LETTERS

PUBLISHED ONLINE: XX MONTH XXXX | DOI:10.1038/NCLIMATE1264

Regional carbon dioxide implications of forest

bioenergy production

Tara W. Hudiburg1

*, Beverly E. Law1

, Christian Wirth2 and Sebastiaan Luyssaert3

1 Mitigation strategies for reducing CO2 emissions include

substitution of fossil fuel with bioenergy from forests12 , where

3 carbon emitted is expected to be recaptured in the growth

of new biomass to achieve zero net emissions24 , and forest

thinning to reduce wildfire emissions35 . Here, we use forest

6 inventory data to show that fire prevention measures and

7 large-scale bioenergy harvest in US West Coast forests

8 lead to 2–14% (46–405 Tg C) higher emissions compared

9 to current management practices over the next 20 years.

10 We studied 80 forest types in 19 ecoregions, and found

11 that the current carbon sink in 16 of these ecoregions is

12 sufficiently strong that it cannot be matched or exceeded

13 through substitution of fossil fuels by forest bioenergy. If

14 the sink in these ecoregions weakens below its current level

by 30–60 g C m−2 yr−115 owing to insect infestations, increased

16 fire emissions, or reduced primary production, management

17 schemes including bioenergy production may succeed in jointly

18 reducing fire risk and carbon emissions. In the remaining three

19 ecoregions, immediate implementation of fire prevention and

20 biofuel policies may yield net emission savings. Hence, forest

21 policy should consider current forest carbon balance, local

22 forest conditions and ecosystem sustainability in establishing

23 how to decrease emissions.

24 Policies are being developed worldwide to increase bioenergy

25 production as a substitution for fossil fuel to mitigate fossil fuel26 derived carbon dioxide emissions, the main cause of anthropogenic

global climate change4,527 . However, the capacity for forest sector

28 bioenergy production to offset carbon dioxide emissions is limited

29 by fossil fuel emissions from this activity (harvest, transport, and

30 manufacturing of wood products) and the lower energy output

per unit carbon emitted compared with fossil fuels631 . Furthermore,

32 forest carbon sequestration can take from decades to centuries to

33 return to pre-harvest levels, depending on the initial conditions and

amount of wood removed734 . The effects of changes in management

35 on CO2 emissions need to be evaluated against this baseline.

36 Consequently, energy policy implemented without full carbon

37 accounting and an understanding of the underlying processes risks

increasing rather than decreasing emissions4,838 .

39 In North America, there is increasing interest in partially meeting

energy demands through large-scale forest thinning540 , with the

41 added benefit of preventing catastrophic wildfire and concurrent

carbon loss342 . Although forest thinning can be economically feasible,

43 sustainable, and an effective strategy for preventing wildfire where

risk is high9,10 44 , it remains unresolved whether this type of forest

45 treatment can satisfy both the aims of preventing wildfire and

46 reducing regional greenhouse gas emissions.

47 For both aims to be satisfied, it needs to be shown that: (1)

48 reduction in carbon stocks due to thinning and the associated

1Department of Forest Ecosystems and Society, 321 Richardson Hall, Oregon State University, Corvallis, Oregon, USA, 2Department of Systematic Botany

and Functional Biodiversity, University of Leipzig, Johannisalle 21-23, 04103 Leipzig, Germany, 3Laboratoire des Sciences du Climat en de l’Environnement,

CEA CNRS UVSQ, Centre d’Etudes Ormes des Merisiers, 91191 Gif Sur Yvette, France. *e-mail: Tara.hudiburg@oregonstate.edu.

