- Joshua Tree
- Yucca brevifolia Engelm
- Joshua Tree Information – Joshua Tree Growing Tips And Care
- Joshua Tree Information
- How to Grow a Joshua Tree
- Joshua Tree Growing Tips
- Anyone know where I might be able to purchase a Joshua Tree?
- Joshua Tree (Yucca brevifolia)
- Joshua trees are blooming early in the desert. It’s not a good thing — you can thank climate change
Yucca brevifolia Engelm
The Joshua tree, the largest of the yuccas, grows only in the Mojave Desert. Natural stands of this picturesque, spike-leafed evergreen grow nowhere else in the world. Its height varies from 15-40 feet with a diameter of 1-3 feet. They grow 2 to 3 inches a year, takes 50 to 60 years to mature and they can live 150 years.
Joshua trees (and most other yuccas) rely on the female pronuba Moth (Tegeticula) for pollination. No other animal visiting the blooms transfers the pollen from one flower to another. In fact, the female yucca moth has evolved special organs to collect and distribute the pollen onto the surface of the flower. She lays her eggs in the flowers’ ovaries, and when the larvae hatch, they feed on the yucca seeds.
Without the moth’s pollination, the Joshua tree could not reproduce, nor could the moth, whose larvae would have no seeds to eat. Although old Joshua trees can sprout new plants from their roots, only the seeds produced in pollinated flowers can scatter far enough to establish a new stand.
Mormon pioneers are said to have named this species “Joshua” tree because it mimicked the Old Testament prophet Joshua waving them, with upraised arms, on toward the promised land. This unique species grows abundantly at Joshua tree.
Joshua trees, Yucca brevifolia, grow in the Mojave Desert of southwest California, Nevada, Utah and Arizona, at elevations from 2,000 to 6,000 feet.
The Joshua tree likes dry soils on plains, slopes and mesas, often growing in groves.
The Joshua tree has bell-shaped blooms, 1.25 to 1.5 inches large, each with 6 creamy, yellow-green sepals, crowded into 12 to 18 inch, many-branched clusters with an unpleasant odor. The trees bloom mostly in the spring, although not all of them will flower annually.
The fruit is elliptical and green-brown. Six-celled, 2.5 to 4 inches, and somewhat fleshy, it dries and falls soon after maturity in late spring revealing many flat seeds.
|Rank||Scientific Name and Common Name|
|Kingdom||Plantae – Plants|
|Subkingdom||Tracheobionta – Vascular plants|
|Superdivision||Spermatophyta – Seed plants|
|Division||Magnoliophyta – Flowering plants|
|Class||Liliopsida – Monocotyledons|
|Family||Agavaceae – Century-plant family|
|Genus||Yucca L. – yucca|
|Species||Yucca brevifolia Engelm. – Joshua tree|
Want to grow your own Joshua tree?
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U2′s Joshua Tree
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Botanical Profile of the Joshua Tree
by Richard Katz
The Joshua tree is an unusual tree-like species of Yucca, a member of the Lily Family (Liliaceae), and sometimes considered in the Agave Family (Agavaceae).
Habitat and range
It grows uniquely in the desert southwest of the United States, principally in California’s Mohave Desert, Antelope Valley and the surrounding area, and also in parts of Arizona, Nevada, and the southwest corner of Utah. It is found typically in the high desert, around 4000 feet (1200 m) elevation where there are freezing temperatures during winter nights, and very hot, dry summers. The small annual rainfall occurs primarily in the winter, with occasional dustings of snow. Thus, while this is a severe climate, it is not quite as hot or dry as the lower elevation Sonoran deserts.
The Joshua tree is not a true “tree,” in that it does not produce a trunk with annual rings. For the first several decades of its life, the Joshua Tree grows as a vertical stem with no branches. It grows very slowly, only 1/2 to 3 inches (1 to 7 cm) per year, typically reaching 5-10 feet (1.5 to 3 meters) before the first blossoms appear. At this point, the Joshua tree literally takes a new turn in its development. After flowering, the blossoms drop off, leaving a length of dried stalk. New leaves grow beneath this dead portion, and a new branch begins its growth in another direction.
Unlike a typical tree branch, this new stem grows rigidly in a totally different direction, at an angle, horizontally, or even down towards the ground. Each branching stem also abruptly ends its growth after blossoming, and further branches veer off in new directions. As well as ending in blossoming, branching may occur where a stem has been damaged by insects.
