Download Izote (Yucca brevifolia)

Izote (Yucca brevifolia)
Si n ón i mos: Yucca arborescens, Cleistoyucca arborescens, Cleistoyucca brevifolia, Yucca draconis var. arborescens
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Taxon biology
Maxwell [68] describes Joshua tree as a "delight to the eye and a fascinating feature of the western
landscape." More specifically, however, Joshua tree is a 20- to 70-foot (5-20 m) tall, evergreen, tree-like
plant. Trees exceeding 40 feet (10 m) are rare, and height is easily overestimated [51,62,72,76,77]. Tree
size and growth form often vary with site and climate conditions [37,68,92]. Typically trees have 1 main
stout stem that measures 1 to 3 feet (0.3-0.9 m) in diameter and have an expanded base
[21,50,56,105,107]. Growth forms with several large stems are noted as well [92,107,110]. Trunks are
fibrous, and the bark or periderm is "soft and cork like" [55,66,92]. Mature tree trunks typically measure
1 to 3 feet (0.3-0.9 m) in diameter. Bark plates measure 3 to 6 inches (7.5-15 cm) long by 1 to 2 inches
(2.5-5 cm) in thickness [72].
Branching is often extensive on old plants, and rounded open crowns are common [37,50,62,92]. Young
trees typically lack branches and are covered with persistent reflexed leaves [105]. Trees normally
reach 3 to 9 feet (0.9-3 m) tall before branching [66]. Johnson [47] describes Joshua tree branching as
"grotesque" and random. However, branching is formally referred to as dichotomous or almost
dichotomous. Branches are formed following terminal bud death due to flowering or insect damage
[50,66,68,88]. Branches are often 7 to 20 feet (2-5 m) or longer and fork at 2- to 3-foot (0.6-0.9 m)
intervals. Inner branches are typically erect, and outer branches can be horizontal or drooping
[21,50,62,72,110].
Joshua tree is slow growing and long lived [22,62]. Wallace and Romney [105] indicate that height,
growth rings, or number of leaf blades may be used to age Joshua tree, but they caution that height
may not accurately age "very mature" plants. Webber [107] reports that 21-year-old Joshua trees were
unbranched, and the average annual growth rate was 5.9 cm/year. Other Y. b. var. jaegeriana plants
grew an average of 11.7 cm/year. Johnson [47] indicates that large trees can be 300 years old, and Keith
[55] suggests that Joshua tree has an average life span of 150 years. Little [62] suggests that Joshua tree
is among the among the desert's "oldest living plants." An approximately 60-foot-tall (20 m) tree in
California was an estimated 1,000 years old [62].
Leaves are clustered in rosettes at the branch ends. Clusters are commonly 1 to 5 feet (0.3-1.5 m) long
and 1 to 2 feet (0.3-0.5 m) in diameter. Leaves are linear, needle shaped and measure 5.9 to 14 inches
(15-35 cm) long by 0.3 to 0.6 inch (0.7-1.5 cm) wide. Enlarged bases attach the leaves to the branch. Leaf
shape is slightly triangular and leaf margins are lined with small teeth. Spines measuring 0.3 to 0.5 inch
(7-12 mm) occur at the leaf tips [6,21,37,50,51,62,76,77,107,110]. Leaf clusters are longer (3 to 5 feet (1-1.5
m)) on juvenile plants than on mature plants (1-3 feet (0.3-1 m)) [72]. Outer leaf layers are thick and
waxy to reduce water loss [66]. Dead leaves are persistent and fold down, covering the branches and
coating the trunks of young trees [47].
Joshua tree flowers occur in dense, heavy panicles that measure 8 to 20 inches (20-40 cm) long.
Individual flowers are round to egg shaped and measure 1 to 2 inches (2.5-5 cm) by 0.4 to 0.8 inch (1-2
cm) wide [21,37,47,51,62,76,77,110]. Fruits are indehiscent capsules, which become spongy and dry with
age. Egg-shaped capsules are 2 to 4 inches (6-10 cm) long and approximately 2 inches (5 cm) in
diameter. Fruits develop at the base of the inflorescence while the upper portion is still in flower.