emissions are offset by avoiding fire emissions and substituting 49

fossil fuel emissions with forest bioenergy, (2) the change in 50

management results in less CO2 emissions than the current or 51

‘baseline’ emissions, and (3) short-term emission changes are 52

sustained in the long term. Determination of baseline forest 53

sector carbon emissions can be accomplished by combining 54

forest inventory data and life cycle assessment (LCA) that 55

includes full carbon accounting of net biome production (NBP) 56

on the land in addition to carbon emissions from bioenergy 57

production and storage in wood products (LCA; ref. 6). NBP 58

is the annual net change of land-based forest carbon (NEP; 59

photosynthesis minus respiration) after accounting for harvest 60

removals and fire emissions. 61

Our study focused on the US West Coast (Washington, Oregon 62

and California), a diverse region due to the strong climatic gradient 63

from the coast inland (300–2,500 mm precipitation per year) and 64

a total of 80 associated forest types, ranging from temperate 65

rainforests to semi-arid woodlands (Supplementary Table S1). The 66

region is divided into 19 distinct ecoregions11 on the basis of climate, 67

soil, and species characteristics, and includes a broad range of 68

productivity, age structures, fire regimes and topography. Mean 69

net primary production (NPP) of the forest types range from 70

100–900 g C m−2yr−1(this study), falling within the global range 71

of 100 to 1,600 g C m−2yr−1reported for temperate and boreal 72

forests12. Forest land ownership is divided fairly evenly between 73

public and private sectors having different management histories 74

and objectives that affect forest carbon dynamics13. 75

Carbon sequestration rates vary greatly across the region, with 76

mean NEP ranging from −85 g C m−2yr−1in the dry Northern 77

Basin to more than 400 g C m−2yr−1in the mesic Coast Range. After 78

accounting for fire emissions and substantial harvest removals, 79

regional NBP remains a significant sink of 26 ± 3 Tg C yr−1 or 80

76 ± 9 g C m2yr−1, similar to the US average14 and estimates for 81

the member states of the European Union15. Sixteen of the 19 82

ecoregions, representing 98% of the forest area in the region 83

are estimated to be carbon sinks (Fig. 1a; exceptions are drier 84

ecoregions where annual productivity is low and fire emissions are 85

relatively high). Thus, the observed regional sink is not solely due 86

to the region’s highly productive rainforests, which occupy 15% of 87

the area. Within the region, California’s NBP is higher than that of 88

Oregon andWashington (107 versus 53–61 g C m−2yr−1), primarily 89

owing to differences in NEP (Supplementary Table S2) and harvest 90

between similar forest types within the same ecoregions that cross 91

state boundaries (Supplementary Discussion and Table S3). 92

In addition to current management or Business-As-Usual 93

(BAU, characterized by current preventive thinning and harvest 94

levels), we designed three treatments (Supplementary Fig. S1a) 95

to reflect the varying objectives of potential forest management 96

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LETTERS NATURE CLIMATE CHANGE DOI:10.1038/NCLIMATE1264

Current NBP

(g C m¬2 yr¬1) 

NBP uncertainty

(g C m¬2 yr¬1)

NBP

(g C m¬2 yr¬1)

Δ

NC NR

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ab c

Figure 1 | Maps of US West Coast NBP and uncertainty for current and threshold conditions. Map a shows current NBP or BAU; positive values (warm

colours) indicate forest sinks whereas negative values (cool colours) are carbon sources to the atmosphere. Map b shows the current NBP uncertainty

estimates that were calculated using Monte Carlo simulations of mean forest type values for the components of NBP (net ecosystem productivity, fire and

harvest) combined with the uncertainty associated with remote sensing land cover estimates. Map c represents the amount NBP would need to decrease

to reach a threshold NPB where bioenergy management may result in emission decreases to the atmosphere.

1 systems: forest fire prevention by emphasizing removal of fuel

2 ladders (‘Fire Prevention’) in fire-prone areas, making fuel

3 ladder removal economically feasible by emphasizing removal of

4 additional marketable wood in fire-prone areas (‘Economically

5 Feasible’), or thinning all forestland regardless of fire risk to

6 support energy production while contributing to fire prevention

7 (‘Bioenergy Production’). Removals are in addition to current

8 harvest levels and are performed over a 20-year period such that

9 5% of the landscape is treated each year. Our reliance on a

10 data-driven approach versus model simulations strengthens our

11 analysis in the short term, but limits our ability to make long-term

12 predictions. Extending our study beyond a 20-year timeframe

13 would overstretch data use because current forest growth is unlikely

14 to represent future growth due to changes in climate, climaterelated disturbance, and land use16,17 15 .

