Boreal Buzz: CO2 sink or source?

Boreal Buzz: CO2 sink or source?

3 November 2007

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It’s one of the world’s most extensive and least visited ecosystems —the vast boreal forest that circles the Far North in a band of horizon-spanningconifer forests.

Wildfires have consumed 17 million acres in Alaska
since 1998, delivery vast quantities of CO2 into the air.
Source: AFS gallery Reaching from the Siberian taiga through Alaska’s Yukon basin to the remote fringes of Nunavut in Canada, the Boreal world covers 17 percent of the planet’s land mass, home to raven and brown bear, complex Native cultures and unique languages, spawning salmon and Northern pike, caribou and moose and wolverine.

And it’s also one of the world’s largest reservoirs of carbon. And it’s this characteristic that has got scientists worried, especially with climate change simultaneously drying out and warming up the boreal world.

Does this immense ecosystem suck up CO2 from the atmosphere, mitigating one major trigger of global warming as it soars to the highest levels in 650,000 years. Or is the boreal forest poised to release tremendous quantities of greenhouse gas from warming peat and wildfires?

The boreal world has been burning. Consider Alaska: During the past 10 years, 4,773 fires have consumed more than 17 million acres, a rate almost double previous decades.

Several new studies focus on the role wildfires now play in boreal forests, and how that relates to the global carbon equation.


A team of forest ecologists at the University of Wisconsin-Madison studiedboreal forests in sub-Arctic Canada and concluded that wildfires have become thebiggest influence in the region’s carbon budget, with possible worldwideimpacts.

A 2003 fire in the boreal forest of Manitoba, Canada.
Photo: Wolfgang Hoffmann / UW-Madison “A new study uses a computer model to simulate competition between trees and moss across a million square kilometres of Canadian forest,” says the summary of the article published this week in Nature.

“The results show that the carbon balance — the amount of carbon gained or lost by the soil and vegetation — of this region was driven largely by changes in the fire regime, rather than climate or rising CO2, between 1948 and 2005. More frequent and larger fires in the late twentieth century promoted growth of deciduous trees and mosses at the expense of coniferous trees.”


An onlinestory at UW-Madison offers more details:

Second in size among forests only to the tropical rainforests, the boreal forests form a massive green band spanning the higher latitudes of Canada, Alaska, Siberia, China, and Scandinavia.

Their sheer size, coupled with the fact that they are expected to experience the greatest warming of any forest biome as global temperatures rise, means that climate-related changes here are likely to resonate well beyond the forest boundaries, says S. Tom Gower, UW-Madison professor of forest ecology and management and primary investigator of the project.

In the new study, Gower and his colleagues used a computer model to simulate the carbon balance of one million square kilometers of the Canadian forest over the past 60 years, to determine the relative impacts of climate and disturbance by wildfire.

The group found that the effects of carbon dioxide and climate — temperature and precipitation &151; varied from year to year but generally balanced out over time and area.

Instead, forest fires during the 60-year period had the greatest direct impact on carbon emissions from the system. …

Historically, scientists believe the boreal forest has acted as a carbon sink, absorbing more atmospheric carbon dioxide than it releases, Gower says. Their model now suggests that, over recent decades, the forest has become a smaller sink and may actually be shifting toward becoming a carbon source.

A different new study of U.S. wildfires found the burns can belch as much CO2into the air in a few weeks as a state’s cars and trucks produce in a year,according to scientists at the NationalCenter for Atmospheric Research (NCAR) and the University of Colorado atBoulder.

“The amount of CO2 emitted from fires in the US is equivalent to 4-6percent of anthropogenic emissions at the continental scale and, at thestate-level, fire emissions of CO2 can, in some cases, exceed annual emissionsof CO2 from fossil fuel usage,” the scientists wrote in Estimatesof CO2 from fires in the United States: implications for carbon management— published last week in the journal CarbonBalance and Management —

More details were posted in thisonline story:

The authors, Christine Wiedinmyer of NCAR and Jason Neff of the University of Colorado, used satellite observations of fires and a new computer model, developed by Wiedinmyer, that estimates carbon dioxide emissions based on the mass of vegetation burned.

Photo: AFS Gallery They caution that their estimates have a margin of error of about 50 percent, both because of inexact data about the extent of fires and varying estimates of the amount of carbon dioxide emitted by different types of blazes.

Overall, the study estimates that fires in the contiguous United States and Alaska release about 290 million metric tons of carbon dioxide a year, which is the equivalent of 4 to 6 percent of the nation’s carbon dioxide emissions from fossil fuel burning.

But fires contribute a higher proportion of the potent greenhouse gas in several western and southeastern states, especially Alaska, Idaho, Oregon, Montana, Washington, Arkansas, Mississippi, and Arizona. Particularly large fires can release enormous pulses of carbon dioxide rapidly into the atmosphere.


“A striking implication of very large wildfires is that a severe fire season lasting only one or two months can release as much carbon as the annual emissions from the entire transportation or energy sector of an individual state,” the authors write.

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