ALEX PAJUNAS — The Daily Astorian Beverly Law, professor of forest science at Oregon State University, directs the AmeriFlux network, a group of 90 research sites in North and Central America that helps to monitor the carbon dioxide “budget” in forests worldwide. As the world looks for ways to mitigate the effects of climate change, she’s suggesting a new approach to forest management that could help offset carbon dioxide emissions by letting trees grow longer before harvesting.
ALEX PAJUNAS — The Daily Astorian Beverly Law, professor of forest science at Oregon State University, describes the bandage-like wrappings on the Douglas fir trees that she uses to monitor the carbon intake of Coast Range forests at her research site near Corvallis earlier this year. The wrappings contain devices that measure the size of the tree and the rate of sap flow through the tree trunk. This data helps determine how much carbon a tree is taking up and giving off.
First in a series: Forest research helps scientists study carbon 'storage' Trees hold part of the key to learning more about climate change
CORVALLIS - At a forest research site in the Coast Range, Beverly Law is studying the breathing patterns of a fast-growing Douglas fir stand.
A tower shooting up from the forest floor is rigged with highly calibrated sensors to measure the carbon dioxide concentration of the air 20 times per second.
The water vapor being released from the trees, the sap moving through their trunks, and the growth and decomposition of their roots below are all being carefully measured through automated devices that compile data in a computer nearby.
"This forest is wired," said Law, stepping over a bundle of cords tethered to the ground.
A forest science professor at Oregon State University, Law is the director of the AmeriFlux Network, which is measuring the carbon intake and output of 90 forests across the continent.
Measuring precisely how much carbon forests can store over time will be key to determining their value in carbon offset markets as regional and international governments move forward with policies to combat global climate change.
The issue is part of a fresh look at Northwest climate change beginning today by the news staffs of the East Oregonian Publishing Company, including The Daily Astorian, which focused on the issue in an award-winning series in 2006.
The trees in Law's Coast Range research site are around 40 years old - close to their maximum growth rate. But the surprising fact she's finding through her analysis of 90 is that the trees won't stop taking up and storing carbon once they're past their peak production.
"When we figured out that older trees store more carbon, the question became how can you make more?" she said.
Giving carbon a cash value
Trees are on our side when it comes to mitigating climate change.
By taking up carbon dioxide and releasing water vapor, they naturally offset some of the greenhouse gas emissions from human activities and provide a much-needed carbon sink for the planet.
Through the Western Climate Initiative, Oregon is looking at launching a cap-and-trade system to regulate greenhouse gases; under the plan, forest management that increases carbon storage could have a cash value on a carbon offset market.
A forest carbon offset market would allow companies exceeding the regulatory cap on carbon dioxide emissions to buy an equivalent carbon offset from forest land owners based on increases in carbon sequestered in trees and wood products.
As the specifics get hashed out, Law's research suggests that the best way to increase carbon storage in forests is to leave the trees alone.
Law's studies show it can take anywhere from five to 20 years after a harvest for a forest to return to "carbon sink" status - absorbing more carbon than it releases.
And several studies have shown the amount of carbon actually sequestered in wood products is only 30 percent of the total storage capacity. The rest is lost through the logging and milling processes, or it ends up in a landfill.
"When you cut an old stand, you're automatically saying you're going to release about 70 percent of that carbon back into the atmosphere over the next number of years," said Law.
Some conservation groups argue carbon offset credits should only be given to forestland owners for leaving forests intact, but timber companies and small woodlands owners would like to be eligible to sell credits for turning trees into wood products, converting woody debris into biofuels and for using wood to replace energy-intensive building materials like concrete and steel.
The Western Climate Initiative includes a group called the Carbon Forest Working Group, which is looking at all the possibilities and debating their virtues.
Greg Miller, public affairs manager for Weyerhaeuser Co., has been participating in the conversation and says he hopes the new market will include a spectrum of credits for a variety of carbon storage and emissions reduction efforts.
"We don't have to exclude things," he said. "You can have a permanent conservation easement and long rotations. That's one way to get at it, but it's not the only way."
Making wood products doesn't store as much carbon as leaving trees in the forest, he said, but the right system could reward both actions appropriately.
Let the trees grow?
Traditional forestry wisdom suggests after 150 years forests become "carbon neutral," giving off as much carbon dioxide through decay as they take up.
But Law says that wisdom is based on outdated and selective information and doesn't apply to all forests.
Her analysis shows old forests will serve as carbon sinks for centuries - absorbing more carbon than they emit for up to 800 years - if they're left intact.
"Young, fast growing trees don't capture more carbon than older ones," she said. "Older forests store huge quantities, and they continue to absorb through age 80."
Even as the absorption of carbon in older trees plateaus, she said, "the trees continue to form a bank of stored carbon that cannot be equaled by a newly sprouted stand."
According to Law, measuring the carbon storage potential in forests isn't as simple as tracking tree growth.
"There's more to the story than growing trees and above-ground production," she said. There's soil respiration, foliage, underground root systems..."
An evaluation of logged forests showed carbon emissions from the soil increase for years as the leftover material - smaller roots, for example - decomposes.
In fact, she found 70 percent of respired carbon dioxide in the forest comes from the soil surface.
Increasing storage levels
Law found Oregon's forests absorbed 50 percent of the state's fossil fuel emissions in 2000; in 2003, a record fire year, the number was still 30 percent.
One way to increase that percentage, she said, would be to leave more trees on the ground longer to increase carbon uptake and storage - at least until renewable energy sources are developed.
Even though forests may be replanted after clear-cuts, she said, the microbes in the soil continue to emit more carbon than the young trees for years.
"Microbes in soil dominate the carbon balance after logging - not trees," she said.
On the Coast Range, where the Douglas fir and hemlock thrive in the temperate rainforest climate, the carbon storage rate is about twice the global average.
"These forests can store a lot of carbon. In terms of worldwide forests, it's amazingly high," said Law. "The coast range is phenomenal. They are up there with tropical rainforests."
In a recent study, Law looked at what would happen to the net carbon uptake in various forests if the trees were allowed to grow for another 50 years without harvest. For the coast range, she found the amount of carbon storage on the ground could increase by 15 percent.
Mike Cloughesy, forestry director for the Oregon Forest Resources Institute and a member of the Carbon Forest Working Group, said there are two schools of thought: One believes the best way to store carbon is to grow trees as long as possible and store the maximum amount of carbon in the forest. Another argues forest management can maximize the increase in carbon storage by growing trees for 50 or 60 years, turn them into wood products and repeat that process.
On one hand, not cutting trees poses the risk of fire and creates the possibility that timber and wood products will have to come from a place with fewer environmental regulations. On the other hand, offering rewards to companies cutting trees for wood products risks a diminishing return of net carbon storage in the forests.
"My view, shared by a lot of people in forestry, is there's kind of room for both," Cloughesy said. "Both can work, but they have to be done carefully, with measuring and monitoring so you can show how much carbon we're storing."
Reader Comments Posted: Friday, December 26, 2008
Article comment by:
Andy Burns
Is Carbon, a pollutant? Our forest's are our most renewable resource. The "downed" tree's that are used for lumber, stores all that carbon, unless its burned, which what happens to forests that are not thinned and over grown. Im not a forester, nor a logger, but I think, this is pretty basic as forestry goes. I am also lead to understand that young tree's produce more oxygen than older tree's do. How does that fit in this scheme of leaving these tree's to live till they die and live with the carbon they give off?
