Study finds trees not so large carbon sinks

Oct 27, 2010 By Bob Beale
Study finds trees not so large carbon sinks
Photo: Bob Beale

The capacity of trees to counter rising carbon dioxide levels in the atmosphere may not be as great as previously thought, according to a new study with significant implications for predicting future climate change.

While initially seem to grow faster or larger as dioxide (CO2) levels increase, the higher growth rates cannot be sustained because the availability of remains finite, suggests the study by US and Australian scientists published in the journal .

The study, led by Dr. Richard Norby of the Oak Ridge National Laboratory, Tennessee, included Professor Ross McMurtrie of the UNSW School of Biological, Earth and Environmental Sciences.

It updates a long-running experiment in a deciduous forest stand in Tennessee that has been exposed to elevated CO2 levels about 25% above the current atmospheric concentration – effectively exposing the trees to what that ambient CO2 concentration is expected to be in about 2050.

It had been widely thought that increasing CO2 concentrations would stimulate plant growth, which in turn would absorb enough carbon from the atmosphere to slow the rate of CO2 increase.

That belief appeared to be confirmed by the first six years of the experiment, during which the net productivity of the forest was significantly increased. But the new report has revealed that in the subsequent five years the net productivity of the forest has declined, a fall attributed by the researchers to the limited availability of nitrogen in the soil.

The researchers say the experiment provides strong rationale and process understanding for incorporating nitrogen limitation and nitrogen feedback effects in ecosystem and global models used in assessments. In short, the study suggests that terrestrial vegetation will not be as large a carbon sink as previously thought.

"We're going to have to learn not to trust in trees to remove as much carbon from theatmosphere as we had hoped," says Professor McMurtrie.

He has also been part of a similar study, the Hawkesbury Forest Experiment, near Sydney, in which the responses of Australian eucalypt trees are being followed.

The new findings may be especially pertinent for trees growing in low-nutrient soils, as occurs in much of Australia

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User comments : 24

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Uri
not rated yet Oct 27, 2010
Straight from the source:

http://face.ornl....lts.html
GSwift7
not rated yet Oct 27, 2010
This isn't earth-shattering news. Trees aren't much of a carbon sink in the first place. A forest will reach a point of equilibrium once it is mature. Then the rate of growth becomes equal to the rate of decomposition minus the tiny amount of carbon that becomes new topsoil over time. I also wonder about water supply. I would assume that no matter how much carbon is in the air, and no matter how much nitrogen is in the soil, a tree won't grow without water.

As Uri's link points out, it's mainly an increase in turnover rate, not sequestration rate that results from increased CO2. That's what I've heard before, so this isn't big news.
Uri
not rated yet Oct 27, 2010
Not trying to spark a debate, just looking for someone with a biology background to reconcile the article with the last bullet in my link from above.

Annual N uptake increased linearly with fine-root length duration and was significantly greater in elevated [CO2]. Leaf and litter N concentrations were reduced in elevated [CO2], but there was no indication of a negative feedback of N availability on NPP. The need to elucidate changes in stand-level biogeochemical cycling is one of the foremost reasons to conduct FACE experiments in forests, but these responses require a long-term perspective.

GSwift7
not rated yet Oct 27, 2010
I would like to see an experiment like this one performed in a commercial logging forest, like the big plots of southern pine here in south carolina. If increased CO2 has an effect on the number of years it takes for a plot of land to be harvested, it could have huge economic effects in places like south carolina and alabama, where the paper industry is important. I noticed that the Australian partners in the above article specifically mentioned the eucalyptus tree, which is the australian paper pulp tree of choice.

In your link above, they said that woody growth wasn't affected much, so maybe little effect on the paper crops. Still, it's an entirely different soil type here, so I would like to see a long term study. Perhaps even a study of a plot of land over multiple cycles of logging and replanting would be good.
GSwift7
not rated yet Oct 27, 2010
Even if long term growth cycles remain nearly the same, a boost to tree growth in the early part of the tree's life could have a positive impacte due to young trees getting strong enough to withstand storm damage at an earlier age. They indicated increased root growth too, and that's a good thing in terms of having more trees survive to maturity, I would expect.
Uri
not rated yet Oct 27, 2010
How about North Carolina?
http://face.env.d...main.cfm

Doesn't seem to offer a summary like the ORNL site does, but maybe you can do some more looking.

Oh and it appears there were / are quite a few FACE sites:
http://public.orn...ce.shtml

yOnsa
not rated yet Oct 27, 2010
Gee George, tell me about the rabbits again. Uhhh hey George, study finds trees not so large carbon sinks derr...

anyone else thinks the title reads weird?
Otherwise I found the article interesting.
GSwift7
not rated yet Oct 27, 2010
OH cool! Thanks for the links. :)

The third one down on the Duke site was especially interresting. It's not a summary of results, but rather a suggestion for immediate research goals. I like reading and thinking about the unanswered questions. Very good stuff.

If i had to summarize, it sounds like they are wanting to figure out which processes will speed up and slow down and by how much, so that they can figure out which processes will dominate. Results from previous studies seem to have conflicting results so far, in that regard.
GSwift7
not rated yet Oct 27, 2010
Gee George, tell me about the rabbits again. Uhhh hey George, study finds trees not so large carbon sinks derr...

anyone else thinks the title reads weird?
Otherwise I found the article interesting.


lol. good point. Creative use of punctuation could produce some entertaining versions of that headline:

Study finds trees. Not so large carbon sinks.

