June 20, 2009

Desert icon Joshua trees are vanishing, scientists say

Mike Cipra, a desert program manager for the National Parks Conservation Association, examines a burned Joshua tree showing signs of growth. Scientists say the effects of global warming could make Joshuas extinct within a century. (Kurt Miller / The Press-Enterprise)

The Press-Enterprise

A breeze stirs the silence at Joshua Tree National Park as a red-tailed hawk takes flight from the spiky arm of one of the namesake plants in search of breakfast.

It's a scene that national parks protector Mike Cipra has witnessed many times. Still, he can't contain his enthusiasm on this early morning outing, despite the gloomy topic he's discussing with a visitor -- the probable extinction of the Joshua tree in the park that bears its name.

The ancient plants are dying in the park, the southern-most boundary of their limited growing region, scientists say. Already finicky reproducers, Joshua trees are the victim of global warming and its symptoms -- including fire and drought -- plus pollution and the proliferation of non-native plants. Experts expect the Joshuas to vanish entirely from the southern half of the state within a century.

The loss would be devastating, said Cipra, who is California desert program manager for the National Parks Conservation Association, a nonprofit group that evaluates conditions at national parks and lobbies for their preservation.

"Joshua trees aren't just iconic pictures on a postcard. They're essential to a functioning ecosystem," he said. "We're going to be losing a lot of what makes this place special."

The quirky, almost comical trees are really plants, a relative of the yucca.

Pictured on U2's 1987 album "The Joshua Tree," they look like desert sentries, with fibrous trunks and twisting, outstretched arms.

Joshua trees are a foundation species, providing habitat for other animals that otherwise would disappear, said Cipra, 34, his brown boots crunching on the desert floor as he surveys the boulder-studded Queen Valley. Besides the foraging hawk and a scrub jay calling nearby, there are Scott's orioles that build hanging nests in the trees, rodents that pry food from its seed pods and the Yucca night lizard, the smallest lizard in North America, which nests under its fallen branches, he said.

Growing up in Long Beach, Cipra discovered Joshua trees at 16, when he asked his parents if he could ditch school to camp and explore with a friend in what was then the national monument. The city boy, who went on to USC on an academic scholarship, drew up a list of reasons he wanted to visit the park, top among them the variety of animals he would see.

Cipra said his experience in the desert was life-changing. He went on to become an interpretive ranger at the park -- where his wife works as a biologist -- and now lobbies for governmental policy to protect it. Among the causes he supports is the pending congressional cap-and-trade plan that would limit carbon dioxide emissions and provide money from refiners and power plants to manage the effects of climate change.

"Some experiences in the natural world can be transformative. That's the power of national parks," Cipra said.

'Worst-case scenario'

Predictions for the fate of the Joshua trees, and the web of life they support, are based on six models of climate change developed by Ken Cole, a biologist and geologist with the U.S. Geological Survey in Flagstaff, Ariz., and plant ecologist Kirsten Ironside of Northern Arizona University.

In all of the climate models that looked ahead 100 years, there were no new trees in Joshua Tree National Park, and significant death of existing trees.

"With the Joshua tree, it's like a worst-case scenario. Maybe 80 percent of the current populations will be unable to persist," he said.

The plants were prolific and widespread 11,000 years ago, Cole said, when their seeds were carried long distances from Mexico north to Nevada in the dung of the Shasta ground sloth, now extinct. Now, seeds are transported only short distances by rodents.

The future will bring a temperature increase of about seven degrees, similar to the change between the Ice Age and modern time, Cole said, and with that will come drought and fires.

Fires in Joshua Tree National Park used to be rare, occurring every 50 to 100 years, he said. But in the 1970s, the frequency of fires in the park increased to every three to 10 years.

Fires are fed by non-native plants such as red brome and cheatgrass that remain dry after wildflowers and other natives blow away. Where there used to be dirt patches between vegetation, the invasive grasses provide a continuous bed of tinder that carries fire from plant to plant, he said.

As an example, park spokesman Joe Zarki points to the largest blaze in park history, the Juniper Complex Fire of 1999. Caused by a lightning strike and fed by non-native grasses, the blaze consumed almost 14,000 acres of century-old junipers, pinyon pines, scrub oak and healthy Joshua tree forests, and forced evacuation of the west end of the park. The invasive species, often transported along roads by passing cars, feed on the nitrate and ammonium deposited in the soil by car emissions. Edith Allen, a UC Riverside professor of plant ecology, has found that the levels of those chemicals in the park are 15 to 30 times higher than those in an undisturbed ecosystem.

The park has changed its policy on fires from letting them burn to suppressing them entirely because so much habitat was being destroyed. It can take as long as 200 years for some desert plants to mature.

"The big question that a lot of people are asking about Joshua trees and plants in general: 'Can they (plants) move into new habitats fast enough to keep pace with climate change?' They are running a very slow race," said Christopher Smith, an assistant professor of biology at Willamette University in Salem, Ore.

"The current levels of carbon dioxide in the atmosphere are higher than at any time in the past million years of the Earth's history, and it is clear beyond any reasonable doubt that increasing carbon dioxide will cause the Earth's climate to warm very rapidly," he said.

Park scientists are trying to prevent the spread of the invasive grasses into new areas of the park through monitoring and removal.

They also are encouraging re-vegetation after fires by planting "seed islands," sprouts of native plants surrounded by fencing and a slow-release watering gel. One of those plants, blackbrush, is critical to development of new Joshua trees. The Joshuas grow through the middle of the dry, prickly bush, which protects seedlings from gnawing rabbits and rodents.

No new trees

The National Park Service is grappling with a plan for dealing with climate change. The agency is waiting for national direction on the issue, and so far there is no battle plan, said Zarki, the park spokesman.

Eventually, it could mean mass plantings of Joshua trees and other threatened species, but that raises ethical and logistical questions that are far from being resolved, said Todd Esque, a research ecologist with the USGS in Henderson, Nev. Among those considerations is the source of the seed; purists emphasize local seed to preserve existing resources, while other advocate hybridized seeds to help the plants respond to change, he said.

While Joshua trees will be the losers in the global warming lottery, other plants will thrive.

Palm Springs biologist Jim Cornett, who has studied Joshua trees throughout the Southwest for 20 years, has found that desert fan palms have dramatically increased in the region, as has saguaro cactus of the Sonoran desert.

Cornett has monitored Joshua trees on 10 study sites in California, Utah, Nevada and Arizona. On all but two of the 2½-acre plots, Joshua trees are dying; at Saddleback Butte State Park near Lancaster, there hasn't been a new tree in 20 years.

But in the upper elevations of Cima Dome, in Mojave National Preserve north of Joshua Tree National Park, and Lee Flat at Death Valley National Park, the plants are flourishing, he said. They also are prospering in Tonapah, Nev., their northern boundary where none existed a century ago because it was too cold. Those locations provide more rainfall and the winter cold snaps necessary for the Joshua trees to flower and produce seeds, he said.

Cornett blames the plant deaths on drought, which could be a result of global warming, he said. After each period of drought, more new Joshua trees died off, he said. That included the 42-foot Emily's tree, the largest in Joshua Tree National Park, which was estimated to be 150 to 300 years old when it died three years ago.

"The good news is that humans have the capacity to slow down this rate of climate change and to minimize these impacts," Cornett said. "Other animals don't have that capacity. They're helpless witnesses."