After many years, some Joshua trees develop a complex system of twisted branches growing in many directions. Others develop a more harmonious tree shape, while still others remain mostly vertical. The amazing variety of shapes and growth patterns imparts an unusual individuality to each tree.
The largest Joshua tree on record was 80 feet (24 meters) tall and was estimated to be about 1000 years old. Joshua trees typically grow more than 20 feet tall (6 meters). They may take 60 years to come to maturity, and can live more than 500 years.
Young Joshua Trees have soft, tender leaves which make them vulnerable to desert animals. Therefore, they do best when they are seeded next to a “nurse plant” which protects them when they are first growing.
After they are about 10-12 inches (25-30 cm) tall they develop their characteristic sharp, pointed leaves, sword-like in their intensity. These not only afford protection, and because of their form, they minimize the loss of water through evaporation. During infrequent rain showers, the concave shape of the leaves captures the water and directs it to the trunk and down to the roots. As well, the mass of foliage tends to create a still-air zone around the plant, further reducing the evaporative effects of the drying desert winds.
Leaves are generally 5-12 inches (12-30 cm) long. The younger ones remain green, but as they age the leaves fade to gray and become a fibrous residue which droops and finally covers the branch or trunk in a protective coating. As mentioned above, the leaves are somewhat concave, which allows rain to collect and be drawn into the plant, where it can make its way down the trunk to the roots. Thus the leaves embody this plant’s ability to survive in the harsh, dry desert climate.
Flowers and pollination
The flowers begin as greenish buds clustered near the end of the branches. The six tepals (3 petals and 3 similar sepals) then open up, to reveal a pod-like ovary, surrounded by six stamens, with one pistil. The flowers are waxy, white-to-greenish-white, and 2-3 inches long (5-7 cm). The flowers emit a sweet fragrance reminiscent of coconut.
The Joshua Tree pollen is so sticky that it cannot be carried by the wind. Pollination is accomplished only with the help of the tiny Yucca moth, with which this species has evolved a symbiotic relationship. This moth (Pronuba yuccasella) collects the pollen from a number of flowers and then chooses one flower as a home for its offspring. It deposits the pollen on the flower’s stigma in the process of laying eggs in the flower’s ovary. The newly hatched larvae will feed on the seeds (consuming only about 20 out of 200 in each ovary).
After the Joshua Tree flower is pollinated, the ovary swells with seeds and the flower falls away. The ripened fruit then falls to the ground where the seeds are scattered, often taken up by the wind. Very few will be able to germinate in the harsh desert conditions, but it is by this process of seed propagation that the new plant colonies are established.
The Joshua Tree can also propagate by shoots from its roots or crown, and this is particularly important when the upper part of the tree is destroyed by fire.
Seasonal and Diurnal Cycles
The blooming cycle of the Joshua Tree is totally dependant on climatic conditions. Depending on the timing and intensity of winter rains, blossoming can occur any time from March to May, and can very from very sparse to a rare abundance of blossoms in relative wet years.
Joshua Tree has a special relationship with the night. The leaves actually remain dormant during the day, and save their respiration cycle (exchange of carbon dioxide and oxygen) for the night-time hours when the air is cooler, and moisture can be conserved. It is also at night, after dusk, when the Pronuba moth pollinates the flowers. A number of observers have noted that the Joshua Tree flowers, which never appear fully open, reveal themselves more to the night, as well as releasing their fragrance into the night air. Joshua Tree is in its full glory in a moonlit desert night, as its white flowers glow in the eerie luminescence of reflected light.
History and Lore
Archaeological evidence indicates that the Joshua Tree dates back to the Pliocene Epoch, some two million years ago, when the climate was more moist and warm, and its habitat more extensive.
Native Americans knew the Joshua tree as a source of food and fiber. The flowers were considered a sweet delicacy, roasted over a fire. The leaves were used for baskets and cordage.
Early European settlers often saw the Joshua Tree as grotesque and misshapen. However, the Mormons, trying to find their way back from California to Utah, used the Joshua Tree as a guide. They gave the plant its name in the early 19th century, because it reminded them of the biblical prophet Joshua, with his arms upraised in prayer. They saw this plant as a spiritual sign of welcome into the Promised Land.
The Joshua Tree (Yucca brevifolia) is the largest of the Yucca species. Often considered part of the Agave family (Agavaceae), or grouped with Agave (Century Plant) in the Lily family (Liliaceae), the Joshua Tree has the same linear, sharply pointed leaves as Agaves and other Yuccas. The species name brevifolia describes the shortness of the leaves. Joshua Tree differs from other Yucca not only in its size and longevity (well over 500 years), but also in their irregular growth patterns (described previously).
