From the University of Michigan
U-M ecologist: Future forests may soak up more carbon dioxide than previously believed
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An aerial view of the 38-acre experimental forest in Wisconsin where U-M researchers and their colleagues continuously exposed birch, aspen and maple trees to elevated levels of carbon dioxide and ozone gas from 1997 through 2008. Credit: David Karnosky, Michigan Technological University
ANN ARBOR, Mich.—North American forests appear to have a greater capacity to soak up heat-trapping carbon dioxide gas than researchers had previously anticipated.
As a result, they could help slow the pace of human-caused climate warming more than most scientists had thought, a U-M ecologist and his colleagues have concluded.
The results of a 12-year study at an experimental forest in northeastern Wisconsin challenge several long-held assumptions about how future forests will respond to the rising levels of atmospheric carbon dioxide blamed for human-caused climate change, said University of Michigan microbial ecologist Donald Zak, lead author of a paper published online this week in Ecology Letters.
“Some of the initial assumptions about ecosystem response are not correct and will have to be revised,” said Zak, a professor at the U-M School of Natural Resources and Environment and the Department of Ecology and Evolutionary Biology in the College of Literature, Science, and the Arts.
To simulate atmospheric conditions expected in the latter half of this century, Zak and his colleagues continuously pumped extra carbon dioxide into the canopies of trembling aspen, paper birch and sugar maple trees at a 38-acre experimental forest in Rhinelander, Wis., from 1997 to 2008.
Some of the trees were also bathed in elevated levels of ground-level ozone, the primary constituent in smog, to simulate the increasingly polluted air of the future. Both parts of the federally funded experiment—the carbon dioxide and the ozone treatments—produced unexpected results.
In addition to trapping heat, carbon dioxide is known to have a fertilizing effect on trees and other plants, making them grow faster than they normally would. Climate researchers and ecosystem modelers assume that in coming decades, carbon dioxide’s fertilizing effect will temporarily boost the growth rate of northern temperate forests.
Previous studies have concluded that this growth spurt would be short-lived, grinding to a halt when the trees can no longer extract the essential nutrient nitrogen from the soil.
But in the Rhinelander study, the trees bathed in elevated carbon dioxide continued to grow at an accelerated rate throughout the 12-year experiment. In the final three years of the study, the CO2-soaked trees grew 26 percent more than those exposed to normal levels of carbon dioxide.
It appears that the extra carbon dioxide allowed trees to grow more small roots and “forage” more successfully for nitrogen in the soil, Zak said. At the same time, the rate at which microorganisms released nitrogen back to the soil, as fallen leaves and branches decayed, increased.
“The greater growth has been sustained by an acceleration, rather than a slowing down, of soil nitrogen cycling,” Zak said. “Under elevated carbon dioxide, the trees did a better job of getting nitrogen out of the soil, and there was more of it for plants to use.”
Zak stressed that growth-enhancing effects of CO2 in forests will eventually “hit the wall” and come to a halt. The trees’ roots will eventually “fully exploit” the soil’s nitrogen resources. No one knows how long it will take to reach that limit, he said.
The ozone portion of the 12-year experiment also held surprises.
Ground-level ozone is known to damage plant tissues and interfere with photosynthesis. Conventional wisdom has held that in the future, increasing levels of ozone would constrain the degree to which rising levels of carbon dioxide would promote tree growth, canceling out some of a forest’s ability to buffer projected climate warming.
In the first few years of the Rhinelander experiment, that’s exactly what was observed. Trees exposed to elevated levels of ozone did not grow as fast as other trees. But by the end of study, ozone had no effect at all on forest productivity.
“What happened is that ozone-tolerant species and genotypes in our experiment more or less took up the slack left behind by those who were negatively affected, and that’s called compensatory growth,” Zak said. The same thing happened with growth under elevated carbon dioxide, under which some genotypes and species fared better than others.
“The interesting take home point with this is that aspects of biological diversity—like genetic diversity and plant species compositions—are important components of an ecosystem’s response to climate change,” he said. “Biodiversity matters, in this regard.”
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Co-authors of the Ecology Letters paper were Kurt Pregitzer of the University of Idaho, Mark Kubiske of the U.S. Forest Service and Andrew Burton of Michigan Technological University. The work was funded by grants from the U.S. Department of Energy and the U.S. Forest Service.