16 In our study region, we found that thinning reduced NBP

17 under all three treatment scenarios for 13 of the 19 ecoregions,

18 representing 90% of the region’s forest area. The exceptions where

19 NBP was not reduced were primarily due to high initial fire

20 emissions compared to NEP (for example, Northern Basin and

21 North Cascades; Supplementary Fig. S2). The dominant trend at

22 the ecoregion level was mirrored at the regional level, with the

23 Bioenergy Production scenario (highest thinning level) resulting in

24 the region becoming a net carbon source (Supplementary Table S2

25 and discussion of state-level estimates). Regionally, forest biomass

26 removals exceeded the potential losses from forest fires, reducing

27 the in situ forest carbon sink even after accounting for regrowth,

28 as found in previous studies with different approaches or areas

of inference8,18 29 . Because we have assumed high reductions in fire

30 emissions for the areas treated in each scenario, it is unlikely we are

31 underestimating the benefit of preventive thinning on NBP.

32 It is important to recognize that even if the land-based flux

33 is positive (a source) or zero (carbon neutral), decreases in NBP

from BAU can increase CO2 emissions to the atmosphere. LCA was 34

used to estimate the net emissions of carbon to the atmosphere 35

in each treatment scenario (Supplementary Fig. S1b and Tables S4 36

and S5). LCA at the ecoregion level revealed that emissions are 37

increased for 10 out of 19 of the ecoregions (Fig. 2), representing 38

80% of the forest area in the region. The combination of in situ 39

and wood-use carbon sinks and sources emit an additional 46, 40

181 and 405 Tg C to the atmosphere over a 20-year period (2–14% 41

increase) above that of the BAU forest management scenarios 42

for the Fire Prevention, Economically Feasible, and Bioenergy 43

Production treatments, respectively (Fig. 3). 44

Sensitivity analysis of our results to a range of fire emission 45

reductions, energy conversion efficiencies, wood product decom- 46

position rates and inclusion of wood substitution showed that 47

carbon emissions varied by −10 to 28% from the optimum values 48

across the scenarios, depending on the combination of assumptions 49

(Supplementary Discussion and Table S6). The analysis revealed 50

that an increase in estimated current fire emissions (which effec- 51

tively reduces the baseline sink) may decrease total atmospheric C 52

emissions in the Fire Prevention scenario, but only given optimum 53

conditions for all of the other parameters (for example 100% 54

energy efficiency). Nevertheless, if fire frequency and intensity 55

increase in the future19, emissions savings through forest bioenergy 56

production may become possible, especially in ecoregions where 57

the sink is already weak. 58

Previous case studies showed that harvesting an old-growth 59

forest in the Pacific Northwest20 or increasing the thinning removals 60

of temperate forests is likely to deteriorate the forest and wood 61

product carbon stock21. However, these studies were limited to a 62

handful of sites, relied primarily on modelled results3,18 and did 63

not account for the energy requirements of forest management and 64

wood processing nor for the potential to substitute fossil fuels with 65

bioenergy. We build on these results by including all ecoregions, 66

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NATURE CLIMATE CHANGE DOI:10.1038/NCLIMATE1264 LETTERS

0.1 0.5 1 3 9 15

Total harvest (Tg C yr¬1)

Total CO2 flux (Tg C yr¬1)

CO

CR

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Figure 2 | Life Cycle Assessment carbon emission trends by ecoregion

under various management scenarios. The x axis is the total harvest

(BAU+treatment) and the y axis is the total CO2 flux in Tg C yr−1for each

ecoregion. Coloured circles represent each scenario (Green = BAU,

Yellow = Fire Prevention, Orange = Economically Feasible,

Red = Bioenergy Production). Grey circles are the values for each sensitivity

analysis set of parameters and the error bars represent the estimate

uncertainty. The locations of the ecoregions indicated by labels are shown

in Fig. 1a. For most ecoregions, the treatments increase emissions to the

atmosphere.

