Joshua Tree Survival Threatened Due to Climate Change
At the end of January 2019, following the longest-ever government shutdown in United States history, news outlets began reporting on damage at Joshua Tree National Park. A lack of staff supervision during the shutdown created chaos in the park, as visitors engaged in vandalism, disturbed fragile desert soil, and cut down some of the park’s namesake Joshua trees. According to the park’s former superintendent, it could take hundreds of years for Joshua Tree – one of the most famous of the US national parks – to recover.
Unfortunately, unruly park visitors are not the only threat to the Joshua tree survival. They are also under increasing stress due to climate change.
The Joshua Tree: Climate Change Putting Stress on California’s Iconic Plant
Joshua trees – one of the most iconic desert plants – grow mainly in the Mojave Desert, a southwestern corner of North America that stretches across Arizona, southern California, Nevada and Utah, in the US, and the northeastern tip of Mexico. Though they are most prevalent here, Joshua tree plants can also be found in the Sonoran desert and the San Bernardino Mountains.
It’s the higher elevation and cooler climate of places like the Mojave Desert that they prefer. However, hotter temperatures, increasing drought, and the loss of groundwater are taking their toll.
A recent study found that unmitigated climate change with business-as-usual greenhouse gas emissions would reduce the Joshua tree’s habitat to a mere 0.02% of its current range by sometime between 2070 and 2099.
This projected decline is perhaps all the more alarming given the changes the plant has successfully weathered over the millennia. As a species, Joshua trees are around 2.5 million years old and, over the period of their existence, they have experienced many climatic changes.
Joshua Tree History & Evolution
Today, Joshua trees are restricted to a fairly narrow range, mainly growing in a series of isolated patches in the higher elevations of the Mojave Desert.
25,000 years ago, though, the Mojave “Desert” was a very different place.
During the late Pleistocene epoch, several pluvial lakes could be found in what is now the southwestern United States. A series of lakes and rivers and greater precipitation fed a much more lush environment than we see today. The valleys that we now associate with desert scrub were once forested with junipers and piñon pines. The mountain slopes today covered in iodine bush and Mojave yucca were once home to cottonwood trees, firs and aspen. It was also home to a wide range of animals, from bears, wolves, and elk, to mammoths, giant ground sloths, and saber-toothed cats.
During this lush period in the desert’s history the Joshua tree thrived. Their range was much more extensive, reaching as far south as the Colorado River delta in Mexico – more than 480 km (300 mi) from the southern-most Joshua tree that can be found today. And unlike their favoured higher elevations of today, there is evidence that they grew as low as 60m (200 ft) below sea level, in Death Valley.
Around 12,000 years ago, though, as the Pleistocene ended, everything started to change. The era of ice ages was ending. As glaciers retreated northward – taking the polar jet stream with them – less rain started to fall in the Mojave, and it started to get warmer. Those lakes and rivers dried up and, over time, the area’s flora and fauna was transformed.
While animals can more easily migrate to better climates when things change, plants don’t have that luxury. The key to surviving climate changes depends in large part on seed dispersal – and luck that animals and birds will carry their seeds to regions where the climate is more favourable.
Joshua Tree Adaptations No Match for the Fast Pace of Climate Change Today
The Joshua tree may be considered one of the lucky ones to have been able to stick around well past the end of the Pleistocene. But past climatic changes took place over millennia. There was time for the Joshua tree – through fortuitous seed dispersal – to gradually move to higher elevations, to settle into new pockets of cooler, wetter climates, and to otherwise adapt.
The current speed of global warming today, though, is proving too much, and it’s hard to say whether the Joshua tree will be able to keep pace. Though scientists have hope for the Joshua tree’s survival in what they term “climate refugia” – in the case of the Park, this means cool, high-elevation pockets towards the north – their simple existence might not be enough.
That’s because of a tiny, unassuming insect that the Joshua tree just happens to be in a pretty exclusive relationship with.
The Joshua Tree, Climate Change & The Yucca Moth
In a textbook example of symbiosis, Joshua trees have an interesting co-evolutionary relationship with the yucca moth (also known as the Pronuba moth). And they’re completely dedicated: without the Joshua tree, the yucca moth could not produce larvae; and without the yucca moth, the Joshua tree could not produce seeds.
