The Joshua tree, Yucca brevifolia, is a giant member of the lily family. Like the
California fan palm, Washingtonia filfera, the Joshua tree is a monocot, in the
subgroup of flowering plants which also includes grasses and orchids. The
Joshua tree provides a good indicator that you are in the Mojave Desert, but
you may also find it growing next to a saguaro cactus in the Sonoran Desert in
western Arizona or mixed with pines in the San Bernardino Mountains.
Years ago, the Joshua tree was recognized by Native Americans for its useful
properties; tough leaves were worked into baskets and sandals, and raw or
roasted flower buds and seeds made a healthy addition to the diet.The local
Cahuilla tribe has long referred to the tree as "hunuvat chiy'a" or
"humwichawa;" both names now rest with a few elders still fluent in the
By the mid 19th century, Mormon migrants had made their way across the Colorado
River. Legend has it that these pioneers named the tree after the
prophet Joshua, seeing the Joshua tree limbs outstretched in supplication,
guiding the travelers westward. Concurrent with Mormon settlers, ranchers
and miners arrived in the high desert with high hopes of raising cattle and
digging for gold. These homesteaders used the Joshua tree's limbs and truncks
for fencing and corrals. Miners found a source of fuel for the steam engines
used in processing ore.
Today we enjoy this yucca for its grotesque appearance, a surprising sight in the
landscape of biological interest. The Joshua tree's lifr cycle begins with the
rare germination of a seed, its survival dependent upon well timed rains.
Young sprouts may grow several inches in the first five years, then slow dow,
averaging one half inch per year thereafter. The tallest Joshua tree in the park
looms a whopping forty feet high, a grand presence in the Queen Valley
forest; it is estimated to be over nine hundred years old. These "trees" do not
have growth rings like you would find in an oak or pine. This makes aging
difficult, but you can divide the height of a Joshua tree by the average annual
growth of one half inch to get a rough estimate.
Spring rains may bring clusters of white green flowers on the long stocks at branch
tips. Like all desert blooms, Joshua trees depend on just the perfect
conditions: well timed rains and for the Joshua tree, a crisp winter freeze.
Researchers believe that below freezing temperatures may damage the
growing end of a branch and stimulate flowering followed by branching. Some
Joshua trees grow straight stalks; these trees have never bloomed,
which is why they are branchless. In additions to ideal weather, the pollination
of flowers requires a visit from the yucca moth. The moth collects
pollen while laying her eggs inside the flower ovary. As seeds develope and
mature, the eggs hatch into larve which feed on the seeds. The tree relies on
the moth for pollination and the moth relies on the tree for a few seeds for her
young, a happy symbiosis. The Joshua tree is also capable of sprouting
from roots and branches. Being able to reproduce vegetatively allows a much
quicker recovery after damaging floods or fires which may kill the main tree.
Many birds, mammals, reptiles and insects depend on the Joshua tree for food and
shelter. Keep your eyes open for the yellow and black flash of a Scott's oriole
busy making a nest in the yucca branches. At the base of rocks you may find a
wood rat nest built with protective spiny yucca leaves. As evening falls, the
desert night lizard begins poking around under the log of a fallen Joshua tree
in search of tasty insects.
The Joshua tree is and important part of the Mojave Desert ecosystem, providing
habitats for numerous birds, mammals, insects and lizards. Joshua tree forests
tell a story of survival, resilience, and beauty borne through