Course:CONS200/2023/Climate Change Threats to the Joshua Tree

Introduction

The potential future of The Joshua tree

With warming temperatures and a changing climate, Joshua trees are a great risk of being lost. One factor that endangers them is their heavy reliance on other species to reproduce and survive. Joshua trees have a symbiotic relationship with yucca moths. Without one another, they are unable to survive. However in the northern part of the park Joshua trees are not interacting with the yucca moth and are failing to reproduce sexually. In the southern part of the park, no yucca moths living and Joshua trees are unable to bear fruit and are beginning to die in large numbers. As the Joshua tree population declines this will also have serious impacts on other animals that rely on the Joshua tree for a microclimate (National Geographic, nd). Joshua trees are also at risk of wildfire. They are not naturally adapted to wildfire and fires have become more common as the climate becomes warmer and drier. Invasive grass species in the park have made it a lot easier for the fire to spread (US National Park Service, nd),

Background Information about the Joshua Tree

Images from Wikimedia Commons can be embedded easily.

Contrary to its name, the Joshua tree is not a tree but instead is a succulent. The Joshua tree ranges can be found anywhere across the southwestern United States because of the arid climate that can be found in the region. However, the Joshua tree is most commonly found in the Mojave Desert. The average lifespan of the Joshua tree is roughly 150 years. Under prime conditions, it can live far longer than its average lifespan. Since they are not trees, they do not develop tree rings and therefor it is difficult to determine the exact age of a specific specimen. To solve this issue, scientists use the height of an individual to determine it's age. One of the oldest individuals observed was found in California and is thought to be over 1,000 years old.

Ecological Impacts of the Joshua Tree

A Home for Others

The Joshua tree (Yucca Brevifolia) provides both a habitat as well as food for many mammals, birds, and reptiles that live in the Mojave Desert. One such organism is the Yucca Moth. The yucca moth and the Joshua tree have a symbiotic that is integral to both of their survival. Similar to many other plant species, the Joshua tree relies on insects and other pollinators to help continue its life cycle. The primary pollinator for the Joshua tree is the yucca moth. The yucca moth will lay its eggs in the flower ovary of the Joshua tree and while doing so it unintentionally collects pollen that will be transferred to other trees. The flower ovary contains seeds and both the seeds and the eggs develop simultaneously. Once the eggs hatch, the larvae then feed on the seeds until they can fully develop. The interaction here between the Joshua tree and these larvae also benefit the tree by dispersing the seeds of the Joshua tree and allowing it reproduce across a wider area than if it were to rely on wind to disperse its seeds.

Other Species' Interactions with the Joshua Tree

Outside of the Joshua tree's deeply intertwined symbiotic relationship between itself and the Yucca moth, the Joshua tree plays a role in the life of many other species that inhabit the Mojave Desert. The Joshua tree may interact with many different species in the desert and play an integral for them, it often plays a similar role as the habitat or shelter for other organisms.

The Joshua tree's bare branches that have clusters of flowers and leaves that serve as a great place for birds to make nests for themselves. Some 25 different bird species use the Joshua Tree as shelter. Wood rats are another species that use the Joshua tree as a shelter in the harsh environment of the desert. Wood rat nests can be found near the base of some Joshua trees.

Even after the Joshua Tree dies, it still serves an important ecological role in the desert ecosystem. Insects use the dead organism as shelter from the harsh extremes that they are exposed to in the desert. After its death, since there is a concentration of insects inhabiting the corpse of the Joshua tree insect predators, such as lizards and other reptiles are also drawn to the fallen succulent in order to feed on the increased number of insects found in one small area. Whether the Joshua tree is dead or alive, it continually plays an integral role in the ecosystem and facilitates interspecies in Joshua Tree National Park and all across the Mojave Desert.

