Pine numbers sapped

Monday, Oct. 17, 2005 | 7:21 a.m.

Researchers are continuing to raise an alarm about the number of pinyon pines, the usually hardy sentinel trees of the high elevation forests of the Southwest, that have been dying off.

Millions of trees in Nevada and nearby states have been hit harder by this drought than previous droughts, and some researchers suspect one reason for the broader die-off may be global warming.

Gail Durham, a forest health specialist with the Nevada Division of Forestry, said surveys of forest damage from this year are not yet complete, but the agency has seen millions of the trees die, especially in Southern Nevada.

"The Spring Mountains were definitely hit," Durham said.

"We started seeing an increase in mortality in 2002," she said. That year, the agency tallied a loss of 64,000 acres of pinyon pine with a die-off of nearly 400,000 trees in Nevada and the eastern slopes of the Sierra Nevada mountains in California.

In 2003, about 260,000 acres were lost with 3 million trees killed. In 2004, 740,000 acres and 4.4 million trees died. The numbers from this year are still being compiled, but a wet winter appears to have eased the trend somewhat, Durham said.

If anything, the numbers are understated because the state doesn't have the resources to study all the pinyon forests, Durham said.

"We attribute it to drought," Durham said.

Water, which pines turn into sap, is a critical element of the pinyon's defense system.

"Normally the tree has enough sap to pitch them (insects) out in attacks. When there is not enough water, there is not enough sap to pitch them out."

The invader is usually a kind of male bark beetle that burrows into the tree's bark. If it successfully penetrates into the soft wood underneath, it sends out a chemical signal called a pheromone to attract females. After mating the females lay hundreds of eggs, which turn into tree-devouring larvae.

David Charlet, a Community College of Southern Nevada biologist specializing in the study of pine trees, estimated that 10 to 15 percent of all pinyon forests here are affected negatively by several factors, including the bark beetle. Another problem is that other species are competing for the resources of the forests and raise the danger of fire.

Human activity, including construction of homes in and around pinyon forests, also stresses the trees, he said. But today's pressures are nothing compared to past years, when pinyon forests were cleared wholesale to make room for cattle or to make charcoal for industrial needs.

What is different about the last several years is that trees that might have once survived the drought are dying with as much as 90 percent mortality, according to a team of researchers led by University of Arizona ecologist Dave Breshears.

"Across a whole landscape, this system got whacked," said Breshears, whose findings were reported this week in the Proceedings of the National Academy of Sciences. His team has been doing long-term studies of the Jemez Mountain ecosystem in New Mexico in 2002 and 2003.

Warmer temperatures only 1 to 2 degrees Fahrenheit higher than the long-term average appear to have contributed, the scientists found. Tree deaths occurred in areas that were relatively unaffected by a drier drought during the 1950s.

"This is a different kind of response than we saw following the 1950s drought," said Breshears, who has been studying pinyon woodlands since the 1980s. "This drought was hotter."

Charlet said changing temperatures have in the past caused pinyon trees, which can live for 300 to 500 years, to change their regional distribution.

"They have seen many, many climate changes in the past," Charlet said. "We will see decline in some areas and expansion in others."

Breshears didn't blame the 2002 die-off on human-caused global warming, saying no single event can be unequivocally linked to the planet's long-term rising temperature trend. But he said dramatic drought-induced changes in the Southwest landscape since the turn of the 21st century are consistent with global climate change projections.

"We're more likely to get more frequent, more intense droughts," Breshears said.

Durham said she doesn't know if climate change in the West has contributed to the massive die-off in Nevada. She does believe the impacts have eased over the last year.

"It has definitely gone way down. We lost a lot of pinyon but it has tapered off because we had such a good water year last year."

U.S. Geological Survey ecologist Julio Betancourt disagreed with conclusions reached by Breshears' team. Betancourt questioned whether scientists know enough about what happened 50 years ago to be sure the recent drought was worse.

However, he praised the scientists for trying to quantify effects of warming temperatures.

"All of us are seeing these temperatures going up, and we know it's going to have an effect," Betancourt said.