Trees absorb about 8% of carbon emissions from fossil fuels
CORVALLIS, Ore. -- The forests of the United States are currently absorbing about 8 percent of the carbon that the nation is injecting into the atmosphere, but that number could shrink to a "break-even" level by 2020. Amid concern about carbon emissions and their impact on global warming, recent research at Oregon State University and the Environmental Protection Agency suggests that these forests can help address this problem, but in no way solve it by themselves. In new studies, scientists have found that forests are now absorbing about 100 of the 1,300 "teragrams" of carbon emitted each year by fossil fuels and other sources in the United States.
However, in a second report they concluded that increasing forest harvests, a decreasing forest land base and a reduction in average stand age could reduce the carbon "sequestration" ability of these forests to about a break-even point, or carbon equilibrium within 25 years.
A single teragram represents one million metric tons of carbon, which in forms such as carbon dioxide is a key element of the greenhouse effect. "The U.S. is following the same trend as many northern temperate-zone countries," four EPA and OSU researchers said in one of the reports. "Recovery from earlier periods of extensive forest harvest and limited management is now resulting in carbon accumulation."
Less will be absorbed each year
to David Turner, an OSU forest ecologist, this research grew out of the 1992 U.N. Conference on the Environment and Development.
"Our goal is to quantify the biologically driven uptake and release of carbon dioxide," Turner said. "As a result of the 1992 conference, the U.S. is committed to developing an inventory of greenhouse gas sources and sinks, and that includes the forest land base.
"A related commitment is to reduce carbon emissions to 1990 levels by the year 2000," he added.
If that goal is to be met, Turner said, current trends would have to change. Fossil fuel emissions are continuing to increase by a small amount each year and forests -- almost the only practical way to sequester that carbon -- will be soaking up less of it each year.
In these studies, scientists from agencies such as the EPA and the OSU Department of Forest Science outlined forest types, ages, productivity, ownership, harvest levels and management intensity.
Carbon in trees, soils, the forest floor, woody debris and the understory were all considered. However, the potential accumulation of carbon in forest products and landfills was not addressed.
The research found, among other things, that the heavily forested Pacific Northwest is not actually the dominant force in this carbon "budget." Only about 12 percent of the nation's forest-related carbon was related to Oregon and Washington forests, which in 1990 had a small net loss of carbon.
"Carbon budgets and commercial forestry are two different things," Turner said. "We found that the largest gains in carbon storage were in the Northeast. There, marginal farmlands have been reverting back into forest lands, the demand for hardwoods is low, and carbon is being sequestered."
In the studies, the researchers also explored how changes in forest area or recycling practices could increase the amount of carbon sequestered.
that aggressive approaches, such as increased paper recycling or planting millions of acres of pine on marginal lands in the South, would prove of some value -- increasing the carbon sequestration by about 15 teragrams per year. However, that amount is small relative to the trend of increasing fossil fuel emissions.
"The carbon sink associated with the forest sector in the U.S. will probably offset a decreasing proportion of national fossil carbon emissions over the coming decades," the researchers concluded in the study.
The recent papers were published in two professional journals, Tellus and Ecological Applications, a publication of the Ecological Society of America.
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