As the world looks for ways to keep carbon dioxide - the greenhouse gas produced by burning fossil fuels - out of our atmosphere, science tells us managed forests will play a key role.
Trees are the most powerful concentrators of carbon on Earth. Through photosynthesis, they absorb carbon dioxide from the atmosphere and store it in their wood, which is nearly 50 percent carbon by weight.
You might be surprised to learn young forests outperform old growth in carbon absorption. Although old trees contain large amounts of carbon, their rate of absorption has slowed to a near halt. A young tree, although it contains little fixed carbon, pulls carbon dioxide from the atmosphere at a much faster rate.
While it is true that cutting down an old tree results in a net release of carbon, new trees growing in their place can more than make up the difference. And wooden furniture made in the Elizabethan era still holds the carbon fixed hundreds of years ago.
The relationship between trees and greenhouse gases is simple enough on the surface. Trees grow by taking carbon dioxide from the atmosphere and, through photosynthesis, converting it into sugars. The sugars are then used as energy and material to build the cellulose and lignin that are the main constituents of wood.
When a tree rots or burns the carbon contained in the wood is released back to the atmosphere. Active forest management, such as thinning, removing dead trees, and clearing debris from the forest floor is very effective in reducing the number and intensity of forest fires. And the wood that is removed can be put to good use for lumber, paper and energy.
The impact of forests on the global carbon cycle can be boiled down to these key points:
On the negative side, the most important factor influencing the carbon cycle is deforestation, which results in a permanent loss of forest cover and a large release of carbon dioxide into the atmosphere. Deforestation - which occurs primarily in tropical countries where forests are permanently cleared and converted to agriculture and urban settlement - is responsible for about 20 percent of global carbon dioxide emissions, according to a United Nations-World Meteorological Organization Intergovernmental Panel on Climate Change report.
Absorbing carbon dioxide
On the positive side, planting fast-growing trees is the best way to absorb carbon dioxide from the atmosphere. Many countries with temperate forests have seen an increase in carbon stored in trees in recent years. This includes New Zealand, the United States, Sweden and Canada. Plus, using wood sustainably reduces the need for non-renewable fossil fuels and materials such as steel and concrete - the very causes of carbon dioxide emissions in the first place.
The good news is that forests in the United States are net carbon sinks, since annual growth exceeds annual harvest. We are currently experiencing an increase in forested land as forests are being re-established on land previously used for agriculture. Catastrophic wildfires are uncommon in managed forests, whereas millions of acres of unmanaged forests burn every year due to excessive build-up of dead trees and woody debris.
Every wood substitute, including steel, plastic, and cement, requires far more energy to produce than lumber. More energy usually translates into more greenhouse gases in the form of fossil fuel consumption or cement production.
Some activists would have us believe using wood is bad for forests. Yet we are the largest per-capita consumers of wood in the world, and North American forests cover approximately the same area of land as they did 100 years ago. According to the United Nations, our forests have expanded nearly 10 million acres over the past decade. This is precisely because we use a lot of wood, which sends a signal to the marketplace to grow more trees to meet demand.
This is a win-win situation for both the economy and the environment. One of the best ways to address climate change is to use more wood, not less. Wood is simply the most abundant, biodegradable and renewable material on the planet.
It is hard to imagine a more all-purpose, environmentally friendly act than that of contributing to the number and variety of trees growing throughout the world. In the age of climate change, Johnny Appleseed takes on a new meaning.
Patrick Moore, a co-founder of Greenpeace, is chairman and chief scientist of Greenspirit Strategies Ltd. in Vancouver, Canada.