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September 2007

The Future of Forests

As the earth warms, here's how higher temps will affect our forests.

Home to more than half of all land species, forests hold moisture, regulate rainfall and runoff, filter our drinking water, and clean our air. Forests also play a critical role in regulating climate. Plants act as a carbon sink by trapping and storing CO2 through photosynthesis and releasing oxygen via respiration. But the fast pace of climate change spells trouble for forests throughout North America. Scientists’ greatest worry: Large-scale changes don’t tend to happen quietly or gradually with forests, but in nonlinear fashion, through catastrophic die-offs and fires. Here’s a look at the latest research on the varied changes hikers are likely to encounter.

1. Disappearing western evergreens
Higher temperatures open the door to parasites like the mountain pine beetle.
Less overall precipitation and much longer dry seasons weaken trees, making them susceptible to bark beetle attacks. In British Columbia, beetles wiped out 21 million acres of timber in one year, and the Canadian Forest Service predicts that 80 percent of BC pines will be dead by 2015. Similar scenarios are playing out in Southwest plateau country, the Sierra Nevada, and the Rockies. “Conifer- and moss-dominated landscapes will turn to alder and aspen parkland, scrub trees, and grass patches,” says Glen Juday, a forest ecologist at the University of Alaska.

2. Drier canyon country
The Colorado River Basin will see annual precipitation drop by 55 percent by the end of the century.
Climatologists predict that Colorado River reservoir levels will decrease by more than a third, dam releases by 17 percent, and available hydroelectric power by as much as 40 percent. “Sadly, these predictions are based on one of the most conservative climate models,” said Dennis Lettenmaier, a University of Washington hydrologist. Expect slower, more rowing-intensive Grand Canyon rafting trips, streambeds choked with tamarisk, and normally reliable backcountry water sources going dry. Some popular redrock hiking routes will become nearly impassable–unless you fancy hauling 60 pounds of water for a three-day trek.

3. More devastating wildfires
Earlier spring snowmelt will lead to fires that burn so hot, there’s simply nothing left.
“Look at a Yellowstone landscape, burned in the 1988 fires, and you’ll see 19-year-old trees. That’s how it’s supposed to be,” says Thomas Swetnam, director of the University of Arizona’s Laboratory of Tree Ring Research. “But in high-severity crown fires, like we’re increasingly seeing, it burns so hot that it even burns through the soil, torching all the organic matter down to mineral gravel.” This leads to catastrophic erosion of forest soils that have taken millennia to develop. Scientists are particularly worried that millions of acres in the northern Rockies in areas like the Frank Church/River of No Return Wilderness, already weakened by drought and beetle infestation, could succumb to massive conflagrations this century.

4. Less diverse plant and animal populations
Adaptation will not keep pace with speedy temperature rise.
In a 2006 study of 800 North American plant and animal species, University of Texas lepidopterist Camille Parmesan came up with some startling results: Most plants and animals simply can’t adapt quickly enough to compete with rising temperatures. “To really [evolve] something new that’s going to allow a species to live in a completely new environment takes a million years,” Parmesan notes. “It’s not going to happen in a hundred years, or even a few hundred.”

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