Northern forests may be losing their ability to trap carbon

Northern forests may be losing their ability to trap carbon
Credit: Linnea Hanson/U.S. Forest Service. Young aspen grove.

The northern forests of western Canada are likely absorbing less carbon dioxide because of climate change, and the decline may be making a bad situation worse, researchers from Quebec and China have concluded.

If the situation remains as it is, the forests may actually put more dioxide back into the air than they absorb, the researchers said. While researchers have seen this happen in , the new result suggests that this problem could be much more widespread.

The scientists at the University of Quebec’s Montreal campus and from several Chinese institutions, reporting in this week’s Proceedings of the National Academy of Sciences, have been able to put numbers to the fears that the ability of northern forests to absorb carbon -- to act as carbon sinks -- was decreasing.

The researchers studied 96 permanent old-growth forests out of 20,000 candidates, concentrating on aspens, which are more sensitive to changes in precipitation.

They deliberately chose forests that were not affected by insect infestation or fires. They then estimated biomass production -- the growth of the -- from 1968 to 2008.

Trees in both east and west were dying sooner, but the eastern forests were replacing biomass while the forests in the western provinces of Manitoba, Alberta and Saskatchewan were not. The west has had less precipitation and rising temperatures, which they believe is the cause.

"Our results indicate that since 1963, drought-induced water stress has led to a weakening of the biomass carbon sink across a large area of the western Canadian boreal [northern] forests, with the largest reduction after 2000," they wrote.

Eastern Canadian boreal forests are not showing a similar phenomenon, they said, because trees are being replaced fast enough.

A reduction in biomass does not necessarily mean the forests are actually shrinking. There could be the same number of trees over the same area, but they might be smaller. In this study, the scientists reported the forests actually were getting smaller.

"Over time, more trees died than were regenerated," said Changhui Peng, Director for Ecological Modeling and Carbon Science, Institute of Environment Sciences, University of Quebec at Montreal. "The population of trees is declining."

Dead trees release the carbon back into the atmosphere as they decompose, Peng said.

Peng said until recently, scientists thought the decrease in the carbon sink was restricted to tropical rain forests, but apparently it is happening in the northern latitudes as well.

The theory is that the more and larger the trees and the larger the forests, the more will be captured, mitigating the greenhouse effect.

The Canadian research seems to indicate that may not be so, Peng said.

Almost half the carbon stored in the world’s forests is in northern latitudes.

The same thing appears to be happening in the American West as well, according to the U.S. Forest Service, although the forests of Western Europe are growing.

"In interior Alaska, we’re seeing very big decreases in productivity," said Teresa Nettleton Hollingsworth, a research ecologist for the U.S. Forest Service in Fairbanks. Productivity means the growth in biomass.

There also has been higher mortality in trees. But Hollingsworth said there is no evidence the change was due directly to in Alaska. It could also be the result of insect infestation and the increase in fires, which are endemic in the area, the indirect results of climate change.

"It could be that the number of trees have stayed the same but that they are not growing as much as they were in the past," she said.


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Feb 02, 2012
Northern forests may be losing their ability to trap carbon


Are they or aren't they?

The theory is that the more and larger the trees and the larger the forests, the more carbon dioxide will be captured, mitigating the greenhouse effect.


Is this actually the case? Any evidence?

A reduction in biomass does not necessarily mean the forests are actually shrinking. There could be the same number of trees over the same area, but they might be smaller. In this study, the scientists reported the forests actually were getting smaller.


Finally, we have something to work with. The forests are getting smaller. Though, after all of the hemming and hawing, I'm not sure that I believe it. Are they being replaced by deserts, undergrowth, or grasslands?

I"m sorry, I was hoping that this article would actually say something. It may or might be doing something isn't telling us anything. Please, try again!

Feb 02, 2012
Thanks for pointing out these works Joel. It's pretty evident that over the past 5 decades we have seen a non-negligible loss of boreal forest. Like they say, it is likely due to drought, since there is a major hit during the early 2000s drought, plus since there is no negligible loss in Ontario where there was no drought.

It doesn't take a rocket scientist to see that any tree is a carbon sink. How do you think the things grow? By magic? No, they absorb CO2 and turn it into cell walls.

I don't know if I truly believe in the CO2-drought link that they imply, but if it is true, and there is a nonlinear feedback loop that leads to the accelerating desertification of the prairie provinces, then we could be in serious trouble. A non-negligible loss of farmland due to desertification would wreak havoc on the food supply for all of Canada and for a whole lot of developing countries that rely on Canada for assistance.

