Problems like global warming are so overwhelming that most citizens feel there's nothing they can do to help. That's wrong.
If you want to help, scientists across the country are saying these days, plant a tree. Better yet, work with your city to improve its urban forest.
But here's the hard part. We've all known for years that trees are good for the environment, soaking up air pollutants and greenhouse gases, and a little shade in the middle of what scientists are calling urban heat islands can't hurt. However, not all trees are the same. They all help to clear the air, in varying degrees, but many also contribute to air pollution by emitting volatile organic compounds, such as isoprene, which help form ozone, a health hazard.
That led researchers at the State University of New York in Syracuse to come up with a new angle. There's lots of trees in Syracuse, but many of them are the wrong kind.
Allan Drew, a forest ecologist in SUNY's College of Environmental Science and Forestry, teamed up with several colleagues to see if Syracuse could create a much more effective urban forest. They found that simply mixing the types of trees could make a huge difference.
"We've demonstrated that it's feasible," Drew says.
The researchers took a national program, sponsored by the Forest Service, a step further. For years now, the Forest Service has worked with cities to help local officials understand the complex problems associated with creating an effective urban forest. If you want to clean the air, don't plant willows, for example, because they don't absorb very much carbon as they grow, and they emit a lot of junk.
Syracuse researchers found that if they could replant their city with trees that are great at sequestering carbon compounds, especially carbon dioxide, they could increase the removal of carbon by more than 300 percent. But they also found that air quality would actually suffer from an increase in volatile compounds.
So they looked at mixing the forest, emphasizing trees that are good performers when it comes to carbon sequestration and don't emit a lot of junk. They came up with a list of 31 species, including American basswood, dogwood, Eastern white pine, Eastern red cedar, gray birch, red maple and river birch. That combination, they found, would increase carbon sequestration by 86 percent, and reduce the emission of volatile compounds by 88 percent.
They also eliminated trees that are so invasive they become pests, like the European buckthorn, and the American elm, which is vulnerable to Dutch elm disease.
Drew says the Syracuse plan would probably work in many other areas, but trees can be fickle. They don't perform the same way in different regions, and their ability to clean up the air varies with age, rate of growth, and many other factors.
"You could predict what the emissions might be for a red oak (fairly high) but if that tree is growing in a shaded area, its emissions are going to be less than if it was out in an open, sunny area," he notes. "There's a certain amount of variability."
Emissions increase with temperature.
"The warmer it is, the more of a potential problem you have," Drew says. "It's probably more of a factor in the sun belt, but the potential to vary the species mix and achieve good results are probably better."
Many cities across the country have completed studies of their urban forests, and some of the figures are impressive.