According to the story, Joshua trees were named by Mormon pioneers crossing the Mojave Desert who thought the trees’ outstretched branches resembled the prophet Joshua waving them on to the promised land. These striking trees are mostly confined to the Mojave Desert, where the oldest trees can live up to a thousand years! To survive in the desert environment, the Joshua tree uses its deep and extensive root system to reach what little water is available in the parched soil.
CLIMATE CHANGE IMPACTS
Unlike the Mormon pioneers who named it, the Joshua tree cannot pack up and migrate to a new home if its habitat becomes unsuitable. To expand to new locations, the Joshua tree depended on the giant sloth to disperse its seeds—an animal that unfortunately went extinct 13,000 years ago. These relic trees literally have nowhere to go if global warming renders the Mojave desert unsuitable for its survival.
The problem is seed dispersal. Joshua trees don’t do it well. Oh, ladder-backed woodpeckers will hammer at fallen fruit to get the worms that live inside, thereby spilling seeds all over, and pack rats will pick up seeds and fruit and carry them 50 feet from the tree or so, and there are a few other birds and rodents that play a role in moving Joshua tree seeds around. Every once in a while, a coyote might eat a fruit and excrete it 10 miles away. But unless the tree is on a long, steep hill, its golf-ball-sized fruit tend to stay within a few meters of the parent tree. The seeds are large, and seem to have no adaptations allowing birds to carry them long distances by accident: no sticky burrs, no sweet pulp surrounding a gut-proof seed coat, nothing but a delicate little black flake. Most of the time when something eats a Joshua tree seed, it kills the seed.
No more Joshua trees?
Climate change may wipe out the signature tree of the Mojave.
BY CHRIS CLARKE
I started wondering a few years back, as I learned more and more about Joshua trees, whether there might not be a piece missing in this puzzle. Joshua trees are tall, heavily defended plants with fleshy fruit growing at the top, sometimes 30 feet off the ground. There are quite a few plants in the Americas that, like the Joshua tree, seem ill-adapted to seed dispersal because their fruit isn’t designed for any living animal to disperse it efficiently: the Osage orange, the pawpaw, the avocado. Many of these plants have been linked to the giant extinct animals of the Pleistocene, big beasts who could denude a pawpaw or avocado tree of all its fruit, walk a distance away and excrete the tree seeds, seasoned only slightly by digestive juices. Could Joshua trees be another such plant, dependent for seed dispersal on an animal species that will never come back?
Joshua Tree National Park
About the Park
Joshua Tree’s nearly 800,000 acres were set aside to protect the unique assembly of natural resources brought together by the junction of three of California’s ecosystems, the Colorado Desert, the Mojave Desert and the Little San Bernardino Mountains. This is a land shaped by strong winds, sudden torrents of rain, and climatic extremes. Rainfall is sparse and unpredictable. Streambeds are usually dry and waterholes are few. Viewed in summer, this land may appear defeated and dead, but within this parched environment are intricate living systems waiting for the opportune moment to reproduce.
Climate change presents significant risks and challenges to the National Park Service and specifically to Joshua Tree National Park. Scientists cannot predict with certainty the general severity of climate change nor its impacts but at Joshua Tree National Park, increasing temperatures and changing precipitation patterns will alter park ecosystems, changing vegetation communities, habitats available for species, and the experience of park visitors. Ecological models indicate that Joshua trees could be lost from the park in the future. Staff is working with researchers to determine the level of impacts to and to understand effects on the Park. Recent research topics include impacts to reptiles and plants.
Joshua Tree Climate Action Plan link