The world’s forests sustain wildlife, clean our air and water, diminish floods, regulate weather—and are growing into potent weapons to help curb climate change.
Bathed in early-morning light, a forest in the Berkshires of Massachusetts evokes the ancient majesty of trees—more essential than ever to the health of our planet. (Photo by Robert Llewellyn)
WHEN EARLY EUROPEAN EXPLORERS first sailed along the shores of New England, Virginia and points in between, they were awed by the towering forests that confronted them, loud with the calls of birds, dazzling with wildflowers, packed with wild, edible fruits—plums, strawberries, grapes and persimmons. Later explorations would find that the forests ran hundreds of miles inland, in many cases clear to the Mississippi River. Within these vast woodlands roamed cougars, wolves, bison, elk and billions of passenger pigeons that fattened on acorns.
Logging began almost immediately, trees cut for wood, then chopped and burned to get them out of the way for farms. By the early 1900s, most eastern forests had been cut or cleared. Wolves, cougars, bison and elk no longer roamed the region, and the passenger pigeon was extinct.
As America’s frontier moved westward and settlers abandoned degraded farmland, trees began to grow back. Today, forest once again covers much of the eastern half of the United States. Modern travelers can drive from Maine through New England and New York State down into Georgia and across the South into eastern Oklahoma and never leave forest. These are not the big trees of yore, of course, and some species of the ancient forests, including the American chestnut, are virtually extinct. Yet today’s widespread eastern woodlands clearly show that destroyed forests can live again.
That’s good news for both wildlife and people. From bears, jaguars, chimpanzees and other charismatic mammals to thousands of bird species and millions of insect species, the world’s forests shelter an estimated 80 percent of all terrestrial biodiversity. They also provide innumerable benefits to humans, including timber and other goods along with many of the ecosystem services that make our lives possible. Trees draw water out of the soil, for example, moving it up through their roots and trunks, then releasing it from leaves into the atmosphere as water vapor. According to the U.S. Geological Survey, water vapor transpired by trees and other plants accounts for about 10 percent of atmospheric moisture. One large oak tree can release 40,000 gallons of water annually.
Forests also filter the water that falls on them and flows through the soil beneath, helping to keep streams clear and clean. In addition, trees reduce the speed at which water moves through an ecosystem, releasing it slowly to flow over and through the soil and, finally, into waterways. When forests are cut, water runs too rapidly across the soil, frequently causing floods, then rushes away so streams that once flowed year-round can become dry much of the year.
Today, a growing number of scientists point out that forests also are among our most-powerful weapons to fight climate change. “Natural ecosystems, especially forests, play a critical role in absorbing carbon dioxide, the greenhouse gas that is the primary driver of climate change,” says National Wildlife Federation Chief Scientist Bruce Stein. By taking in carbon dioxide from the atmosphere, trees, through photosynthesis, are able to harness energy from the sun to generate new leaves and stems and to grow larger. Trees will store that carbon in their tissues as long as they are left standing.
“Trees are nature’s carbon-removal engines,” says Alex Rudee, a carbon-removal associate at the World Resources Institute (WRI). “Restoring them to ecologically appropriate areas while protecting existing trees and forest is critical to keeping the United States on a path to avoid the most-dangerous impacts of climate change.”
According to the Intergovernmental Panel on Climate Change, terrestrial ecosystems, primarily forests, today capture nearly 30 percent of annual global carbon dioxide emissions. More trees could sequester more of the greenhouse gas. Yet the world is losing far more forested land than it is gaining. Data released this June by Global Forest Watch, a WRI-led forest-monitoring program, reveal that 954 million acres of tree cover were lost worldwide between 2001 and 2019, nearly a third of them unlikely to grow back or be replanted. Losses have been particularly severe in species-rich, old-growth tropical rainforests. In 2019 alone, such primary forests lost 9.3 million acres of tree cover—primarily to expanding agricultural commodities such as livestock, timber, soy and palm oil—or about a football field every six seconds for the entire year.
