Forest biomass will not reduce
carbon dioxide emissions
Comments on the final Energy Consultation Document
David G. Patriquin
(Professor of Biology, Dalhousie University, retired).
patriquiATdal.ca
Submitted January 27, 2010 to wheelercomments@gov.ns.ca
(Nova Scotia Department of Energy)
The final Energy Consultation Document (the "Wheeler Report") recommends
use of forest biomass as a component of Nova Scotia's renewable energy
strategy, subject to harvesting standards. Unfortunately the report does not
examine the issue of the carbon emissions associated with forest biomass.
Energy generation from forest biomass is commonly assumed to be "carbon
neutral" and therefore, it is argued or assumed, substituting forest biomass for
fossil fuels reduces carbon dioxide emissions. However, that is true only if there
is some carbon capture involved or forests are fertilized to increase productivity.
These are not components of forest biomass harvesting envisaged for N.S., at
least not in the short term (2015).
I submitted a referenced document to the Renewable Energy Consultation
addressing this issue on Dec. 15th and had some discussion with Dr. Wheeler
about it. He commented that "we will be making clear the need for life cycle
assessments of the carbon costs and benefits of biomass". However, the only
reference to Life Cycle Assessments is on page 42:
It is also recommended that renewable energy standards be reviewed based on
scientific assessments of carbon life cycle considerations and in due course be amended
to recognize that co-firing of biomass in NSP coal fired plants could make a significant
contribution to renewable energy and climate change mitigation targets.
That statement in fact repeats the erroneous assumptions I refer to above, at
least to the extent it refers to forest biomass.
I think that one reason my comments were not taken seriously, perhaps
understandably, is that forest biomass has been treated as carbon neutral under
the Kyoto Protocol. Indeed, that puzzled me, as the scientific papers cited in my
submission were unequivocal in this regard. After submitting my comments to the
Renewable Energy Consultation, I discovered that a key paper addressing this
issue had recently been published in the Policy Forum of the prestigious journal
Science*. This multi-authored paper points out that there is a critical accounting
error in the Kyoto Protocol that allows biomass energy to be treated as carbon
neutral, regardless of the source. The error is very large for forest biomass.
There is no doubt that this error will now be corrected and that the carbon
balance for forest biomass will be examined much more critically in future.
*Fixing a Critical Climate Accounting Error, by T. D. Searchinger et al., Science,
Vol. 326. no. 5952, pp. 527- 528 (23 October 2009).
I urge the Government of Nova Scotia to give serious attention to this issue in
relation to possible forest biomass initiatives. The carbon emissions issue,
combined with biodiversity, environmental and sustainability concerns associated
with clearcutting in N.S., could garner forest biomass a reputation as "dirty
energy". On the other hand, we could reduce our carbon footprint by cutting back
on clearcutting to allow increased sequestartion of carbon by forests. Further,
there are biomass schemes cited in the Wheeler Report that would be carbon
neutral or even result in some net sequestration of carbon, e.g., use of grass or
fast growing trees grown on otherwise unused agricultural lands, and such
schemes should be pursued.
I have appended two documents that elaborate further on this topic.
- Clearcutting N.S. Forests for Biomass: Implications for Carbon
Sequestration and Sustainability. (My submission to REC at Dalhousie
University)
- The Biomass Issue: We should pay woodlot owners to store carbon,
not to burn it! (A perspective published in a recent WRWEO newsletter.)
Thank you for receiving these comments.
David G. Patriquin
Appended Document 1
Clearcutting Nova Scotian Forests for Biomass: Implications for Carbon Sequestration and Sustainability
Comments submitted to the Nova Scotia Renewable Energy Stakeholder Consultation Process in response to the Interim Report To Stakeholders (December 15th 2009)
David Patriquin
Professor of Biology, Dalhousie University (Retired)
Dec 15, 2009.
From the Report to Stakeholders (Dec. 15, 2009):
There is an emerging consensus between the various parties (DNR,
forest managers, academics and industry) that there is sufficient forest biomass to support up to 150 MW of electricity generation. But more discussion regarding forestry management standards and the assurance of ecological integrity of Nova Scotia's forests is required.