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Joshua Tree Information – Joshua Tree Growing Tips And Care
The Joshua tree (Yucca brevifolia) bestows the architectural majesty and character of the American Southwest. It sculpts the landscape and provides important habitat and food for numerous native species. The plant is a yucca and is native to the Mojave Desert. It is an adaptable plant that can tolerate USDA plant hardiness zones 6a to 8b. Gather information on how to grow a Joshua tree and enjoy this plant and its fascinating distinctions in your landscape. Joshua tree growing tips will help you enjoy this majestic and wacky looking tree.
Joshua Tree Information
The Joshua tree is the largest of the yuccas. It is an evergreen perennial plant that starts out as a stem-less rosette and gradually grows a thick trunk decorated by sword-like leaves. The leaves grow in clumps off a scaffold of open ranging branches. The effect is bizarre, yet picturesque, and is a hallmark of the Mojave Desert. Leaves are up to 14 inches long, sharply tipped and bluish green.
The plants may live for 100 years and grow 40 feet tall. In the home landscape they are more likely to top out at 8 feet. Joshua tree care is simple, provided they are installed in appropriate climates, soil and light situations.
How to Grow a Joshua Tree
Joshua trees require full sun and gritty, even sandy, soil. The plants are available at nurseries and some garden centers but you can also grow them from seeds. Seeds need a chilling period of at least 3 months. Soak them after chilling and sow them in 2-inch pots filled with moistened sand. Place pots where temperatures are at least 70 F. (21 C.).
The plants also produce offsets, an important bit of Joshua tree information, which can be divided away from the parent plant. Caring for Joshua tree babies is similar to regular yucca care.
Joshua Tree Growing Tips
Baby plants require more water as they establish roots than their mature counterparts. Water the new plants weekly as part of good Joshua tree care. Mature trees only need water in periods of high heat and drought. Allow the soil to dry out between irrigation periods. Do not give supplemental water in winter.
Older plants will flower in March to May and spent flower stems need to be removed. Plant the Joshua tree in full sun, in sandy or rocky soil, where drainage is excellent. Soil pH may be acidic or slightly alkaline.
You can also grow the yucca in a pot for a couple of years. The plant averages 12 inches of growth per year, so eventually you will need to install it in the ground.
Watch the leaves for signs of fungal disease and apply fungicide as needed. Weevils, thrips, scab and mealybugs will all cause chewing and sucking damage to the leaves. Use a horticultural soap to combat these pests when caring for Joshua trees.
Anyone know where I might be able to purchase a Joshua Tree?
Section 2. Growth and development of article Yucca brevifolia:
Joshua trees are fast growers for the desert; new seedlings may grow at an average rate of 7.6 cm (3.0 in) per year in their first ten years, then only grow about 3.8 cm (1.5 in) per year thereafter. The trunk of a Joshua tree is made of thousands of small fibers and lacks annual growth rings, making it difficult to determine the tree’s age. This tree has a top-heavy branch system, but also has what has been described as a “deep and extensive” root system, with roots possibly reaching up to 11 m (36 ft) away. If it survives the rigors of the desert it can live for hundreds of years with some specimens surviving up to a thousand years. The tallest trees reach about 15 m (49 ft). New plants can grow from seed, but in some populations, new stems grow from underground rhizomes that spread out around the Joshua tree.
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Joshua tree (Yucca brevifolia) is a distinctive and charismatic plant of the Mojave Desert. Although floral biology and seed production of Joshua tree and other yuccas are well understood, the fate of Joshua tree seeds has never been studied. We tested the hypothesis that Joshua tree seeds are dispersed by seed-caching rodents. We radioactively labelled Joshua tree seeds and followed their fates at five source plants in Potosi Wash, Clark County, Nevada, USA. Rodents made a mean of 30.6 caches, usually within 30 m of the base of source plants. Caches contained a mean of 5.2 seeds buried 3-30 nun deep. A variety of rodent species appears to have prepared the caches. Three of the 836 Joshua tree seeds (0.4%) cached germinated the following spring. Seed germination using rodent exclosures was nearly 15%. More than 82% of seeds in open plots were removed by granivores, and neither microsite nor supplemental water significantly affected germination. Joshua tree produces seeds in indehiscent pods or capsules, which rodents dismantle to harvest seeds. Because there is no other known means of seed dispersal, it is possible that the Joshua tree-rodent seed dispersal interaction is an obligate mutualism for the plant.
