Monday, 18 August 2014


California

Battle for Scarce Desert Water Proves Deadly to Joshua Trees

Thirsty rabbits and rodents ravage bark. Officials decide not to interfere in the process.

July 07, 2003|Janet Wilson | Times Staff Writer
 
 

The Joshua trees are dying.
Hundreds of the crooked-limbed trees in the national park that bears their name have succumbed to one of the worst droughts ever recorded, which sparked attacks by desert animals desperate for moisture. Despite the return of life-giving rains last winter, scientists say, thousands more will perish in coming years.
"When you drive through the park, you'd have to be nearly blind to miss the attacks on the Joshua trees. There are incredibly abundant numbers of dead trees," said Jim Cornett, a desert ecologist who has studied the trees in Joshua Tree National Park for 16 years. Based on surveys begun last year, he said, they are dying at 10 times their normal rate.
Cornett said that when scientists and park officials realized what was going on, "we panicked. When it's the namesake of a national park, you panic."
Since then, they have decided there is nothing to do but leave the process of dying and rebirth to nature. Though huge numbers will be lost because of lingering effects of the drought, most of them in much loved areas of the park, the species will probably rebound in 100 to 200 years.
"The short-term prognosis is that a large percentage of the Joshua trees will die in the park, and some of the hardest hit are in areas that visitors will see. But the long-term prognosis is that the Joshua tree will survive," said Cornett.
Scientists with the U.S. Geological Survey who completed surveys this week agreed, saying 57% of trees marked as damaged by rodents a year ago have died; mortality for trees that had not been attacked is 5%.
"The situation is acute," said Todd Esque, a botanist with the Geological Service who first figured out that rabbits and rodents were attacking the trees. "The level of damage going on in some of the little valleys in the park is pretty spectacular."
But he said the hard-hit areas were interspersed with undamaged areas, so a "mosaic" of healthy and dying areas would form.
For now and the foreseeable future, anyone visiting Queen Valley and other popular spots will notice huge swaths of bark stripped from the trunks and limbs, visible tan scars and whole trees standing like straw men or toppling toward the desert floor.
The 794,000-acre park, one of the most popular in the nation, received 1.2 million visitors last year. The Joshua trees, which in spite of their prickly looking exterior can survive only at slightly elevated altitudes where mean temperatures don't top 100 degrees, are mostly clustered in the western portion.
Though large portions of their historical range have been lost to urban encroachment, there are stands across the American Southwest. The Mojave National Preserve, which some researchers say actually has more of the trees, hasn't suffered as much damage to its stands because of monsoonal rains last summer, according to Larry Whalon, a botanist who is chief of resource management at the preserve.
The tree, one of the most familiar emblems of the California deserts, supposedly won its name from weary Mormon pioneers, trekking across the Mojave in the 1800s, who thought the weirdly skinny, outstretched limbs reaching up through the shimmering heat looked like the arms of Joshua leading the Israelites to the Promised Land.
Those same limbs and the trunks of the trees, which push precious moisture outward to the green, blooming edges, have enticed the antelope ground squirrel, the pack rat and possibly other species that would normally feed on young Joshua trees that have not developed their dagger-shaped, spine-tipped leaves.
The problem began in 2002, when the park received less than an inch of rain the entire year, well below the average 4.5 inches.
"As a consequence of the drought, we began noticing that bark was disappearing," said Joe Zarki, chief interpreter for the National Park Service at the park.
"At first it was just a tree here or there; normally you wouldn't even notice," Zarki said. "But then all of a sudden a significant portion of their bark was peeled off, and many of them were dying."
Officials thought a bacterial disease, nonnative grasses stealing water, or even global warming might be the culprit. They called in the Geological Service researchers, who noticed something on the damaged and dying trees.
"If you looked carefully, you could see teeth marks," said Zarki.
Close observation showed that the small rodents were tearing through the bark to reach the moist, pithy interior. Rabbits were standing on their hind legs to get at the bark, and gophers were hollowing out whole trunks from inside. Only termites are equipped to digest wood, but the small creatures were desperate to survive the drought. But researchers still weren't sure the chewing was enough to kill so many.
Three inches of rain last winter provided some relief, but not enough to halt the process.
"The rate of dying is increasing as we speak," said Cornett last week.
Ground squirrels and pack rats have begun tearing at the trees again as another bone-dry summer sets in.

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