What can we learn from the Joshua Tree?
You don’t need to have visited the Mojave Desert to be familiar with the Joshua tree. The unmistakable plants, with an appearance that seems fitting for their otherworldly setting, are a symbol of West Coast Americana. While only growing in a specific area of the southwest US and northern Mexico, they densely populate the cultural imagination through photography and film; decorating iconic album covers including Eagles, 1972 and U2’s The Joshua Tree, 1987.
Gnarled but evergreen, hardy yet vulnerable, bringing shaded forests to a sparse desertland — these are a species of contradictions.
This month, prompted by a petition from California’s Center for Biological Diversity, the Western Joshua tree became the first plant species to gain legal protection by the State of California under the State’s Endangered Species Act (CESA). In a unanimous vote, the California Fish and Game Commission approved the species to protections under the Act for one year, after which the situation will be reviewed.
This landmark ruling is significant because it shows the possibility for a more widespread expansion of protection acts, to now include plant species as well as animals. It also demonstrates the power of citizen protest.
The petition, released October 2019, agues the following:
“The western Joshua tree is eligible for and warrants listing under CESA based on the factors specified in the statute and implementing regulations. Specifically, the western Joshua tree meets the definition of a “threatened species” since it is “a native species or subspecies of a…plant that, although not presently threatened with extinction, is likely to become an endangered species in the foreseeable future in the absence of the special protection and management efforts.”
The western Joshua tree grows close to the coast and LA, in an area that stretches from Joshua Tree Park up to Death Valley. The map below shows the difference in location of Eastern and Western Joshua trees (the latter marked in green). Due to lower elevations, the Western tree is more vulnerable to rising temperatures and drought.
The habitat needed to support Joshua trees is declining rapidly due to the effects of human activity, including climate change, promotion of invasive species and development projects on the land.
The Center for Biological Diversity has been advocating for increased legal protections to the trees’ habitat for years. “Developers are bulldozing Joshua trees every day to build roads, powerlines, strip malls and vacation rentals,” said Brendan Cummings in a statement. “If these beautiful plants are to have any hope of surviving in a warming world, we have to stop killing them. The California Endangered Species Act may be the only hope for saving these iconic symbols of the Mojave Desert.”
So why, in a state of the US that is now notorious for devastating wildfires and habitat loss, has it taken this long for a plant species to be protected under CESA? And why was it the Joshua tree awarded this protection when so many other plant species are also under threat from climate change and human development?
I will discuss here the importance of the Joshua tree as a bioindicator and a cultural symbol, and consider how this step forward in plant conservation can be consolidated in other areas — in California and further afield.
What’s special about the Joshua tree?
The iconic, gnarled Yucca succulents (Yucca brevifolia) have defined California’s sparse desert scrubland for over two millennia. The species is known to grow across the Mojave Desert, an expanse of 124,000 sq. km across the United States and Mexico that includes parts of California, Arizona, Nevada, Utah, and northwestern Mexico — the Joshua tree is known to communities over the Mexican border as izote de desierto, or “desert dagger”. They are most famously found in California’s Joshua Tree National Park, an arid stretch of wilderness where the Mojave and Colorado Desert meet.
These plants are impressive in age, size and ingenuity. It is estimated that the average Joshua tree lives up to 500 years, and some trees can survive up to 1,000. Despite having the appearance of trees, the Yucca brevifolia is a flowering shrub, and lacks the growth rings seen on regular trees; instead, the trunk consists of thousands of tiny fibres. This means it is difficult to work out the true age of a Joshua tree without monitoring it from the start — Scientists have been tracking the lives of some individual trees for 200 years. These impressive plants are larger than many tree species: they have a complex underground root system, and the tallest trees reach over 15 meters high.
Joshua trees aren’t just revered for their unique appearance. They perform a crucial function in the local ecosystem, by providing shade, food, and anchoring the dry topsoil to prevent dust storms. Birds, reptiles and mammals all rely on the Joshua tree, which has transformed a landscape that would otherwise be unsheltered and severe.
An indicator species
The Joshua tree is an indicator species, meaning that it is used to measure the environmental conditions of the local area. The boundary lines of the Mojave Desert have been drawn by Joshua trees — the stretch of land populated by this unique plant indicates the desert. In a time of walls and divisions motivated by political extremism, it’s refreshing to hear of shifting, porous demarcations decided by natural forms. This bio-nationalism speaks to a far greater heritage than the boundaries people care so much about today.
