FORESTS: Carbon-absorption rates increase in Pacific Northwest -- study

FORESTS: Carbon-absorption rates increase in Pacific Northwest -- study
(07/28/2011)
Laura Petersen, E&E reporter

While the Northwest Forest Plan sought to reduce old-growth logging and protect endangered species in Washington, Oregon and California, researchers say the 1993 plan has resulted in an another unforeseen benefit -- turning the region's forests from a carbon source to a carbon sink.

Researchers at Oregon State University, the Forest Service and Oak Ridge National Laboratory used a combination of remote sensing and ecosystem modeling to examine the carbon balance on both public and private lands within the Northwest Forest Plan area from 1985 to 2007.

When timber harvesting was at its peak between 1985 and 1989, both public and private lands released more carbon into the atmosphere than they stored in the soil and trees, the researchers found.

But after the Northwest Forest Plan was implemented in 1993, logging on public lands decreased dramatically -- 82 percent -- and those forests transformed from a carbon source to a major carbon sink.

Researchers have determined that the carbon-absorbing capacity of both public and private forests in the Pacific Northwest has increased in recent years as provisions of the Northwest Forest Plan took effect and logging declined due to regulatory and economic factors. Photo courtesy of NASA.

Meanwhile, private lands, which were not regulated under the forest plan, but account for about half of the land in the study area, moved closer to carbon neutral. Since the late 1990s, the amount of carbon released from logging more evenly matches the amount stored by growing trees, the study found.

"It is a profound change for a whole region to go from being a carbon source to being a carbon sink," said David Turner, a professor of global environmental change at Oregon State University and lead author on the study published in Forest Ecology and Management. "That means a change from aggravating the climate change problem to helping mitigate it."

Carbon dioxide is a greenhouse gas that accumulates in the lower atmosphere and traps heat. Plants and soil absorb CO2 from the atmosphere, an action that is estimated to offset about 15 percent of global fossil fuel emissions.

"Land uptake of carbon is a significant term in the global carbon budget," Turner said. "But we don't have a good handle on where that carbon sequestration is occurring and how long it will continue. Our research helps pin down where it is occurring and by what mechanism."

Sophisticated model

To determine the carbon balance in the Pacific Northwest forests, the researchers developed a sophisticated model that included land cover type, the age of trees, daily climate data, soil texture and depth, harvest removals and fire emissions.

"In our analysis, we simulate the processes of tree growth, litter and woody debris decomposition, harvest removals and fire emissions," Turner said. "That improves our understanding of why carbon stocks are changing."

The model found the ecosystem carbon balance for public lands went from a net release of 48 grams of carbon per meter per year in the late 1980s, to a net storage of 141 grams of carbon per meter per year in the late 1990s.

Even accounting for CO2 emissions released by the massive Biscuit wildfire in 2002, public lands remained a significant carbon sink at 136 grams of carbon per meter per year between 2003 and 2007. Interestingly, researchers found that emissions from the fire, which burned nearly 500,000 acres, were far lower than logging-related emissions that year.

Private lands also have come closer to carbon neutral, according to the researchers. In the late 1980s, private forests released 76 grams of carbon per meter per year. Even though the Northwest Forest Plan did not apply to private lands, there was a small decrease in harvest rates and in the late 1990s, private forest lands stored 29 grams of carbon per meter per year, and 16 grams of carbon per meter per year between 2003 and 2007.

"The original goals of the Northwest Forest Plan had nothing to do with the issue of carbon emissions, but now carbon sequestration is seen as an important ecosystem service," Turner said.

Land managers will now be able to take carbon sequestration into account when weighing the trade-offs between the different services forests provide, such as habitat, timber and carbon storage, Turner said.

Such large reversals have also been observed in the Northeast, where forests were cleared for agriculture in the 19th century and then abandoned around 1900. Since the forests have grown back, the region has turned from carbon source into a carbon sink, Turner said.