There’s a new great wall in China: the Great Green Wall. This modern “wall,” which was initiated by Beijing officials, will be a 2,800-mile network of over 9 million acres of trees planted at a cost of up to $8 billion. This wall isnít meant to keep out military invaders, instead it is designed to stop the advancing Gobi Desert, which is expanding by an estimated 950 square miles a year due to overgrazing, deforestation, and drought.
Trees are sprouting up in cities all over the United States to defend against other invaders: air pollution, carbon emissions, and heat. Mayors across the country in cities such as New York, Sacramento, Atlanta, Seattle, Denver, and Indianapolis are launching tree-planting campaigns of varying sizes to address these concerns. The projects range from the ambitious goal of 1 million new trees in Los Angeles and Salt Lake City to 100,000 in Boston.
These campaigns use trees to remove air pollution, beautify cities, lower energy use, and absorb carbon dioxide—all aims supported by scientific research. A study by the Center for Urban Horticulture at the University of Washington shows that a mature tree canopy in a city reduces air temperatures by 5° to 10°F, lessening the need for air conditioning. And a mature tree absorbs 120 to 240 pounds of air pollution’s small particles and gases each year. The U.S. Department of Agriculture also reports that one acre of forest absorbs six tons of carbon dioxide and puts out four tons of oxygen.
But planting trees may not be as simple as many mayors and city residents hope. Three-dozen cities nation-wide have lost a quarter of their tree canopy since 1972. And rapid urban development has left some cities without space to plant trees. A scientist with the Forest Service working on Los Angeles’ campaign found suitable spots for only 1.3 million trees. And even if the trees are put in the ground, city environments are practically war zones for trees, filled with insects, drought, and drunk drivers, which means the trees need constant care.
Washington, D.C. has less ambitious goals than some other cities, but it is making progress. Community group Casey Trees helped plant 1,500 trees in the city in 2007. The city’s tree canopy cover is 35 percent and the city spends more than New York or Los Angeles per capita on its forest of 120,000 street trees. American Forests, a non-profit organization, recommends that cities east of the Mississippi and in the Pacific Northwest set a goal of achieving a 40 percent tree canopy average, which is the amount needed to maintain environmental quality and help control air and water management costs.
The benefits of having more city trees are worth the effort, despite the difficulties. Los Angeles can take credit for over 70,000 new trees since the program was launched even those it has faced some hurdles. “Everyone in the city is rolling up their sleeves figuring out how weíre going to do this,” said project manager Huston Morris-Irvin, adding that the response to the program has been tremendous. Evidently, it tapped into something in the city—perhaps a longing for more green and less grey. The number of trees already planted is far more than the city was planting before, and seeing success provides momentum for the program to keep going.
If Los Angeles can pull off half a million trees—particularly in an environment that some would say is not ideally suited for leafy, green trees—it would definitely help encourage other cities to reach for similar goals.