If you have ever seen a Joshua tree, you are unlikely to have forgotten this strange, slightly bizarre-looking indicator plant of the Mojave Desert. Resembling a child’s first drawing of a tree, or, to the Mormon travelers who passed through the Mojave in the 19th century, the prophet Joshua raising his arms in supplication and guiding the travelers westward.
If Joshua trees are indeed raising their limbs in supplication, it would be for water. Or perhaps for an end to the drought that, if it continues, may very well wipe them out at lower elevations. But even if the drought ended tomorrow, the rapidly escalating results of man's ability to alter our planet's climate presents an even greater threat to these plants and the life they support.
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Yucca moth (Prodoxidae)
There is one insect whose life cycle is inextricably linked to that of the Joshua tree. The little yucca moth is the sole pollinator of the Joshua tree, laying its eggs in the flower's ovary while it pollinates the tree. When the larvae hatch, they make a meal of a few of the seeds from the tree, which relies on the adult to complete its life cycle.
In 2013, in what some scientists believe may have been an attempt at survival by the Joshua tree, there was a massive spring bloom in the middle of a drought that kept the yucca moths busy. And while it is too soon to know for sure, it is unlikely that the bloom helped reproduce the trees in the lower elevations and the southern range. There are some areas, however, at higher elevations and in the northernmost limits of its range, such as one in Death Valley National Park, that have seen some increase in the growth of seedling Joshua trees.
Joshua Tree National Park is located at the southern edge of the Mojave Desert where it meets the Sonoran Desert, and where the elevations range from less than 1,700 feet in the Pinto Basin to more than 5,800 feet atop Quail Mountain. And it is those higher elevations that will see the 2 percent to 10 percent of the Joshua trees that are expected to survive this century. Also at risk are the pinyon pines that now flourish in many parts of the park. The park service warns that some of the lizard species have reached the limits, in terms of climate, within which they can survive.
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The Colorado River Basin, which provides water from San Diego to Santa Barbara, has seen its most severe 14-year drought in 1,250 years. The giant reservoir of Lake Mead is at less than 45 percent of capacity. Joshua Tree National Park has not gotten its average four inches of precipitation for several years, and this year the total stands at just 1.71 inches. The drought is devastating the reproductive cycle of the Joshua trees. Although the older trees are able to survive for now, the young seedlings cannot.
"For Joshua trees, hotter, drier conditions are a problem — but a bigger problem is that what little rainfall occurs evaporates faster," Barrows said. "So, seedlings shrivel up and die before they can put down strong roots."
Dr. Cameron Barrows Discusses Modeled Climate Change Impacts at Joshua Tree National Park
According to the modeling done by Dr. Barrows and the UC Riverside Center for Conservation Biology, if the current levels of heat continue their increase, 90 percent of the current range of the Joshua trees in the park will be unsustainable by the end of this century. Joshua trees have a lifespan, on average, of 150 years. Some of the trees in the park are estimated at over 200 years old. They have deep root systems that will help them survive for some time to come. It is their replacements that are in jeopardy.
The Joshua tree has faced threats in the past. The 1980s saw the development of the cities of Palmdale and Lancaster that replaced 200,000 Joshua trees with homes, schools, and parking lots. Today they are being displaced in even greater numbers by the increasing growth of massive solar farms.
But no other threat to the Joshua tree is as great as that presented by our rapidly changing climate. Researchers have expressed surprise at how quickly we are seeing the changes in the desert southwest and how little time the plants and animals are being given to adapt. Most past climate changes have happened over a thousands of years, allowing plants and animals time to adapt and move into more suitable ranges. Those that happened more rapidly tended to wipe out large numbers of species.
Man has occupied the area encompassed by the park's 800,000 acres for 5,000 years, beginning with the Pinto man. The Serrano, the Chemehuevi, and the Cahuilla tribes followed, and then, in the 1800s came the cattlemen, miners, and homesteaders. Today the Park is occupied by a immense variety of plants, insects, reptiles, birds and mammals. Joshua Tree National Park maintains a large Flickr collection of photographs here. It is a great place for Sunday armchair travel. A sample is below.
There are entire books on the wildflowers of Joshua Tree, and here are a few:
Clockwise from top left: Desert Aster, Indian paintbrush, tarantula hawks, Joshua Tree poppies, Apricot mallow, desert verbena, globemallow, Indiawheat, Honeybee pollenating brittlebrush
There have been over 250 different species of birds sighted at Joshua Tree National Park. Here are a half dozen of the more common ones:
Clockwise from top left: Black-throated sparrow, Gambel's quail, great horned owl, cactus wren, greater roadrunner, red-tailed hawk chick
Some of the mammals:
Clockwise from top left: Bighorn sheep, bobcat, coyote, deer mouse, yearling mountain lion. Click to enlarge
The desert is a silent and awesome place. Because there are few trees with leaves to rustle in the wind, it makes little sound as it blows across the land. And although a desert landscape looks rugged and hardy, it is actually a fragile land of incredible vulnerability and beauty—with some of the most glorious sunsets in the world.
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