@Greg Cavanagh
We’ve recently had a fuel-oil spill here, and the model failed to predict exactly where it would come ashore.
http://www.stuff.co.nz/environment/5763638/Locals-get-stuck-into-beach-oil-cleanup
So I’m not sold entirely sold on models of water in the real world. Maybe in more enclosed environments the models work better, but then what is the point?
In the case of the oil it was still better to use observation of where the oil came ashore, than rely on models.
Ann Arbor, a scientist I presume, uses the non scientific phrase ‘-heat trapping’ CO2. It might interest her to know that nothing can trap heat since CO2, like everything else, must obey the 2nd law of thermodynamics.
James Reid says:
October 14, 2011 at 12:28 am
Pretty bloody obvious even to a non-scientist like myself
Scientist – Some one who can earn a great deal of money from stating the obvious.
Plant trees, that’s nice and I suppose poor old Columbus will get blamed for the
resulting ice age, again .
I love trees and have planted many over the 60 years I have lived. There is no requirement for a computer model or 12 year long study to tell us the benefits, especially when using the grant money grabbing line, “rising levels of atmospheric carbon dioxide blamed for human-caused climate change” garbage!
“The only significant way to sequester carbon in trees is to replace a “barren” area with trees whose cumulative carbon weight is greater, then to maintain that carbon uptake FOREVER.” GS Quote
Isn’t that what planting more trees is all about, ie doing the above!?!
Geoff Sherrington:
Personally I am not interested at all in what happens in geological times in the future. My future, and that of my children and grandchildren spans perhaps the next 70yrs. So what happens in 1000 or 10,000 years is totally irrelevent to our lives. Geological time spans hold no immediate interest for us and maybe to most of mankind. Here and now and the foreseeable future is what matters to us.
And in this context you are wrong about the time taken to return carbon sequestered by woody plants to decay. 100 yrs is important.
From 1968 to 1998 I lived in a house built with timber cut down in the 1600’s – that timber is now over 400yrs old and the house still stands. Point taken?
In the river bed nearby are stands of bamboo reaching 6m in height; they grow that tall in 2yrs. They die back, leaving the woody stems (30-50mmdia) which rot away very, very slowly. I walk over woody detritus every day which has been there for the past 15yrs or more.
The truth is, woody plants can lock up carbon faster than it is released by natural means and we can lock it up for much longer by using wood for constructional and other purposes.
All it requires is good management.
Plants take in CO2 thru their stomata – holes in their leaves. The density of these (stomata per sq inch) varies with CO2 concentration. Which can be used to estimate CO2 concenration in prehistory, using leaves preserved anaerobically in lake deposits.
But my point here is to ask if stomata concenration is fixed for a given plant. It must be be during the life of each leaf, but do plants control this genetically, so concentrations stay fixed for the life of the tree? Either way, over time, leaves will grow with fewer stomate as CO2 concentation rises, so obviating the effect found in the post above.
The carbon removed from the atmosphere by trees can be sequestered indefinitely, simply by building houses and other wooden structures out of the trees.
AGW does not exist, it is a fallacy. Climate models are seriously flawed, as time goes on the data is retro manipulted. Co2 is a fertilizer, everyone knows that, I fail to see this as 12years other than wasted, non science again.
OMG! Shock Horror!!!! Trees absorb CO2 & grow faster & better!!! It just cannot be true!! Worse still, O3 doesn’t hinder tree growth in the long term, the bloody trees “adapted”, damn them they should have died! This is “revolutionary” stuff, folks, why has nobody come up with this “revolutionary” idea before? How much did this 11 year “revolutionary” jamboree cost you US taxpayers anyway? Next, they’ll be saying that variable Solar output, coupled with variable UV & Extreme UV, plus low magnetic field strengths & Solar wind, assisted with increased Galatic Cosmic Rays, has an effect on Earth’s Climate, ha, pull the other one, oh puurrleeeze, where do they get these ideas from? Sarc off. 🙂 Someone ought to point out that vegetation has been around for eons because it adapted to Climate Changes of the past, & that if the Earth was, for the sake of argument, a year old Humanity turned up around 8:40pm on New Years Eve!!! Stay sharp & get a grip people, we’re still on a learning curve, & I still prefer the Non-UN Agenda 20, where people were free, had justice, & the right to a life, unfettered by dictators & venal mendacious politicians & Socialists! Oh, & while I am about it, when these scientists find out they were wrong about something, why can’t they just grow a pair & say, “sorry, I was wrong!”. HAGWE everyone, I’ll be cheering for Wales in the morning at the RWC!
