A New Leaf on Life
Thursday, May 8, 2008
Over a drink recently, a friend in the horticulture business said I should tell people to plant a tree. I've been doing that for years, I explained. No, she said, to reduce one's carbon footprint. Plant a tree, save the planet. Duh.
Squirming because I hadn't made the link, I cast my mind back to high school biology class. Trees (and other green plants) take carbon dioxide from the atmosphere during photosynthesis and return oxygen to the air. The carbon molecules are used to make sugars and starches, which in turn feed the growth of cell walls, especially in spring, when everything is going gangbusters.
As long as the tree remains healthy, it just keeps stealing carbon dioxide from the air and storing carbon in its cellulose. Carbon remains there even if the tree becomes furniture or lumber. It is released only when the wood rots or is burned.
Carbon dioxide levels in the atmosphere have increased by a third since the start of the industrial revolution, due mostly to the burning of coal and other fossil fuels, and that buildup has been linked to global warming.
According to a neat calculator on the Web site of Casey Trees ( http:/
That sounds like a way of enhancing your yard and giving polar bears a future, until you dig a little deeper.
According to the Environmental Protection Agency, a two-person household in the United States is responsible for releasing 41,500 pounds of carbon dioxide into the air annually through the direct and indirect burning of fossil fuels.
To offset that entirely, you would have to plant 483 young trees and wait 10 years, the EPA says. That might be a recurring yearly challenge if you live on a lot smaller than, oh, 100 acres. Another option, while you are thinking of ways to reduce your carbon footprint, would be to donate money to an environmental group that plants trees. American Forests ( http:/
So is planting a tree in your yard a futile gesture? No, said the group's executive director, Deborah Gangloff. "We aren't going to solve global warming by planting trees, but we can take up a lot of carbon."
And you can increase the carbon benefits of a tree 15-fold by using it to shade the house in summer to reduce the need for air conditioning. American Forests suggests three trees: one on the east side to block morning sunlight and one each on the south and west sides. If you can plant only one, put it on the west side to counter the fierce afternoon sun. Gangloff points out that a deciduous tree will be bare in winter, allowing the sun to warm the house.
Find a site away from utility lines and buried drainage, and plant at least 15 feet from the house. Study the site conditions; most trees would die in a low-lying area prone to flooding, while others (the bald cypress or swamp white oak, for example) would be happy in such a spot.
Gangloff said homeowners play a vital role in preserving and replanting the urban forest because they own most of it. In the District, for instance, only 10 percent of the tree canopy is on public land. And the benefits go beyond carbon sequestration. Trees filter pollution, prevent soil erosion, provide habitat for wildlife and can look pretty good.
Mark Buscaino, executive director of Casey Trees, said that if you plant one tree, you won't make much of a dent in global warming. But if you plant 10 and "multiply it over their lifetime, they're going to sequester a heck of a lot of carbon." Casey Trees is a D.C.-based charity established to protect and restore the city's urban forest.
Using Casey Trees' calculator, I set out to see how much carbon is sequestered in my one-third-acre garden. As Buscaino suggested, it turns out to be quite a lot. The site contains 15 trees that predate my arrival (about half a dozen were taken down over the past 14 years). The largest are two American hollies, each with a trunk diameter of 17 inches; a northern red oak with a 22-inch-diameter trunk; and a saucer magnolia whose four trunks total 35 inches in diameter. The combined carbon sequestration of the 15 trees is 3,827 pounds annually.
I have planted an additional 18 trees, the largest of which is a crape myrtle with five trunks, each four inches across. The smallest and newest are two sourwoods planted 18 month ago, each measuring just one inch in trunk diameter. The 18 new trees sequester 1,163 pounds a year, for a total of 4,990. That is a fraction of my annual footprint, but it makes me feel better about burning wood in the fireplace in winter or flying to England to see my mother.
It's conceivable that a former owner positioned the saucer magnolia to shade a patio, but none of the trees was planted expressly to capture carbon. They were put there to provide privacy, or to yield fruit, or to lend structure to the garden. They were selected for their beauty and multi-seasonal interest, and for textures that contrast with each other. They were picked with their eventual size in mind. I wasn't thinking about all the carbon dioxide swirling about the place.
When I plant more trees I will think about that aspect, though it still won't be my first consideration. I will continue to ask: Do I have room? Have I picked the right tree for the site conditions, and how will it change the garden?
A lot of people are surprised when small trees become large trees and the altered light conditions reduce the number of flowering plants to choose from, or the chances of raising a tomato vine or growing grass. It changes the character of a garden, which is fine, but you should know that.
If you plant a tree, you should do your best to keep it alive, especially during the first few years it takes to get established. "Some experts believe it takes five years to plant a tree," Gangloff said.
Buscaino, who has seen a lot of young trees die from neglect, said a tree "is a natural system, and it requires maintenance and follow-through, and that's where a lot of the problems come up with a lot of the schemes for planting."
A dead tree, of course, no longer captures carbon. And when it is chewed up into wood chips, which decompose, most of the carbon it did purloin goes right back into the atmosphere.
Casey Trees and American Forests offer online advice on correct tree planting athttp:/