Sunday, December 6, 2009

Greenhouse gas carbon dioxide ramps up aspen growth: U.S. study

WASHINGTON, Dec. 4 (Xinhua) -- The rising level of atmospheric carbon dioxide may be fueling more than climate change and could also be making some trees grow like crazy, according to 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 Friday in the journal Global Change Biology, shows that elevated levels of atmospheric carbon dioxide 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 Northern Hemisphere, in particular, act as sinks for carbon dioxide, helping to offset the increase in levels of the greenhouse gas, widely viewed as a threat to global climate stability.

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 forest ecosystems 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 six 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.

Western carbon dioxide emissions increase plant yields in the Third World. So why are they asking for reparations?

By Lawrence Solomon

t Copenhagen, Third World countries are demanding hundreds of billions of dollars in reparations from the West for the consequences of the West’s fossil fuel burning, among them droughts and crop failures.

Third World countries have it backwards. The West’s CO2 emissions have been increasing crop yields while helping to ease the Third World’s water shortages. Rather than plead for reparations, Third World governments should offer a paean to Providence.

The bureaucrats at Copenhagen dread high CO2 levels. The biosphere craves them. Plants evolved when CO2 levels in the atmosphere stood at a healthy 1000 parts per million, two-to-three times today’s paltry level of about 380 parts per million. Plants crave CO2 so much that commercial greenhouse operators often enrich greenhouse air with CO2 — also known as nature’s fertilizer — to levels of 1500 parts per million, or four times that of our current atmosphere.

 Since humans began adding CO2 to the planet’s atmosphere, taking plants off their starvation rations by creating a planet-wide greenhouse, plants have thrived. Data from NASA satellites, which since the early 1980s have been tracking the amount of biota on Earth, vividly demonstrate the results. As CO2 emissions grew in leaps and bounds, so did plants — the data shows planet Earth is now greener than when those satellite measurements began.

 Growth in greenery varies from country to country, and within countries, because climatic factors are so many and so varied, but the overall trend is clear, and especially in the Third World. The Indian subcontinent, the Amazon, the tropical countries generally, all show marked improvement, with studies pointing to improvements in carbon dioxide levels as an important factor.

 China, which includes some of the most resource-stretched regions on the planet, provides the most dramatic demonstration of the boon in biota. As shown in a 2007 analysis by academics at the country’s prestigious Beijing Normal University, China’s plant growth increased by an astounding 24 % over the 18-year period studied, 1982 to 1999. The Chinese analysis, which like many others was based on satellite data, notes that China’s resource-constrained regions sometimes did particularly well. In water-constrained Northwest China, for example, plant growth increased by 29%. In Northeast China and the Tibetan Plateau, where temperatures ordinarily place severe limits on vegetation, plant growth increased by 30%. South China and East China, where sunlight is a limiting factor, saw plant growth increase by a still-impressive 19%. Changes in CO2 during those 18 years correlated well with the changes in vegetation.

 That plants love CO2 comes as no surprise — CO2 is not only their food, it is a gas to which they are superbly adapted. When the air is rich in CO2, plants don’t need to work as hard to breathe it in, letting them reduce the number of stomata, or air pores, on the surfaces of their leaves. Fewer pores means the plants breathe out less water vapour, letting them conserve moisture and better survive droughts. CO2 also helps plants survive droughts and other adverse conditions by extending their root systems, allowing them to collect minerals and moisture from afar. Through other mechanisms, CO2 protects plants against insect infestations, soil salinity and other environmental threats.

 This gas — also known as the gas of life — is healthful and helpful to humans, too. CO2 not only boosts agricultural yields, it boosts the antioxidant and vitamin content in plants, as well as their essential minerals. Also importantly, CO2 helps make hospitable marginal areas of the world that would otherwise be inhospitable.

Industrialization in the West, along with the fossil fuel burning that it has entailed, has been a win for the West and a win for the world, including the Third World. The colourless, odourless, tasteless gas called CO2 is indispensable to life and, because China and India are certain to rapidly increase their CO2 emissions, the world will soon be getting more of it. They say you can have too much of a good thing. With CO2, the science tells us, the planet is far, far away from reaching its cornucopia potential.

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