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Temperate and boreal forests are among our best assets in the fight against global warming; but without better management, scientists say these woodlands instead may become part of the problem

  • John Carey
  • Sep 15, 2011

THE TROPICAL RAIN FOREST gets most of the press. After all, it has become the symbol of primeval wilderness and a poster child for protecting the natural world. But it's worth also taking a look at woodlands closer to home. Forests are growing all around us: stately white pines and spreading oaks in the Northeast; delicate longleaf pine and rich bottomland hardwoods in the South; silvery aspen and gnarled pinyon pine in the Southwest; magnificent redwoods in California and a vast expanse of spruce and fir all across Canada.

These temperate and boreal forests are home to an astonishing variety of life, from the red-cockaded woodpecker of the Southeast to the wolverines and bears of the Northwest. A single southeast Alaska forest harbors 750 species of lichen. And the 797 million acres of temperate forest in the United States, 1.5 billion acres of boreal forest in Canada and hundreds more millions of forested acres worldwide are vital for humans as well: We build our houses out of wood. Forest canopies and roots filter our water and protect our streams. "There's a long list of things that forests do,"  says Geoffrey "Jess" Parker, a senior scientist at the Smithsonian Environmental Research Center (SERC) who has been studying forests for more than 25 years.

At a time when rising emissions of greenhouse gases such as carbon dioxide (CO2) threaten the planet with a changing climate, these forests also are helping save the Earth from a worse fate by grabbing huge amounts of CO2 from the atmosphere. "One of the surprising results of our recent work is that temperate and boreal forests store a lot of carbonÑas much, if not more, carbon per acre than some tropical forests," says William Keeton, associate professor of forest ecology and forestry at the University of Vermont.

In fact, the world's carbon storage champ may not be a tropical rain forest at all—it is probably the rainy coastal temperate forest of the Pacific Northwest. With their massive tree trunks, jumbles of huge fallen logs on the forest floor and thick rich soils, coastal coniferous forests in this region store nearly 772 tons of carbon in live and dead tree biomass per hectare, compared with 77 to 330 tons for most tropical and temperate forests. What's more, research by forest ecologist Beverly Law of Oregon State University and others demonstrates that "contrary to the long-standing view that old-growth forests are carbon neutral, they can continue to accumulate carbon," says Law.

Perhaps as encouraging, new research also is showing that it's possible to wring more benefits for both humans and wild creatures from temperate and boreal forests than we're getting now. At its simplest, this new and controversial idea is to let forests grow for longer periods of time before harvesting them—and then leave more old trees behind. It's also possible to restore forests actively and take steps to make them more resilient. "We are trying to push a revolution here," says Jerry Franklin, professor at the College of Forest Resources at the University of Washington and legendary forest graybeard. The payoffs for wildlife, for people and for climate could be enormous, says Eric Palola, senior director of NWF's Forests, Climate and Energy Program. "Right now, the estimate is that U.S. forests are mopping up 10 to 15 percent of U.S. emissions of CO2," he says. "But they could do a lot more."

Good News and Bad

Yet even as temperate and boreal forests are gaining new respect, they are facing some serious threats. "U.S. forests are just fine in some ways, but in others they are really struggling," says Tom Martin, president and CEO of the American Forest Foundation. The same is true for Canada's boreal forests.

First, the good news. Trees have made a remarkable resurgence in this country, particularly in places like New England, where most of the original forest was cleared for farming during the 1700s and the first half of the 1800s. Since the 1950s, the total volume of wood in standing trees in the United States has actually doubled, says Richard Guldin, director of quantitative sciences at the U.S. Forest Service. Moreover, 250,000 tree measurements taken since 1987 by Parker's SERC team in Edgewater, Maryland,  show an unprecedented and still unexplained spurt in growth rate.

The bad news? High-quality forests are increasingly rare, and new threats are emerging. "While forest cover has come back in the Northeast, nearly all old-growth forest in this region is gone," says ecologist Dominick DellaSala, president of the Geos Institute. "In the Southeast, virtually all long-leaf pine wiregrass is gone, and the Pacific Northwest has lost all but about 15 to 20 percent of its old-growth." Overall in the lower 48 states, he adds, "we have only about 5 percent of historic old growth and very few large intact areas."

