Greenhouse gas carbon dioxide ramps up aspen growth

December 4, 2009

The rising level of atmospheric carbon dioxide may be fueling more than climate change. It could also be making some trees grow like crazy.

That is the finding of a new study of natural stands of quaking aspen, one of North America's most important and widespread deciduous trees. The study, by scientists from the University of Wisconsin-Madison and the University of Minnesota at Morris (UMM) and published today (Dec. 4) in the journal , shows that elevated levels of during the past 50 years have boosted aspen growth rates by an astonishing 50 percent.

"Trees are already responding to a relatively nominal increase in atmospheric carbon dioxide over the past 50 years," says Rick Lindroth, a UW-Madison professor of ecology and an expert on plant responses to climate change. Lindroth, UW-Madison colleague Don Waller, and professors Christopher Cole and Jon Anderson of UMM conducted the new study.

The study's findings are important as the world's forests, which cover about 30 percent of the Earth's land surface, play an important role in regulating climate and sequestering greenhouses gases. The forests of the , in particular, act as sinks for carbon dioxide, helping to offset the increase in levels of the , widely viewed as a threat to global climate stability.

What's more, according to the study's authors, the accelerated growth rates of aspen could have widespread unknown ecological consequences. Aspen is a dominant tree in mountainous and northern forested regions of North America, including 42 million acres of Canadian forest and up to 6.5 million acres in Wisconsin and Minnesota. Aspen and their poplar cousins are considered "foundation species," meaning they exert a strong influence on the plant and animal communities and dynamics of the where they reside.

"We can't forecast ecological change. It's a complicated business," explains Waller, a UW-Madison professor of botany. "For all we know, this could have very serious effects on slower growing plants and their ability to persist."

Carbon dioxide, scientists know, is food for plants, which extract it from the air and through the process of photosynthesis convert it to sugar, plant food.

Previously, scientists have shown that plants and trees in growth chambers respond to levels of carbon dioxide well above levels in the atmosphere. The new study is the first to show that aspen in their native forest environments are already growing at accelerated rates due to rising ambient levels of carbon dioxide in the atmosphere.

"It's a change hiding right in front of us," says Cole, a biologist at UMM. "Aspens respond to all sorts of things we had to account for — water, genetics and other factors — but the strong response to carbon dioxide surprised all of us."

The study measured the growth rates of 919 trees from Wisconsin forests dominated by aspen and birch. Trees ranging in age from 5 to 76 years old were sampled and subjected to tree-ring analysis. Comparing the tree-ring data, a measure of annual tree growth, with records of atmospheric carbon dioxide, the researchers were able to correlate increased rates of growth with changes in the chemistry of the air.

The surprising increase in growth rates for the trees sampled in the study is coupled, the authors note, with moist conditions. By contrast, aspen in the western United States do not seem to grow as fast as those in the American Midwest, most likely due to recent extended periods of drought. Also, while the researchers found that aspen grow much faster in response to elevated carbon dioxide, similar effects have not been observed in other trees species, notably oak and pine.

Findings from the new study, the authors note, could augur revisions of the estimates of how much carbon northern temperate northern forests can sequester.

"Forests will continue to be important to soak up anthropogenic carbon dioxide," says Waller. "But we can't conclude that aspen forests are going to soak up excess . This is going to plateau."

"Aspens are already doing their best to mitigate our inputs," agrees Cole. "The existing trees are going to max out in a couple of decades."

Source: University of Wisconsin-Madison (news : web)

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4.3 / 5 (6) Dec 04, 2009
"The rising level of atmospheric carbon dioxide may be fueling more than climate change. It could also be making some trees grow like crazy."

The evidence presented here is that CO2 IS "making trees grow like crazy" however, there is no such evidence (not diddled with, that is) that it is contributing to global warming, just the belief that it must be.
3 / 5 (4) Dec 04, 2009
""Aspens are already doing their best to mitigate our inputs," agrees Cole. "The existing trees are going to max out in a couple of decades." "

Aspens are just 'trying' to survive given the conditions they are in. Do the authors think there is a aspen tree union that is trying to help AGW worshipers in their cause?
4.4 / 5 (8) Dec 04, 2009
OK, put the following comments together:
- "the strong response to carbon dioxide surprised all of us."
- "Findings from the new study, ... could augur revisions of the estimates of how much carbon northern temperate northern forests can sequester"

What now of the IPCC statement that the science (of Global Warming) is conclusive?
When every second day, it seems, scientists are finding new, unknown effects such as the one above, then the science is NOT conclusive.
To say that it is, is just a sham. They even admit, in their own reports, that there are mechanisms that they know nothing about!
Conclusive? CONCLUSIVE?
4 / 5 (4) Dec 04, 2009
since global warming and CO2 increase is all a sham, then it must be that the aspen trees are part of the conspiracy and are faking their own increased growth rates. But shouldn't we have expected that from the rocky mountain deciduous elite?
2.6 / 5 (5) Dec 04, 2009
Toyo: You misunderstand; the IPCC's statement was that global warming was very likely (>90%, if I recall what the phrase indicates?) anthropogenic in nature. The details of the warming, the sources and sinks of different gas, and the magnitudes of different feedback effects are all less well-know, and I'm sure that any reputable climate scientist would say as much. It's pretty much certain that humans are causing global warming; it's probable that the overall effect of natural feedbacks will be to exacerbate that warming.

But the details? That's what this study is focusing on, and that's where things begin getting fuzzy.
Dec 04, 2009
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5 / 5 (1) Dec 04, 2009
I wonder where the nutrients for such rise in growth level are coming from. Considering that CO2 is an important but tiny part of the biological process of organic growth.

A recent article talks about the related cycles:

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