John Marshall says:
October 14, 2011 at 1:40 am
“Ann Arbor, a scientist I presume, ….”
Ann Arbor is actually the name of a city in Michigan, rather than the name of the author of the article. The author appears to be anonymous.
I do remember in the past that some one mentioned that North America as a whole is a nett carbon sink. The forests you have in the last hundred years have actually increased in size as marginal farm land is abandoned and and people as a habit plant trees. North America may use a lot of fuel and coal but I fear you have been branded as evil CO2 producers but are in reality a carbon sink. Thus these trees are telling us the truth. CO2 monitoring stations on the coast lines and in continental USA may be a cause of severe embarrassment to the AGW crowd. One half an hour after sunrise the CO2 levels in a corn field are depleted, this tells us we are lacking CO2.
Push for more CO2 monitoring over continental USA and Canada and a surprise awaits.
In articles ‘solar climate no longer taboo’ and this one there seems to be a need by the authors to still point to CO2 as the cause of global warming. If trees can feed on the CO2 removing it from the atmosphere, plant lots of trees and stop global warming if that’s the case. My son pumps CO2 into his fish tank to help the plants grow, it’s not new knowledge, but maybe admitting it is.
to the rising levels of atmospheric carbon dioxide blamed for human-caused climate change
This is a new level of assumption. ‘Human caused climate change is real and CO2 is being blamed for that climate change’ appears to be a reversal of the logic. Given that the research is based on a falsified hypothesis it would appear to be a waste of funds. You would get more and better information from a forester who would point out that there are several areas of the world where forests have been growing in the same place for centuries – and the nitrogen cycle hasn’t stopped.
It seems odd for the UM team to introduce two (in their own words) mutually canceling variables in the same experiment. CO2 and ozone (smog) act (according to them) in opposite directions, so to have them applied simultaneously to the same experimental subjects seems capricious at best. The trees grew in spite of all that; CO2 is plant food.
This has been my response to AGW proponents who want to wag their finger at me over my carbon footprint. I simply tell them that I own and maintain over 50 acres of forest land in Michigan which sinks far more carbon than my family and I produce. It also produces far more fresh, clean air than we use. That means that, those who don’t own and maintain forest land are actually getting a free-ride off of me. So, if they’re so worried about carbon, go buy land, plant trees and keep it undeveloped – put your money where your big mouth is. Stop being a deadbeat freeloader. Oh, and by the way, you’re welcome.
When the trees “hit the wall” you cut them down and plant new ones. Why do they insist on adding complication?
I told you so. Many times.
The only question is,: Why I should work hard, while these “scientists” lazily walk along their orangeries with cups of coffee, then lazily typing a few word of their trite blah-blah (“Genetic diversity and plant species compositions—are important components of an ecosystem’s response to climate change” — who would have thought? Except there’s no “climate change” to speak of), and then receive their lazy salaries financed by… hapless me.
I am burning with the class hatred. Ignorant parasites. Hang them all high!
Trees have had several million years more eco-bio-diversity evolutionary experience than us johnny come latelys. They adapt to climate change, not fight it.
If we consider atmosphere around the earth an enclosed system, then total CO2 available in the system remain constant. Actual problem is population explosion in the third world countries needing fossil fuel, housing resulting in deforestation and uncontrolled emissions CO2 from the factories. In populous cities like Bombay and Karachi, if you walk out wearing white shirt durring peak hours, you will find flakes of carbon deposited on your shirt. The point is the carbon present under the earth crest is coming out and trees are disappearing at very fast pace.The trees will grow faster only if they continue existing, otherwise we will definitely have ever increasing surplus CO2. The soil nitrogen may reduce in your part of globe it will remain surplus in this part of globe. We need a global approach to address this problem.
Higher ozone in the future? What a joke! Seriously. Where did that come from?
I’ll bet the tree rings on those trees are real fat. Maybe tree rings are a better indicator of changing CO2 levels than temperature.
The best way is actually to plant more trees and to use more wood, the carbon is sequestrated in the lumber for many years while news trees are growing in place of the used ones.
Yes, and stop recycling paper. Trees are grown as crops for paper. “Recycle your breadcrumbs! Save the wheat!”
Faugh.
Where’s the evidence that ozone levels are currently increasing?