1 all age classes (not just old-growth), three treatments including

2 bioenergy production, and sector-based LCA. We found that even

3 though forest sector emissions are compensated for by emission

4 savings from bioenergy use, fewer forest fires, and wood product

5 substitution, the end result is an increase in regional CO2 emissions

6 compared to BAU as long as the regional sink persists.

7 To determine a threshold NBP for which bioenergy management

8 reduces atmospheric CO2 emissions compared to BAU, we applied

9 the same assumptions as used in the LCA. We found that if the NBP

drops by 50–60 g C m−2yr−110 in currently productive ecoregions

or 15–30 g C m−2yr−111 in currently less productive ecoregions,

12 bioenergy management would come with CO2 emissions savings

compared to BAU (Fig 1c). Aggregating the ecoregion thresholds 13

translates into a regional mean NBP of 45 g C m−2yr−1 or a 14

41% reduction on average. Reductions in NBP may occur 15

due to increased mortality and/or decreased growth due to 16

climate, fire, or insect outbreaks. However, reductions in NBP 17

from increased harvest do not qualify because harvest increases 18

emissions; wood carbon enters the products/bioenergy chain, 19

where subsequent losses occur. We cannot predict from the 20

data when the threshold NBP would occur because a high 21

resolution process-based model with the ability to incorporate 22

future climate, nitrogen deposition, age dynamics, disturbance and 23

management would need to be used, which is beyond the scope of 24

this study. 25

Ecoregion threshold NBP is dependent on the scenario treatment 26

removals and area because the Fire Prevention treatment targets 27

only those areas most likely to burn. For example, to reduce 28

emissions in the Sierra Nevada, baseline NBP would have to 29

decrease by as much as 84 for the Bioenergy Production scenario 30

versus only 13 g C m−2yr−1for the Fire Prevention scenario. In 31

ecoregions where current sinks are marginal or weakened by 32

climate, fire, or insect outbreaks there may be a combination of 33

harvest intensity and bioenergy production that reduces forest 34

sector emissions. In nine of the ecoregions where forests are 35

carbon neutral or a source of CO2 to the atmosphere and/or 36

fire emissions are high for BAU, total CO2 emissions under the 37

Fire Prevention scenario could be reduced compared to BAU. 38

They provide examples where management strategies for carbon 39

emission reduction or sequestration should differ from the majority 40

of the region; a one-size-fits-all approach will not work22. Finally, 41

large areas in the Northern Rockies (for example, Colorado and 42

Wyoming) are at present experiencing increases in forest mortality 43

due to beetle-kill, a trend which could continue in a warmer 44

climate23. These areas may already be at or below the threshold NBP; 45

if so, they could benefit from targeted bioenergy implementation. 46

However, simply lowering current regional harvest intensities 47

in areas where NBP is not weakened also reduces emissions 48

(Supplemental Discussion and Fig. S3). Also, as we have assumed 49

large-scale implementation of these strategies in addition to BAU 50

harvest, we may be overestimating future harvest even though 51

harvest has declined significantly since 1990 because of restrictions 52

placed on harvest on federal lands as part of the Northwest Forest 53

Plan. If the strategies were used to substitute for BAU harvest, the 54

outcome on NBP would be much different (that is, increased for the 55

Fire Prevention scenario). 56

Sinks Sources Added

emissions 

Sinks Sources Added

emissions 

Sinks Sources Added

emissions

Sink Sources Added

emissions 

Scenario sinks, sources and added emissions (Tg C yr¬1)

NEP Forest sector FFE Wood decomposition FF substitution 

Regrowth Biofuel emissions Fire emissions Added emissions 

BAU Fire prevention Economically feasible Bioenergy production 

0

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Figure 3 | Total US West Coast forest sector carbon sinks, sources, and added emissions relative to BAU under various management scenarios. Units are

in Tg C yr−1. Life cycle assessment estimates account for changes in carbon on land in addition to emissions associated with production, transport and

usage of wood, and substitution and displacement of fossil fuel emissions associated with use and extraction. BAU results in the lowest anthropogenic

emissions from the forest sector.

