The Future of Forests

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

5. Less colorful autumns in the Northeast

Milder winters cause sugar maples to migrate out of the U.S.

Sugar maples depend on a prolonged cold season for optimal sugar content and sap production. Due to warmer winters, syrup producers in Vermont and New Hampshire are already tapping trees one month early, and climate models predict that the maple will migrate to Canada between 2070 and 2090, crippling New England's syrup industry and fall foliage.

6. Fewer trout

As streams warm, habitat will decline by 50 percent.

Trout and steelhead (seagoing rainbows) need cold, swift, highly oxygenated water. As a river's temp approaches 70°F, they stop feeding. Once it hits 80°F, many varieties such as cutthroat and bull simply die. Researchers at the University of Wyoming estimate that a 5.4°F increase in July air temperatures (predicted by most 100-year climate models) could eliminate half of Rocky Mountain trout habitat. The EPA predicts up to a 50 percent loss of cutthroat habitat throughout Oregon, Montana, Utah, Wyoming, and Colorado, and greater than 50 percent in Washington, Idaho, California, and New Mexico. In the Northeast, an EPA study concluded that rainbow, brook, and brown trout will likely be "partially or completely eliminated" by the middle of this century–to be replaced by bass, carp, and catfish.

7. Evaporating wetlands

Decreasing soil moisture will likely reduce waterfowl populations across the Upper Midwest.

The northern Great Plains region along the U.S.-Canada border is a glaciated landscape of fertile soil, rugged hills, and small, shallow ponds known as prairie potholes. Besides being awfully scenic, this 310,000-square-mile wetland zone is also the breeding ground for 50 to 80 percent of all of North America's waterfowl. At least 350 bird species use this region during migration, and 180 breed here. By 2060, warming is expected to intensify evaporation and reduce soil moisture by 25 percent, decreasing the number of potholes from 1.3 million to about 700,000. At least 14 species of waterfowl will see their populations cut in half, and scientists forecast a 70 percent reduction in ducks, and a 91 percent drop in prairie pothole wetland acreage by 2080.

8. Bigger, itchier poison ivy

Woody vines will thrive in a CO2-rich environment.

Start hoarding calamine lotion. Ecologist Jacqueline Mohan of the Ecosystems Center at the Marine Biological Laboratory in Woods Hole, MA, used a pipe system to boost CO2 levels in a North Carolina forest to the exact concentration expected by the year 2050 if current fossil fuel use rates continue worldwide. The result? The CO2-enhanced vines grew three times larger and produced a more potent form of urushiol, the toxic agent in poison ivy, poison oak, and poison sumac.