Climate change and greenhouse gas (GHG) emissions are perhaps the most important science-based issues affecting agriculture and forestry. I previously wrote about GHG emissions from forest fires versus logging (WLJ, June 20), and I estimated that harvesting half of the trees on 100 acres of a forest in the northern Rockies would yield about 1 million board feet (MMBF) of timber, which otherwise might burn and release GHGs. The economic benefits of harvesting timber rather than spending millions of dollars each year putting out forest fires are obvious. There are also benefits of smaller GHG emissions with harvesting timber instead of it burning.
Calculating GHG emissions from forests is complicated, and here I summarize basic information. Wood is composed of carbon-based compounds, including approximately 40% cellulose, 30% hemicellulose and 30% lignin. Most GHGs of concern are also carbon-based compounds, such as carbon dioxide (CO2) that forms when wood is burned or decays.
GHGs in forests are measured from the amount of carbon in wood, not the timber volume (board feet) or total weight of the wood. For example, 1 MMBF of standing timber might weigh 20 million pounds, of which only part is carbon. Wood contains a lot of water and substances other than carbon that don’t contribute to GHGs, so the weight of the wood is not used for GHG calculations, but the weight of the carbon in the wood is.
The U.S. Forest Service calculated the amounts of carbon in the national forests and grasslands in different regions of the U.S. In the Gallatin National Forest in the northern Rocky Mountain region (Montana, northern Idaho and the western Dakotas), there’s about 60 metric tonnes per acre of carbon. One tonne is 1,000 kilograms, which is 2,205 lbs., so 60 tonnes is 132,300 lbs. of carbon per acre in the Gallatin National Forest. This indicates that forest fires can cause substantial emissions of GHGs.
[inline_image file=”dedc97ee9267793b07f3e789e47ad82d.png” caption=”Figure 1. U.S. Forest Service (2015). Carbon stored in harvested wood products (HWP) manufactured from Northern region timber, including wood products still in use and at solid waste disposal sites (SWDS), such as landfills and dumps (Stockmann et al. 2014). MgC = tonne.”]
The Forest Service also assesses the amount of carbon in harvested wood products like lumber and wood in landfills. This wood will not burn or decay for a long time, and it thus doesn’t contribute to GHG emissions. A considerable amount of forest carbon is stored in wood products (see Figure 1) and is not susceptible to forest fires and GHG emissions.
Estimates of the amount of carbon actually emitted from forest fires are not in the reports I read but should be forthcoming in other reports. It is important for forest management to know if logging and the production of wood products result in lower GHG emissions than not logging and the forest possibly burning. This of course depends on if, when, and how intensely a particular forest stand burns.
The Forest Service also estimates the amounts of carbon in different parts of the forest. Most carbon is in the above-ground parts of trees (trunks, branches and foliage), in material on the forest floor and in soil. How much of this carbon is sequestered with logging, or burned by fire, will depend on many factors, such as slash treatment, logging systems and fire frequency and intensity.
Logging results in much of the carbon in trees being sequestered in wood products, and, importantly, regeneration of new trees sequesters more CO2 from the atmosphere. I think this will result in overall lower GHG emissions than forest fires, which burn much of the above-ground trees and material on the forest floor. The following statements from the Forest Service acknowledge these and other benefits of harvesting timber:
“Rates of net carbon sequestration in forests may be enhanced through management strategies that retain and protect forest land from conversion to nonforest uses, restore and maintain resilient forests that are better adapted to a changing climate and other stressors, and reforest lands disturbed by catastrophic wildfires and other natural events (e.g., mortality following windthrow). Harvested wood is of additional importance when considering carbon benefits from forests. Forest restoration and other treatments that generate long-lived wood products, such as lumber and furniture, transfer ecosystem carbon to the Harvested Wood Products pool (HWP) where carbon remains stored and not contributing to net GHG emissions.
“Substitution of wood for more fossil fuel-intensive building materials, such as concrete, steel, or plastic, has a carbon emissions benefit. Forest vegetation treatments also generate excess material (woody biomass) which, if utilized, can be a renewable energy substitute for fossil fuels. Carbon management is, therefore, an increasingly important consideration in (National Forest System) management.”
Foresters, range managers, elected officials, court judges and climate change researchers should be made aware of the potential benefits of timber harvest for reducing GHG emissions. Perhaps this will raise awareness of the need for active forest and range management to counter the seemingly incessant attempts to restrict forestry and agriculture in the name of climate change. — Dr. Matt Cronin
(Matthew A. Cronin is a scientist with Northwest Biology Company LLC in Bozeman, MT. He can be contacted at croninm@aol.com.)
Forest Service. 2015. Baseline estimates of carbon stocks in forests and harvested wood products for National Forest System Units; Northern Region. 43 pp. Whitepaper.
Forest Service. 1990. An Analysis of the Timber Situation in the United States: 1989-2040. Rocky Mountain Forest and Range Experiment Station Fort Collins, General Technical Report RM-199.
Harlow, W.M. 1970. Inside Wood: Masterpiece of Nature. The American Forestry Association, Washington, D.C.
Smith, J.E., L.S. Heath, K.E. Skog, and R.A. Birdsey. 2006. Methods for calculating forest ecosystem and harvested carbon with standard estimates for forest types of the United States. USDA Forest Service, Northeastern Research Station. General Technical Report NE-343.
Stockmann, K., et al. 2014. Estimates of carbon stored in harvested wood products from United States Forest Service Northern Region, 1906-2012. Unpublished report. Missoula, MT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Forestry Sciences Laboratory. 27 p.https://www.fs.usda.gov/treesearch/pubs/46647
University of Tennessee Extension. Estimating weight of logs and standing timber. (SP748.pdf (tennessee.edu)
Mississippi State University Extension. Pine timber volume-to-weight conversions. Publication 2244 (POD-11-19).Pine Timber Volume-to-Weight Conversions | Mississippi State University Extension Service (msstate.edu)).
Notes: Weight and volume calculations.
MBF = Thousand board feet; MMBF = Million board feet; Ton = 2,000 pounds; DBH = diameter at breast height; calculations were done for softwood logs and processed lumber.
Log weight conversions depend on DBH (10” to 36”) and range from 4.4 to 14.0 tons/MBF (Mississippi State Univ. Extension) and average 10.364 tons/MBF =10,364 tons/MMBF = 20,728,571 pounds/MMBF.
Carbon weight in the Gallatin National Forest is estimated 60 metric tonnes/acre (from Forest Service 2015, Figure 7). 1 tonne = 1,000 kilograms = 2,205 pounds; 60 tonnes = 132,300 pounds carbon/acre.
Lumber weight is 0.974 tons/MBF (Forest Service 1990, Table B-7) = 974 tons/MMBF = 1,948,000 pounds/MMBF.
Lumber is estimated as 36.2% of raw log volume (Forest Service 1990, Table B-6): 1 MMBF logs = 362,000 BF (362 MBF) lumber.