Study finds trees; not! So large carbon sinks.

Study finds trees not so large. Carbon sinks.
PPihkala
not rated yet Oct 27, 2010
How about planting nitrous fixing plants near the roots of trees? That should help if nitrogen is the limiting factor.
Noumenon
5 / 5 (44) Oct 27, 2010
Interesting study. I can see that a particular tree being inspected would eventually reach a equilibrium wrt soil nutrients, however can this be interpolated to imply that a greater number of trees (vegetation) would not grow. In other words, does this study say that vegetation in general (in more areas, less sparse, etc), does not grow more vigorously? (notice the ? mark)
Userless_Id
not rated yet Oct 27, 2010
how convenient.
PinkElephant
not rated yet Oct 27, 2010
@Uri & GSwift7,

The ornl link currently shows data only up to 2003. This update extends up to current time, as far as I understand. The drop-off in productivity was not yet as perceptible back in 2003, although that last bullet does hint that the scientists suspected it might/should be kicking in. Now they find it in full bloom, so to speak...

@PPihkala,

Nitrogen-fixing (or most any other type) of plants may not be as productive (and might not be able to compete successfully with other plants) when permanently shaded by a forest canopy...

@Noumemon,

Most of these FACE studies don't focus on individual trees; they study small groves -- something on the order of a quarter-acre.

One would expect the same dynamics WRT nutrient constraints to apply to any climate zone, soil conditions, or tree type.
Uri
not rated yet Oct 28, 2010
@Uri & GSwift7,
The ornl link currently shows data only up to 2003. This update extends up to current time, as far as I understand. The drop-off in productivity was not yet as perceptible back in 2003, although that last bullet does hint that the scientists suspected it might/should be kicking in. Now they find it in full bloom, so to speak...


Yeah I noticed that and should have reposted. I did some more digging and found.
http://public.orn...8-08.htm

And you can definitely see the fall-off in NPP in the more recent data. The only comment I can make is that the decline in NPP appears to be present in the control group as well so it makes me wonder if there isn't some other effect contributing.....

GSwift7
not rated yet Oct 28, 2010
This is the Duke publication I was talking about:

http://face.env.d...2-10.pdf

It's from this year. The conflicting results I mentioned are the ones in her report. It's not so much a paper outlining any conclusions, rather a grocery list or wish list for future study. According to her summary, long term net results are inconclusive, mainly because soil is so hard to measure. She suggests using some newer methods to test the soil.
lengould100
not rated yet Oct 28, 2010
Should waste less trees by publishing fewer papers and starting to do something about AGW.
dpwozney
1 / 5 (3) Oct 29, 2010
Carbon dioxide is removed immediately from the lower atmosphere by rainfall. Carbon that does not enter plants through roots, in the form of carbon dioxide dissolved in water, stays in the soil and in between layers of sediments.
CarolinaScotsman
1 / 5 (1) Oct 30, 2010
The Duke study showed increased nitrogen. The study has been running continuously since 1996. Details and latest results that I could find are at

http://face.env.d...7-06.pdf

Also article in Physorg

http://www.physor...465.html
CarolinaScotsman
1 / 5 (1) Oct 30, 2010
Also:
One study to watch in future. Also has links to other FACE sights.

http://aspenface.mtu.edu/
PinkElephant
5 / 5 (1) Oct 31, 2010
@CarolinaScotsman,
The Duke study showed increased nitrogen.
No it did not. Read it more carefully.
ODesign
not rated yet Nov 01, 2010
Should waste less trees by publishing fewer papers and starting to do something about AGW.


actually the way to reduce carbon would be to bury the trees. Or turning the trees into paper and then burying the paper might work too.
Ravenrant
not rated yet Nov 01, 2010
Which only means they are even MORE important and need to be BETTER preserved since anything that replaces a forest, jungle or rain forest will be even less effective a carbon sink.
GSwift7
not rated yet Nov 01, 2010
@ CarolinaScottsman: The 2006 paper you linked to isn't the most recent. The one I linked to a couple posts before yours is from this year. If you look at the Duke web site, there is a link to recent publications. Follow that and you'll see a bunch of publications more recent than 2006. The one I linked to is from the FACE group and is from this year. It talks about variations in the results at different sites in regard to carbon and nitrogen and inconclusive patterns over time.
BarryCarter
not rated yet Nov 02, 2010
Trees grow in soil. There is evidence that a minor increase in soil carbon sequestration would pull enough carbon from the atmosphere to get us into a safe range. There is also evidence that we can double soil carbon sequestration in a couple years if we apply certain sea minerals to the soil.

These minerals can be concentrated from sea water or sea salt using simple, open-source methods. This reduced-salt, mineral concentrate can be made at a cost of about two dollars per acre, per year.

Any individual with access to dirt can get these results by applying these minerals to the dirt they have access to. You don't need permission or cooperation of corporate, government or belief structures to implement this on your own soil. If a few million people were to do this, we could pull enough carbon out of the atmosphere to get us back to safe levels.

Contact me for a link to my web page on this subject.

Barry Carter
bcarter at igc.org