Resource Science: Forest fires, CO2 in harvested and regenerated trees 

You are probably aware there is a lot of media attention, research and government policies regarding climate change, which is thought to be caused by greenhouse gas emissions (carbon dioxide (CO2) and methane) from fossil fuels, livestock and forest fires. You might also have noticed an increase in wind and solar power facilities in the western states with the objective of reducing CO2 emissions from fossil fuels like coal.

Forest fires also produce large amounts of CO2, and it is common sense that reducing forest fires also reduces CO2 emissions, and prevents destruction of timber, wildlife and property. In previous WLJ articles (see the references), I described how timber harvest can prevent forests from burning and locks up CO2 in wood products and regenerates new trees. Trees convert CO2 in the atmosphere into wood cellulose, hemicellulos and lignin, and release CO2 when burned or decayed. The climate change term for locking up CO2 is carbon sequestration. Forests currently sequester 12.4% of the U.S. greenhouse gas emissions and good forest management can substantially increase this.

There are several benefits of managing forests with timber harvest (logging): forests don’t burn and emit CO2, CO2 is locked up in lumber and other wood products, wildlife habitat and livestock grazing can be improved, and local communities benefit from jobs and income. Foresters know how to manage forests to achieve these objectives but are often prevented from doing so by environmental regulations and lawsuits which stop timber harvests. A well-known example is the Endangered Species Act (ESA) listing of the northern spotted owl which stopped timber harvest and devastated the timber industry in the Pacific Northwest. Readers of the WLJ are familiar with similar environmental regulations and lawsuits trying to stop livestock grazing.

I calculated the amount of CO2 (called CO2 equivalents by climate scientists) that could be locked up in harvested wood products and in regenerating trees after harvest. I estimated tons of CO2 in wood products and regenerating trees by converting the volume (board feet) of green wood to weight in tons, minus the weight of the water content of green wood, times the proportion of wood that is carbon, plus the weight of the oxygen combined with the weight of the tree carbon to form CO2 (see the references).

You can see in the table that about 200 to 250 tons of CO2 per acre of forest can be locked up in harvested wood products. Another 123 tons of CO2 per acre can be locked up in new tree regeneration after about 60 years. So, harvest followed by regenerating trees can lock up about 325 to 375 tons of CO2 per acre. The table also shows that the five-year average (2019-23) timber harvest in just one state, Montana, was 334.4 million board feet which represents about 2.2 million tons of CO2 per year. See the references for the information in the table.

These are general estimates because the amount of CO2 in trees will vary considerably depending on the tree species, age and location. Some forests will have more CO2 per acre and other forests will have less. The point is that timber harvest followed by regeneration of new trees will result in more sequestration of CO2 and less CO2 emissions compared to untreated forests that might burn. Timber harvest is a basic objective of forest management, as recognized by the American Loggers Council and the U.S. Forest Service who agree that logging is an effective tool for reducing hazardous fuels and achieving forest management goals.

It is remarkable that forests in the U.S. currently absorb about 12.4% of the total GHG emissions in the U.S. Trees actually remove CO2 from the atmosphere while forest fires emit large amounts of CO2. It is obvious that preventing large forest fires can reduce the amount of CO2 emissions, and timber harvest and regeneration of trees can too. Common sense forest management should be implemented on a large scale to reduce the damage done by forest fires, increase the productivity of our forests, and improve rural economies. — Dr. Matt Cronin

(Matthew Cronin is a scientist at Northwest Biology & Forestry Co. and a teaching professor at Montana State University, Bozeman. He was a research professor at the University of Alaska.)

References and notes

Note: The amount of CO2 (tons)in harvested and regenerating trees is calculated with a conversion of 6.1 tons of green wood per thousand board feet; minus the weight of the water content of green wood (0.4 times green wood weight); times the fraction of wood that is carbon (0.5 times the dry wood weight); plus the weight of the oxygen combined with the weight of the tree carbon to form CO2 (3.67 times the weight of carbon in the tree).