Lives of the Vines

A tree in full bloom in St. Helena.

Jesse Duarte, Star

In the holiday pantheon, Arbor Day is taken about as seriously as Groundhog Day. The last time you gave it a thought was probably second grade, when your class went on a tree-planting field trip. But I’m going to make the case that Arbor Day is the perfect 21st-century holiday, a celebration of something that can make a dent in our most modern problems: food production and climate change.


I take them for granted. My husband and I live on two acres of them, and they house our wildlife, heat our home, and, in the fall, bury our driveway in an unconscionable volume of leaves. But they do something else, as well. Thanks to the miracle of photosynthesis, trees sequester carbon. They take carbon dioxide out of the air and turn it into carbohydrates that are stored in the tree and its root system, locking away that carbon and releasing oxygen in the process.

All green plants do this, of course, so what makes trees so special? Size. The bigger the plant, the bigger the sequestration, and trees are enormous. I asked Thomas Crowther, of the Netherlands Institute of Ecology and recently the lead author of a global tree census, to walk me through the math.

On average, a tree will sequester 50 pounds of carbon per year—small trees, less; big trees, more. Compare that to the savings you get when you switch to a hybrid car—about 3,300 pounds per year—and it sounds like a small number. But factor in a tree’s life span, which is often centuries, and the tree looks better and better. By the time the tree you plant this Arbor Day (April 28) is 70 years old, it’ll have the same carbon value of one Prius-year. If it lives to 200, well, you see the potential. The net of it is that a step as simple as a yearly tree planting can be as effective as a switch to a hybrid at reducing the atmosphere’s carbon load.

So let’s widen the lens. Could we have a real impact on CO2 levels if we Americans started taking Arbor Day seriously, and planted trees? “I think it’s a beautiful idea,” said Crowther.

“If each of those 300 million new trees were planted and monitored and grew, that’s not an insignificant little chunk. It would show people how easy it is to have an effect, and it would connect people with the environment. It might spur on a hell of a lot more.”

Crowther’s tree enthusiasm is catching, and I find myself believing in trees as environmental superheroes, fighting climate change and raising environmental consciousness in a single bound.

But can they help fight the problems on American farms? Incorporating trees into farming—agroforestry, it’s called—has benefits beyond carbon sequestration. Ravi Prabhu, deputy director general for research of the World Agroforestry Center, ticked off that list of benefits: as windbreaks, they decrease the stress on crops; they can decrease temperatures; they can fix nitrogen and increase soil fertility; they decrease erosion and nutrient runoff; they can prevent water from running off, forcing it into the ground. And, some trees can be harvested for timber or grow fruits or nuts.

In the developing world, where farms tend to be smaller and more diverse than they are in the United States, the potential for agroforestry is large and varied. Here at home, where a typical farm is hundreds, or maybe thousands, of acres of just a few crops, it’s harder to find an economically feasible way to incorporate trees. I talked with Richard Straight, technology transfer leader at the USDA’s National Agroforestry Center (NAC), about how American farmers use—or can use—trees.

The most common use is as a windbreak, Straight explains. Plant a row of trees alongside a field, and it can increase the downwind yield to a distance of about 10 times the height of the tree. Farmers also use trees as riparian borders—forested strips along waterways that prevent runoff, increase biodiversity and act as windbreaks.

The USDA doesn’t have good data on how many farmers use these techniques, but Straight says that the NAC is seeing increased interest. The biggest obstacle, as it so often is in farming, is cost.

It’s just a back-of-the-envelope calculation, but Straight walked me through an example that came to just under $200 per acre. If you’re farming 1,500 acres, that’s a big chunk of money that you won’t see much return on for a decade.

And it’s possible there won’t be a return at all. Charles Barden, professor of forestry at Kansas State University, is researching the effect of windbreaks on yield and has found that the percentage of fields with windbreaks that saw a statistically significant increase in yield varies from 17 to 45 percent. Yield isn’t the only benefit, but it’s the one that’s reflected in the farm’s bottom line.

Get tips on free stuff and fun ideas delivered weekly to your inbox

There was a time when USDA helped out with that cost. “In the late ‘80s, there were bonuses for signing up that made it easy,” says Straight. “It was financially a good choice.” But those incentives have since changed, and a lot of those windbreaks have come out. Straight acknowledges the difficulty of a long-term, uncertain benefit coupled with the financial hit not just of the expense, but of the land you take out of production.

Meanwhile, in other parts of the world, trees are more than paying for themselves. “In the Punjab [in India], farmers are planting poplar and wheat together and making more money on the poplar,” says Prabhu. If there were opportunities like that here, it would change the calculus.

That’s the line the NAC is pursuing, but it’s hard to find a profitable way for a highly mechanized farm, optimized for just a few crops, to find the time, workforce and market for a different kind of crop.

Straight’s looking into a possible solution. What if agroforestry were the one-stone-two-birds solution to two ag-related issues: row-crop management and opportunities for young farmers. What if the farmers with the thousands of acres leased areas for windbreaks and riparian borders to beginning farmers trying to get hold of land? The area would then be a moneymaker for the row-crop farmer, who would also accrue crop yield and ecosystem benefits down the line. The new farmer would have a chance to try fruit, timber, mushrooms, medicinals or some other kind of perennial agriculture on a very long, skinny farm.

It wouldn’t be an easy balance to orchestrate, Straight warns. What would a lease look like? Could rent scale up as the crop matured? Could several contiguous farmers lease together to one new guy?

But it sure is an intriguing idea.

I try hard not to fall victim to the starry-eyed romanticism that sometimes informs the public conversation about farming (and I’ve found that actually farming helps me do that). But trees—on farms and off—are something that absolutely everyone seems to support. I’m going to plant a tree this Arbor Day. Will you join me? We’ll all sequester carbon, celebrate biodiversity and break wind together.

Haspel writes about food and science and farms oysters on Cape Cod. On Twitter: @TamarHaspel.