The carbon released when forests, especially old-growth forests, are razed contributes significantly to climate change. According to Thomas Lovejoy, a professor at George Mason University and senior fellow at the United Nations Foundation, the Amazon rainforest, for example, stores about 80 to 100 billion tons of carbon in its trees and other above-ground plants and 16 to 20 billion tons in the soil. “If we cut that forest, we will get a huge effect on the atmosphere,” he says.
Yet the Amazon forest is falling fast. In Brazil, which contains 60 percent of that 2.1 million-square-mile forest, ranchers, farmers, miners, loggers and road builders cleared 3,769 square miles between August 2018 and July 2019, according to Brazil’s National Institute for Space Research, a 30 percent increase over the previous year. More than 1,000 additional square miles disappeared between August 2019 and March 2020.
To mitigate deforestation’s harm and reap more benefits from trees—including additional carbon capture—development banks, national governments and nonprofits have launched projects to plant billions to trillions of trees worldwide. But planting trees is not always the right solution. Indeed, the practice “can cause more harm than good,” says Stein—if invasive, nonnative trees are planted, for instance, or trees are introduced to habitats, such as grasslands, that were not formerly forested. Both actions can decrease biodiversity. “Because it sounds so simple, the idea of planting trees has widespread appeal,” he says. “But you have to plant the right trees in the right places.”
In many cases, better management of existing forests can result in more carbon capture and storage than tree planting alone, Stein adds. In forests that are regularly logged, for example, managers could increase the amount of time between timber harvests. Preventing destructive megafires with techniques such as low-intensity prescribed burns and strategic thinning would result in more-extensive and healthier forests capable of soaking up more carbon dioxide, he says.
In situations where reforestation is warranted, the best strategy sometimes is to encourage trees to grow naturally rather than planting new ones. Agronomist Tony Rinaudo, now with the Melbourne-based World Vision Australia, learned that lesson while working on reforestation projects in Africa’s Sahel region beginning in the 1980s. After many years of disappointing results from tree-planting efforts (barely 10 percent of the newly planted seedlings survived), Rinaudo pioneered a technique to generate trees from the stumps, roots and seeds that had been left behind in the wake of deforestation—an invaluable resource he calls the “underground forest.”
By encouraging these embryonic trees to sprout up and grow, then persuading local people to protect and selectively prune them, Rinaudo’s “farmer-managed natural regeneration method” has restored nearly 12.4 million acres of degraded land in Niger with more than 200 million native trees, such as baobabs, acacias and shea, that provide goods and other benefits to local communities—improving the lives of millions of people in one of the world’s most impoverished regions.
Such benefits are key to the long-term success of any reforestation effort, whether carried out by tree planting or natural regeneration. “The real challenge is to find a way to retain forests while providing value to landowners,” says Julie Sibbing, NWF’s associate vice president for land stewardship.
But the best way to help forests everywhere is to prevent deforestation in the first place. In an article published in Science this May, environmental scientists Karen D. Holl of the University of California–Santa Cruz and Pedro H. S. Brancalion of Brazil’s University of São Paulo put it bluntly: “The first priority to increase the overall number of trees on the planet must be to reduce the current rapid rate of forest clearing and degradation in many areas of the world.”
Even as we turn to trees to help us fight global warming, a changing climate already has begun to impact forests, mostly in negative ways. Patterns of precipitation have been altered, for example, with more-frequent short, intense bursts of rain or snow followed by long dry spells. The result may be massive tree mortality, as occurred recently during California’s four-year drought, when nearly 150 million trees died. Higher temperatures also can kill trees directly or, when winters become warmer, trigger outbreaks of destructive insect pests such as the mountain pine beetles that have wiped out hundreds of thousands of acres of forest in the Rocky Mountains.
