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Goodbye, Joshua trees? Wildfires, heat may doom them at California park, study finds

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Joshua Tree National Park is famous for the iconic plant in its name — but the bizarre-looking species may be destined for extinction at the Southern California park, a new study says.

Scientists at the University of California in Riverside found that even if humans cut carbon emissions at middling or high levels to slow climate change, only 14 or 19 percent of the park’s current Joshua tree habitat will still be suitable for the species to grow by the end of this century.

And predictions are dire if humans don’t cut emissions, and instead continue business as usual: In that scenario, Joshua trees will be almost completely eliminated from the park between 2070 and 2100, according to findings researchers published in June in the journal Ecosphere.

“The fate of these unusual, amazing trees is in all of our hands,” Lynn Sweet, the UC Riverside plant ecologist who led the project, said in a statement the school released. “Their numbers will decline, but how much depends on us.”

Earlier research predicted that climate change would be a big threat to the trees at the park, researchers wrote in the abstract of their study. But the new findings show that in the worst-case scenario, climate change could mean there is almost no Joshua tree habitat left in the park at all.

Researchers said this “newer study considered a climate change scenario using twice as many variables, including soil-water estimates, rainfall, soil types, and more.”

An army of volunteers helped researchers collect data from 4,000 Joshua trees to complete the study, which helped scientists discover that the species has retreated to higher areas and cooler climates in the park, where there’s more water in the ground, researchers said.

Meanwhile, in spots that are drier or warmer, adult Joshua trees don’t have as many offspring — and the ones they manage to produce aren’t living, the study found.

Joshua trees have been around for roughly 2.5 million years, and each tree lives up to 300 years by collecting water reserves to weather drought; but younger trees can’t store water that way, meaning climate change-fueled periods of drought could spell doom for saplings.

Researchers said the study also found that fire is a major threat to trees in wetter, cooler parts of the park where they could still thrive.

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In this photo taken May 24, 2009, fires continue to burn in Joshua Tree National Park in the Mojave Desert outside Palms Springs, California. Preston Drake-Hillyard AP

Fewer than one in 10 trees survives a wildfire, researchers said.

The kind of blazes that could kill off the species have grown worse because of industrial exhaust and vehicle smog, which leaves nitrogen on the ground, spurring the growth of invasive grasses that can fuel a fire, according to researchers.

“Fires are just as much a threat to the trees as climate change, and removing grasses is a way park rangers are helping to protect the area today,” Sweet said. “By protecting the trees, they’re protecting a host of other native insects and animals that depend on them as well.”

Researchers wrote in their study that the findings pinpoint refugia, or possible future habitat, for the trees as the climate changes.

“Rather than an ominous prediction of extinction, climate refugia provide land stewards with targets for focusing protective management, giving desert biodiversity places to weather the future,” the study authors wrote.

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Jared Gilmour is a McClatchy national reporter based in San Francisco. He covers everything from health and science to politics and crime. He studied journalism at Northwestern University and grew up in North Dakota.
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