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Wood Bioenergy Carbon Accounting –
Beyond Carbon Neutrality
2011 National FIA User Group Meeting
Sacramento, CA
March 8-10, 2011
Ken Skog, Project Leader
USDA Forest Service
Forest Products Laboratory
Madison, Wisconsin
Topics
What are the “right” or “helpful” research questions to ask
about wood bioenergy carbon emission offsets?
A Joanneum Research study – GHG offsets by wood
source over time
– Carbon neutrality number over time – CN(t)
• Logging residue [temperate forests]
• Intensified thinnings [Austria]
• Intensively managed forest plantations
– on fallow ag land
– by clearing existing forest (if time)
More forestry research questions
Possible “right” or “helpful” questions
(my translation of sources)
Searchinger et al. – to what degree does an increase wood energy
use decrease GHG emissions [over time] by alteration of forest
growth/ emissions.
6/18/2010 letter from Forestry groups to EPA Administrator – Is an
increase in wood energy use “good” as long as forests are
managed sustainably and forest carbon is increasing? (letter says
yes) Good? = less carbon emissions “overall” to the atmosphere?
Manomet study – How quickly (years) and by how much will
emissions from fossil fuel power system be offset by increasing
use of Mass. forest biomass in selected wood-power systems?
Joannuem Research – By increasing use of a specific source of
wood fuel use in place of fossil fuel for power, what fraction of a
fossil systems emissions would be offset by using specific wood
sources in t years?
Question: By increasing use of a
specific source of wood fuel use in
place of fossil fuel for power,
what fraction of a fossil power
emissions would be offset by using
specific wood sources in t years?
Bioenergy
system
Fossil fuel
system
Source: Giuliana Zanchi
Setting up the problem - 1
Focus:
– What is the emission offset of an increase in
wood use ( to a new constant level) to make
electric power/ heat and power
Assume
– kwh / kg wood carbon = kwh / kg of coal carbon
– Kwh / kg natural gas carbon = 0.6 kwh / kg wood
carbon
Exclude emissions to obtain and transport wood or
fossil fuel
Setting up the problem - 2
Compute carbon neutrality number, CN(t)
– Fraction of fossil emissions offset by time t
by increase in wood use from a given source
CN (t) = [EFF(t) – NEw(t)] / EFF(t)
EFF(t) = Cumulative fossil fuel emissions avoided
NEw(t) = Cumulative wood emissions to time t –
Change in forest growth/ emissions due wood energy
use to time t
CN(t) < 1 cumulative net wood emissions > than fossil emissions
CN(t) = 0 cumulative net wood emissions = fossil emissions
CN(t) = 1 net wood carbon storage totally offsets fossil emissions
Examples: CN(t) for wood use from
1. Additional harvest from a managed forest
2. Logging residues from a managed forest
3. New plantations on fallow land
4. New plantation after harvesting existing forest
Illustrative case studies
Model: GORCAM (Graz Oak Ridge Carbon Accounting Model)
Growth curve based on Austrian yield table for Spruce
No disturbances included
35
1.5
1.0
15
0.5
5
-5 0
50
100 150
0.0
200 250 300 350 400
CN
Emissions (Gg CO2)
25
• Biomass net emissions
(green)
• Fossil fuel emissions
(orange)
• CN factor (black)
-0.5
-15
Biomass
Fossil Fuel
-25
-1.0
CN
-35
-1.5
Year
Source: G. Zanchi
1. Additional fellings from a managed forest (1)
Rotation period: 90 years
Rotation forest: 90 hectares
Harvesting:
a) Baseline: 60% of increment
b) New Management: 80% of increment
The additional biomass is used for bioenergy
C stock
50
1000 tC
40
30
20
Bioenergy system
10
Fossil fuel system
(baseline)
0
-270
-180
-90
0
90
Year
180
270
360
Source: G. Zanchi
1. Additional fellings from a managed forest (2)
Rotation period: 90 years
Rotation forest: 90 hectares
Harvesting:
a) Baseline: 60% of increment