I suggest that in addition, we need to give careful consideration to the implications of various regimes for net carbon sequestration. Because of the history of forestry in Nova Scotia, our forests are relatively young, averaging perhaps 40 years1. Left undisturbed after clearcutting, forests in northeastern North America continue to accumulate carbon and sequester atmospheric carbon dioxide for well over 100 years2. If we clearcut our forests for biomass, whether by whole-tree or stem-only harvest, the implications for net carbon sequestration must be taken into account - at least if we want to reduce CO2 emissions, as well as substitute for petroleum based energy generation.
Whether or not harvesting biomass for energy is carbon neutral depends very much on site and process specific factors.3 I suspect that detailed carbon accounting would show that clearcutting forest for biomass would be far from carbon neutral for the typical Nova Scotian scenario; it would in fact reduce net carbon sequestration substantially. The contention that biomass is carbon neutral is based on the assumption that the carbon dioxide released when biomass is burned (or respired) is taken up stoichiometrically when the biomass crop re-grows. For biomass crops such as switchgrass or sugarcane, the CO2 released on burning can be recaptured within one growing season; if it is grown on degraded land with fertilization, there can even be net carbon sequestration. Harvesting standing forests for biomass is, however, a quite different matter. If we clearcut a 40 year old forest now for biomass energy, all of the harvested biomass carbon is going into the atmosphere now; then it will take a full 40 years to take up an amount of carbon dioxide equivalent to that released, assuming that the forest recovers to its previous state. So, in the short term, e.g., over the ensuing decade at least, burning of the forest biomass will result in net carbon emissions.
Further, in order to realize carbon neutrality over 40 years, we have add to the carbon that needs to be recaptured: (i) losses of soil carbon associated with clearcutting (ii) carbon costs of harvesting and processing the biomass, (iii) the additional carbon that would have been taken up had the forest not been cut. To the extent that these amounts (including the initial biomass carbon) are not recaptured, there will be net emissions of carbon dioxide to the atmosphere.4
It is for this reason that biomass energy schemes of this sort are generally considered to cause net emissions of CO2 unless there is (i) significant carbon capture and storage associated with the combustion of the biomass and/or (ii) conversion of a significant portion of the harvested biomass into a slowly degrading form (carbonization, biochar) and/or (iii) biomass production sites are fertilized to substantially increase productivity over background levels.5
In the short term (2015), forest biomass projects in N.S. are not likely to involve any of these three conditions. Further, in considering forest biomass as a substitute for fossil fuels, the lower efficiency of biomass compared to fossil fuels in generating electricity must be taken account. Given the potential of N.S. forests to sequester carbon if they are NOT harvested, a full carbon accounting would likely indicate that we could reduce carbon emissions much more by substantially reducing clearcutting in Nova Scotia than we could by substituting clearcut forest biomass for fossil fuels in power generation.
At the very least, we need to do this sort of carbon accounting before embarking on an ambitious forest biomass cutting to meet 2015 substitution goals.
Recent studies/modeling by forest and ecology scientists in relation to using forest biomass in the well-studied Massachusetts forests provide an example. Thompson et al.6 modeled the implications of potential future demand for biomass electricity of around 165 MW, which would require up to 2 million Mg of woody biomass annually from Massachusetts forests:
Changes in species composition were small, but present, under the biomass energy scenarios, with white pine and red oak increasing relative to the baseline scenario, and black birch, beech, and hemlock decreasing. Living aboveground biomass increased by 2.0%, from 225 to 229 Mg/ha under the baseline scenario, while decreasing to 207 Mg/ha (-7.9%) and 201 Mg/ha (-10.7%) in the two biomass scenarios. The difference in standing biomass translates to a net carbon sequestration of 1.9Tg over 50 years under current trends, compared to a 7.3 and 9.9Tg of net emissions in the biomass energy scenarios. In spite of this, the amount of biomass feedstock harvested in the biomass future scenarios was only enough to generate 90 and 100 MW of power, well short of potential future demand. These results indicate that demand for biomass energy is likely to greatly increase the importance of harvesting as a disturbance on the forest landscape. Furthermore, pursuing a renewable energy policy that relies heavily on biomass power is likely to come at the cost of a diminished forest carbon sink.
