Forest Management
There is a firm and growing body of science that shows that active forest management can lower the threat and severity of wildfire and reduce the amount of forest carbon returned to the atmosphere. Such forest management provides jobs, a renewable clean-energy source, and even some budget relief while reducing greenhouse gas emissions.
Forests are tremendous carbon sinks, second only to oceans as Earth's largest repositories of atmospheric carbon. As forests grow, trees and plants absorb carbon dioxide from the atmosphere, release oxygen, and store carbon in roots, branches, needles, leaves and soils. Younger forests, because they grow faster than older forests, excel at removing carbon from the air. Older forests may hold vast carbon reserves dating from the Civil War, but they don't scrub much carbon from today's air. They act like a stagnant carbon "bank account,” holding a steady amount but with little coming in.
Active management can keep forests growing rapidly so they remove carbon efficiently. Thinning the understory to remove undergrowth and ladder fuels that can carry low-level ground fires into tree crowns can help contain wildfires and protect carbon in stored trees. Crown fires release carbon in huge pulses and burn so fiercely that they cannot be suppressed. Managed forests can sequester up to 400 percent more carbon than unmanaged forests.
Young, vigorously growing trees have a higher rate of CO2 conversion than mature trees. Trees typically grow in what is described as a sigmoid curve, with growth rate being greatest in the early to middle years, and dropping off as they reach maturity. When a tree is harvested, about half of the carbon stays in the forest and the rest is removed in the logs, which are then converted into forest products. Some carbon is released when the forest soil is disturbed during harvesting, and the roots, branches and leaves left behind release carbon as they decompose.
Once the harvested area is regenerated, either naturally or by planting seedlings, the forest once again begins to absorb and store carbon. This combination of harvest and re-growth, along with the fact that most wood products store carbon for long periods of time, means that harvesting practices have minimal impact on greenhouse gas emissions.
North American forests are a mosaic of different forest types with different forest ecologies and life cycles. Historically - or at least since the last ice age - these forests have been rotating themselves in keeping with their natural cycle. Most interior pine forests, for example, live for about 120 years and then succumb to either insects or disease, prior to being cleansed by fire and regenerating themselves from the seeds that come from their fire-resistant cones.
In the past century, however, we've stopped allowing wildfires to burn unchecked and, as a result, the average age of our forests has increased. As a tree becomes over-mature, its growth rate declines, and the rate of carbon absorption is reduced. Older trees add less new wood each year and start releasing their stored carbon into the atmosphere as they decompose.