It's fair to say that I am deeply versed in the science of climate change and its technological solutions. But not until I walked the Massachusetts woods a few years ago with forest expert Bob Leverett did I truly grasp the major role that forests could play in moving the world beyond net-zero carbon emissions and putting brakes on global warming.
At a state forest less than an hour from my western Massachusetts home, Bob led me through woods he knows well to a grove of towering white pines, seventy-six trees that got their start around the time of the Civil War.
Nearly my age, Bob is a retired engineer, big-tree expert, and co-founder of the Native Tree Society. He and his colleagues have developed state-of-the-art methods to measure tree volume, and calculate the weight of trees from their density. Since wood is half carbon by weight, he and I have determined precisely how much carbon mature trees contain between ground and crown.
Bob pointed to a tree he called "Pine 58," and we craned our necks. "This tree has grown 21 feet taller in the thirty years I have been measuring it," he told me. "At 176 feet and still growing, it is the tallest accurately measured tree in New England."
Taller than a 15-story building, Pine 58 has captured nearly 20 tons of carbon dioxide from the atmosphere and stored six tons of elemental carbon in the wood of its trunk, branches, and roots. Additional soil carbon has accumulated as fallen trees, branches, and needles decompose and networks of carbon rich fungi connect tree roots throughout the soil. From root tips to pine cones, this tree is a carbon champion.
Unlike the two of us standing in its shadow, Pine 58 is barely middle-aged. Barring storms or saws, this pine has at least another century of life ahead of it. Such trees should not be rare in our forests, but they are. Nearly 96 percent of all American forests are younger than Pine 58, even though most tree species can live for two hundred years or much longer. And throughout their lifespans, trees accumulate carbon.
"Many people think trees stop growing productively long before they do," Bob tells me. "Pressure to log them for profit and misinterpretation of data on how trees actually grow perpetuate a myth of early senescence."
It can take more than 30 younger trees half the height of Pine 58 to store as much carbon as one mature tree like Pine 58. Protecting mature trees so they can keep growing (instead of cutting them down)—a management practice I call "proforestation"—can deliver three to ten times the carbon storage benefit of planting new trees during this critical century. In 2022, the Intergovernmental Panel on Climate Change, "protection of existing natural forest ecosystems is the highest priority for reducing (carbon) emissions …" citing our proforestation paper.
Large older trees maintain their carbon storage advantage over small younger trees as they age. The total amount of carbon captured and stored above ground by forests is greater in older stands, and the amount of carbon accumulated continues to increase well beyond 150 years.
Trees can no longer accumulate carbon when they are cut down. Even though lumber contains carbon, less than half the wood in a harvested tree ever becomes a board. The rest winds up, sooner or later, as released carbon dioxide.
Planting trees is an excellent thing to do, but from a carbon point of view, saplings will always lag the amount of carbon being kept out of the atmosphere by existing trees that are allowed to keep growing. Wouldn't it be wonderful to live among trees fulfilling their potential to accumulate carbon at high rates for centuries?
In Seattle last April, President Biden directed federal agencies to safeguard mature and older forests on public lands. Just one month before that report is due, agencies are announcing major harvests including in older forests. A few months following the President's directive, the US Department of Agriculture launched its "Partnerships for Climate-Smart Commodities" program, including incentives to log on private forestlands.
"Climate-smart commodities?" I am not convinced. By contrast, Washington State's Department of Natural Resources is on track to designate 10,000 acres of timberland as "carbon reserves," older forests protected from logging. Creating carbon and biodiversity reserves, spared from the saw, is central to proforestation management.
Here's how you can help: Let local leaders know that you recognize the climate importance of larger trees. Protect trees on your local landscape.
Both in our eighties, Bob and I are healthy and expect to live past 2030, the year by which humanity must slash carbon emissions by half to have a shot at "net zero carbon" by mid-century and a tolerable limit on global temperatures. That's the point at which carbon removed by nature equals carbon emissions.
Then, to avoid irreversibly severe floods, droughts, heatwaves, and wildfires, humans must emit less carbon dioxide than land and sea absorb each year, until and beyond the year 2100.
The oaks and pines near his Walden Pond cabin inspired Henry David Thoreau to write that "a man is rich in proportion to the number of things he can afford to let alone." Pine 58, left alone on a hillside for 160 years and counting, continues to add steadily to the six tons of carbon already stored in its trunk, branches, and roots.
Making sure that our forests grow more trees like Pine 58 will allow natural forests to assist carbon drawdown for centuries after Bob and I—and the rest of us—are gone. Let's accept this gift that forests are offering us—that strikes me as "climate-smart."