Joshua Tree (Yucca brevifolia)
Joshua Tree in Bloom
Joshua Trees have a woody, tree-like structure with evergreen leaves that are like bayonets (extremely sharp) at the tip. Though they are unbranched when they are young, they generally branch when they are older and more mature (more than 3 feet high). Joshua Trees are found in dry desert flats and on slopes from about 2000 feet to about 6000 feet. Joshua Trees can grow to 30 ft. tall and live for hundreds of years.
The Joshua Tree’s habitat is primarily the Mojave Desert across Southern California, but it is also found in southwest Utah, southern Nevada, and western Arizona. It can grow in dense groups suggesting woodlands. (1)
Joshua Trees are a valuable resource in the landscape because of the wildlife they support. In the desert, they are a critical habitat for many small creatures such as pack rats and the Yucca night lizard, who may nest in holes in the trunk or in the litter at the base of the Joshua. Flickers, wrens, woodpeckers, flycatchers and titmice use the Joshua Tree for nesting in an otherwise bleak landscape.(2)
Joshua Tree leaves appear in dense clusters at the tip of its branches. The dagger-like leaves are sturdy and sharply pointed at the tip—dangerous to the touch! Older leaves dry up and point downward along the trunk or branch, and remain equally dangerous to handle. This prevents animals from climbing the trunk. New leaves emerge from the growing tip.
Joshua Trees typically don’t branch until they are decades into their lives.
Unbranched young Joshua.
Thus, tall Joshuas that have many branches may be over 100 years old.
Cluster of Joshua Tree Seeds
Joshua Tree Flowers
Creamy-white flower clusters form at the tip of branches from February to late April. They dry into clusters of large seed pods, and when dry, the black seeds can be harvested and used to sprout new trees.
Joshua Trees are pollinated by the yucca moth while laying eggs inside the fertilized flower. Larvae eat the seeds as they develop, but many more seeds are produced than are eaten, so any seed pod will likely have viable seeds. Pods dry to a creamy off-white color with a tough skin. Seeds are jet black when mature. One pod can produce more than 50 seeds.
Seeds are relatively easy to sprout if you know how. Visit our page on how to sprout Joshua Tree Seeds!
Joshuas grow painfully slowly but are an extremely hardy plant given the conditions that they tolerate in the desert — blazing sun, blistering heat, complete lack of moisture, sometimes for months.
Cluster of Joshua Tree Seed Pods
Joshua Trees are fast-growing when they are young (under 10 years old), but slow to an inch a year in some cases, when they are older (3 years+). If they survive the first years, they can live for hundreds of years and branch into extremely large trees. “Fast-growing” is a relative term, of course. Plants that are up to 5 years old may still be only 6 inches tall. They are tough as nails in the environment, and can survive in a gallon can (pot) with almost complete neglect (for example, watering every 3 weeks or once a month in the summertime). This is not to say that this is a good way to treat them, but going on vacation with many pots of Joshua Trees is usually not a problem.
1. The Jepson Desert Manual: Vascular Plants of Southeastern California. Bruce G. Baldwin, …, editors. Berkeley and Los Angeles, CA: The Regents of the University of California, c 2002.
2. Dole, Jim W. and Betty B. Rose. Shrubs and Trees of the Southern California Deserts. North Hills, CA: Foot Loose Press, c 1996.
Joshua trees are blooming early in the desert. It’s not a good thing — you can thank climate change
On Nov. 16, 2018, I received a most surprising email from Joe Zarki. Zarki was formerly the Chief of Interpretation at Joshua Tree National Park. Though now retired, he is still a dedicated naturalist primarily interested in birds and butterflies. On Nov. 16, however, Zarki was focusing on Joshua trees.
Zarki had found several Joshua trees that were developing flower clusters. Normally, this would not be news; not worth the time of notifying me or the nine others Zarki had sent his email to that day. This is because at least a few Joshua trees bloom every year. In a few special years, nearly all of them bloom.
But Zarki was contacting me in November and Joshua trees never develop flowers in November; and he had found not just one but eight trees with flowers. Neither Zarki nor I could ever remember Joshua trees flowering in November, or even December for that matter. But memories can be flawed so I thought it best to check what had been written about the seasonal appearance of blossoms.
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I first reviewed a book known as “The Jepson Manual,” the holy grail of California plant life. In it was written that Joshua trees bloom not in mid-November but in April and May. A second book, the late Philip Munz’s “A Flora of Southern California,” indicated that Joshua trees bloom anytime between March and May. A technical paper written just last year asserted Joshua trees bloomed between February and April. Though closer to fall, the latter reference was still more than two months later than what was happening with Zarki’s trees.