Mature fruits contain 30 to 50 seeds, which are flat to thickened with smooth to undulate surfaces.
Seeds are 0.3 to 0.4 inch (7-11 mm) long [3,21,47,50,61,62,72,76,77,107]. Fruit clusters often weigh over 9
pounds (4 kg), while a single capsule frequently weighs over 8.8 ounces (250 g). Fruits borne on erect
branches are not easily detached [61]. Average individual seed weight ranged from 0.0025 to 0.0035
ounce (0.07-0.1 g) based on several seed collections in the Southwest [3]. In Los Angeles County,
California, the average fruit length was 2.7 inches (69 mm), the number of seeds per locule averaged 26,
and individual seed weight averaged 99 mg [53].
Distribution
Yucca brevifolia occurs in parts of Southern California, southern Nevada, western Arizona and
southwestern Utah. In California the range includes the High Sierra Nevada (eastern slope), parts of the
Tehachapi Mountains and the Mojave Desert. The reader should note that there are certain revisions
being analyzed in the California distribution, and those differences create the discrepancies between
two different versions of the Jepson Manual. Here we follow the online version.
Description 1,2
Plants usually solitary, erect, arborescent, to 15 m. Stems usually 1, occasionally several–many, simple or
usually branched distally; branches 1–3 m. Leaf blade green, 15–35 × 0.7–1.5 cm, rigid, smooth,
glabrous, margins nearly entire, minutely denticulate, yellow. Inflorescences erect, paniculate, densely
crowded, ca. 1/2 enclosed in rosettes, ellipsoid-ovoid, 3–5.5 × 3–3.8 dm, glabrous. Flowers erect, 4–7 cm;
perianth oblong-ellipsoid to globose; tepals barely connate at base, greenish white to cream, lanceolate
to oblong, 2.5–7 × 1.1–2.2 cm; filaments 1–1.2 cm; anthers 3–3.2 mm, short-pubescent to papillate; pistil
2–3.5 cm; ovary ovoid, 2.5–3 cm, longer than broad; style ca. 1.6 mm; stigmas distinct. Fruits pendent,
capsular, indehiscent, deeply furrowed, ellipsoid, 6–8.5 cm, dry, spongy. Seeds dull black, thin, 8–12 mm
diam., smooth.
Synonym 1,2
Yucca draconis Linnaeus var. arborescens Torrey, Pacif. Railr. Rep. 5(4): 147. 1857; Cleistoyucca
arborescens (Torrey) Trelease; C. brevifolia (Engelmann) Rydberg; Yucca arborescens (Torrey) Trelease;
Y. brevifolia var. herbertii (J. M. Webber) Munz; Y. brevifolia var. jaegeriana McKelvey
Mojave desert habitat 3,4
This taxon is found in the Mojave Desert, the smallest of the four North American deserts. While the
Mojave lies between the Great Basin Shrub Steppe and the Sonoran Desert, its fauna is more closely
allied with the lower Colorado division of the Sonoran Desert. Dominant plants of the Mojave include
Creosote Bush (Larrea tridentata), Many-fruit Saltbush (Atriplex polycarpa), Brittlebush (Encelia
farinosa), Desert Holly (Atriplex hymenelytra), White Burrobush (Hymenoclea salsola), and Joshua Tree
(Yucca brevifolia), the most notable endemic species in the region.
The Mojave’s warm temperate climate defines it as a distinct ecoregion. Mojave indicator species
include Spiny Menodora (Menodora spinescens), Desert Senna (Cassia armata), Mojave Indigobush
(Psorothamnus arborescens), and Shockley's Goldenhead (Acamptopappus shockleyi ). The Mojave
supports numerous species of cacti, including several endemics, such as Silver Cholla (Opuntia
echinocarpa), Mojave Prickly Pear (O. erinacea), Beavertail Cactus (O. basilaris), and Cotton-top Cactus
(Echinocactus polycephalus).