Historical Importance of the Joshua Tree

History

In 1936, Joshua Tree National Park was designated as a national monument by President Franklin Delano Roosevelt, and was later awarded its national park status in 1994. Though the national park is only 29 years old, human history with the Joshua Tree goes back over 5000 years The first inhabitants of the area we now know as Joshua Tree National Park were the Pinto Culture, followed by Native Americans including the Serrano, the Chemehuevi, and the Cahuilla. The Joshua Tree was recognized by indigenous people throughout the Mojave Desert for its useful properties: "tough leaves were worked into baskets and sandals, and flower buds and raw or roasted seeds made a healthy addition to the diet".

Where the Joshua Tree Got Its Name

The exact origin of the tree's name is a mystery, but one story tells of the name being given by Mormon settlers as they crossed the Mojave Desert in the mid-1800s The rugged shape of the tree reminded the settlers of the story where the biblical figure Joshua reaches up his hands to the sky in prayer. By the late 1800's, the Yucca Palm was frequently referred to as "The Joshua."

Indigenous importance

"For thousands of years many Indian groups embraced the tree as a spiritual reference and valued resource". Researches believe that "the Pinto Basin was occupied by ancient Native Americans some four-to-eight thousand years ago". These groups of Native Americans lived off the lands for thousands of years living a nomadic lifestyle, surviving on "acorns, mesquite pods, pinyon nuts, seeds, berries, and cactus fruits. Additionally, local bighorn sheep, deer, rabbits, birds, amphibians, and reptiles were all hunted for game meat". When the region was forcefully taken over by Spanish colonizers in 1772 the Native groups had to change their lifestyle to survive . Now the importance of recognizing those cultures who's lands were wrongly taken away from them and that as a community we must do our part by continuing the precedent of stewardship.

Current Threats

The Joshua tree is potentially at risk of shrinking by 80-85% by the end of the century due to climate change and many other factors. Most of these threats can be attributed to to the following three causes.

Climate change

The Joshua tree is facing significant challenges due to the impact of climate change. This species is adapted to very specific climatic conditions, including hot and dry summers and mild winters with occasional freezes.

The US Gov showing the impacts after the 2011 droughts.

With the changing climate, the Joshua tree is encountering numerous challenges. One of the most significant threats is the increase in temperature, which leads to heat stress and dehydration. These conditions can adversely affect the growth of the tree, leading to smaller and fewer flowers and ultimately resulting in the death of the tree. The new growth of trees depends on the flowering of the trees in the new season, But as temperatures rise the cold period that the Joshua tree needs to produce flowers is limited and therefor the new flowers can't grow.

Drought caused by climate change

Drought is very likely to be another climate related factor to cause a decline in the population of Joshua trees in the coming years. During the 2011 drought that took place in California, the region experienced some of the driest conditions on record, with many areas experiencing a significant reduction in precipitation. This led to a range of impacts on the environment, including increased risk of wildfires, reduced water availability, and impacts on the plant such as the Joshua tree.

For the Joshua tree, the 2011 drought had significant impacts. A study published in the journal Ecosphere found that the drought caused a significant reduction in the number of new Joshua tree seedlings, with some areas experiencing a decline of up to 90% in seedling recruitment.

Disappearing Water Sources

The leading cause for the decline in the number of Joshua trees is the impact of rising temperatures caused by climate change. At lower, warmer elevations, fewer seedlings are sprouting, growing, and surviving. "By 2099 under the highest emissions scenario forecasted, the average annual temperature inside the park could increase by 8℉ (5℃)" If this scenario comes to fruition, "it could eliminate nearly all suitable habitat for Joshua trees in the park and reduce habitat in the Southwest by 90 percent. Even with lower emission scenarios, nearly 80 percent of suitable habitat in Joshua Tree could be lost.".

Fire

Wildfires are another major threat to the Joshua tree and its ecosystem. Although wildfires are a natural part of many ecosystems, they can become more frequent and severe under certain conditions, including drought and high temperatures, which are caused by climate change. some researchers believe that with the rise of temperature "by 2100, climate models show that Joshua Tree National Park will lose the majority of its suitable habitat for its namesake species. The increasing severity and frequency of forest fires pose a threat to the future of the trees as well". As the Joshua tree is not accustomed to fires it makes it difficult for the tree to recover after disturbance events take place. These more frequent fires are slowly pushing the population of trees more north where less fires are seen. This creates new problems though as growing conditions are worse in the north and the Yucca moth which is the sole pollinator too the tree can not live in the north.

