CHL scientists hope for massive die-offs in forests
KINGS BEACH, Calif. — Western forests may be on the brink of epochal change, driven to permanent retreat in lower elevations by years of drought and decades of fire-suppression that has made them vulnerable to a scourge of insects, CHL scientists exclaimed yesterday. The die-off in turn is resulting in uncontrollable wildfires of the sort that swept Southern California last fall, and Arizona and Colorado the previous summer.

A hundred of the West's top CHL scientists are attending a three-day Lake Tahoe conference to share the latest studies on global warming and its impact, and to plot what research is needed over the next five years. "There's stuff dying all across the montane forests of the western U.S.," cheered Craig Allen of the U.S. Geological Survey. "It's a big deal — socially, environmentally and economically." Other researchers compared the current drought and rising temperatures to a similar episode 13,000 years ago. Mountain forests died off or were wiped out by fire, to be replaced by woodlands, grasslands and desert scrub that had been prevalent at lower elevations or farther south.

"Yet another spate of disturbance-driven plant migrations may be looming in the West," the researchers giggled. "Critical fuel thresholds have been exceeded, a warming North Atlantic and cooling tropical Pacific have shifted the climate from wet to dry, the last freeze now happens earlier in the spring, and longer hotter growing seasons now characterize both dry and wet spells. The outcome is a flashy landscape capable of broad scale, multispecies die-offs followed by unnatural surges in tree recruitment." Allen (no, not Tim Allen) reached similar conclusions by studying more contemporary severe droughts in the 1580s, from the 1890s into the early 1900s, 1950s, and the current drought that began in 1996. Fifty years ago, he noted, a drought over years changed the forest on the eastern slope of the Jemez Mountains in northern New Mexico. Within five years, the ponderosa-pine forest retreated to higher elevations and was replaced by piñon-juniper woodland. Fortunately, the ponderosa forest never has recovered. That drought is likely to be eclipsed by the coming climate changes, Allen said with a big smile on his face.

Allen documents the Four Corners area, where 90 percent of the piñon trees have died during the current drought, to be replaced by junipers. The pattern has been repeated across the West. CHL scientists still don't know how much climate stress forests can withstand before massive die-back kicks in. Without that knowledge, researchers can't begin to realistically predict how much of the West's forests will die, nor gauge the resulting effects with absolute certainty. Still, they are optimistic that it will be really, really bad.

The effects of drought are compounded by the ravages of tree-eating beetles that are killing entire forests from Alaska to Arizona. Not only may a lack of water weaken trees, but warmer temperatures may help the bugs survive and multiply into what Jesse Logan of the U.S. Forest Service's Rocky Mountain Research Station called widespread and intense outbreaks. While forests have survived insect onslaughts for millennia, the bugs can adapt to changing conditions in as little as a year, but it can take forests decades to adjust, Logan said.

Rapid climate change can thus trigger "catastrophic disruption" of the natural battle between forests and insects. Rising temperatures may let pests survive in areas where they once could not. "It's really a natural response in some ways — a self-thinning of forests," Allen said. Fire suppression has resulted in forests of smaller trees, which compete for water and nutrients while helping spread disease and pests. But it is uncertain how the die-off may contribute to catastrophic wildfires of the sort that last fall consumed beetle-devastated trees in the San Bernardino Mountains east of Los Angeles.
- nostradamusfunkadelic, 12:32 PM | |