Joshua Trees Do Better In More Extreme Climates

In all, the citizen scientists found 800 baby Joshua trees. They narrowed the field to about 80 of the newest plants that were a foot tall or less, so Barrows could chart their distribution in relation to rising temperatures.

Barrows was not surprised to find evidence that Joshua trees have stopped reproducing in the hotter areas of the park, where yearly low temperatures in the south have increased 3.2 degrees in the past 36 years. But enough recent offspring were found to give him hope for the future.

“What this indicates is more of a hopeful scenario, in that if we as a world of people who consume carbon and expel it, start living more sustainably, then things like protecting Joshua trees in the boundaries of Joshua Tree National Park are possible,” said Barrows, a research ecologist at UC Riverside’s Palm Desert campus.

His findings veer from a 2005 study by Ken Cole of the U.S. Geological Survey showing that Joshua trees likely will be gone from 90 percent of their current range in the next 60 to 90 years.

The spiky trees, plentiful throughout the Southwest and Mexico in the Ice Age, now are limited to Joshua Tree National Park; eastern San Bernardino, Los Angeles and Kern counties; Inyo County; southern Nevada; extreme southwestern Utah; and northwest Arizona.

Cole predicts that all of the Joshua trees in San Bernardino and Riverside counties will migrate to Nevada and the higher elevations of Death Valley by the next century.

The difference, Barrows said, is that Cole’s work covered the entire southwestern United States, while Barrows looked specifically at Joshua Tree National Park.

The park’s location at the southern boundary of their habitat has allowed the plants there to better adapt to drought and high temperatures than those living in less extreme climates, he said.

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