Want to know more about this symbiotic relationship? Click here to read our post on Joshua tree facts!
It turns out the yucca moth is the ONLY insect that can pollinate the Joshua tree plant. And pollination is key to the long-term survival of the Joshua tree.
No pollination = no seeds = no way to propagate the species within these climate refugia.
Right? Well, the Joshua tree might just have another trick up its sleeve. In some of these high-altitude refugia, scientists have noticed what they call “fairy rings” – circles of baby Joshua trees. How did they get there? Not by normal pollination as it turns out. Joshua trees have another hidden superpower: they can produce clones!
Through a network of shallow roots called rhizomes, Joshua trees can self-propagate by producing baby clones. This Joshua tree adaptation is great for recovery after acute disasters like floods, but it is not a winning strategy for Joshua tree populations in the long term. Clones are vulnerable to pests and disease and of course, they can’t disperse the species to new climates. They are stuck where the original Joshua tree was rooted.
So we’re back to the moths. Unfortunately, it’s unclear whether the moths will move in sync with the Joshua tree to cooler climates – yet another potential strain on the ill-fated plant. As this shows, climate change doesn’t only affect individual species, but also how they interact.
Not Just Habitat: Climate Change Spurring Other Threats to Joshua Tree Survival
Even if the yucca moth ends up keeping pace with the Joshua tree, climate change be damned, and together they take shelter in the climate refugia of the Park, there are other threats lurking.
In addition to habitat loss, climate change is spurring more immediate threats to Joshua tree survival. The proliferation of invasive grasses, for one, has contributed to an increased number of devastating wildfires ravaging parts of southern California. As Joshua Tree National Park superintendent David Smith explained to National Geographic, “these plants didn’t evolve with fire, so they just don’t come back from it.”
What is at stake with the loss of the Joshua tree?
Joshua Tree Significance: An Irreplaceable Part of the Ecosystem
Joshua trees play an important role in the ecosystem. They provide food and shelter for a number of mammals, birds, reptiles and insects. Red-shafted flickers drill holes in the branches to make nests which can be later occupied by other birds, too. Desert night-lizards live in the dead leaves and branches, and woodrats gnaw off the spiny leaves for their nests.
And don’t forget about our friend the yucca moth. With the Joshua tree gone, where will the yucca moth lay its eggs?
A Beloved Desert Symbol Lost? Joshua Tree, Climate Change & Human Culture
The iconic Joshua tree plant is known throughout the world as a symbol of the southwestern desert. Though despised by early settlers, their unique appearance draws thousands of visitors to Joshua Tree National Park every year, and it has inspired modern-day musicians, artists and even filmmakers with its unique beauty.
Even before the arrival of Europeans in 1769, many Indigenous nations lived in the area and relied on the Joshua tree for many purposes. The Serrano, Cahuilla, Mojave, and Chemehuevi people used the branches and leaves to create utilitarian items like baskets, among other uses, and they even consumed the flower buds and seeds.
Joshua Tree Survival: Is This the End of this Iconic Plant?
“Right now,” Brendan Cummings, Conservation Director at the Center for Biological Diversity, told The Guardian, the Joshua tree is “a symbol of our utter failure as a society to address climate change. I’d like to think it can become a symbol of us coming together.”
Losing the Joshua tree would be devastating for the environment, and for the people who identify with these plants as part of their home.
Can the Joshua tree be saved? It’s hard to say. Even if significant action is taken to curb climate change and reduce greenhouse gases now, it is estimated that as little as 18.6% of the Joshua tree’s original habitat can be saved by the end of the century.
But there are definitely those who are fighting for Joshua tree survival. After a failed attempt to have the Joshua tree listed as a threatened species under the Endangered Species Act, WildEarth Guardians are now fighting that decision in court.
Want to support WildEarth Guardians and help put the Joshua tree on the list of California protected trees? Click this link to sign their petition.
About the Author
Katherine is a lawyer whose work focuses on climate change, human rights, and environmental governance. Originally from Vancouver Island, she has lived in Europe and Asia, and currently resides in Montreal.
Lady Bird Johnson Wildflower Center
The Joshua Tree Genome Project
KCET (a broadcaster in Southern and Central California)
The National Park Service
The National Wildlife Federation