Despite my hesitancy in relying upon the recollections of individuals, I thought it might help if I contacted local experts to either corroborate or dispute the words I had read. Ten individuals were contacted who lived or worked in the Yucca Valley/Twentynine Palms area and were familiar with Joshua tree blooms. All had lived or regularly visited the area for the past two decades, five for more than four decades. All confirmed they had never seen or heard of Joshua trees blooming any time in fall.
With the support of the Garden Club of the Desert, I have been monitoring 10 Joshua tree study sites since 1988. I checked my records and the earliest date in which a Joshua tree produced an inflorescence (flower cluster) was Feb. 26. Rumors abound about Joshua trees blooming in late January, but I couldn’t find documentation of such early blooming. Even if the rumors were true, that would still be more than two months away from the blooming date of Zarki’s trees.
At this point, readers might ask what difference it makes if Joshua trees are blooming in either April or November. What’s the big deal?
More: Here’s why you shouldn’t damage Joshua trees (if it’s not already obvious)
Most of us know about basic plant life cycles. Joshua trees survive by producing seeds that potentially germinate and, after about 40 years, grow into adult trees. But nearly all Joshua trees will be eaten by rodents and birds. The tiny fraction of seeds that germinate and produce sprouts will be eaten by rabbits. I estimate that less than one seed in a million ever becomes an adult Joshua tree.
Every few years, a mature tree produces flowers. A tiny moth, known as the Joshua tree yucca moth (Tegeticula synthetica), is the only animal capable of pollinating Joshua tree flowers. The female moth injects her eggs into each flower’s ovary and then inserts pollen into the ovary as well. The ovary swells into an apricot-sized fruit with both seeds and seed-eating moth larvae inside. The larvae consume only a fraction of the seeds, leaving most seeds to fall to the ground. The relationship between moth and Joshua tree is an example of mutualism whereby both species benefit from the relationship.
Having absolute fidelity between host and pollinator works great so long as one species can count on the other to always be there ready and waiting. But what happens when flower appearance and pollinator appearance get out of sync because, say, the flowers appear before the moths emerge from the soil?
On Nov. 19, I visited Zarki and he showed me the eight trees in various stages of flowering. My first question was whether Zarki’s trees were some sort of very local anomaly — that his trees were a strange exception not duplicated elsewhere. I visited two other sites and discovered another eight trees in bloom out of several hundred examined. Neil Frakes, vegetation chief for Joshua Tree National Park, reported that he and his staff had located another dozen trees in bloom prior to Dec. 1. In short, Zarki’s tree were not exceptions. Something unusual was obviously happening.
Were Joshua trees starting their blooming cycle everywhere or just in and around Joshua Tree National Park? I contacted personnel at four other preserves from Nevada to Los Angeles County. None of the Joshua trees in their preserves had started to bloom. I concluded the early initiation of the blooming season was restricted to the area in and around Joshua Tree National Park.
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By mid-January, the bloom had expanded from just 2 percent of the trees to nearly 10 percent. At the same time, I revisited the eight trees that were in bloom in November. All the first-appearing flower clusters had withered away without ever being pollinated. There was one exception. One flower on one inflorescence apparently had been pollinated since there was a single, poorly developing fruit. Under normal circumstances I would have expected more than 100 fruits from all eight inflorescences instead of just one. The November bloom was a dismal failure since it resulted in almost no production of seeds. In short, a few Joshua trees bloomed but there were no moths to pollinate them and the early bloom in November did not set the stage for any meaningful seed production.
Why did the seasonal bloom of Joshua trees begin more than two months early? Zarki informed me that in October a major storm passed through the area that deposited a lot of rain. He speculated the storm and resultant local flooding might have had something to do with the early bloom. He noted that it was not just a few Joshua trees that were blooming months ahead of schedule but some Mojave yuccas (Yucca schidigera) as well. Was the deluge responsible for the bloom? If it was responsible, then the event must have been unique since there were no records or recollections of an early bloom prior to 2018.
The rain event in October 2018 was a doozie. I examined local weather records and found that 2.04 inches of rain had fallen in a 24-hour period on Oct. 12 and 13. That figure is nearly six times above the norm for October and represents about a third of the precipitation expected in an entire year. Despite the data, however, the October rain event was not unique. Since 1990, similar October totals were recorded in both 2004 and 2005 but these failed to initiate an early Joshua tree bloom. Why?