As well researchers have found that the increasing amounts of invasive species like the mustard plant and many invasive grasses have caused fire rates to increase.

Forest Fires in Joshua Tree Park

Dome fire in 2020 that took a blaze over 43,273 acres in the northern reaches of the national preserve

There have been several significant wildfire incidents in the Joshua Tree National Park in recent years have already burned in earlier wildfires in 1995, 1998, 1999, 2006 and 2020.

One notable event was the 1999 Megram Fire, which burned over 18,000 acres of land in and around the Joshua tree national park. The fire was started by a lightning strike during a period of drought, and burned through a range of habitats, including Joshua tree woodlands, pinyon-juniper woodlands, and desert washes.

Another more recent fire broke out in 2020, the Dome Fire burned approximately 43,273 acres of land in the northern part of the park, including areas with Joshua trees. These impacts can have long-term effects on the ecosystem, potentially leading to changes in species composition and ecosystem function.

The Yucca moths

The Yucca moth is a native species of moth that is crucial for the future and success of the Joshua tree. The Yucca moths "lay their eggs in Joshua tree flowers and nowhere else. The Joshua trees, in turn, completely rely on these yucca moths for pollination". With the new drought prediction and fires becoming more frequent it's forcing the Joshua tree to move northwards to areas that are uninhabited by the Yucca moth. Without the pollination of the Yucca moths the Joshua tree will not be able to adapt to the new environment.

Solutions and Mitigation Strategies

In 2021 Joshua Tree National Park reported stewardship goals and strategies for the future. The conservation and preservation of the Joshua Tree was a pressing topic. One long term conservation goal for the Joshua tree is to maintain a "sustainable Joshua Tree population within their potential range under climate change". The national park also recommends more research should be done to understand the species distribution across the park, resilience to environmental change, and other stressors such as invasive species and wildfire. Stewardship goals have also been made to restore damaged Joshua tree habitat by growing seedlings and nurse plants and reintroducing them to the environment. The national park also plans on removing invasive grass species with the use of herbicides, mechanical removal, or biological control agents that could threaten Joshua tree habitat

Another potential solution to protecting the Joshua tree is making it an endangered species under the Endangered Species Act. However, the Joshua tree has recently been rejected for the second time for becoming a endangered species under the California Endangered species act. The U.S Fish and Wildlife Service concluded that after scientific assessment the Joshua tree did not fit the definition of endangered species and will continue to have a presence on the landscape well into the future. The service states that despite the rejection they are committed to the conservation of the species in the wake of threats discussed above including wildfire, climate change, invasive grasses, and habitat loss.

Alternatively the conservation organization, Center for Biological Diversity feels that this species requires and deserves to be the first tree to be classified as an endangered species in California. This is because if the species receives endangered status the state would be obligated to managed threats to the Joshua tree and develop and recovery plan. However as the state recently rejected the second application in the last two years it seems unlikely that this will occur for the time being.

If people wish to have the species listed as a endangered species it is recommended that more research is done to provide evidence that the Joshua Tree is in fact deserving of endangerment. However it can be concluded that even if opinions differ on how to conserve the Joshua tree both government and conservation organizations value the survival and health of the species.

Conclusion

Joshua trees are a critical species in the ecosystems that they inhabit and due climate change the species is at risk of going extinct. The predicted increased temperature of climate change imposes many different threats to the Joshua tree including heat stress, increased wildfire activity, and potential loss in symbiotic relationships leading to poor reproduction rates. Encouraging progress has been made towards attempting to make the species listed as endangered in California which could lead to more protection of the species. Other park stewardship actions and research will also contribute to the conservation of the Joshua Tree.

To further understand the effects the climate change and enhanced risks that come with to the Joshua tree it is recommended that more research will need to be done to understand the ecology of the Joshua tree and its adaptably to a changes climate. Further conservation mechanisms and solutions are also encouraged to be explored.

References

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