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LETTERS NATURE CLIMATE CHANGE DOI:10.1038/NCLIMATE1264

1 Our study is one of the first to provide full carbon accounting,

2 including all of the sinks and sources of carbon emissions from the

3 forestry sector and the current in situ sink, for such a large area.

4 Given the diversity of woody ecosystems in the study region, ranging

5 from highly productive temperate rainforests to less productive

6 semi-arid woodlands, the trends in response probably apply to

7 other temperate regions globally (Supplementary Table S1) where

8 forests are at present a strong net carbon-sink (for example,

9 Eastern US, China and Europe), although the extent of the effect

10 remains to be established.

11 Greenhouse gas reduction plans call for up to 10% reductions

12 in emissions by 2020 and forest-derived fuels are being proposed

13 as a carbon-neutral solution to reducing energy emissions. In all of

14 our proposed scenarios, increases in harvest volume on the US West

15 Coast will on average result in regional emission increases above

16 current levels, although there are a few ecoregions where the tested

17 scenarios could result in emission savings. As long as the current in

18 situ NBP persists, increasing harvest volumes in support of bioen19 ergy production is counterproductive for reducing CO2 emissions.

20 In this study region, the current in situ NBP in tree biomass, woody

21 detritus and soil carbon is more beneficial in contributing to re22 duction of anthropogenic carbon dioxide emissions than increasing

23 harvest to substitute fossil fuels with bioenergy from forests.

24 Although large uncertainty remains for regional forecasts to

25 year 2050 or 2100, it is expected that forest carbon sinks will

26 diminish over time because of ageing of the forests, saturation

27 of the CO2-fertilization and N-deposition effects, and increased

mortality due to climate or insects24,25 28 . This would require new

29 assessments to identify management options appropriate for each

30 situation. Carbon-management is not the sole criteria that should

31 be considered when planning forest management. Our findings

32 should thus also be evaluated against other ecosystem services, such

33 as habitat, genetic and species diversity, watershed protection, and

34 natural adaptation to climate change.

35 Methods

36 We quantified forest sequestration rates and test forest thinning scenarios across

37 the region using a data-intensive approach which, for the first time, takes into

38 account the diversity of forest characteristics and management. We combined

39 Landsat remote sensing data with inventories and ancillary data to map current

40 forest NEP, NBP, and changes in NBP with three thinning scenarios. The approach

41 can be applied at multiple scales of analysis in other regions.

42 We combined spatially representative observational data from more than 6000

43 FIA plots (see Supplementary Methods and Table S7) with remote sensing products

on forest type, age and fire risk26 44 , a global data compilation of wood decomposition

data and 200 supplementary plots13 45 to provide new estimates of US West Coast

46 (∼34 million hectares) forest biomass carbon stocks (Supplementary Table S8),

47 NEP (the balance of photosynthesis and respiration) and NBP (the in situ net forest

48 carbon-sink accounting for removals). We included all forestland in our analysis,

49 across all age classes (20–800 years old) and management regimes. Plot values

50 were aggregated by climatic region (ecoregion), age class and forest type, and this

51 look-up table was used to assign a value to each associated 30 m pixel.

52 We use regional combustion coefficients to determine fire emissions. Only

53 3–8% of live tree biomass is actually combusted and emitted in high severity fire in

the Pacific Northwest31 54 , contrary to other studies that report much higher emissions

because they assume 30% of all aboveground woody biomass is consumed27 55 .

