UNB Study Changing Forest Carbon Accounting

As concern about climate change increases, the forest’s tremendous capacity to sequester carbon has become an important consideration for forest managers and the public. 

Recent work by Dr. Chris Hennigar is changing forest carbon accounting which will impact management strategies and silviculture prescriptions and help further reduce carbon dioxide (C02) emissions.

Hennigar’s computer modeling builds on the Canadian Forest Service’s national carbon accounting model (CBM-CFS3) which factored both the carbon stored in the forest and the carbon released by forest ecosystem dead organic matter in projecting carbon yields. Hennigar’s doctoral research showed that adding the carbon retained in wood products to the carbon held in the forest significantly increases net carbon storage. His analysis of the J. D. Irving, Limited Black Brook District projected a net carbon increase of 90,000 tonnes per year until 2062 for that land base. According to United States Environmental Protection Agency calculations, this offsets the emissions of more than 16,000 cars.

Living trees sequester carbon dioxide. Once they die from old age or a natural disturbance such as fire or insect outbreak, some of the carbon stored in the trees is transferred to litter, coarse woody debris and other dead organic matter, all of which release carbon dioxide back into the atmosphere. When a tree is harvested before nature takes its course, current carbon accounting rules consider that an immediate release of carbon dioxide. However, carbon is locked in the resulting consumer products like wood flooring and newsprint, often for many years, depending on the product and its use. Eventually, the product goes to the landfill where it begins to break down and release carbon. Hennigar’s simulations factored all stages from living tree to landfill and showed an overall increase in carbon storage of five percent. The modeling also showed that when maximizing total (forest + products) carbon, mean harvest and total carbon storage over 200 years was 173% and 5% higher, respectively, than when maximizing only carbon in the forest. These results indicate that more carbon can be sequestered by harvesting products and re-growing the forest than by setting aside unharvested forest”, said Dr. David MacLean, who has been working with Hennigar. “Carbon stored in the forest and in wood products should be integrated in forest management planning”.

A focus solely on the economic benefits of carbon tied up in forest biomass could result in management strategy of growing individual trees as long as possible, causing a reduction in harvest levels. Fewer wood products would be produced and people would turn to concrete, steel, plastic and other construction products made from fossil fuels, increasing greenhouse gas emissions. Hennigar’s work demonstrates that the “substitution” benefits of using wood in construction are substantial and should be calculated in forest carbon accounting. “We have shown that using renewable wood resources rather than steel and concrete has an important role in influencing forest management strategies to minimize greenhouse gas emissions,” he said.

“This analysis may influence the policy around carbon credit accounting nationally and internationally,” MacLean added.

As trees age, the rate at which they store carbon slows: a forest’s carbon storage capacity is finite. Harvesting trees that are declining in biomass and regenerating stands increases the uptake of carbon.The uptake is repeated each period of new growth, resulting in an accrual in carbon storage.

Pest management strategies also impact carbon sequestration. Measures to reduce tree mortality during insect outbreaks have economic and societal benefits, and protect carbon in living biomass as well as timber supply. If Hennigar’s J. D. Irving, Limited Black Brook District forest simulations are extrapolated to all forests in New Brunswick, results suggest that potential forest carbon losses from a severe spruce budworm outbreak without pest management could increase New Brunswick’s total mean annual greenhouse gas emissions by up to 40% over the next 20 years.

Nova Scotia and Ontario provincial governments are already using this method of carbon accounting in their management strategies.

Hennigar’s work has been published in refereed journals and presented provincially, nationally, and internationally between 2007 and 2010 to such organizations as: FAO, IUFRO, New England Society of American Foresters, Canada’s National Carbon Sinks Committee, the Pollution Probe, and others. This research has been supported by funding from NSERC, the ACOA Atlantic Innovation Fund, Sustainable Forest Management Network Center of Excellence, J.D. Irving, Limited, and the Canadian Forest Service.

– Barb Scott