While the Mojave Desert is not so biologically distinct as the other desert ecoregions, distinctive
endemic communities occur throughout. For example, the Kelso Dunes in the Mojave National Preserve
harbor seven species of endemic insects, including the Kelso Dunes Jerusalem Cricket (Ammopelmatus
kelsoensis) and the Kelso Dunes Shieldback Katydid (Eremopedes kelsoensis). The Mojave Fringe-toed
Lizard (Uma Scoparia), while not endemic to the dunes, is rare elsewhere. Flowering plants also attract
butterflies such as the Mojave Sooty-wing (Pholisora libya), and the widely distributed Painted Lady
(Vanessa cardui).
There are a total of eight amphibian species present in the Mojave Desert all of which are anuran
species: the endemic Relict Leopard Frog (Lithobates onca); the endemic Amargosa Toad (Anaxyrus
nelsoni ); Lowland Leopard Frog (Lithobates yavapaiensis); Red-spotted Toad (Anaxyrus punctatus);
Southwestern Toad (Anaxyrus microscaphus); Great Basin Spadefoot (Spea intermontana); Great Plains
Toad (Anaxyrus cognatus); and the Pacific Treefrog (Pseudacris regilla).
The native range of California’s threatened Desert Tortoise (Gopherus agassizii ) includes the Mojave
and Colorado Deserts. The Desert Tortoise has adapted for arid habitats by storing up to a liter of water
in its urinary bladder. The following reptilian fauna are characteristic of the Mojave region in particular:
Gila Monster (Heloderma suspectum NT); Western Banded Gecko (Coleonyx variegatus), Northern Desert
Iguana (Dipsosaurus dorsalis), Western Chuckwalla (Sauromalus obesus), and regal horned lizard
(Phrynosoma solare). Snake species include the Desert Rosy Boa (Charina trivirgata gracia), Mojave
Patchnose Snake (Salvadora hexalepis mojavensis), and Mojave Rattlesnake (Crotalus scutulatus).
Endemic mammals of the ecoregion include the Mojave Ground Squirrel (Spermophilus mohavensis)
and Amargosa Vole (Microtus californicus scirpensis); and the California Leaf-nosed Bat (Macrotus
californicus).
Broad scale impacts of plant response to fire 5
More info for the terms: cover, density, frequency, rhizome, root crown, shrubs, tree
In the few Joshua tree fire studies published to date (2006), Joshua tree cover or density
was commonly lower on burned than unburned sites. In 1 case, reduced Joshua tree density on
burned sites was apparent for 17 years following a severe fire [60]. In another case,
Joshua tree density was equal on burned and unburned sites 10 years
following fire, and the researcher suggested that early postfire coverage
of Joshua tree may be greater on burned than unburned sites due to postfire sprouting
[5].
Two days after a late June fire in California's San Bernardino County,
researchers found that some aboveground stems had survived and that rhizomes
approximately 1 foot (0.3 m) below ground were uninjured. Fire
characteristics were not described [92].
Joshua tree sprouts were observed 1 year following an August fire in Joshua Tree
National Park. High winds were reported but other fire characteristics were not.
Three to four sprouts sometimes occurred where a single tree had burned. Sprouts
were much more common from small Joshua trees (under 10 feet (3 m)) tall that were
approximately 5 to 50 years old than from large burned trees. The researcher
suggested that large trees had more area covered with fire-fueling dead leaves
and may have burned at a higher temperature than small trees. Mortality was
greater for large than small trees [5].
Researchers found Joshua tree root crown sprouts and canopy sprouts following a
July 1995 lightning fire in the Lower Covington Flats area of Joshua Tree
National Park. Twenty-eight percent of Joshua tree plants along five 1,000-m²
belt transects had root crown sprouts 16 months following fire. Canopy sprouts
occurred in 4% of the plants, but no plant had both rhizome or root crown and canopy sprouts.
Researchers speculated that root crown sprouting was likely related to extent of
tissue death, which was determined by fire temperature [64].
