Climate change is thought to be caused by fossil fuels (oil, gas and coal), livestock and forest fires that produce carbon-based greenhouse gases (GHG), primarily carbon dioxide (CO2) and methane. Whether or not politicians’ declarations that climate change is an existential threat to humanity are legitimate, many people think they are, and we must deal with the resulting regulations and policy.
The impact of GHG is measured by the amount of carbon being put into and taken out of the atmosphere. I’ll consider this issue as it relates to forests as in previous articles (June 17 and Nov. 11, 2022, WLJ articles). The Environmental Protection Agency (EPA) and U.S. Forest Service produced reports on forests’ contribution to carbon in the atmosphere (see the References online). These reports are on the national and global scales. For example, Figures 1 and 2 show the total amounts of carbon and GHG emissions for the U.S. as million metric tons of carbon dioxide equivalents (mmt CO2 Eq.).
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These reports are complicated but have good news: overall, forests absorb more CO2 than they emit. Worldwide forests absorb almost half (46%) of the CO2 emissions from fossil fuels each year, although deforestation in the tropics and other factors reduce the net worldwide forest absorption. The net absorption of CO2 in forests in the U.S. is about 12.4% of the total GHG emissions in the U.S. This means that forests actually remove CO2 from the atmosphere. Better forest management could absorb even more
An exception is in the Rocky Mountain region (Montana, Colorado, Utah, New Mexico, Wyoming and Idaho) where more CO2 is emitted than absorbed. This is indicated by the bars above the horizontal line in Figure 1 and yellow color in Figure 2. The other states, especially the southern states, absorb more than they emit, as indicated by the bars below the horizontal line in Figure 1 and the blue color in Figure 2. This is probably due to frequent fires in the Rockies and intensive forest management in the South.
Because the Forest Service and EPA report national and global data, they are hard to relate to everyday experience. I’ll provide a more local assessment to provide perspective at the level of the tree, the log truck load and per acre. I make a lot of assumptions and used data from forestry reports for the weight, water content and other factors which vary between tree species and geographic location (see the References). Consider these as estimates:
A Douglas fir tree:
• Logs 12 inches in diameter at the base, cut into four 16-foot-long logs = 64 feet = 960 pounds.
• Slash, the tree top smaller than 4-inch diameter, branches and needles = 194 lbs.
• Logs + slash = 1,154 lbs. wood.
• 1,154 lbs. – 40% water content = 692 lbs. dry wood.
• Carbon comprises half of dry wood, 692 lbs., dry wood = 346 lbs. carbon.
• The weight of CO2produced from the carbon in wood when it’s burned or decayed is 3.67 X the weight of carbon (CO2/carbon ratio = 3.67).
• 3.67 X 346 lbs. carbon = 1,269 lbs. CO2 = 0.63 tons potential CO2 in the tree.
A log truck load:
• With 28 tons of logs = 56,000 lbs.
• 56,000 lbs. – 40% water content = 33,600 lbs. dry wood.
• With carbon comprising 1/2 of wood = 16,800 lbs. carbon.
• 3.67 X 16,800 lbs. = 61,600 lbs. CO2 = 30.8 tons potential CO2 in a log truck load.
Per acre:
• 132,300 lbs. carbon/acre.
• 3.67 X 132,300 lbs. = 485,104 lbs. CO2 = 242 tons potential CO2 per acre.
The carbon compounds in the tree must be oxidized (burned) to create CO2 with the basic chemical reaction of burning wood:
Cellulose-hemicellulose-lignin (CHO) + oxygen (O2) = CO2 + water (H2O) plus heat.
Trees might not completely burn in a fire. Assuming that 50% or 80% of the wood in a forest burns:
• For a tree 50% burned = 0.32 tons CO2released from a burned tree.
• For a tree 80% burned = 0.51 tons CO2released from a burned tree.
• For a log truck load 50% burned = 15 tons CO2released from a burned load of logs.
• For a log truck load 80% burned = 25 tons CO2released from a burned load of logs.
• For an acre 50% burned = 121 tons CO2released from a burned acre of forest.
• For an acre 80% burned = 194 tons CO2released from a burned acre of forest.
If you prevent one tree from burning, you prevent a half a ton, a truck load of logs (25 tons), and an acre of forest (194 tons) of CO2 emission. Although these numbers are estimates, it is clear that preventing forest fires keeps CO2 out of the atmosphere.
Managing forests by preventing forest fires, harvesting and sequestering wood products, and regenerating young trees after harvest can result in less GHG emissions and more absorption of CO2 into trees. This can be done while maintaining wildlife habitat, livestock grazing, and watersheds, while enhancing local economies and employment with productive industry. — Dr. Matt Cronin
(Matt Cronin is a biologist with Northwest Biology and Forestry Company LLC in Bozeman, MT, croninm@aol.com. He was a research professor at the University of Alaska.)
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