a general range. Juvenile Joshua trees are generally
unbranched; middle-aged plants are forked and dense [26]. Older trees
generally have a single stem and an open crown [26].
Varieties: Important differences in morphology and general growth form
of varieties are as follows [28,33,43]:
var. brevifolia - tall, stout stem, branches mostly 3 to 10
feet (1-3 m) above the ground.
var. jaegeriana - smaller, 10 to 20 feet (3-6 m) tall, branches
mostly 2.3 to 3.3 feet (7-10 dm) above ground,
more compact.
var. herbertii - many stems forming clumps up to 33
feet (10 m) in diameter, long rhizomes.
RAUNKIAER LIFE FORM :
Phanerophyte
Therophyte
REGENERATION PROCESSES :
Seed and seed dispersal: Seeds are contained in dry, spongy,
indehiscent baccate fruits which average 3 inches (69 mm) in length
[18,26,45]. Fruit first develops near the base of the inflorescence
while the upper part is still in flower, and averages 25 to 40 per
cluster. Annual fruit production varies greatly under natural
conditions [26]. Generally, fruit is produced only in wetter years. On
extremely harsh sites the Joshua tree flowers rarely, if at all [21].
Seeds are dispersed chiefly by wind and animals. Birds frequently open
the fruit, exposing seeds for subsequent wind dispersal [26]. A number
of desert rodents are known to cache Joshua tree seeds [21] and may also
disperse seed. Fruit can persist on the tree, but usually disintegrates
rapidly [26].
Pollination: One of the most interesting and well-studied aspects of
yucca ecology centers around the symbiotic relationship between yuccas
and their yucca moth pollinators. The Joshua tree relies solely on the
yucca moth (Tegeticula synethetica) for pollination. Seed production is
totally dependent on the availability of this pollinator, which in the
larval stage, feeds on a small percentage of seeds (generally around 7%)
[18]. In years of extremely low pollinator availablity, sexual
reproduction may be very limited.
Germination: Most yucca seeds germinate well when temperature and
moisture conditions are favorable [19]. Laboratory experiments indicate
good germination potential for Joshua tree seed, with viability
approaching 96 percent [2]. Germination can begin within only 3 days if
seed is soaked in water for 24 hours prior to planting [43].
Germination capacity may be severely reduced if seeds are subjected to
high temperatures for even brief periods.
Seedling establishment: Seedlings are uncommon on many harsh sites and
even under laboratory conditions, only 24 percent of the seed actually
produced viable seedlings [2]. Some researchers believe that sexual
reproduction was much more important during more favorable climatic
regimes, such as during the late Pleistocene, when summers were cooler
and annual precipitation greater. Vegetative reproduction is now the
most important mode of regeneration on many sites.
Growth: Joshua tree grows an average of 3 inches (8 cm) annually for
the first 10 years, then slows to 1.5 inches (1.3 cm) [21].
Vegetative regeneration: Joshua tree can sprout from the roots and from
underground rhizomes [9,20,26,42]. Joshua tree rhizomes are
fast-growing and numerous, and possess many scalelike leaves [43].
Specific characteristics differ by variety as follows [43]:
var. herbertii - aerial stems connected by underground
rhizomes 1.6-4.3 feet (0.2-1.3 m) in
length which quickly grow to the
surface.
var. jaegeriana - rhizome development may be related to
precipitation, and is believed to be
stimulated by damage or injury to the
stem.
SITE CHARACTERISTICS :
Joshua tree grows on desert plains, alluvial fans, slopes, ridges,
bajadas, mesas, or foothills [25,35,43]. Trees are often smaller and
less common away from the base of desert mountain ranges [32]; the
species is generally absent along the eastern edge of the Mohave Desert
[7].
Associated species: The Joshua tree grows in open desert scrub,
pinyon-juniper woodlands, and in desert grasslands [7,19,35]. Much
variation has been reported on Joshua tree sites [30], but the following
species are common associates: Nevada ephedra (Ephedra nevadensis),
broom snakeweed (Gutierrezia sarothrae), blackbrush (Coleogyne
ramosissima), creosote bush (Larrea spp.), bursage (Ambrosia dumsa),
California buckwheat (Eriogonum fasciculatum), Wright eriogonum
(Eriogonum wrightii), desert sage (Salvia carnosa), catclaw acacia
(Acacia greggii), and oaks (Quercus spp.) [7,15,16,30,32,34,43]. The
following grasses frequently grow in the understory of Joshua tree
woodlands: big galleta (Hilaria rigida), galleta (Hilaria jamesii), and
bush muhly (Muhlenbergia porterii) [7,16].
Soils: Joshua trees have been reported on coarse sand, very fine silt,
gravel, or sandy loam [8,20,43]. Many sites have bimodal soils with
both coarse sands and fine silts [20].