In addition, trees are beginning to die at an increasing rate. Forest Service data show that death from insect attacks has jumped three-fold in the last decade, led by devastating outbreaks of mountain pine beetle in the West. And when Phillip van Mantgem, research ecologist at the U.S. Geological Survey's Redwood Field Station in California, looked at study plots in old-growth forests of giant sequoia, sugar pine, cedar, ponderosa pine and others, "one surprising pattern kept popping up," he says. "Mortality rates have doubled. It's kind of a hair-on-fire moment. If these trends continue, they have the ability to really change the forest."

What's going on? Many scientists suspect the underlying culprit may be climate change, which can be a double whammy. A warming world not only stresses trees and makes them less able to withstand attacks by disease and insects, it also extends the range and power of attackers like the pine beetle.

At the same time, higher temperatures also are changing the composition of forests themselves—which can then exacerbate global warming. University of Virginia researchers, for example, have shown that a warmer climate will convert large areas of Russia's boreal forest from larch to evergreen conifers. Since deciduous larch trees drop their needles in winter, a switch from larch to spruce and fir would change the winter landscape from heat-reflecting, snow-covered ground to a heat-absorbing green canopy. That would raise temperatures and melt permafrost, causing the release of carbon from the soil. "Warming creates more warming," warns University of Virginia environmental sciences professor Herman Shugart.

From Sink to Source?

The worst case scenario is that a combination of insect mortality, increased fires and other changes might eventually flip temperate and boreal forests from carbon sinks to sources of carbon, says Werner Kurz, senior research scientist at the Canadian Forest Service. "If we let climate change advance too far, and forests pump out a lot of carbon, our efforts to reduce emissions could be completely swamped by the responses of terrestrial ecosystems," he says.

That's why optimizing carbon uptake from temperate and boreal forests is now so urgent, researchers say. Fortunately, scientists are learning how to do this. One of their key lessons came, ironically, from a forest catastrophe: the eruption of Mount St. Helens in 1980. "It was a real epiphany," says Franklin. "Sometimes you need something like that to remind you of what you already know."

The message was that natural disturbances, unlike the clear-cuts of loggers, leave behind a rich legacy of downed trees, standing snags and other types of organic material. "When trees die, they don't go to heaven—they remain on Earth," says Olga Krankina, associate professor of forest ecosystem science at Oregon State University. Krankina's own work shows that even after fires, up to 95 percent of the original carbon remains in a burnt-out forest. And whatever the cause—or the size—of natural disturbances, the complex environment they help create is a boon for wildlife. "Mount St. Helens is now the biological hot spot in the Cascades, brimming with diversity," Franklin says. Elk, cutthroat trout and an array of birds have rebounded in astonishing numbers, and some species that had never been seen in the area beforeÑsuch as the western meadowlark—have moved in.

Even without volcanoes, old-growth forests experience periodic disturbances such as windstorms that open big holes in the canopy by toppling a few giant trees, making them more complex and diverse. "We can learn a lot from old growth about how to make our managed forests more resilient and persistent—and how to increase the amount of carbon," says Paul Alaback, professor of forest ecology at the University of Montana.


Old-growth Lessons

The first lesson is to hang onto as much old growth as possible, since those forests are still bulking up on carbon while providing key habitat for wildlife. Indeed, work by economist Duncan Knowler of Simon Fraser University shows that old-growth forests in British Columbia are worth more standing than logged because of their ability to capture carbon dioxide as well as provide habitat, recreational opportunities and a variety of ecosystem services.

The second lesson is that in forests that are harvested, trees should be allowed to grow older and bigger than they are today—and loggers should leave behind a number of big old trees. "We need to replace clear-cutting with what I've called "variable retention harvesting"leaving little islands of up to 3 to 4 acres in size behind to provide structural diversity," says Franklin. The patchy forests would also be less susceptible to insects like bark beetles.

