Common Misconceptions about Forest Carbon


Misconceptions:

1. "Young stands take up carbon quickly, therefore we should convert old-growth and harvest at max MAI."
2. "It's best to maximize carbon storage in the ecosystem therefore we should stop harvesting."
3. "Bioenergy is always good/clean/C-neutral."
4. "Short rotation managed stands are better at carbon storage than unmanaged stands".
5. "All harvested carbon is stored for a long time."
6. "Converting riparian hardwoods to conifers is a good idea for carbon storage."
7. "Converting conifers to hardwoods is a good idea for carbon storage." 

Diagram of Forest Sector Carbon Flows

1. "Young stands take up carbon quickly, therefore we should convert old-growth and harvest at max MAI."Top

Actually:

  • Harvesting an old stand with a low or zero yield increment and replacing it with a young vigorous stand seems to make sense for mitigating climate change since the growth of the tree is a sign of carbon uptake.  While that statement is true from a "flux" or "annual uptake" point of view, it's less certain when you think about carbon stocks. What are you doing with the harvested carbon? Is it being burned in slash piles, turned into paper or solid-wood furniture? The amount of carbon stored in a 300 yr old stand is huge. It's going to take maybe 250 yrs or more to get back to the same carbon density per hectare.

  • From a carbon storage point of view, longer rotations result in more carbon stored per hectare.  The carbon benefit of longer rotations is not only due to the rate of uptake (which slows after 80-100 years).  The benefit is due to the storage in the biomass and relative balance of the annual turnover (litterfall & mortality) with the decomposition of dead wood and soil carbon. If a stand that's historically been disturbed every 350 years starts to be part of a 30-yr rotation plan there will be a lot of CO2 released from the soil. There just isn't as much carbon being transferred from the living biomass to the dead wood and soil to maintain the carbon stocks on the site. On the other hand, if a site has already been harvested and is part of a short-rotation system, it might be better to maintain the short-rotation and have the carbon stored as forest products.

2. "It's best to maximize carbon storage in the ecosystem therefore we should stop harvesting."Top

Actually:

  • Maximizing carbon storage in the ecosystem makes sense only if society stopped building new homes, acquiring new furniture and consuming in general. If the flow of forest products stops, society will simply turn to other products with higher greenhouse gas footprints, e.g. plastics, metal, or concrete.
    In addition if we were to stop harvesting and continue to try to suppress natural disturbances there is the potential for larger catastrophic disturbances in the future.

3. "Bioenergy is always good/clean/C-neutral."Top

Actually:

  • This misconception stems, in part from an artefact or distortion caused by the GHG accounting rules. All harvested carbon is currently reported as an immediate emission under the forest sector. Therefore, using fibre for energy does not appear as a carbon-emission in a GHG inventory.

  • Wood has a lower energy density than fossil fuels so burning it to produce heat or electricity produces more CO2 per kWh or BTU.

  • Substituting bioenergy for hydro power results in much more CO2 per kWh.

  • Things to consider as arguments to support bioenergy are that the wood is renewable over long timescales (>75 yrs in most cases) and it uses carbon that’s already within the biosphere. As long as the fibre is dead anyways, we’re not adding carbon to the atmosphere that would otherwise be stored in living trees or rock.

4. "Short rotation managed stands are better at carbon storage than unmanaged stands".Top

Actually:

  • This misconception hinges on the assumption that carbon stored in deadwood and soils are inconsequential and decomposition is the same in managed and unmanaged stands. We know that’s simply not true. There would be more storage in the unmanaged stands if the whole ecosystem was considered.

  • This misconception relies on estimates of carbon storage in wood products, landfills & avoided emissions which have uncertainty of +40%. We need better data for BC before we can properly compare unmanaged with short-rotation stands.

  • The fibre produced from short rotation stands may have a shorter lifecycle. Eg Cottonwood, small diameter wood producing low quality/value products.  Wood products from large diameter high value species have been used to build structures that have life expectancies in the hundreds of years. Old timbers and furniture built with high quality wood retain their value and last longer. This wood is easily re-used. Eg timbers in old warehouses.

5. "All harvested carbon is stored for a long time."Top

Actually:

  • Accounting for harvested carbon is complicated and we lack proper decision-support tools. Therefore, people tend to over-simplify, assuming either all harvested carbon is stored permanently or all carbon is emitted to the atmosphere in the same year it’s harvested. The true answer lies somewhere in between. Ignoring imports and exports, anywhere from 25-40% of carbon harvested in BC is probably stored for a long period of time in products.

6. "Converting riparian hardwoods to conifers is a good idea for carbon storage."Top

Actually:

  • The idea is to harvest short-lived alder in riparian areas and replace them with longer-lived and larger conifer species. Over the long term (>75 yrs) that approach may result in an increase in net carbon storage on the site, but there are many risks. These areas may be populated by alder or cottonwood because of a fluctuating water  table or because they are prone to flooding, whereas many conifers require good drainage. Harvesting itself causes a net loss of carbon from the ecosystem through reduced net growth and increased decomposition at the site. In addition, carbon in the soil could be lost through stream-bank erosion. Other non-timber forest values could be jeopardized by harvest activity in riparian areas: e.g. water quality, fish habitat, biodiversity, ecosystem resilience.

7. "Converting conifers to hardwoods is a good idea for carbon storage."Top

Actually: 

  • Many British Columbia conifers have a higher wood density than our hardwoods and therefore more carbon. Coastal Douglas fir for example is equal in wood density to birch and much higher than aspen and cottonwood. Douglas fir is also very fast growing for a longer period of time and lives longer than most native and exotic hardwood species.

  • This misconception probably stems from hardwoods in eastern North America which are high density and long-lived species (e.g. sugar maple, oak).

Click to see larger image.

Carbon is taken up from the atmosphere as trees grow (green arrow). From there, carbon may be released back to the atmosphere (blue arrows) or transferred within the ecosystem or to the forest products industry (yellow arrows). Plant respiration, forest fires and natural decay cause releases of carbon to the atmosphere. Harvesting triggers the release of carbon from forests due to burning for bioenergy and decay. Long-term storage of carbon occurs in the trees themselves, in forest soils, in long-lived forest products and in landfills. (Image credit: C. Dymond and M. Apps)

Ministry Contact

Caren Dymond, Research Scientist, Carbon Modeller

Ministry contact: Evelyn Hamilton.
Please direct questions regarding webpage to For.Prodres@gov.bc.ca

Updated January 2009