(Photo: Eppic Photography)

Oregon State University forestry scientists have a habit of redefining the conversation about carbon and forests. Professors Beverly Law, Mark Harmon and their colleagues have demonstrated that old-growth stands on the west side of the Cascades store as much carbon or more than that held in tropical rain forests.

In 2009, Law reported that forests from the San Francisco Bay Area to the Columbia River could theoretically double the amount of carbon they currently contain.

In 2007 and 2009, her research group determined that Pacific Northwest fires emit less carbon than previously thought. Most emissions were from combustion of the forest floor and understory vegetation, and only about 1 to 3 percent of live tree mass was burned.

Not surprisingly, tree cutting turns forests from carbon sinks to carbon sources. Law has determined that it may take 15 years or more for young trees to begin absorbing more carbon than is lost through decomposition of branches, roots and other dead material. She conducted her studies in ponderosa pine, and her conclusions were later confirmed in an international study of boreal and temperate forests.

Ameriflux Network

Now, Law has co-authored a national study concluding that forests and other terrestrial ecosystems in the lower 48 states can sequester up to 40 percent of the nation’s fossil fuel carbon emissions, a larger amount than previously estimated, unless a large drought or other major disturbance occurs.

Carbon dioxide, when released by the burning of fossil fuels, forest fires or other activities, is a major “greenhouse gas” and factor in global warming. But vegetation, mostly in the form of growing evergreen and deciduous forests, can play an important role in absorbing some of the excess carbon dioxide.

Widespread droughts, such as those that occurred in 2002 and 2006, can cut the amount of carbon sequestered by about 20 percent, Law and her colleagues concluded in a study that was supported by the National Science Foundation and U.S. Department of Energy.

The research, published by scientists from 35 institutions in the journal Agricultural and Forest Meteorology, was based on satellite measurements and data from the AmeriFlux network, a system of nearly 100 carbon-monitoring sites in the Americas.

Not all of these data had been incorporated into earlier estimates, and the new study provides one of the most accurate assessments to date of the nation’s terrestrial carbon balance.

“With climate change, we may get more extreme or frequent weather events in the future than we had before,” Law adds. “About half of the United States was affected by the major droughts in 2002 and 2006, which were unusual in their spatial extent and severity. And we’re now learning that this can have significant effects on the amount of carbon sequestered in a given year.”

Climate Mapping

Such information is important to understand global climate issues and develop policies, the researchers note. This study examined the carbon budget in the United States from 2001 to 2006. Also playing a key role in the analysis was OSU’s PRISM climate database, a sophisticated system to monitor weather on a very localized and specific basis.

The period from 2001 to 2006, the researchers say, had some catastrophic and unusual events, not the least of which was Hurricane Katrina and the massive destruction it caused. It also factored in the 2002 Biscuit Fire in Northern California and southwest Oregon, which burned nearly 500,000 acres and was among the largest forest fires in modern U.S. history.

The research found that temperate forests in eastern states absorbed carbon mainly because of forest re-growth following the abandonment of agricultural lands, while some areas of the Pacific Northwest assimilated carbon during much of the year because of the region’s mild climate.

Croplands were not considered in determining the annual magnitude of the U.S. terrestrial carbon sink, because the carbon they absorb each year during growth will be soon released when the crops are harvested or their biomass burned.

The study was led by Jingfeng Xiao, a research assistant professor at the Complex Systems Research Center, Institute for the Study of Earth, Oceans, and Space, at the University of New Hampshire.

“Our results show that U.S. ecosystems play an important role in slowing down the buildup of carbon dioxide in the atmosphere,” the researchers wrote in their conclusion.

Ø Online: See more about Beverly Law’s terrestrial ecosystem research at terraweb.forestry.oregonstate.edu/

Illustration by Teresa Hall

It helps to have your old bills handy if you use the Household Emissions Calculator created by the U.S. Environmental Protection Agency. You’ll need to enter how many kilowatt-hours of electricity and therms of natural gas or gallons of heating oil you’ve used in the past year. Add miles traveled in the car, whether or not you recycle your trash or turn down the thermostat at night and myriad other details, and the calculator will tell you how many tons of carbon emissions you can call your very own. The per-person average for 311 million Americans, according to the EPA calculator, is about 10 tons per year.

However, missing from these numbers is a factor that, in the long term, can overwhelm our efforts to live more lightly on the planet: the choice to reproduce. “It’s probably the most basic of all biological urges,” Paul Murtaugh told a Corvallis audience in February. “To hint that there might be some benefit to controlling that urge is very controversial.” Last year, Murtaugh personally found out just how strongly people feel about it.

All in the Family

The Oregon State University professor of statistics and OSU colleague Michael Schlax published a paper in the journal Global Environmental Change describing an individual’s “carbon legacy” — the amount of carbon likely to be emitted in the future by one’s descendants. Parents, they reasoned, could be held accountable for one half of their children’s emissions, one quarter of their grandchildren’s and declining portions down through the generations.

Murtaugh and Schlax took a mathematical approach to understanding the consequences. They estimated how large a parent’s carbon legacy might be by creating a model based on per capita carbon emissions and a country’s population trends (fertility and mortality rates and average longevity). They used data from the Intergovernmental Panel on Climate Change and the United Nations to compare the carbon legacies of parents in 11 of the world’s most populous countries.