b) New Management: 80% of increment
The additional biomass is used for bioenergy
35
1.5
1.0
15
0.5
5
-5 0
50
100 150
0.0
200 250 300 350 400
-0.5
-15
Biomass
Fossil Fuel
-25
-1.0
CN
Emissions (Gg CO2)
25
• Biomass net emissions
(green)
• Fossil fuel emissions
(orange)
• CN factor (black)
• CN(t) = 0 at ~ t = 180 yrs
• CN(400) = ~ 0.5
CN
-35
-1.5
Year
Source: G. Zanchi
2. Felling residues from a managed forest
30
1.5
20
1.0
10
0.5
0
0.0
400
0
50
100
150
200
250
300
350
-10
• Biomass net emissions
(green)
• Fossil fuel emissions
(orange)
• CN factor (black)
CN
Emissions (Gg CO2)
• Rotation period: 90 years (90 ha)
• Baseline: Logging residue left in the forest
• New Management: 2/3 logging residue to bioenergy
For a coal alternative
CN(30) = 0.6
-0.5
Biomass
Fossil Fuel
-20
-1.0
If natural gas is the alternative
CN(30 ) = 0.3
CN
-30
-1.5
Year
Source: G. Zanchi
3. New plantations
• Baseline: low carbon change land (e.g. cropland)
• New Management: new forest to produce bioenergy (no forest land
use change)
100
100.0
75
10.0
25
0
0
100
200
300
1.0
400
-25
-50
-75
Fossil Fuel
Biomass
CN
CN
Emissions (Gg CO2)
50
• Biomass net emissions
(green)
• Fossil fuel emissions
(orange)
• CN factor (black)
0.1
• CN(t) >1 for all t
-100
0.0
Year
Source: G. Zanchi
Forestry research questions for the U.S.
on wood energy carbon offsets
For logging residue – what is CN(t) by location? (generate
U.S. map using logging residue decay curves)
Are there better metrics of emission offset over time ? (e.g.
relative cumulative radiative forcing – wood vs fossil fuel)
CN(t) for current timber management with more thinnings,
by forest type
CN(t) for fire hazard reduction thinnings?
CN(t) for mill residue (is landfill the alternate decay if not
used? Composite products? pulp?)
Are there broad management guidelines for thinnings to
attain say CN(100) > 0.5? (e.g. Marland and Marland
1992)
Publications
Manomet study: Walker, T. (Ed.). Contributors: Cardellichio, P., Colnes, A., Gunn, J., Kittler, B.,
Perschel, R., Recchia, C., Saah, D., and Walker, T. 2010. Biomass Sustainability and Carbon
Policy Study: Report to the Commonwealth of Massachusetts Department of Energy
Resources. Manomet Center for Conservation Sciences. Report No.: NCI-2010-03.
Repo A., Tuomi M., Liski J., 2010. Indirect carbon dioxide emissions from producing bioenergy
from forest harvest residues. GCB Bioenergy, no. doi: 10.1111/j.1757-1707.2010.01065.x
McKechnie J., Colombo S., Cheng J., Mabee W., MacLean H.L. Forest bioenergy or forest
carbon? Assessing trade-offs in greenhouse gas mitigation with wood-based fuels. Environ Sci
Technol. 2011 Jan 15;45(2):789-95
Palosuo T, Wihersaaari M, Liski J, 2001. Net Greenhouse Gas Emissions due to energy use of
forest residues –Impacts of soil carbon balance. Woody biomass as an energy source –
Challenges in Europe. EFI proceedings no 39, 2001
Schlamadinger B and Spitzer J, 1994. CO2 mitigation through bioenergy from forestry
substituting fossil energy. In: Biomass for energy, environment, agriculture and industry.
Proceedings of the 8th European Biomass Conference.Vienna, Austria, 3-5 October 1994,
Volume 1. Ed. Chartier P., Beenackers A.A.C.M., Grassi G., pp. 310-321.
Schlamadinger B, Spitzer J, Kohlmaier GH, Lüdeke M, 1995. Carbon balance of bioenergy from
logging residues. Bioamss and Bioenery 8 (4): 221-234.
Schlamadinger B and Marland G, 1996. The role of forest and bioenergy strategies in the global
carbon cycle. Biomass and Bioenergy 10 (5/6): 275-300.
Source: G. Zanchi
Thank you
Ken Skog – [email protected]
4. New plantations – existing forest is converted
• Baseline: Existing forest is converted
• New Management: new forest to produce bioenergy
• Biomass net
emissions (green)
• Fossil fuel emissions
(orange)
• CN factor (red)
• CN(t) < 0 for t < ~80
years
Source: G. Zanchi