Such management changes will not be easy. Environmentalists are skeptical because of the less-than-stellar record of past forestry practices. And the timber industry has a history of resisting change that would seem to cut into revenues. As Krankina says: "The conflict in boreal forests is diversity and carbon storage versus the interests of timber companies." But while imposing longer periods between harvests and putting constraints on how many trees can be cut would bring short-term pain to the industry, in the long run "they can actually harvest more," Krankina argues, since the trees will be bigger.

In a new book, Temperate and Boreal Rainforests of the World, DellaSala and colleagues argue that "the world is dangerously close to a tipping point on forests." With the right protections and policies, temperate and boreal forests can be a major weapon in both the fight against climate change and the battle to preserve wildlife, ecosystems and all the benefits, such as clean air and water, that they provide. But if we take a wrong turn, these same forests instead could become part of the problem. "In light of climate change and other stressors, the question becomes how can we best manage our forests without pushing them over the edge," says Palola.

Birds of the Boreal Forest

Extending across Canada from Alaska to Newfoundland, North America's boreal forest provides critical breeding grounds for billions of the continent's birds. According to the Boreal Songbird Initiative, nearly half of the 700 species that regularly occur in the United States and Canada rely on these forests for survival; more than 300 species regularly breed in the boreal region.

Boreal breeders include 80 percent of North America's waterfowl species, 63 percent of the continent's finch species and 53 percent of its warbler species. For close to 100 species, 50 percent or more of the entire breeding population is found in the boreal. These include many colorful warblers beloved by bird-watchers: Blackburnian (right, 55 percent), magnolia (74 percent), Cape May (83 percent) and palm (98 percent) warblers, to name just a few.

Though much of Canada's boreal region remains intact, the forests face a number of mounting threats such as timber harvesting, oil and gas development, mining and hydroelectric power development. The Boreal Songbird Initiative provides information about these forests' importance to the continent's birds and steps you can take in your daily life to help boreal forests.

International Year of Forests

The United Nations General Assembly has declared 2011 as the International Year of Forests. The goal of the celebration is to raise awareness of conservation and sustainable development of all types of forest worldwide.

Reversal in Recovering New England Forests 

After being cleared for farming during the 1700s and 1800s, New England's forests resurged during the two centuries that followed—one of the nation's top conservation success stories. But a study led by David Foster, director of Harvard University's Harvard Forest in Petersham, Massachusetts, reveals a troubling setback: For the first time in 150 years, forest cover is declining in all six New England states (Acadia National Park, Maine, below). Each year thousands of acres of forests and farms are razed for houses, lawns, commercial buildings, roads and parking lots.

"This second wave of deforestation poses far greater challenges than the previous episode," notes a recent report, Wildlands and Woodlands: A Vision for the New England Landscape, coauthored by Foster and published by Harvard University Press. "The permanent development and landscape fragmentation of today, often involving asphalt, concrete and steel, are much harder to reverse than the historic clearing of land for farms and pasture."  

NWF Priority: Promoting Healthy Forests 

NWF works on many fronts to conserve forests and promote sustainable use of our nation's public and private woodlands while elevating their critical role in fighting climate change.
"The United States has a rich forest heritage that includes more than a dozen major forest ecosystems," says Eric Palola, senior director of NWF's Forests, Climate and Energy Program. "The potential for conserving and restoring these woodlands is great in many parts of the country." In King County, Washington, for example, NWF is helping county officials develop new tools to maintain the carbon-rich urban forests of the Seattle area. In the Southeast, the Federation is leading efforts to reclaim former floodplain forests along the Mississippi River and helping African-American landowners integrate restoration of longleaf pine forests into farming practices.

NWF also works closely with the Forest Stewardship Council, the world's leading independent certifier of wood and paper products, which is active in more than 50 countries. And among its efforts to connect children with nature, NWF's Trees for the 21st Century program combines hands-on, science-based education with tree-planting and stewardship. "The initiative aims to prepare the next generation of environmental stewards to protect and improve the world's natural resources," says Eliza Russell, NWF's director of education.

John Carey is a Northern Virginia-based science writer.

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