Boreal forests threaten to produce climate-warming gases

Boreal forests threaten to produce climate-warming gases

06 December 2013

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Canada — The immense forests of Canada’s north, relied on as a natural way to soak up greenhouse gases, are threatening to become major emitters of these gases instead.

Canada has told the world for years that our forests help soak up carbon dioxide and store carbon. The argument is that this cancels out some emissions from our cars, homes and industries.

But this is already shifting in the boreal forests, covering three million square kilometres from Newfoundland to the Yukon.

A wide-ranging review of climate change in these forests says that dead trees will rot as the temperature rises instead of being stored as peat, releasing carbon dioxide and methane. Both are greenhouse gases. As well, a greater number of forest fires will release carbon dioxide.

“Large C (carbon) stocks have accumulated in the boreal because decomposition is limited by cold temperatures and often anoxic (low-oxygen) environments. Increases in temperatures and disturbance rates could result in a large net C source during the remainder of this century and beyond,” the paper from Natural Resources Canada says.

While not a sure bet, the shift is seen as having a strong chance, and would affect world levels of carbon dioxide.

This conclusion is just one element in five sweeping new studies of how climate change affects Canada’s three million square kilometres of boreal forest. Nine more are still to be published.

All come from Natural Resources Canada. Rather than presenting new research, they summarize the most current information available about boreal forests in Canada and elsewhere.

They are printed in Environmental Reviews, a science journal published in Ottawa by NRC Research Press.

Editor John Smol says these are “consequences of global warming that people often don’t think about, and these are all in our back yard.”

“That’s a big worrying factor,” Smol said of the forests’ shift from soaking up greenhouse gases to emitting them. “What happens if you get more forest fires? What happens if wetlands dry out and stop accumulating peat and they start decomposing? That’s a big concern.”

Smol said the package of reviews provides a big picture of the boreal region that Parliament and forest managers will need to understand. The overview forecasts a rise of two degrees by 2050, and 4.5 degrees by 2100. Among the predictions:

• More pests:

“The most immediate threats may be the rapid expansion of populations of endemic insect pest species, including budworm defoliators and spruce bark beetles, in years when critical temperature thresholds are exceeded. Risks of widespread tree diseases may also exist but remain largely unquantified.”

• More fires:

“Forest fires will likely increase gradually in terms of occurrence, area burned, and severity over the next few decades.”

• Melting permafrost:

There have been warnings about melting permafrost for years, but the report now concludes much of this melting is “irreversible.”

“A major concern must be that some 40 per cent of the present-day boreal forest area overlays (sic) permafrost. These ecosystems are particularly vulnerable to permafrost degradation, which is already widespread and expected to expand rapidly in response to warming trends that have already begun.”

Once an area melts, it takes several decades before the soil readjusts and new trees can grow, it says.

“The process of degradation will occur on a vast scale, causing the release of even more GHGs (greenhouse gases), for a period lasting well into the 22nd century,” the authors write.

• Western drought:

Warmer temperatures and drought are likely in Western Canada, “with the potential for large-scale dieback of commercially important tree species in central Alberta and Saskatchewan. Natural recolonization by more drought-tolerant species may be possible, but that will be a comparatively slow process.”

But from the Great Lakes east the long-range forecast shows more rain, so these forests could grow faster with warmer temperatures.

• Lakes and rivers:

Thirteen per cent of the forest area is water. “Lakes are downhill, so what happens in the ecosystem affects lakes,” Smol said. “If different tree species move in it could affect the water quality. If you have forest fires it could affect water quality.”

The Natural Resources analysis says that warmer forests will attract more logging and mining, which could cause water pollution.

• What to do about it:

The reviews are much less clear about how to reduce the effects of climate change. Some of the possibilities include planting new forests, cutting fewer trees, managing forests to make them more dense so that they store more carbon, and using biomass to replace fossil fuels.

But the Natural Resources Canada scientists warn there are few simple solutions.

• Government cuts hurt:

“In recent years, the numbers of climate-monitoring stations, permanent sample plots, and flux towers in Canada’s boreal forest have all decreased while the need for monitoring data has increased, and the ability

to extract scientifically relevant knowledge from such measurements has improved.” (Flux towers in forests measure carbon dioxide in the air.)

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