In such a barren landscape it might seem that there isn’t much competition to be an indicator species, but the Joshua tree happens to be the ideal candidate. This is because the plant has developed precise ways to survive in this solitary part of the world. Therefore, it only grows in the specific area that caters to these distinct adaptations.
Shallow roots that spread out across the earth’s surface mean these plants can absorb maximum water from infrequent rainfalls; matured Joshua trees can go up to a year without rain. This network of slender roots can stretch out for five meters around the plant, lying in wait just below the surface. When a storm finally arrives, a single plant can collect and store water over a distance of 10 meters.
These roots serve a double purpose: the Joshua tree can sprout and reproduce from its roots and branches as well as from its flowers. This provides a second line of defence if the main body of the plant is damaged in a fire or flood.
The primary way that the Joshua tree has ensured its survival is by developing a mutually beneficial relationship with female yucca moths. The yucca moth is the only animal capable of pollinating the plant, and as a result moths in this species have evolved specialised mouths with the sole function of pollinating the flower of the Joshua tree, while simultaneously laying her eggs inside the tree’s flower. In return, the moth’s larvae feed on the plant’s seeds until they mature and continue the cycle. This reciprocal relationship means that both species rely on each other for survival.
The hardiness of this plant seems at odds with the specific conditions required for survival. Every year, the emergence of white and green flowers depends on a good amount of spring rain, and a crisp frost the previous winter. It is also dependent on the survival of its partner moth, and as insect numbers decline, the trees will struggle to reproduce. Increased temperatures and prolonged droughts have been detrimental even to this resilient species. Even more pressing is the destruction of thousands of acres of Joshua trees from wildfires, exacerbated by dry conditions and invasive grasses.
While an indicator species is used by biologists to define the boundaries of an ecosystem or geographic area, it can also be a marker of ecosystem stability. Indicator species are chosen for their particularities, so they are typically very sensitive to environmental change. Therefore, declining numbers of Joshua trees over the past few decades shows conditions in the area have changed significantly. Like a canary in a mine, a break in the song of Joshua trees signals a danger that will affect us all.
Declining numbers and climate change
In a 2018 study on the impact of climate change on Joshua tree flowering seasons, ecologists Samuel B. St. Clair and Joshua Hoines stated the following:
“Desert flora can be sensitive to climate change due to the moisture and temperature extremes of deserts. Joshua tree forests are an ecologically important vegetation type in the Mojave Desert and have potential for range contraction in response to climate change, although the mechanisms of contraction are not well understood.”
The two years since St. Clair and Hoines’ study have seen increasingly invasive wildfires across North America’s West Coast, which have strengthened the causal link between climate change and the decline in Joshua tree numbers.
Alongside this, years of severe droughts have impacted baby Joshua trees. Unlike their older neighbours, young and juvenile plants rely on more than one rainfall a year, because they haven’t grown the complex system of underground roots that makes this species so hardy. California-based ecologist Cameron Barrows, is conducting a 20-year biological study on the Joshua Tree National Park. In his first year, from 2014–2015, Barrows found few to no young trees in roughly 30% of the park. Based on his findings, Barrows has created a model to predict the future landscape of the national park. Using Barrow’s model, Joshua tree numbers could be reduced by 90% as the species will only be able to survive in sheltered pockets — climate refugia — on higher ground.
More recently, and a testament to accelerating temperature rise, a 2019 study in Ecosphere estimated that only 0.02% of this habitat will remain by the end of the century if climate change continues at the current rate.
Human-caused threats go beyond climate change. Increased nitrate levels in the LA basin have boosted the growth of invasive grass species that feed forest fires, and outside of the protected Joshua Tree National Park, off-road vehicles, grazing livestock, and the construction of large-scale energy projects, power lines and pipelines have also damaged the habitat.
The solar paradox
The influence of energy projects in the region can’t be overlooked. California’s vote on including the western Joshua tree in the State’s Endangered Species Act was delayed twice in 2020 due to opposition from the renewable energy industry.
Renewable companies like Terra-Gen Power argued that clean energy projects will be halted and the development of needed infrastructure in the region will be more challenging going forward. In light of these arguments, the commission voted to allow an exemption to the new state laws for 15 solar projects in Kern and San Bernardino, which were in the process of removing Joshua trees from the construction site. These projects were operating under the California Environmental Quality Act, which allowed these projects to go ahead.
