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Which Trees Offset Global Warming Best?

Some trees are better than others at absorbing carbon dioxide

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Aspen trees changing colors in the fall
Jordan Siemens/Digital Vision/Getty Images
Dear EarthTalk: Which trees are best to plant to help combat global warming?
-- Tim C., Perrineville, NJ

Trees are important tools in the fight to stave off global warming, because they absorb and store the key greenhouse gas emitted by our cars and power plants, carbon dioxide (CO2), before it has a chance to reach the upper atmosphere where it can help trap heat around the Earth’s surface.

All Plants Absorb Carbon Dioxide, but Trees are Best
While all living plant matter absorbs CO2 as part of photosynthesis, trees process significantly more than smaller plants due to their large size and extensive root structures. In essence, trees, as kings of the plant world, have much more “woody biomass” to store CO2 than smaller plants, and as a result are considered nature’s most efficient “carbon sinks.”

According to the U.S. Department of Energy (DOE), tree species that grow quickly and live long are ideal carbon sinks. Unfortunately, these two attributes are usually mutually exclusive. Given the choice, foresters interested in maximizing the absorption and storage of CO2 (known as “carbon sequestration”) usually favor younger trees that grow more quickly than their older cohorts. However, slower growing trees can store much more carbon over their significantly longer lives.

Plant the Right Tree for the Right Location
Scientists are busy studying the carbon sequestration potential of different types of trees in various parts of the U.S., including Eucalyptus in Hawaii, loblolly pine in the Southeast, bottomland hardwoods in Mississippi, and poplars in the Great Lakes.

“There are literally dozens of tree species that could be planted depending upon location, climate and soils,” says Stan Wullschleger, a researcher at Tennessee’s Oak Ridge National Laboratory who specializes in the physiological response of plants to global climate change.

Choose Low-Maintenance Trees to Maximize Carbon Absorption
Dave Nowak, a researcher at the U.S. Forest Service’s Northern Research Station in Syracuse, New York has studied the use of trees for carbon sequestration in urban settings across the United States. A 2002 study he co-authored lists the Common Horse-chestnut, Black Walnut, American Sweetgum, Ponderosa Pine, Red Pine, White Pine, London Plane, Hispaniolan Pine, Douglas Fir, Scarlet Oak, Red Oak, Virginia Live Oak and Bald Cypress as examples of trees especially good at absorbing and storing CO2. Nowak advises urban land managers to avoid trees that require a lot of maintenance, as the burning of fossil fuels to power equipment like trucks and chainsaws will only erase the carbon absorption gains otherwise made.

Plant Any Tree Appropriate for Region and Climate to Offset Global Warming
Ultimately, trees of any shape, size or genetic origin help absorb CO2. Most scientists agree that the least expensive and perhaps easiest way for individuals to help offset the CO2 that they generate in their everyday lives is to plant a tree…any tree, as long as it is appropriate for the given region and climate.

Those who wish to help larger tree planting efforts can donate money or time to the National Arbor Day Foundation or American Forests in the U.S., or to the Tree Canada Foundation in Canada.

GOT AN ENVIRONMENTAL QUESTION? Send it to: EarthTalk, c/o E/The Environmental Magazine, P.O. Box 5098, Westport, CT 06881; submit it at: www.emagazine.com/earthtalk/thisweek/, or e-mail: earthtalk@emagazine.com.

EarthTalk is a regular feature of E/The Environmental Magazine. Selected EarthTalk columns are reprinted on About Environmental Issues by permission of the editors of E.

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