Climate: Annual preciptation in many Joshua tree woodlands averages
only 5 inches (13 cm) or less [32], although some sites receive as much
as 8 to 10 (20-25 cm) inches [25]. Most precipitation occurs in winter
or early spring with very little rainfall during the summer [32]. The
distribution of this species is limited by low temperatures at higher
elevations but is largely unaffected by high temperatures [34]. The
Joshua tree can tolerate temperature extremes [6,34]. Evidence suggests
that the Joshua tree was much more widely distributed in more humid
prehistoric times [20]. During moister full-glacial periods of the late
Pleistocene, the range of the Joshua tree extended to the valley floor
of the Mohave Desert in areas where it is now restricted to uplands
above 5,576 feet (1,700 m) [45].
Elevation: Elevational range of Joshua tree is 2,000 to 6,000 feet
(610-1,829 m) in California [42], 2,000 to 6,900 feet (610-2,103 m) in
Nevada [35], and 2,624 to 7,216 feet (800-2,200 m) in Utah [46].
SUCCESSIONAL STATUS :
The slow-growing, long-lived Joshua tree is an important constituent of
a number of climax desert communities. It is generally not well
represented in most seral communities.
SEASONAL DEVELOPMENT :
Joshua tree requires sufficient precipitation for flowering to occur.
On some extremely harsh, arid sites, flowering rarely if ever occurs
[20]. Start of flowering is probably controlled primarily by daylength
[1]. Variation in flowering dates according to taxonomic variety and
geographic location has been noted. Generalized flowering and fruiting
dates are as follows [11,26,28,35]:
Location Beginning of End of Variety Fruiting
flowering flowering
CA March May brevifolia ----
CA ---- ---- jaegeriana April
NV April May ---- ----
UT March March ---- ----
Annual variation in floral development has been reported. The following
data, collected over a 3-year period at a Nevada site, illustrate the
range of annual phenological development in this species [1]:
Stage 1971 1972 1973
bud March February March
flower April March April
fruit May-June May-June May-June
Most annual vegetative growth of the Joshua tree occurs during a
5-month-long winter-spring growing season [34].
FIRE ECOLOGY
SPECIES: Yucca brevifolia | Joshua Tree
FIRE ECOLOGY OR ADAPTATIONS :
Joshua tree exhibits numerous specialized adaptations to fire. Fire may
be extremely important in both producing and maintaining large pure
stands [42]. Fires may be frequent in some Joshua tree woodlands. In
some areas, these tall, arborescent plants are frequently struck by
lightning [R. Hunter, pers. comm. 1989].
Trees tend to become more fire resistant with age. The thick mat of
dried leaves along the trunk decreases with age, and the flaky
alligator-like bark of older trunks serves as a firebreak between
surface fuels and the flammable shag on upper limbs [42]. Torching of
the crowns is less likely in older stands. Here, terminal buds are
protected by the height of older trees which may grow to 30 feet (9.2 m)
or more, and by protective sheaths of thick, green leaves which surround
the buds [42].
Joshua tree is generally capable of vigorous root and stump sprouting
after fire [9,42]. Seed can remain viable in the soil for a number of
years [43], and reestablishment through on-site or off-site seed is
possible, particularly on more mesic sites or in favorable years.
POSTFIRE REGENERATION STRATEGY :
survivor species; on-site surviving root crown or caudex
survivor species; on-site surviving rhizomes
off-site colonizer; seed carried by wind; postfire years 1 and 2
off-site colonizer; seed carried by animals or water; postfire yr 1&2
FIRE EFFECTS
SPECIES: Yucca brevifolia | Joshua Tree
IMMEDIATE FIRE EFFECT ON PLANT :
Plants are generally not killed by fire even when aboveground vegetation
is consumed or badly damaged.
DISCUSSION AND QUALIFICATION OF FIRE EFFECT :
NO-ENTRY
PLANT RESPONSE TO FIRE :
Joshua tree generally sprouts vigorously from the roots, stump, or
rhizomes after foliage is removed or damaged by fire [9,42]. The
numerous, fast-growing rhizomes [43] are well protected from heat by
overlying layers of soil. Plants often appear more dense and shrubby
after fire because of prolific sprouting [9]. Individual trees are
often surrounded by a close group of sprouts [42]. Joshua trees in
previously burned stands may form clumps up to 33 feet (10 m) in
diameter [42].
Evidence suggests that Joshua tree seed can remain viable buried in the
soil for a number of years [43]. Rodents are known to cache seed [21],
and germination of seeds protected by soil in caches is possible.
Reestablishment through on-site or off-site seed may occur on more mesic
sites or in exceptional years. Postfire recovery time of the Joshua
tree has not been well documented but probably varies with fire
intensity and severity, season of burn, and site characteristics.
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE :
NO-ENTRY
FIRE MANAGEMENT CONSIDERATIONS :
NO-ENTRY
REFERENCES
SPECIES: Yucca brevifolia | Joshua Tree
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Index
Related categories for Species: Yucca brevifolia
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