The Massachusetts forests occur on better soils than in Nova Scotia and have been subject to much less clearcutting. We could expect equivalent or larger effects on carbon sequestration in N.S. forests.
Sustainability
As emphasized by Goldmsith in 19801, an important factor to be considered in relation to repeated clearcutting, whatever the use, is loss of nutrient capital in the harvested forest biomass and through enhanced erosion and leaching: at some time in the future, that will result in lower forest productivity and reduced uptake of carbon dioxide. Susceptibility of N.S. forests to this type of degradation is especially high in SW Nova Scotia because of acid rain and the poor buffering capacity of soils on granitic bedrock.7 Loss of calcium is a key concern for both forests8 and the downstream riparian and aquatic systems.9 Other regions of N.S. might be able to withstand repeated clearcuts for a longer period, but that is only a matter of degree and, as illustrated by the Massachusetts study, clearcutting for biomass even on better sites is likely to increase carbon emissions, not reduce them.
Conclusion
There is a role for forest biomass in energy production in N.S., e.g., using processing wastes, selective cutting for firewood, growing fast growing trees coupled with use of biosolids as fertilizers, especially when combined with energy efficient conversion technologies and/or carbon capture/biochar production. However, clearcutting forests for biomass energy is a questionable strategy. Indeed, given the generally degraded state of Nova Scotia's forests and evidence that our forests go on accumulating carbon for well over 100 years after a clearcut, a case could likely be made for gaining carbon credits by substantially reducing the current annual cut in Nova Scotia, even with ongoing use of fossil fuel to generate energy (where we might otherwise substitute clearcut forest biomass).
References
1. Pannozzo, L. & Colman, R. 2008. GPI forest headline indicators for Nova Scotia
Haifax: GPI Atlantic. For the history of forest harvesting in N.S., see Goldsmith, F.B. 1980. An Evaluation of a forest resource a case study from Nova Scotia. Journal of Environmental Management 10:83-100
2. Wofsy, S. 2004. The Harvard Forest and understanding the global carbon budget. Chapter 19 in Forests in time; The environmental consequences of 1000 years of change in New England (D.R. Foster & J.D. Aber, eds). New Haven: Yale University Press. For data pertinebts to N.S, see Diochon, A et al. 2009. Looking deeper: An investigation of soil carbon losses following harvesting from a managed northeastern red spruce (Picea rubens Sarg.) forest chronosequence. Forest Ecology and Management 257: 413-420.
3. Schlamadinger, Bet al., 2001, Carbon sinks and biomass energy production. A study of linkages, options and implications. Climate strategies Network, London. Available at www.climate-strategies.org
4. Ornstein, L. 2009. Replacing coal with wood: sustainable, eco-neutral,
conservation harvest of natural tree-fall in old-growth forests An editorial essay.
Climatic Change 97:439-447
5. Christian, A. et al. 2006. Carbon capture and storage from fossil fuels and biomass: Costs and potential role in stabilizing the atmosphere. Climatic Change 74: 47-79.
6. Thompson, J. et al. 2009. Biomass energy and a changing forest landscape: Simulating the effects of intensified timber harvest for biomass energy. Poster presentation at 2009 LTER All Scientists Meeting, Sept. 14-16th 2009, Estes Park Colorado. Available at http://asm.lternet.edu/2009/posters/biomass-energy-and-changing-forest-landscape-simulating-effects-intensified-timber-harv
7. Clair, T.A. et al. 2007. Freshwater acidification research in Atlantic Canada: a review of results and predictions for the future Environmental Reviews 15: 153-167.
8. Freedman, B. et al. 1986. Biomass and nutrients in Nova Scotia
forests, and implications of intensive harvesting for future site productivity.
Forest Ecology and Management 15, 103-127.
9. Jeziorski, A. et al. 2008. The widespread threat of calcium decline in fresh waters. Science 322, 1374
Appended Document 2
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