Dramatic-looking Joshua trees have survived since the Pleistocene era, about 2.5 million years. Now, because of climate change, their extinction is looming.
In a new study, researchers and a team of volunteers gathered data on more than 4,000 trees in Joshua Tree National Park in southern California. They discovered the trees have been migrating to parts of the park with higher elevations that offer cooler weather and more moisture in the ground — safe zones for the trees. Adult trees in drier, hotter areas aren't producing as many young plants, and those that are produced aren't surviving.
Their findings were published in the journal Ecosphere.
Considering the predicted impacts of climate change, the researchers estimated how many of these safe zones — or "refugia" — would survive. They predict that in the very best-case scenario, if major steps are taken to lower carbon emissions, about 19% of the trees will remain after 2070.
However, if things continue as they are and there's no attempt to reduce carbon emissions and temperatures continue to rise, only .02% of the trees will remain.
"The fate of these unusual, amazing trees is in all of our hands," lead study author Lynn Sweet, a plant ecologist at the University of California, Riverside said in a statement. "Their numbers will decline, but how much depends on us."
Water and wildfires
Individual Joshua trees can live as long as 300 years. One of the ways adult trees survive so long is their camel-like ability to store large amounts of water, which helps them make it thorough the area's severe droughts.
However seedlings and young trees aren't able to store water this way. During long dry spells — such as the 376-week-long drought in California that lasted through March 2019 — the ground is too parched in the park to support new young plants. With climate change and rising temperatures, long droughts are expected to occur more often, which means fewer Joshua trees will likely survive into adulthood.
But climate change isn't the only threat to these trees. They are also threatened by wildfires, which have been occurring more frequently in recent years. Fewer than 10% of Joshua trees survive wildfires.
"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."