Study: Forests May Help Counteract Greenhouse Gas
Copyright 2000, Reuters
November 9, 2000
By Maggie Fox, Health and Science Correspondent
WASHINGTON (Reuters) - Letting forests grow on abandoned farmland and logging grounds may do more than beautify the countryside -- they may be soaking up greenhouse gases blamed for global warming, scientists said on Thursday.
But as the forests mature, this effect will decrease, the researchers at Princeton University, the U.S. Forest Service and elsewhere, said.
"Today we are seeing the effects of past changes in use," ecologist John Casperson at Princeton said in a telephone interview.
"Throughout the East, in the last century a lot of forests were cut down either for agriculture or for logging. When those lands were no longer valuable as agricultural land, those lands just reverted to forest."
As the trees grew, they used carbon dioxide -- a lot of it, according to the study, published in Science.
Casperson said government planners can use the information in future projections about global warming.
An estimated six billion tons of carbon dioxide are emitted each year -- much due to burning fossil fuels such as gas and coal. But only three billion or four billion tons accumulate in the atmosphere, forming a kind of blanket that can hold the sun's heat in and contribute to global warming.
Scientific study has suggested that big areas of plants, such as forests and prairies, soak up some of this carbon -- not surprising, as plants use carbon dioxide to grow.
Much of this seemed to be going on in the United States, a phenomenon known as the "North American carbon sink."
Scientists trying to figure out how this might happen proposed that the build-up of carbon itself was acting as a fertilizer and speeding the growth of trees. Others suggested that nitrogen coming from automobile emissions and industrial pollution was falling on the land and acting as fertilizer.
SCIENTISTS COMPARE FOREST GROWTH RATES
Casperson's team decided to check by comparing recent growth of forests to old growth rates, looking at the forest inventory database collected by the Forest Service.
"They go out and measure the trees to make predictions about timber production. It also allows you to assess changes in stocks of carbon in forests ... by looking at how much timber there is. They measure things like tree volume," he said.
The researchers found that most of the carbon "sink" could be attributed to the new growth of trees.
Casperson's team looked at new forests in Minnesota, Michigan, Virginia, North Carolina and Florida.
"It takes like 200 to 500 years for them to mature," Casperson said, adding that most of the forests in the Eastern United States are at most 50 to 60 years old. Their growth will eventually slow as they mature, he said.
"The sink will disappear unless there is some future fertilization effect," Casperson said.
Negotiators from around the world are due to meet in The Hague in the Netherlands starting on Monday to resolve details of the 1997 Kyoto Protocol, which seeks to limit the production of carbon dioxide and other greenhouse gases.
Casperson said this information could be taken into account. Countries can get "credit" for sinks that offset carbon production, although his study is unlikely to do the United States much good.
"Kyoto specifically excludes using any sinks that include land use changed prior to 1990," he said.