High carbon stock forests around the world have an important part to play in the capture, storage and release of carbon in the fight against global warming.
When people talk about greenhouse gas (GHG) emissions, one of the most maligned gases is carbon dioxide. Excess carbon in the atmosphere is not good, but carbon is one of the essential gases that make life on earth possible. Forests both store and release significant amounts of carbon as part of a natural cycle. And good forest management not only reduces a forest’s potential as a carbon source, it can also increase the effect of its carbon storage capacity.
- The boreal forest is a carbon source and sink
Carbon moves in and out of the atmosphere through a natural process called the carbon cycle. This is where carbon gets exchanged among oceans, soil, rocks and plant life. Forests actually contain a tremendous amount of carbon. In fact, there’s more carbon in living trees and plants, as well as in a forest’s organic matter and soil, than there is in the atmosphere.[i]
Some years, forests hold more carbon than they release. When they capture more CO2, they are called carbon sinks. But carbon is part of a ‘catch and release’ cycle, and with that much carbon, these same sinks can sometimes become major carbon sources. For example, trees can burn or fall prey to insects and ultimately decompose. In either case, they release the carbon they once held back to the air.
- Forestry supports carbon sequestration
The process of capturing CO2 from the atmosphere and storing it for a long time is called sequestration. Trees store carbon by converting CO2 into plant material through photosynthesis, which uses the energy from the sun and releases oxygen.
When a tree is harvested and milled into lumber, a small amount of that carbon escapes, but most of it remains trapped within the cellular structure of the wood, effectively prolonging the effect of sequestration.
Replacing dying or low productivity stands can improve a forest’s ability to capture and store carbon and contribute to climate change mitigation. This can be done by planting tree mixes that are more resilient and protecting young sprouts from damage after harvest.[ii]
- Forest fires and insects release more carbon than harvesting
Less than 0.5% of managed forests are harvested annually in Canada, according to Natural Resources Canada (NRCan). And these areas regenerate so that there is substantial new storage of carbon occurring in any given year.
The amount of carbon released into the atmosphere from harvesting activity is small when compared to the amount released by forest fires through combustion and insect infestations that kill trees and cause premature decomposition. On average, areas affected by forest fires, for example, are 2.5 times larger than areas harvested, according to NRCan, representing a significant amount of carbon that goes up in smoke.[iii]
- The boreal forest holds a lot of carbon, but tropical forests hold more
For a long time, the boreal was thought to sequester more carbon than tropical forests. This was based on an understanding of global airflow that has since been revised. (Researchers at the National Centre for Atmospheric Research in Colorado studied measurements made by aircraft and concluded that existing climate models were underestimating the carbon absorption of tropical forests.[iv])
A recent NASA study estimates that tropical forests annually absorb 1.4 billion metric tons of carbon dioxide out of a total global absorption of 2.5 billion metric tons. Researchers say that this is more than the amount absorbed by the boreal forest in Canada, Siberia and other northern regions.
- Deforestation in tropical forests emits carbon
Countries in which tropical forests are found can be less stringent when it comes to sustainability practices. Slash and burn harvesting is common, where all the trees are cut and only select wood is removed, with the rest left to decompose. This generates a tremendous amount of methane, which is one of the worst gases when it comes to global warming potential, trapping 56 times more heat than carbon emissions over its first 20 years in the atmosphere.[v]
- There are many ways to measure carbon storage
The boreal forest’s potential as a carbon sink is widely accepted, but what is not clear is exactly how much carbon is actually stored. That’s because measuring carbon storage is not straightforward; results differ depending on the approach. Canada, for example, estimates forest carbon stocks, changes in carbon stocks, and emissions of non-CO2 greenhouse gases in its managed forests using the National Forest Carbon Monitoring, Accounting and Reporting System.
If you look at the absolute carbon stored in the boreal, there is a substantial amount. But if you look at a forest’s capacity to sequester carbon over time, the tropical forest has more potential. Effectively, there is little agreement on what makes a high carbon stock forest. One way to gain perspective is to develop a consensus among researchers so that studies can be compared and uncertainties addressed.[vi]
- There are many ways to maximize carbon sequestration
Besides supporting more research, the Canadian government is looking at a number of strategies to optimize the carbon storage potential of its forests. One study shows that a mix of strategies – depending on location – can maximize carbon sequestration potential over the long term. The combination of the “better utilization” approach (increasing the utilization of wood harvested and ensuring that a higher percentage of residues are used as fiber inputs and/or in bioenergy production), along with promoting the development of products that can store carbon for longer, was by far the most effective strategy for most Canadian forest locations.
- Lowering harvest volumes is not always a good way to improve carbon sequestration
Simply reducing harvest volumes in Canadian forests is not the only way to improve a forest’s carbon sequestration potential.[vii] This is an idea supported on a global scale by the United Nations International Panel on Climate Change. This U.N. report explains that the largest GHG emission mitigation benefit, in the long term, comes not from reducing harvest volumes but from adopting a sustainable forest management strategy aimed at maintaining or increasing forest carbon stocks, while producing an annual yield of timber, fiber or energy from the forest.[viii]
[i] http://www.sfmcanada.org/images/Publications/EN/C02_Sink_EN.pdf
[ii] http://www.nature.com/news/carbon-sequestration-managing-forests-in-uncertain-times-1.14687
[iii] http://www.nrcan.gc.ca/forests/climate-change/13097
[iv] http://news.discovery.com/earth/plants/tropical-forests-gulp-co2-slowing-climate-change-150106.htm
[v] http://unfccc.int/ghg_data/items/3825.php
[vi] http://www.nature.com/news/carbon-sequestration-managing-forests-in-uncertain-times-1.14687
[vii]http://www.academia.edu/4461702/Effects_of_harvesting_on_spatial_and_temporal_diversity_of_carbon_stocks_in_a_boreal_forest_landscape; http://www.nrcresearchpress.com/doi/abs/10.1139/er-2013-0039#.VQNEh47F_Mg
[viii] https://www.ipcc.ch/pdf/assessment-report/ar4/wg3/ar4-wg3-chapter9.pdf
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