Magazine article American Forests

Urban Carbon: A Look Behind the Research

Magazine article American Forests

Urban Carbon: A Look Behind the Research

Article excerpt

Atmospheric carbon dioxide levels have risen swiftly and steadily over the last several decades, due to a combination of increased fossil fuel burning and deforestation. The 1992 Rio Summit opened the world's eyes and ears to a growing concern about global climate change, which occurs when carbon dioxide gas traps heat in the atmosphere and raises temperatures worldwide. While scientists disagree on the ultimate effect on our climate, countries including the United States agreed to reduce these greenhouse gases. The U.S. is committed to voluntarily reducing greenhouse gases to 1990 levels by the year 2000.

The USDA Forest Service has conducted research on urban forests for more than 20 years, including trees' ability to store atmospheric carbon. Since the ecological study is complicated, several staff scientists selected areas in which they had expertise, and Chicago was chosen as the focus.

There is a direct link between the amount of fossil fuels used in heating and cooling buildings and the carbon emitted in that process. Thus, each scientist studied an interlocking piece of the energy/carbon puzzle. For example, David Nowak, who conducted his doctoral research dissertation on the structure and function of the urban forest in Oakland, California, focused on air quality, specifically trees' direct uptake and storage of carbon. Greg McPherson, who had conducted several Arizona studies on how trees save energy, considered Chicago's urban forest from an energy savings and avoidance (of building power plants) perspective. Gordon Heisler focused on trees and microclimate issues.

Carbon research from the Chicago Urban Forest Climate Project revealed that urban residential greenspaces can act as net carbon sinks. Forest Service scientists measured carbon storage and uptake from trees in a residential block in Chicago and recorded management practices - such as pruning, watering, and fertilizing - to determine net carbon gain or loss. The study reported that, as with rural forests, the largest proportion of carbon in urban forests is found in the soil - 78 percent compared to 63 percent in the average rural forest. Trees and shrubs accounted for 21 percent of total carbon storage and less than 1 percent of all carbon was found in herbaceous plants and grasses. …

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