Feb 02, 2012
Another example of fraud being passed off as "science".
As only one example, consider the now boldly declared decision to use only specially chosen samples, rather than random ones. "96 permanent old-growth forests out of 20,000 candidates". That spells "ringer"! A "study" is supposed to include random samples, not a handful out of a preponderance of alternatives! And they admit they were specially chosen for not having been affected by insects or fires. But that could just as well mean the forests they looked at were unnatural, comprising trees that don't burn and are so abnormal they don't attract insects! Remember, a rule is that the random sample represents what affects a system and, since that means that forests affected by insects or that experienced fire, since19,904 out of 20,000 forests seem to qualify, that means that, whether you like those forests or not, those ar ethe ones you have to look at!

Feb 02, 2012
... trees that don't burn, and trees that don't attract insects. Ok then.

Imagine this: In order to do a survey over a large period of time, you have to choose old trees. I know it's difficult to understand.

Feb 02, 2012
Not all trees in areas that either suffer fires or insect attack are killed. In fact, there is no forest that hasn't suffered fire or insect attack at one time or another! The article specifically spoke of "forests", which meant live trees, meaning even those that had fires or insect attacks were still thriving! And it didn't say that those chosen were the only old growth stands. It's unreasonable, out of 20,000 candidates, only 96 were "permanent old growth" stands! And, consider, the "study" is not being done over time, it is looking at the condition of the trees now! The article "forests" are losing their ability to remove carbon dioxide form the air, not just "aging forests". That means new trees are no longer capable of taking carbon dioxide from the air. But, since carbon dioxide is crucial to tree growth, does that mean that trees are all being scraggly, anymore?

Feb 02, 2012
It is true that 96 samples out of 20000 samples doesn't give a good confidence level. The forest industry in Saskatchewan is gigantic, and I'm certain that more tests will be done in order to gain greater confidence -- either to confirm or deny this early finding.

You have to see this from the point of view of someone from central Saskatchewan. To the north, we have vast areas of desert and rock. To the south, we have vast areas of farmland. If the farmland succumbs to desertification in a non-negligible way, then Canada, the US, and many developing countries will be in serious trouble. The fact of the matter is that Saskatchewan is deeply important to the stability of more than just Saskatchewan.

If it is possible to partially avoid desertification through reforestation, then it seems like it's kind of straightforward that we should increase reforestation efforts just to be on the safe side.

This has nothing to do with whether or not the drought was anthropogenic or not.

Feb 02, 2012
OK, now you're just being a troll. Do you know how to monitor the growth of a tree over time? You kill it now, take a cross-section, and look at the rings.

Feb 02, 2012
They study a 40 yr span of time and come to a conclusion like this? Can we call that climate science? I could see maybe 400 years being more clear and concise of any immediate cycle causing the data to be worthless.

Feb 02, 2012
rubberman most eminently displays the behavior of a shill. They talk about the 96 out of 20,000 forests as if it is a normal, if small, sample. Bu they're not a normal sample. They are a specially defined collection of forest types. The very fact that they specify they must never have had fires or insect invasions suggests, if not implies, that their forests do not constitute a genuine, legitimate sample of the region! And, as for their "not having time", are the "researchers" on some kind of New World Order time clock to get fraudulent results in in time for an anti-forest bill to be passed? Aren't researchers supposed to take however much time is needed to get their results right? This entire project is a fraud and those who defend it stink like card carrying New World Order quislings.

Feb 02, 2012
Your missing a the point J-Rod and Mr Nig; Those forests have been there for 10s of 1000s of years. (10,000year ). They have a solid foundation which a scientists can use for a timescaled measurement.

Isolating the measurements to certain species of trees, simply removed all of the variables that having multiple species would introduce.

To me, it sound these scientists took a good approach to the data acquisition processes.

Feb 05, 2012
Why limit the "stress" to just drought? Insect infestations and fires are part of the regular strees evidently most forests experience, too! In fact, it can be suggested that trees that don't attract insects and do not burn so readily are already abnormal, likely providing far fewer carbon related molecules either for insects to ingest or to feed fires. And how legitimate is it to extend a judgement across all species when only one particular species is studied? Do they all react to this supposed "drought" the same way?
And, consider, just what are they saying when they say carbon is not being absorbed from the atmosphere? Carbon is basic to the molecules associated by "science" with living tissue on earth. If they don't absorb carbon, that means they aren't making carbon molecules for their own cells! So, on the basis of a variety with body chemistry different from all others, the "researchers" are going to conclude necessarily how all the others must behave now.

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