Ask the Conservationist

Save a Tree, Save How Much CO2?

A reader from Ohio helped save 170 acres of forest from development. But now he’s wondering if such efforts to save small forest tracts really have much of an impact. Our conservation director adds up the numbers and calculates the carbon savings of this grassroots effort—find out his conclusion.

Kip Sekulic of Avon Lake, Ohio, writes:

I wonder what the small efforts of saving trees mean? Our town was successful in saving approximately 170 acres of woods (maple and oak) from development. It was a grassroots, citizen-led effort that has now donated the property to our Metro Parks System. Another reason for doing this type of activity is to help control the emission of carbon dioxide. Can anyone estimate the effect of keeping 170 acres of trees?

Bill Stanley, the conservation director for The Nature Conservancy in Ohio, replies:

First off, thanks for doing your part for conservation, Kip.

As you seem to know, forests not only have ecosystem, biodiversity, recreational, social and aesthetic values, they also capture and lock up heat-trapping gases that are contributing to climate change.

I think all of us learned at some point that plants do this wonderful thing called photosynthesis. Trees absorb carbon dioxide and convert it into solid carbon in the form of leaves, bark, wood and roots, as the trees grow. Unfortunately, once a tree is cut down and burned or left to decay, this solid carbon is broken down and released into the atmosphere as carbon dioxide gas.

In fact, about 15 percent of annual global greenhouse gas emissions are from deforestation. That’s more than all planes, trains and automobiles combined.

To get back to your question, a 170-acre tract of woods can capture and store a surprisingly large amount of carbon. How much depends quite a bit on the composition, age and quality of the forest. Despite having not yet been in your neck of the woods to measure carbon, I can still give you a ballpark answer for the carbon benefit of preserving 170 acres of woods containing oak and maple.

First, I will assume that the forest is around 55 years of age (probably a decent guess for your area) and well stocked (meaning not a lot of harvesting has occurred). Since the answer will also vary depending on whether oak or maple is the dominant species (differences in the growth rates, relative sizes, and densities of various species influence the amount of carbon they capture over time), I will give you an estimate for both.

At 55 years, 170 acres of well-stocked oak/hickory forest in your region contains about 41 thousand metric tons of carbon dioxide, while a similar maple/beech forest would contain about 28 thousand metric tons of carbon dioxide. A good estimate may be around 35 thousand metric tons of carbon dioxide. For context, on average, cars emit around 5 tons of carbon dioxide per year. So your 170-acre tract has pulled in the emissions of almost 130 cars per year, over the last 55 years. Not bad.

To do this quick estimate I had to make some other assumptions. For example, I didn’t consider the likelihood that the amount of carbon preserved in the soil increased over time, which would have made the numbers higher. On the other hand, I also assumed the forest would have been completely converted (e.g. into a strip mall rather than a development where some trees are left standing), and that no wood was harvested and made into long-term wood products (e.g. furniture) where the carbon would have remained out of the air for a long time. Even so, taking whatever your situation might be into account, we would still find that  your work to protect the forest has helped quite a bit.

Another positive thing to remember is that a forest left standing continues to grow, while an area converted to development doesn’t. As such, in another 30 years, the forest would have grown and captured something like 9 thousand metric tons more of carbon dioxide. While your forest will grow more slowly as it ages, it will still be doing its thing for the planet.

You might also be interested to know that The Nature Conservancy has been working on a forest conservation project of roughly twice the size of your town’s example, down in the Lower Mississippi Valley in Louisiana, called the Tensas River Climate Action Project.

*Calculations based on “Evaluation Tool for Reforestation- and Afforestation-based Carbon Sequestration Projects in the United States,” developed in 2006 by The Nature Conservancy and WestWater Research, LLC, and funded by a generous grant from the Department of Energy.

Originally posted in March 2011.



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