California's ongoing drought is being blamed for accelerating the decline of Joshua trees, iconic symbols of the state's desert regions, researchers say.

Young seedlings of the distinctive trees, found mainly in the Mojave Desert, are shriveling and dying from lack of water before they have a chance to put down strong roots, ecologists say.

"For Joshua trees, hotter, drier conditions are a problem — but a bigger problem is that what little rainfall occurs evaporates faster," says researcher Cameron Barrows from the University of California, Riverside.

That leaves the seedlings in a weak state, he says, and some Joshua trees have not reproduced in decades.

The Mojave region, including Joshua Tree National Park, has gotten less than half of its usual annual four inches of rain for several years.

If current conditions continue for decades, 90 percent of the trees in the park could vanish by the end of this century, the researchers say.

The state's current drought is the worst in the last millennium, a study in the journal Geophysical Research Letters reports.

The drought not only threatens the iconic trees but also many species dependent on them, including desert night lizards, yucca moths, kangaroo rats, plus some 20 species of birds, the scientists point out.

California's deserts would not look the same without the trees, they say.

"Beyond its importance as a critical refuge for desert species, the Joshua tree is a cultural signature of California's desert landscape," added UC Berkeley biologist Rebecca R. Hernandez.

Mormon settlers trekking through the Mojave in the mid-19th century gave the trees their name for their distinctive shape, which reminded them of the Bible story of Joshua extending his arms skyward in prayer.

Despite the name, however, they are not actually trees at all but succulents of the genus yucca.

Joshua trees, properly named Yucca brevifolia, can grow as high as 40 feet high, and can live more than 200 years.

While an estimated 2.5 million Joshua trees exist, scientists worry that climate change and drought represent a one-two punch that puts them at serious risk.

A global temperature rise of five degrees Fahrenheit could see the trees' range shrink to between just two to 10 percent of its current extent, computer models by Barrows and his colleagues suggest.

That could spell trouble for the desert icon, says David Smith, superintendent of the 800,000-acre Joshua Tree National Park.

"Since they grow for about 200 years, we won't see massive die-offs in our lifetime," he says. "But we will see less recruitment of new trees."