Joshua tree was classified as an increaser following fire when burned and unburned
sites were compared in the Joshua tree woodland-singleleaf pinyon-California
juniper ecotone in the Victor Valley of the southwestern Mojave Desert. Six
burned and adjacent unburned sites were evaluated. Sites had burned
approximately 3 to 13 years earlier in June, July, or August. No other fire
characteristics were reported. Joshua tree density was determined using 0.025-acre
quadrats. Density averaged 71 individuals/acre on unburned sites and 142.7
individuals/acre on burned sites. Frequency of Joshua tree was slightly lower on burned
(29.2%) than on unburned (36.3%) sites. The
clumped nature of postfire sprouts explained the increases in density and decreases in
frequency. Methods for delineating individual plants for density estimates were
not reported. Mature trees without shaggy dead leaves at the base of the plant
had outer periderm exposed, which reduced the chance of fire in the crowns and
increased the chance of apical meristem survival [96].
Researchers found that Joshua tree height and
basal diameter generally increased with increased time since fire in a study of
burned sites in Joshua Tree National Park. Visited sites had burned 1 to 28 years
previously. Sites with longer recovery time had the most Joshua trees growing
independently of a nurse plant and the fewest fire surviving plants (identified
as sprouts in the table). Sites burned 9 to 12 years earlier were a mixture of Joshua tree sprouts and
seedlings (mostly emerging from the canopy of nearby vegetation), while sites burned 1
year earlier were populated only by sprouting Joshua trees. Study results are
summarized below [64]:
Site
Frequency (%)
Time since fire (years)Number of trees measuredIndependentCanopy emergentSprout (based on fire
scars)Lost Horse Valley282277.29.113.6Covington Falls181566330Hidden Valley12147.128.664.3Lost
Horse Mine91216.641.641.6Lower Covington Flats13700100
In Joshua Tree National Park, Joshua tree was absent from early postfire communities,
but density on burned and unburned sites was equal 10 years following fire.
Joshua tree was only found on unburned sites following an August lightning fire in
the western part of Joshua Tree National Park. Burned areas were visited 3
months, 6 months, and 8 months following the fire. Fire characteristics were not
reported [59]. In other studies, Joshua tree density was equal on 10-year-old burned and
unburned sites in Joshua Tree National
Park. No information about the fire was provided [5]. Joshua tree was
present on 3 burned sites in the Mojave Desert. Sites had burned 6, 8, and 14
years earlier. Neither absolute coverage percentages on burned and unburned sites
nor fire characteristics were
reported [16].
Joshua tree density
was greater on unburned than burned sites in southern Nevada's Spring Mountain area.
Joshua tree was absent from sites burned 8 and 13 years before the study, but present on sites
burned 17 years earlier. Differences between burned and unburned densities were
greatest on severely burned sites. Generally, burned soils had higher soil
temperatures but lower organic matter and moisture contents than unburned soils.
The table below summarizes fire characteristics and Joshua tree density on burned and
unburned plots [60]:
SiteElevation
(m)Fire
causeSeverity
ratingPostfire
yearBurned density
(plants/100 m²)Unburned densitySandy Valley1300naturalsevere800.5Bird
Spring1200humansevere1301.5Sandstone Canyon1400 humanmoderate170.010.02Blue
Diamond1250humansevere17<0.011.9
Hughes [40] provides purely descriptive studies of burned and unburned sites within
the Big Hole grazing allotment in northwestern Arizona. Sites were visited in late 1990s or
early 2000s. In 1 area, the prefire community was dominated by blackbrush, creosotebush, and
Joshua tree.
The area burned in the 1940s, and most of the burned area was dominated by
unidentified annual species. Hughes [40] reported that Joshua tree and other shrubs were returning to
the burned sites. In
another area burned between 1970 and 1980, annuals were dominating burned sites, and
Joshua tree was conspicuous only on unburned sites [40].
Flowering/fruiting 1,2
Flowering late winter--mid spring.
