As I walked through a local tree farm recently, I noticed signs pointing out the timber, wildlife, and recreation values of the forest. In the Northeast, we are accustomed to thinking of the woods as places where deer, sawlogs, and walking trails abound. But is it also possible that forests could help regulate our climate?
According to a panel of over 2,000 scientists, the earth’s surface has warmed 0.5 to 1.0˚F since the late nineteenth century. During this same period, the concentration of CO2 in our atmosphere has increased 30 percent, while fossil fuel emissions have tripled. Carbon dioxide in our atmosphere acts as a greenhouse gas and helps trap heat – which has the potential to lead to global warming.
Whether you are a skeptic or believer in global warming, it may interest you to know that our forests might be able to help modify the carbon balance of our atmosphere. Forests have a natural ability to take in carbon dioxide and to use it for creating living tissue – wood, leaves, and roots. As trees grow, they convert this carbon dioxide into wood via photosynthesis. In a sense, trees act as CO2 scrubbers for our atmosphere.
But forests not only store carbon but also they emit it. As trees die and decay, or as wood is burned, the carbon they’ve stored in their boles and branches is released to the atmosphere as CO2. For example, in a typical timber harvest, only about a third of the carbon removed in trees is stored in a product that will hold on to that carbon for 100 years or more. The remaining carbon is released from tree parts that are left behind to rot, burned off through processing, or stored temporarily in short-lived products such as paper.
The carbon balance of a forest is based on the amount of carbon the forest accumulates and holds (known as sequestration), minus the amount lost when it is disturbed or converted to development. In 1999, it is estimated that forests in the U.S. sequestered 310 million metric tons (MMT) of carbon. In that same year, U.S. carbon emissions (from all sources, including timber harvesting and fossil fuel use) totaled 1,460 MMT.
In the Northeast, we have a landscape dominated by forests. According to data from the U.S. Forest Service, the Northeast gained about 580,000 acres of forestland between 1982 and 1997 (Vermont and New York gained while New Hampshire and Maine lost). State governments are now thinking about how we could take advantage of our forested landscape and manage land to take up carbon.
The experts say that, in order to contribute to climate protection, forests would have to be managed so that they take up more carbon in the future than they have in the past. And they must store that carbon for a period of 100 years or more in order to contribute significantly. While the science is still coming together, three basic practices may help maintain or increase carbon uptake and storage in the Northeast: conservation of forestland, restoration of forestland, and carbon-savvy forest management.
Protecting forests from development and re-growing areas that have been deforested can expand carbon storage in the Northeast by increasing the potential for carbon uptake. Savvy forest management for carbon storage will allow the forests to grow more wood than dies or is harvested each year and will allow the average age of our forests to increase.
Most people assume that young forests are better at storing carbon than old forests. There is some logic to this perspective. After all, young forests do grow faster and are generally more vigorous. But while small trees in young forests grow and accumulate carbon at a higher annual percentage rate than old forests, old forests with large trees generally have higher carbon stocks and accumulate greater amounts of carbon each year. Increasing the average age of the forest so that a stand reaches its maximum annual growth before harvesting, therefore, will increase carbon storage.
The age of most industrial forests in New England ranges from 50 to 80 years, whereas pre-settlement forests were often 150 to 250 years old. Forest ecologists have suggested that forest age can be increased by leaving more large trees behind at the time of a harvest and extending the time between harvests.
So can trees protect our climate? As decision-makers struggle with climate policy, there may be an opportunity to work with forestland owners to provide incentives for forest management that not only offers wood, wildlife, and recreation but also contributes to climate protection.