Although the latter contradicts extensive field observations28,29 56 and modelling

studies30 57 in the region, we included 30% as the upper-end combustion factor in

58 our sensitivity analysis (Supplementary Table S9).

59 In addition to the spatially explicit estimates of stocks and fluxes under current

60 management or BAU (current forest harvest), three treatments were designed (Fire

61 Prevention, Economically Feasible, and Bioenergy Production; Supplementary Fig.

62 S1a) to reflect the varying objectives of potential future forest management over the

63 next 20 years; within the proposed time period for CO2 reductions in the US Areas

64 were prioritized for treatment by fire risk and frequency. The proposed treatments

65 result in additional harvest removals because we assume the current harvest rate

66 for wood products will continue in the future. We limit our specific analysis to the

67 short term because this is the timeframe suitable for policymakers, effectiveness of

68 fire protection treatments, and an appropriate use of the data-driven approach.

69 However, to investigate conditions (for example, sink saturation) that could

70 invalidate our short-term results in the long term, we also calculated the in situ NBP

at which the atmosphere may benefit from bioenergy removals.

Last, we studied the net effects of the thinning treatments on atmospheric 71

CO2 by LCA of carbon sources and sinks that includes the post-thinning NBP 72

and wood use (harvest, transport, manufacturing, decomposition, wood product 73

substitution, conversion and use of bioenergy, and displacement of fossil fuel 74

extraction emissions; Supplementary Fig. S1b and Table S4,S5). 75

Received 19 July 2011; accepted 30 September 2011; 76

published online XX Month XXXX 77

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NATURE CLIMATE CHANGE DOI:10.1038/NCLIMATE1264 LETTERS

1 30. Ottmar, R. D., Pritchard, S. J., Vihnanek, R. E. & Sandberg, D. V. 14 Final

2 Report JFSP Project 98-1-9-06, 2006.

3 Acknowledgements

4 This research was supported by the Office of Science (BER), US Department of Energy

5 (DOE, Grant no. DE-FG02-07ER64361), for the North American Carbon Program

6 study, ‘Integrating Remote Sensing, Field Observations, and Models to Understand

7 Disturbance and Climate Effects on the Carbon Balance of the West Coast US’. We

8 further thank M. Harmon for discussions of wood product life-cycle assessment. T.W.H.

9 is funded by a DOE global change education program PhD fellowship (GREF). S.L. is

funded by ERC Starting Grant 242564.

Author contributions 10

T.W.H. designed and implemented the study with guidance from B.E.L. and S.L. 11

T.W.H., S.L. and B.E.L. co-wrote the paper and S.L. contributed to parts of the 12

analysis. C.W. provided essential data and methods for the analysis and valuable 13

comments on the manuscript. 14

Additional information 15

The authors declare no competing financial interests. Supplementary information 16

accompanies this paper on www.nature.com/natureclimatechange. Reprints and 17

permissions information is available online at http://www.nature.com/reprints. 18

Correspondence and requests for materials should be addressed to T.W.H. 19

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‘84’?

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Query 9: Line no. 54

Please check whether the above given ‘31’ is a

reference. Only 30 reference are there.

Query 10: Line no. 79

Please provide volume and page range for ref. 1.

Query 11: Line no. 79

Because of the odd symbols appearing in the

authors of Ref. 2, we have checked and corrected the

name of the second author.

Query 12: Line no. 116

Please provide page range/article id for

refs 18, 28.

Query 13: Line no. 119

Any update for ref. 19.

Query 14: Line no. 147

Please provide publisher for ref. 30.

Page 5

Query 15: Line no. 8

As NPG do not allow unnamed individuals in the

acknowledgement we have modified ‘We further

thank an anonymous reviewer for discussions

of economic analysis of bioenergy production,

an LCA specialist for helpful comments on our

LCA, and M. Harmon for discussions of wood

product life-cycle assessment.’ to ‘We further

thank M. Harmon for discussions of wood product

life-cycle assessment.’