Life cycle 6
Persi sten ce : PERENNIAL
Reproduction 6
Seeds dispersed by seed caching rodents. Most seeds were cached within 30 m of host plant (Wall et al
2006).
National nature serve conservation status 6
United States
R ou n d ed N ati on al Statu s R an k : N4 - Apparently Secure
Management considerations 5
More info for the term: tree
Bi omass esti mati on s:
Researchers developed a method for estimating the biomass of Joshua tree in an entire watershed.
Estimations are based on Joshua tree size classes and their corresponding mean weights [10].
Cl i mate ch an ge:
Numerous studies have investigated the potential changes in Joshua tree growth and
distribution based on climate change and elevated CO2 levels.
Huxman and others [45] conducted experiments on Joshua tree growth and photosynthetic
capabilities under elevated CO2 levels and increased temperatures.
Dole and others [25] modeled changes in
Joshua tree's distribution based on climate change and increased CO2
levels. Based on work by Loik and others [63], the lethal low temperature
tolerance for Joshua tree seedlings is lowered by 2.9 °F (1.6 °C) under doubled CO2
concentrations. The model predicted that a considerable portion of Joshua tree's
current range would become unsuitable, but that some new habitat would be made
suitable. However, occupation of new habitats would depend on successful
recruitment and availability of the new habitats. For
maps of the future distribution of Joshua tree with climate change, increased CO2
levels, and/or altered freezing tolerance, see [25].
Other uses and values 5
More info for the term: tree
Joshua tree may have been an important part of giant ground sloth diets. The analysis of giant ground
sloth dung found in Nevada's Gyssum Cave revealed that ~80% of the fecal material was Joshua tree
[50]. Maxwell [68] also noted that Joshua tree was a regular part of the giant ground sloth diet.
However, evidence provided by Lenz [61] suggests that the importance of Joshua tree in giant ground
sloth diets has been exaggerated.
Native people of the Mojave Desert used Joshua tree for food and in construction. Cahuilla people of
southern California used Joshua tree fibers to make sandals and nets and consumed Joshua tree
blossoms [8]. Red Joshua tree rootlets were utilized as a dye for baskets and blankets [2,55], and sweet
Joshua tree flowers were roasted and eaten by Native people [55]. Joshua tree seeds were eaten raw or
ground into a mash and cooked by southern California Natives [79]. In a review, Webber [107] reports
that Joshua tree beams and timber have been found in ancient cliff dwellings.
Comments 1,2
There is disagreement regarding the status of entities within Yucca brevifolia. S. D. McKelvey (1935)
described var. jaegeriana, the miniature Joshua tree, and L. D. Benson and R. A. Darrow (1981)
recognized the variety as well; however, J. L. Reveal (1977c) declined to recognize it, a decision with
which we agree.
Taxonomy 5
More info for the term: tree
The scientific name of Joshua tree is Yucca brevifolia Engelm. (Agavaceae) [29,37,49,50,110]. Joshua tree
is
part of the spongy-fruited or Clistocarpa section of the Yucca genus [72,107].
The following varieties are recognized, although not consistently:
Yucca brevifolia var. brevifolia Engelm.
Yucca brevifolia var. jaegeriana McKelvey [49,50]
In the Tickapoo Valley of southern Nevada, the distributions of
Y. b. var. brevifolia and Y. b. var. jaegeriana
overlap, and hybridization may occur [88].
The scientific names given above will be used when discussing varieties in
this review.
References
1. Flora of North America Vol. 26: 421, 424, 426, 427 in eFloras.org, Missouri Botanical Garden.
Accessed Nov 12, 2008.
2. © Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO, 63110 USA, some rights
reserved
3. C. Michael Hogan & World Wildlife Fund. 2013."Mojave Desert". Encyclopedia of Earth, National
Council for Science and the Environment, Washington DC ed.Mark McGinley.
4. © C. Michael Hogan & World Wildlife Fund, some rights reserved
5. Gucker, Corey L. 2006. Yucca brevifolia. In: Fire Effects Information System, [Online]. U.S.
Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences
Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/
6. © NatureServe, some rights reserved