I looked at temperature records. Was it warmer or colder than either 2004 or 2005 in the 30 days following the 2018 storm? It was warmer. The mean temperature for the 30 days following the 2018 storm was 60.8 degrees Fahrenheit. The same figure for 2004 was 51.8 and for 2005 was 58.6. In summary, what was unique about the storm of October 2018 was that a lot of rain fell followed by warmer temperatures than had been experienced in similar events in the past.
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If this combination of weather events was the cause of the bloom, it did not appear to initiate a flight of yucca moths. Most, possibly all, of the moths stayed in the ground. Presumably, the moths won’t emerge until February, the beginning of the normal flight and blooming season for moths and Joshua trees.
What was observed this fall easily slips into an ever-broadening category of plants that are blooming earlier and earlier in response to a warming climate. As every plant and animal on earth is dependent upon another species, we can expect that a changing climate is likely to unbalance untold numbers of mutualistic relationships such as the one between the yucca moth and Joshua tree. These relationships have evolved over thousands, in some cases millions, of years. It is hard to imagine that they will remain intact in the face of a changing climate.
It would be hard to imagine the Mojave Desert without Joshua trees. Dozens of bird, mammal and reptile species depend upon the trees for shelter, nesting sites, food, and in times of drought, life-giving moisture. Over vast areas there is no substitute plant species that provides these necessities. Loss of the trees would undoubtedly result in a cascading effect impacting hundreds of species over much of the Mojave Desert ecosystem.
Already, the tree populations in Joshua Tree National Park are declining because of warmer temperatures and increased frequency and severity of drought. These effects have made Joshua tree populations more vulnerable to wildfires than in the past. Now a new threat may be on the horizon: a pollinator and its host that may no longer be in perfect synchronization.
James W. Cornett is a desert ecologist living in Palm Springs. He has published more than 40 books as of 2018, and is a regular contributor to The Desert Sun and DESERT magazine.
Joshua Tree National Park was unattended by any park service personnel on Saturday December 22, 2018 as the budgetary shutdown of the federal government kicked in in California. In this photo, Los Angeles residents Gustavo and Shelly Huber set up camp with their daughter, Zia. The couple, who said they were married in Joshua Tree about six years ago, did first-come, first-serve camping with their Volkswagen van and a tent at Jumbo Rocks Campground. Omar Ornelas A over stuffed restroom trash can at Joshua Tree National Park entrance on Friday, December 28, 2018. The government shutdown have left the park unstaffed while its gates remain open to visitors. Richard Lui/The Desert Sun The shuttered ticket booth at Joshua Tree National Park on Friday, December 28, 2018. Visitors continue to enter the park despite it being unstaffed due to the government shutdown. Richard Lui/The Desert Sun Trash is visible in a bin at Joshua Tree National Park. Volunteers have been helping to remove trash ever since the government shutdown began last month. Colin Atagi/The Desert Sun Ranger Ameet Amir maintain the restrooms at Hidden Valley Campground at Joshua Tree National Park during partial government shutdown on Thursday, January 10, 2018. The park’s status is in flux due to the partial government shutdown. Richard Lui/The Desert Sun Rep. Raul Ruiz, D-Palm Desert, visits Joshua Tree National Park on Martin Luther King Jr. Day to survey the park and help clean trash left behind from campers as the partial government shutdown continues on Jan. 21, 2019. Omar Ornelas/The Desert Sun
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Joshua trees need to undergo a dormant period of cold weather before flowering, but once they flower, they are dependent upon one tiny insect for pollination. Yucca moths (genus Tegeticula) transfer pollen between flowers to ensure seeds will form, and then they lay their eggs inside the pollinated flower. When the larvae hatch, they feed on some of the seeds and the rest are able to disperse and grow into new Joshua trees. This type of interaction, where two organisms are dependent upon each other for mutual benefits, is called a mutualistic symbiotic relationship. A number of other animals are also served by Joshua trees. For example, 25 bird species nest in Joshua trees. Lizards and invertebrates use various parts of the tree for cover, and a number of mammals rely on Joshua trees for food. Humans have used the trees for food and to make baskets and sandals.
Joshua trees are slow-growing, but because of this, they live for a long time. Joshua trees don’t have annual growth rings like actual trees, so accurately determining their age is quite difficult. Instead scientists measure the height of a Joshua tree and divide it by an estimate of growth per year. One Joshua tree in California is thought to be over 1,000 years old. A more common lifespan is about 150 years.