Fire emissions estimates by year and ecoregion
B.E. Law, T.W. Hudiburg, L. Berner
Publication in preparation. Do not cite or distribute.
Oregon State University
October 20, 2016
Fire emissions should be computed using annual burn area estimates for each severity class (low,
moderate, high), biomass data and region-specific combustion factors for each pool (large stems, small
stems, downed dead wood, understory vegetation, standing dead, litter pools; Campbell et al. 2007,
Meigs et al. 2009).
FIA data are used for biomass estimates in live and dead stems, downed dead wood, and forest floor
pools (litter and duff). These estimates are averaged by ecoregion and ownership and used to calculated
average fire emissions (combustion by pool) by ownership within each ecoregion.
Live and dead tree biomass are calculated using an ecoregion and species specific database of allometric
equations (Hudiburg et al., 2009; Hudiburg et al., 2011) that use both height and diameter (DBH) in the
equations for predicting bole volume and bark and branch biomass. In cases where an ecoregion and or
species-specific equation is not available, substitutions are made by genus, like form, etc. Ecoregionspecific wood density data from 200 supplementary ORCA plots (Hudiburg et al. 2011) were used to
convert bole and coarse root volume to biomass. Average wood densities were used for species not
measured. Downed dead wood estimated are calculated using the methods utilized by the FIADB v.4.0
(line transect method for piece volume by size class) and species and size specific wood densities
reduced by decay class. Understory vegetation (seedling and shrubs) biomass is calculated using shrub
volume (percent cover and height) combined with an allometric equation database developed from
harvested shrubs on the supplementary ORCA plots. Again, substitution for species not represented in
the database was applied by genus, like form, etc. Litter and duff biomass estimates are simply the
product of plot average depth and material density. Conversions to carbon were calculated based on a
carbon density of 0.5 for all pools.
The observational dataset Monitoring Trends in Burn Severity (Eidenshink et al. 2007; www.MTBS.gov) is
spatially-explicit and combines a consistent analysis of a long-term record (1984 to present) with fine
spatial resolution (30 m pixels) and large areal extent to produce the gold standard by which other
spatial burn area data are evaluated. MTBS provides burn area by severity class, and it is mapped for all
ownership classes. Most burn area analyses use low (<25% tree mortality), moderate, and high severity
(>75% tree mortality) classes. MTBS burn areas are at least 404 hectares in size (1000 acres), which
accounts for 92% of the total burn area of forests in the western US (Short 2015). It is consistently
correlated with field measurements in conifer forests of the western US.
To classify burn areas by forest type, Ruefenacht (2008) 250m data were resampled to 30m in this
exercise, which could overestimate the extent of forest area. Alternatively, finer resolution (30 m pixel)
National Land Cover Database (NLCD) can be used. Reserved land areas are obtained from the Protected
Area Database (PAD) of the United States (CBI edition). The ‘off limits’ reserved land ownership category
includes all of the federal, state, and local conservation-oriented areas (e.g., wilderness). The 60
1
different classes of reserved areas from the Protected Area Database are grouped into six simplified
classes (federal, state, local, private, native, off-limits). For simplicity, we group federal, state, and local
into the 'public land' and private and native into 'private land' in this report.
Fire emissions estimates are summarized annually by ecoregion and ownership (thousand metric tonnes
C/year; Omernik Level III) and state (Tg C/yr and Tg CO2e/year, where a teragram equals a million metric
tonnes i.e. MMT C/year). We used Tg C to be consistent with forest sector units typically used, but we
also convert it to Tg CO2e for comparisons with the other sectors (Tg C x 3.667 = CO2e).
The fire emissions estimates are averaged and summed over the two periods (2001-2005 and 20112015) by ecoregion (Tables 1 and 2) and by ownership within ecoregion (Tables 3 - 6) to be consistent
with the FIA data analysis periods. These tables exclude the 'off limits' category which is represented by
ecoregion totals in Table 7. Because 2015 MTBS data have not become available yet, we used the
average TgC/ha burned in 2001-2014 in each severity class (Hudiburg et al. 2011) and multiplied that by
preliminary public estimates of total 254,952 hectares burned in 2015 (630,000 acres; USDA 2015). The
2015 estimate should only be considered a rough estimate, as the data have not been validated, and
actual burn area by severity class is unknown.
Uncertainty estimates:
We use the propagation of error approach to combine the uncertainty estimates of each component as
a measure of uncertainty. We use the following equations as advised by the 2006 IPCC good practice
guidelines report:
(1)
Combining Uncertainties (percentages)
Where, Utotal = the percentage uncertainty in the product of the quantities (half the 95 percent
confidence interval divided by the total and expressed as a percentage); and Un = the percentage
uncertainties associated with each of the quantities.
MTBS perimeters can include up to 20% unburned areas, leading to overestimation of burned areas.
However, the unburned fraction decreases with larger fire size and higher severity (Kolden et al. 2012).
Estimated uncertainty in the biomass estimates varies from 5 to 15%. In Hudiburg et al., (2011), biomass
estimate uncertainty quantification was attributed to the uncertainty in the allometric equations and
was calculated using Monte Carlo simulations sampling from a distribution of biomass estimates
produced using the variation in region or species-specific allometry. We use the average uncertainty
associated with each ecoregion for the estimates reported here.
This analysis is preliminary and has not been peer reviewed, as it is part of a manuscript in preparation.
It is intended to serve as a demonstration of how fire emissions can be computed using a defensible
approach. Annual computations should be produced as MTBS data become available (within ~1 year).