Since family size and longevity vary widely even within the same population, they ran the model thousands of times country by country. Each time, the model chose a random parent with a specific number of descendants who lived and reproduced until the lineage ran out. From those hypothetical examples emerged an average parent’s carbon legacy for each country.

Murtaugh and Schlax didn’t stop there. On top of these calculations, they added another factor: future changes in annual carbon emissions. While there are wide disparities between rich and poor countries, today’s global average is about four metric tons (as carbon dioxide or CO2) per person. If new carbon-free energy technologies take hold, emission rates could drop. If not, they could stay the same or rise. So, looking forward to the year 2100, they used scenarios that were “optimistic” (drop to 0.5 tons), “constant” (stay at four tons) and “pessimistic” (50 percent increase to six tons).

The results were clear. “If you accept our method of accounting, a decision to have a child amplifies a single parent’s lifetime emissions by three or four times in most countries, by virtue of the carbon legacy that perpetuates through generations,” says Murtaugh. “Remember these emissions accumulate over hundreds of years and many generations.”

Lifetime Legacies

The effect was most dramatic in the U.S. On average, the additional emissions per child — about 9,400 tons under the “constant” scenario — was almost six times the amount of carbon emitted by a parent over his or her own lifetime. Not only that, it was 20 times more than the amount that could be saved over an 80-year lifetime by the energy conservation measures included in the EPA’s emissions calculator.

Nevertheless, Murtaugh calls those short-term reductions essential. “It’s not that we can solve the global warming problem by reducing the number of children that we have,” he adds. “It will help immeasurably in the long term, but in the short term, it’s essential that we reduce our per capita emissions right away.” In fact, under the “optimistic” emissions scenario, the drop in per capita emissions reduces future impact per child by almost 90 percent.

Slowing population growth can also help, but “the savings from these reductions in fertility aren’t going to be that meaningful unless we get our per capita emissions under control,” Murtaugh adds.

After the paper was published and featured in an OSU news release, news of their analysis splashed across international headlines and caught the attention of environmentalists, newspaper columnists and conservative bloggers. Some critics responded to a misperception that Murtaugh and Schlax had called for government policies to curb an individual’s right to have children. “We said nothing in our paper about policies,” says Murtaugh. “We just did the calculations and laid them out there for people to think about. But most of the people had obviously never seen the paper. We were called Nazis and Eugenicists.”

One individual phoned Murtaugh and suggested that he consider killing himself to reduce his own carbon emissions. The caller then proceeded to reach every member of the OSU statistics department demanding that Murtaugh be silenced. “I began to fear for my safety. Fortunately the blogs, calls and emails stopped after a few weeks,” Murtaugh adds.

More than climate and reproductive rights are at stake. Rapid population growth affects other species (think ivory-billed woodpecker, passenger pigeon, blue whale and Fender’s blue butterfly) and exhausts the planet’s carrying capacity, Murtaugh says. At current levels of production, it has been estimated that it would take 1.4 Earths to maintain today’s population into the future. “In other words,” he concludes, “we’re living off the capital now.”

The United Nations Population Division expects the global population to reach 7 billion in October.

Air flowing through mountain valleys carries clues about forest health. New monitoring and analytical methods may also improve understanding of the global carbon cycle. (Illustration: Christina Ullman)

Under a blue sky in mid-March, an Oregon State University research team left Corvallis to collect data in a valley deep in Oregon’s western Cascades. The two-hour ride to the H.J. Andrews Experimental Forest gave the technicians and graduate students time to catch up before arriving at the facility’s headquarters near Blue River. They would need their energy for what lay ahead.

Their destination was a place known on the Andrews map as watershed 1. Its 60-degree slopes reach almost 1,500 feet from valley floor to ridge. Equipped with lunches, laptops and emergency radios, computer modeler Dave Conklin, technician and graduate student Adam Kennedy and other members of the team drove to the top of the watershed and descended into the forest through dark thickets of ferns, downed wood and moss covered rocks. Once they found the six temperature sensors (known as “HOBOs”) that had been set in a line down the mountain, they checked each HOBO’s battery and downloaded three months worth of data. At lower elevations, graduate student Claire Phillips collected data in soil plots that had been wired and plumbed to monitor temperature, moisture, root growth and CO₂ production. Despite the cool temperatures, this was sweaty science, a cycle of rigorous bushwacking followed by meticulous routine.

It was a typical day at the office for Andrews Forest researchers. Over the years, scientists here have hoisted themselves with climbing ropes high into the tree canopy, launched tons of soil and rock down a “debris flow flume” and spent sleepless nights observing boulder-tossing floods and recording wildlife behavior. Their results (described in the OSU Press book, The Hidden Forest, by Jon Luoma) have recast the national debate over old-growth forests, northern spotted owls, storm-generated erosion and other aspects of forest management. In watershed 1, they hope to create a new way to monitor mountain forests, which play a poorly understood but important role in the carbon cycle and climate system.

Since 2003, with support from a National Science Foundation grant, OSU scientists have been sampling the air in this watershed and in a neighboring valley. The latter is home to 450-year-old stands of Douglas fir and hemlock. In contrast, watershed 1 was clearcut in the mid-1960s to test the long-term effects of tree removal on ecosystem processes. Its young fir, hemlock and red alder already reach 80 to 120 feet high.