The Iconic, Vanishing Joshua Tree: Making Priorities
Editor's Note: This is Part 3 of a three-part series about the precarious survival of the Southwest's iconic Joshua Trees, which are threatened by evolution, climate change and urban sprawl. Click here for Part 1, and here for Part 2.
The trees require specific conditions to thrive. Most Joshua trees grow between an elevation of 3,000 and 6,000 feet and prefer 5-10 inches of rain and a few cold snaps every year to foster the growth of new branches. And, without a way for Joshua tree seeds to move to relatively cooler and moister areas of the desert, maintaining a stable population in the face of global warming could be impossible, Cole said. He estimates that in the next 60 to 90 years, Joshua trees will be unable to reproduce within 90 percent of their current range due to climate change.
Scientific models also show that future hospitable regions will likely fall outside of Joshua Tree National Park’s boundaries, a fact that poses additional challenges to Joshua tree survival, Smith said.
“Given that Joshua Tree National Park is on the extreme southern end of the current distribution of Joshua trees, that area is very likely to experience extinctions,” he said.
Outside of the park, Joshua trees do not have protected status. And given the choice between saving Joshua trees or the economic benefit of building strip malls, many people would opt for construction. Several significant Joshua tree populations are close to booming urban areas, such as Los Angeles and Las Vegas, the fastest growing metropolitan area in the country, according to the USGS. Therefore, there is a strong possibility these valuable populations could disappear, Smith said.
The loss of plants would also mean a loss of genetic diversity that would make it difficult for Joshua trees to survive, he added. In the face of unexpected challenges, such as new diseases or predators, a varied population can be the difference between survival and extinction. Some members of a population could have genetic resistance that can be passed on to offspring. With dwindling numbers, however, the chance of adapting to new challenges significantly decreases. Right now, more genetic diversity is found in Joshua Tree National Park, one of the points of origin for current Joshua tree populations, than anywhere else, Smith added.
And, if the trees do start to disappear, few alternatives would be viable.
“The most effective thing would be to identify places where even under very extreme climate change scenarios, Joshua trees are likely to be able to persist and make sure we don’t build condominiums on those places,” Smith said.
The loss of Joshua trees would have a devastating ripple effect on the desert ecosystem. It would transform the landscape and impact the myriad creatures that depend on the tree, including the yucca moths, ground squirrels and bird species, Smith said.
Joshua tree conservation and the preservation of the desert landscape and species thus again returns to a question of ethics and priorities, Smith said.
“To me, being able to go to the desert and see flowering cacti and Joshua Trees and creosote [bushes]–that is really meaningful,” he said. “I derive personal, almost spiritual, inspiration from that. As a society, as a species, we need to decide what is important. If that is important to us, we need to give it value and we need to protect it.”