2
Table 1. Average annual fire emissions by ecoregion for the periods (2001-2005 and 2011-2014).
Ecoregion
Blue Mountains
Cascades
Coast Range
Columbia Plateau
East Cascades
Klamath Mountains
Northern Basin
State average
Tg C yr-1
2001 – 2005
Tg CO2e
0.05
0.29
0.00
0.00
0.19
0.56
0.00
1.09
Tg C
0.18
1.06
0.00
0.00
0.69
2.07
0.00
4.00
2011 – 2014
Tg CO2e
0.10
0.13
0.00
0.00
0.18
0.19
0.00
0.61
0.35
0.48
0.01
0.01
0.67
0.69
0.01
2.22
Table 2. Total (summed) fire emissions by ecoregion and state (2001-2005 and 2011-2015). Uncertainty
estimates are in parentheses (±).
2001 - 2005
2011 - 2014
Ecoregion
Tg C
Tg CO2e
Tg C
Tg CO2e
Blue Mountains
0.25
0.90
0.38
1.40
Cascades
1.45
5.32
0.53
1.93
Coast Range
0.00
0.02
0.01
0.03
Columbia Plateau
0.00
0.00
0.02
0.06
East Cascades
0.93
3.43
0.73
2.69
Klamath Mountains
2.82
10.33
0.75
2.76
Northern Basin
0.00
0.02
0.01
0.03
OR state total
5.46 (1.54)
20.01 (5.65)
2.42 (1.18)
8.89 (4.32)
20151
2.09
7.66
Total w/2015
4.51
16.55
1 2015 is a preliminary estimate, as MTBS data were not available.
Table 3. Average annual fire emissions on public forestland by ecoregion for the periods (2001-2005 and
2011-2015). Uncertainty estimates are in parentheses.
Ecoregion
Blue Mountains
Cascades
Coast Range
Columbia Plateau
East Cascades
Klamath Mountains
Northern Basin
State Average
-1
Tg C yr
2001 - 2005
Tg CO2e
0.04
0.25
0.00
0.00
0.15
0.55
0.00
0.99
Tg C
0.16
0.93
0.00
0.00
0.54
2.02
0.00
3.65
3
2011 - 2014
Tg CO2e
0.07
0.09
0.00
0.00
0.12
0.15
0.00
0.43
0.27
0.32
0.00
0.00
0.43
0.55
0.00
1.57
Table 4. Total fire emissions by ecoregion and state on public forestland (2001-2005 and 2011-2014).
Uncertainty estimates are in parentheses.
Ecoregion
Blue Mountains
Cascades
Coast Range
Columbia Plateau
East Cascades
Klamath Mountains
Northern Basin
OR state total
2001 - 2005
2011 - 2014
Tg CO2e
Tg C
Tg CO2e
0.21
0.78
0.29
1.07
1.27
4.66
0.35
1.28
0.00
0.02
0.00
0.01
0.00
0.00
0.00
0.00
0.73
2.69
0.47
1.73
2.75
10.08
0.60
2.20
0.00
0.00
0.00
0.01
4.97 (1.48)
18.23 (5.42)
1.72 (1.10)
6.30 (4.05)
Tg C
Table 5. Average annual fire emissions on private forestland by ecoregion for the periods (2001-2005
and 2011-2014).
Ecoregion
Blue Mountains
Cascades
Coast Range
Columbia Plateau
East Cascades
Klamath Mountains
Northern Basin
State average
-1
Tg C yr
2001 - 2005
Tg CO2e
0.01
0.04
0.00
0.00
0.04
0.01
0.00
0.10
Tg C
0.02
0.13
0.00
0.00
0.15
0.05
0.00
0.36
2011 - 2014
Tg CO2e
0.02
0.04
0.00
0.00
0.07
0.04
0.00
0.18
0.08
0.16
0.01
0.01
0.24
0.14
0.00
0.65
Table 6. Total fire emissions by ecoregion and state on private forestland (2001-2005 and 2011-2014).
Uncertainty estimates are in parentheses (±).
Ecoregion
Blue Mountains
Cascades
Coast Range
Columbia Plateau
East Cascades
Klamath Mountains
Northern Basin
OR state total
Tg C
2001 - 2005
2011 - 2014
Tg CO2e
Tg C
Tg CO2e
0.03
0.12
0.09
0.32
0.18
0.67
0.18
0.65
0
0
0.01
0.02
0.00
0.00
0.02
0.06
0.20
0.74
0.26
0.96
0.07
0.24
0.15
0.57
0.00
0.01
0.00
0.02
0.49 (0.93)
1.78 (3.43)
0.71 (0.97)
2.59 (3.57)
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Table 7. Total fire emissions by ecoregion and state on 'off limits' forest land for the periods (2001-2005
and 2011-2014). Uncertainty estimates are in parentheses (±).
Ecoregion
Blue Mountains
Cascades
Coast Range
Columbia Plateau
East Cascades
Klamath Mountains
Northern Basin
OR state total
Tg C
2001 - 2005
Tg CO2e
0.24
0.48
0.00
0.00
0.01
1.75
0.00
2.49
Tg C
0.90
1.78
0.01
0.00
0.03
6.41
0.01
9.13
5
2011 - 2014
Tg CO2e
0.16
0.30
0
0.00
0.02
0.02
0.01
0.51
0.60
1.10
0
0.00
0.09
0.07
0.03
1.88
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