| “I Speak for
the Trees” Dr. Seuss, The Lorax |
| by Vegetation Specialist Jane Rodgers |
|
| Surrounded by twisted, spiky trees straight out of a Dr. Seuss book, you
might begin to question your map. Where are we anyway? In wonder, the traveler
pulls over for a snapshot of this prickly oddity; the naturalist reaches
for a botanical guide to explain this vegetative spectacle; and the rock
climber shouts “Yowch!” when poked by dagger-like spines on the
way to the 5.10 climbing route. |
|
| Known as the park namesake, the Joshua tree, Yucca brevifolia,
is a giant member of the lily family. Like the California fan palm, Washingtonia
filifera, the Joshua tree is a monocot, in the subgroup of flowering
plants that also includes grasses and orchids. Don’t confuse the Joshua
tree with the Mojave yucca, Yucca schidigera. This close relative
can be distinguished by its longer, wider leaves and fibrous threads curling
along leaf margins. Both types of yuccas can be seen growing together in
the park. 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 American Indians for its useful
properties: tough leaves were worked into baskets and sandals, and flower
buds and raw or roasted seeds made a healthy addition to the diet. The local
Cahuilla have long referred to the tree as “hunuvat chiy’a”
or “humwichawa;” both names are used by a few elders fluent in
the language. |
| By the mid-19th century, Mormon immigrants had made their way across the
Colorado River. Legend has it that these pioneers named the tree after the
biblical figure, Joshua, seeing the limbs of the tree as 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 trunks 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 life cycle
begins with the rare germination of a seed, its survival dependent upon
well-timed rains. Look for sprouts growing up from within the protective
branches of a shrub. Young sprouts may grow several inches in the first
five years, then slow down, 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 about 300
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 long stalks
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 freezing temperatures may damage the growing
end of a branch and stimulate flowering, followed by branching. You may
notice some Joshua trees grow like straight stalks; these trees have never
bloomed—which is why they are branchless! In addition 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
develop and mature, the eggs hatch into larvae, 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 a yucca’s branches. At
the base of rocks you may find a wood rat nest built with spiny yucca leaves
for protection. As evening falls, the desert night lizard begins poking
around under the log of a fallen Joshua tree in search of tasty insects.
|
| You may be at ease with pine or hardwood, or find shade under the domesticated
trees in your city park, but in the high desert, Joshua is our tree. It
is an important part of the Mojave Desert ecosystem, providing habitat for
numerous birds, mammals, insects, and lizards. Joshua tree forests tell
a story of survival, resilience, and beauty borne through perseverance.
They are the silhouette that reminds those of us who live here that we are
home. Like the Lorax we speak for the trees, but often the trees speak to
us. |
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http://www.nps.gov/jotr/plants/plants/trees/speak.html
last modified: 1/06/05
web editor: Sandra kaye |