The renewable energy industry has a vested interest in keeping the natural world at the heart of their business model. Under the California Environmental Quality Act, projects that may impact vulnerable species require an analysis, public disclosure, and plans for mitigation of harm. This often involves re-planting saplings or attempting to move the original tree to a new location.
Re-growing Joshua trees is anything but a quick fix. As Joshua trees are slow to reproduce and often struggle to reach maturity, if developers plant 10 new trees for each one they cut down doesn’t guarantee the number of trees will increase tenfold. In fact, this method could still lead to dwindling numbers.
A recent study on solar energy development in California’s deserts explained the negative effects of solar development on local ecology:
“Deserts are prioritized as recipient environments for solar energy development; however, the impacts of this development on desert plant communities are unknown. Desert plants represent long-standing ecological, economic and cultural resources for humans, especially indigenous peoples…cacti species and Mojave yucca (Yucca schidigera) are particularly vulnerable to solar development (that is, blading, mowing), whereas Schismus spp. — invasive annual grasses — are facilitated by blading.”
However, renewable energy is crucial in the move away from fossil fuels, and large-scale development projects are the answer to providing a cheap energy alternative. Without broader efforts to mitigate rising global temperatures, the Joshua tree’s habitat will be destroyed.
The situation is nuanced and there is not one set answer. One solution could lie in targeting areas that have already seen human development: building solar panels in urban spaces, on roofs and car parks; or “marginalised lands,” places like landfills, mines and contaminated brownfield sites. The Environmental Protection Agency estimates that across the US there are 43 million acres of brownfields and mine lands that meet the specifications for renewable energy development. The process of building on marginalised lands can be more costly for the developer, but the ecological footprint is far smaller.
An iconic symbol
It’s unsurprising that humans have been drawn to Joshua trees over generations: their towering height, evergreen leaves, resistance to the harsh sun and annual burst of flowering colour seem miraculous in such an arid setting.
The English name for these succulents is said to have come from 19th-century Mormon missionaries, who were struck by the unusual appearance of their tall, gnarled trunks with open arms extended to the sky. They named the tree after the Biblical character Joshua, who stretched out his hands to God for guidance when leading the Israelites during their conquest of Canaan.
Before the arrival of Europeans, many local Native Americans also considered the tree to have a religious significance, as well as being a practical resource: the leaves were used as material for shoes and baskets, and the flowers and seeds made a tasty snack. Known to the Cahuilla tribe as humwichawa and the Southern Paiute as sovarampi, the species has been crucial to the culture and survival of humans for centuries.
Today, Joshua trees are a symbol of regional pride; their very existence creates a region that is otherwise divided by state and national lines. On a broader level, they signify nature’s complexity and fragility. These rugged trees are built to survive, and their ability to transform a harsh desert landscape into one that is shaded and green has been given spiritual significance by different communities over centuries — and before humans, they survived periods of cooling and heating for over two millennia. The fact that the effects of the capitalocene have endangered this resilient species highlights the wide-reaching and complex effects of the climate crisis.
A lesson for the future?
Over the coming year, the Joshua tree can enjoy the same protections under the California Endangered Species Act as other vulnerable species in the area, for instance the humpback whale, chinook salmon, California tiger salamander, California condor and the bald eagle. Of course, some of the impacts of climate change can’t be controlled by law, and the dangers of fires and droughts remain a battle for local conservationists.
Looking forward, this ruling has likely set a precedent for other plant species, which could follow suit. By focusing on such an iconic tree, the successful campaign has also raised the profile of plant conservationists, and demonstrated the importance of petitioning and civic action.
A ripple effect could lead to much-needed protections for other threatened plant species, which are now threatened like never before — including the maple tree. Almost coinciding with the vote to legislate further protections of Joshua trees, the Botanic Gardens Conservation International (BGCI) updated their “Red List” to include 36 out of the 158 species of maple of Acer trees as high risk of extinction in the wild in the near future. The report showed that over a third of these trees are facing substantial habitat loss, combined with large numbers lost for timber. Numbers have been steadily declining and, without action, it’s likely these trees will die out in the coming years.
It is also important not to limit protective efforts to species that feature heavily in our society and culture, while more obscure plants, insects and animals fade into extinction without public awareness.
It is now widely acknowledged that we are living through a sixth mass extinction. The massive decline in biodiversity over the last 50 years encompasses hundreds of species of plants and animals, many of which were never known to humans before they became extinct. In 2019, plant and fungi botanists registered almost 4,000 new species — and even at the time of discovery, many were already facing extinction. Researchers are struggling to catalogue as many unknown species as possible before they disappear forever.
