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Just Breathe

July 15, 2010

Take a deep breath.

Hold it.

OK, now let it out.

You just took a nice deep intake of oxygen and let out carbon dioxide.

Simple science. You know this.

You may also know that trees absorb carbon dioxide and give off oxygen.

In fact, CarbonDay.com says a single tree produces approximately 260 pounds of oxygen per year, meaning two mature trees provide enough oxygen for a family of four. And the USDA Forest Service says in 50 years one tree produces $31,250 worth of oxygen, provides $62,000 worth of air pollution control, recycles $37,500 worth of water and controls $31,250 worth of soil erosion.

Carbon dioxide is the leading heat-trapping gas contributing to global warming. And trees are a big player in the carbon dioxide absorption picture. One person causes about 10 tons of carbon dioxide to be emitted a year. One tree removes about 1 ton of CO2 per year, and 1 acre of trees absorbs 2.6 tons of CO2 per year.

What you may not know is that trees use carbon dioxide to grow, according to Scott Maco, manager of ecosystem services at The Davey Institute.

And forests in the eastern U.S. appear to be growing at a faster rate in response to rising CO2 levels, according to new research in "The Proceedings of the National Academy of Sciences."

The study focused on trees in mixed hardwood stands on the western edge of the Chesapeake Bay in Maryland that are representative of much of those on the Eastern Seaboard. All of them are growing two to four times faster than normal. After controlling for other variables, scientists concluded that the change resulted largely from the increase in CO2.

Geoffrey Parker, a co-author of the research and an ecologist with the Smithsonian Environmental Research Center, Edgewater, Md., said his research indicated local forests were adapting to the rise in carbon dioxide by absorbing more.

Parker has been studying these 55 stands of trees since 1987. And recent censuses have shown that compared with earlier years the trees are packing on weight at an additional 2 tons per acre annually; he tracks speed of growth through tree diameter.

Though many variables can affect tree growth, Parker ruled out all causes for recent growth except for warmer temperatures, a longer growing season and the rising level of CO2 in the atmosphere. Carbon dioxide levels around the research center have increased 12 percent in the last 22 years.

Whether or not this trend can be sustained is unclear. This is mainly because other limiting factors may come into play like water availability and soil nutrients, according to Parker.

Since the trees in Parker's study are similar to those common to most of the Eastern Seaboard, he's eager to know whether others in the area are finding similar results.

Whether in a forest setting like in this study or on a more individual basis, "trees are very important to the carbon sequestration picture," Maco says.

There are two ways trees affect greenhouse gases. First, they directly sequester carbon from the atmosphere through photosynthesis. "Basically, they take in carbon through their leaves and store it in their roots, trunk, branches and leaves," Maco says. "They hold it there until the tree dies and composes and then the carbon is released again."

Second, trees reduce the energy people use, which also reduces carbon in the atmosphere. Since the production of fossil fuels emits carbon, and fossil fuels are used for energy, a reduction in energy use is a reduction in carbon, Maco explains.

And - a sizeable side benefit - it's not just carbon trees absorb - they also cleanse the air by intercepting other air pollutants like nitrous oxide, sulfur oxide and particulate matter, so the air you breathe is cleaner, Maco says.

What do you think? Do you breathe easier knowing the trees around you are providing oxygen and reducing carbon and pollution in the air? 

Want to figure out how much your current trees or planned tree additions help cool your home and save energy? Visit the National Tree Benefit Calculator. It allows anyone to make a simple estimation of the environmental and economic benefits individual street-side trees provide. Just type in your zip code, tree species and tree size and you'll get an idea of the annual monetary value of your trees.

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