Forest Carbon Coalition – Science Synthesis

What are the climate impacts of industrial forest practices

Industrial forest practices include clearcutting, short rotation timber plantations, dense networks of logging roads and both aerial and ground-based application of pesticides and fertilizers. These practices both drive climate change and make the land more susceptible to its effects. Industrial logging is a significant source of greenhouse gas emissions. Road construction, logging, transportation of logs to mills and aerial pesticide spraying  involves heavy equipment that burns diesel and gasoline. Production of lumber, pulp, paper and biomass consumes fossil fuels and emits biogenic carbon as wood residues are burned for energy. The vast majority of carbon stored in trees is lost to the atmosphere as wood products are manufactured, used, and discarded into landfills. Clearcuts and roads remove forests that would otherwise be pulling carbon out of the atmosphere. Newly clearcut sites give off more carbon than they sequester for 10-15 years as logging debris decays or is burned.

In addition to these sources of greenhouse gas emissions and sacrificed sequestration capacity, industrial tree plantations make the land more susceptible wildfires, flooding, drought, heat waves, landslides, invasive species, windstorms and other stressors already on the rise due to climate change. Despite these profound climate impacts, the logging and wood products sector is omitted from official GHG inventories and has not been proposed for regulation under federal or state climate action plans.

Key research on the climate impacts of industrial forest practices:

Evers, C., Holz, A., Busby, S., Nielsen-Pincus, M., 2022. Extreme winds alter influence of fires and topography on megafire burn severity in seasonal temperate rainforests under record fuel aridity. Fire 5, 41.

Link: http://doi.org/10.3390/fire5020041

Summary: In 2020, nearly 800,000 hectares of land were burned in the Pacific Northwest over two weeks under record-breaking fuel aridity and winds. The authors quantified the relative influence of weather, vegetation and topography on patterns of high severity burn. This included a comparison between fire effects on unmanaged, older forest landscapes vs. intensively managed tree plantations.

Key excerpts:

  • “Our results confirm that wind was the major driver of the 2020 megafires, but also that both vegetation structure and topography significantly affect burn severity patterns even under extreme fuel aridity and winds.”
  • “Early-seral forests primarily concentrated on private lands, burned more severely than their older and taller counterparts, over the entire megafire event regardless of topography.”
  • “Meanwhile, mature stands burned severely only under extreme winds and especially on steeper slopes.”

Grant, R.F., Black, T.A., Humphreys, E.R., Morgenstern, K., 2007. Changes in net ecosystem productivity with forest age following clearcutting of a coastal Douglas-fir forest: testing a mathematical model with eddy covariance measurements along a forest chronosequence. Tree Physiology 27: 115-131.

Link: https://academic.oup.com/treephys/article/27/1/115/1674502

Summary: The researchers tested the hypothesis that changes in net ecosystem productivity during aging of coastal Douglas-fir forests could be explained by changes in nutrient uptake, declines in canopy water, and changes in the ratio of autotrophic respiration to gross primary productivity. The paper quantifies the post-harvest emissions from the decay of logging residues, which can last 10-15 years.

Key excerpts:

  • “Many forest ecosystems lose more C from heterotrophic and autotrophic respiration (Rh and Ra) than they gain from CO2 fixation (= gross primary productivity GPP) for several years after a stand-replacing disturbance…”.
  • “This period of net C loss (when net ecosystem productivity (NEP = GPP – Ra – Rh) is negative) may continue for 10 years or longer in Canadian forests (Kurz and Apps 1999, Litvak et al. 2003), for at least 14 years in Siberian pine forests (Schulze et al. 1999), and for 14 (Janisch and Harmon 2002) or 20 (Cohen et al. 1996) years in coniferous forests of the Pacific Northwest.”
  • “During the first 4 years after clearcutting, rapid Rh from fine and coarse litter raised ecosystem respiration Re (= Ra + Rh) while GPP remained low, so that estimated and modeled NEP (= GPP–Re) indicated net C losses of 500 to 750 g Cm– 2 year–1.”

Law, B.E., Hudiburg, T.W., Berner, L.T., Kent, J.J., Buotte, P.C., Harmon, M.E., 2017. Land use strategies to mitigate climate change in carbon dense temperate forests. PNAS 115(14) 3663-3668.

Link:  https://doi.org/10.1073/pnas.1720064115

Summary: The research team examined the relative merits of afforestation, reforestation, management changes, and harvest residue bioenergy use in Oregon using net ecosystem carbon balance as the primary metric. The study also quantified the carbon dioxide emissions associated with the logging and wood products sector. This region represents some of the highest carbon density forests in the world, which can store carbon in trees for 800 years or more.

Key excerpts:

  • “In 2011–2015, net wood product emissions were 34.45 million tCO2e and almost 10-fold fire emissions.”
  • “The net wood product emissions are higher than fire emissions despite carbon benefits of storage in wood products and substitution for more fossil fuel-intensive products.”
  • “Harvest-related emissions should be quantified, as they are much larger than fire emissions in the western United States. Full accounting of forest sector emissions is necessary to meet climate mitigation goals.”
  • “Reforestation, afforestation, lengthened harvest cycles on private lands, and restricting harvest on public lands increase NECB 56% by 2100, with the latter two actions contributing the most.”
  • “Converting 127,000 ha of irrigated grass crops to native forests could decrease irrigation demand by 233 billion m3⋅y−1.”
  • “Utilizing harvest residues for bioenergy production instead of leaving them in forests to decompose increased emissions in the short-term (50 y), reducing mitigation effectiveness.”