Recent research suggests that such climate-generated stresses on forests are even decreasing their capacity to help combat the problem. Analyzing three decades of tree growth and death in 565 tropical forest plots across Africa and the Amazon, scientists from the University of Leeds and colleagues recently discovered that the uptake of carbon dioxide by these forests peaked in the 1990s and has been declining since then. Throughout the past decade, the forests soaked up about a third less carbon dioxide than they did in the 1990s. The reason, the researchers reported this March in Nature, has been slower growth and higher mortality of trees due to rising temperatures and drought.
Today’s forest managers must take these and other impacts of climate change into account, Stein says. “We need less focus on our grandparents’ forests and more on our grandchildren’s forests.” As an example of “climate-smart forestry,” he cites an ongoing project in Minnesota’s Northwoods. Because this region’s climate is predicted to become less suitable in the future for historically common trees—such as paper birch, white spruce and other boreal species—a coalition of public and private partners led by The Nature Conservancy is conducting test plantings of seedling mixtures that include both formerly dominant trees and more-southerly species—including maple and oak—on 2,000 acres in need of forest restoration. If adopted widely, Stein says, such innovative management strategies can make tomorrow’s forests more resilient to our rapidly changing climate.
Can healthy forests ultimately save us from climate change? Not on their own, but they still have a vital role to play. According to Shannon Heyck-Williams, NWF’s director of climate and energy policy and co-author of Natural Climate Solutions, a recent Federation policy platform, “Forests and other wooded areas represent perhaps the best opportunity to remove carbon from the atmosphere quickly, reliably and relatively cheaply.” But to limit the world’s warming to 2.7 degrees F above preindustrial levels—as global leaders pledged to do in the 2015 Paris Agreement —“we also have to cut greenhouse gas emissions in half by 2030 and reach net-zero emissions by 2050,” says Heyck-Williams, who worries that politicians could use tree-planting projects as an excuse to avoid the more difficult task of emissions reductions. “It’s not a question of either or,” she adds. “We have to do both.”
From northern boreal stands to lush tropical realms, the world’s forests host some 80 percent of the globe’s terrestrial biodiversity, including animals, plants, fungi and bacteria. Though critical to human and wildlife health, forests are disappearing by millions of acres a year, an unsustainable rate of loss that threatens planetary health.
Forming a tender pyramid, young mountain gorillas rest with their mother as she cradles her newest offspring in the Virunga National Park in Democratic Republic of Congo. The park is home to about a third of the world’s roughly 1,000 remaining critically endangered mountain gorillas, who depend on forested hills—and hundreds of park rangers—for their survival.
NORTHERN SPOTTED OWL
Elusive as they are rare, a northern spotted owl peers from its perch in a Washington forest. Highly dependent on old-growth forests with dense canopy and abundant logs and snags, this threatened species is declining at nearly 4 percent a year due to habitat loss, fire and competition with invasive barred owls.
Damp with rain, a three-toed sloth clings to a tree in Costa Rica. Few creatures on Earth are better suited to life aloft than these slow-moving herbivores, which sleep, eat, mate and give birth in the trees of Central and South American rainforests. Two of six sloth species are now at risk of extinction.
A Bengal tiger rests in a bamboo forest in India’s Bandhavgarh National Park. Largest and most abundant of Asia’s wild cats, Bengal tigers, like all six tiger subspecies, are at risk from rampant poaching and loss of the forest and grassland habitat they need to survive. Fewer than 4,000 tigers remain in the wild.
EASTERN BOX TURTLE
Adorned by a blue damselfly, an eastern box turtle roams a riverside trail in South Carolina. These long-lived omnivores need healthy forests and inland wetlands to survive. Because of habitat loss, fire, pollution, vehicle strikes, climate change, disease and egg predation, the species is in decline.
Throughout its history, the National Wildlife Federation has worked to protect forests—with a special focus in recent years on reducing the loss of species-rich tropical forests, which also capture and store sizable amounts of the carbon dioxide fueling climate change (international.nwf.org). NWF promotes conservation and better management of all natural systems, including forests, for the role they play fighting climate change as well as providing other vital benefits both to people and wildlife (nwf.org/naturalsolutions).
Laura Tangley is senior editor of National Wildlife.
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