In their 2018 study on the Joshua tree, St. Clair and Hoines pointed out: “for such an iconic species it is surprising how little research has been done on the most basic parts of Joshua tree biology and ecology”. This shows the work that needs to be done across ecology to increase scientific understanding even of the most famous species, and within conservation to stop unique parts of the natural world from fading into obscurity before we even know of them.
References
Fig. 1: Map based on Lenz, 2007. Reassessment of Yucca brevifolia and Recognition of Y. jaegeriana as a Distinct Species. Aliso: A Journal of Systematic and Evolutionary Botany, pp. 97–104
Rasha Aridi, “In ‘a Huge Victory,’ California’s Joshua Tree Becomes the First Plant Protected Due to Climate Change” in Smithsonian Magazine, Oct 1, 2020. https://www.smithsonianmag.com/smart-news/huge-victory-californias-joshua-tree-becomes-first-plant-protected-due-climate-change-180975953/
Cameron Barrows, “Tracking Climate Change Through the Joshua Tree”, Mojave Desert Land Trust, 2017. https://www.mdlt.org/tracking-climate-change-through-the-joshua-tree/
Cameron Barrows, “Earthwatch 2018 Annual Field Report: Saving Joshua Tree’s Species” in Earthwatch Institute, 2017–2018, https://earthwatch.org/sites/default/files/2020-03/earthwatch-field-report-saving-joshua-trees-desert-species-2018.pdf
Jim Boone, “Reassessment of Yucca brevifolia and Recognition of Y. jaegeriana as a Distinct Species.” by Aliso, A Journal of Systematic and Evolutionary Botany, 2007. pp. 97–104. https://www.birdandhike.com/Veg/Species/Yucca/Yucca_bre-b/maps/Yuc_bre_map.htm
Botanic Gardens Conservation International (BGCI), “The Red List of Acer: revised and extended”, Sept 2020. https://www.bgci.org/resources/bgci-tools-and-resources/the-red-list-of-acer-revised-and-extended/
Brendan Cummings, “A Petition to List the Western Joshua Tree (Yucca brevifolia) as Threatened under the California Endangered Species Act (CESA) by Center for Biological Diversity.” Oct. 15, 2019. https://www.biologicaldiversity.org/species/plants/pdfs/CESA-petition-Western-Joshua-Tree-10-15-19.pdf
Brendan Cummings, “State Endangered Species Protection Sought for California’s Joshua Trees Iconic Desert Plant Threatened by Climate Change, Habitat Loss”, Oct 15, 2019. https://biologicaldiversity.org/w/news/press-releases/state-endangered-species-protection-sought-for-californias-joshua-trees-2019-10-15/
Osha Greay Davidson, “Climate Change Threatens an Iconic Desert Tree”, National Geographic, Oct. 28, 2015. https://www.nationalgeographic.com/news/2015/10/151028-joshua-tree-climate-change-mojave-desert/#:~:text=Adapted%20to%20a%20dry%20climate,regular%20rain%20events%20to%20survive.
Steven M. Grodsky & Rebecca R. Hernandez, “Reduced ecosystem services of desert plants from ground-mounted solar energy development” in Nature Sustainability, 2020. https://www.nature.com/articles/s41893-020-0574-x
Vivian Ho, “California’s Joshua tree could become first to win protections because of climate crisis” in The Guardian, Sept. 24, 2020. https://www.theguardian.com/us-news/2020/sep/24/california-law-two-million-year-old-joshua-tree-under-threat-climate-crisis
The Royal Botanic Gardens, Kew, “State of the World’s Plants and Fungi 2020”, © The Board of Trustees of the Royal Botanic Gardens, Kew, 2020. https://doi.org/10.34885/172
National Park Service, ”Joshua Tree: Where Two Deserts Meet” https://www.nps.gov/jotr/index.htm
Samuel B. St. Clair, Joshua Hoines, “Reproductive ecology and stand structure of Joshua tree forests across climate gradients of the Mojave Desert”, Ecosphere, Feb. 23, 2018. https://doi.org/10.1371/journal.pone.0193248
Lynn C. Sweet et. al., “Congruence between future distribution models and empirical data for an iconic species at Joshua Tree National Park”, Plos One, Nov. 30 2019. https://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecs2.2763
