The Burning Question: Does Forest Bioenergy Reduce Carbon Emissions? a Review of Common Misconceptions About Forest Carbon Accounting

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J. For. 113(1):57–68 REVIEW ARTICLE http://dx.doi.org/10.5849/jof.14-016 Copyright © 2015 The Author(s) harvesting & utilization The Burning Question: Does Forest Bioenergy Reduce Carbon Emissions? A Review of Common Misconceptions about Forest Carbon Accounting

Michael T. Ter-Mikaelian, Stephen J. Colombo, and Jiaxin Chen

Critical errors exist in some methodologies applied to evaluate the effects of using forest biomass for bioenergy adigm. But, as we shall show, this paradigm on atmospheric greenhouse gas emissions. The most common error is failing to consider the fate of forest carbon fails to account for other aspects of bioen- stocks in the absence of demand for bioenergy. Without this demand, forests will either continue to grow or will ergy use needed for proper assessment of its be harvested for other wood products. Our goal is to illustrate why correct accounting requires that the difference effect on GHG emissions. in stored forest carbon between harvest and no-harvest scenarios be accounted for when forest biomass is used The purpose of this review is to present for bioenergy. Among the ﬂawed methodologies evaluated in this review, we address the rationale for accounting the theory and principles for correctly assess- for the fate of forest carbon in the absence of demand for bioenergy for forests harvested on a sustained yield ing the GHG effects of forest bioenergy. We basis. We also discuss why the same accounting principles apply to individual stands and forest landscapes. discuss common errors that appear in the forest bioenergy literature and explain why, Keywords: bioenergy, no-harvest baseline, reference point baseline, carbon sequestration parity, carbon in the absence of forest management to in- debt repayment, dividend-then-debt, stand versus landscape, plantations crease forest carbon before bioenergy harvesting, the use of forest bioenergy often in-

creases atmospheric carbon dioxide (CO2), nterest in industrial-scale bioenergy scientiﬁc and “gray” literature (e.g., maga- at least temporarily. production using forest biomass is part zines, reports, and opinion letters), despite I of a larger movement to reduce climate having been addressed in prominent publi- Principles of Forest Bioenergy change by using renewable energy in place of cations (e.g., Searchinger et al. 2009, Haberl GHG Accounting fossil fuels. However, if climate change mit- et al. 2012). A common misconception is The primary consideration in GHG ac- igation is indeed a driver for using forest bio- that forest bioenergy is immediately carbon counting for forest bioenergy is to accurately energy, then this energy source must be as- neutral, with no net GHG emissions as long determine the fate of forest biomass in the sessed for its effects on the greenhouse gas as the postharvest forest regrows to its pre- absence of demand for its use to produce (GHG) concentration in the atmosphere. harvest carbon level. From a forest manag- bioenergy. This theme will be repeated Misconceptions and errors in methodolo- er’s perspective, this logic can be appealing throughout this article, because failure to gies continue to affect this topic, both in the because it appears to ﬁt a sustained yield par- correctly address this consideration is the

Received February 4, 2014; accepted October 23, 2014; published online November 27, 2014. Afﬁliations: Michael T. Ter-Mikaelian ([email protected]), Ontario Forest Research Institute, Sault Ste. Marie, ON, Canada. Stephen J. Colombo ([email protected]), Ontario Forest Research Institute. Jiaxin Chen ([email protected]), Ontario Forest Research Institute. Acknowledgments: We thank Lisa Buse (Ontario Ministry of Natural Resources) for editing the earlier version of this article. We also thank the editor-in-chief, associate editor, and four anonymous reviewers, whose valuable comments helped us improve the article. This is an Open Access article distributed under the terms of the Creative Commons Attribution Noncommercial License (http://creativecommons.org/ licenses/by-nc/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial reuse, please contact the Journal of Forestry at [email protected].

Journal of Forestry • January 2015 57 est carbon in the absence of demand for bioenergy represents a forest baseline scenario (red line in Figure 2A and D); in some literature reports on forest bioenergy, the forest baseline scenario is referred to as either “business-as-usual,” “counterfactual,” or “protection scenario.” Forest bioenergy production involves the use of fossil fuels, resulting in GHG emissions that are estimated using life cycle analysis (LCA). An LCA accounts for emissions associated with all phases of bioenergy production and use (the so-called “cradle- Figure 1. Typical change in forest carbon stocks after stand harvest (modified from Ter- to-grave” approach): silvicultural activities, Mikaelian et al. 2014a). Dark and light gray areas represent carbon stocks in live biomass use of logging equipment, transportation of and dead organic matter (DOM), respectively. harvested biomass to a biofuel processing fa- cility, conversion of biomass into biofuel, cause of most errors in forest bioenergy ac- posing dead organic matter are temporarily transportation to the energy plant, and non- counting. not compensated for by carbon sequestered CO2 products of combustion (e.g., Zhang et When tree biomass is burned for energy by live trees that are still small. As trees grow, al. 2010). This is the GHG “cost” of pro- production, sequestered carbon is released to the pattern of net carbon accumulation is ducing and using forest bioenergy. The LCA the atmosphere, mainly as CO2. Typical sigmoidal, characterized by initially rapid of forest bioenergy does not include CO2 sources of forest biomass for biofuel produc- increases that slow as a stand reaches matu- GHG emissions from biofuel combustion, tion include standing live trees, harvest resi- rity (Figure 1). The slowdown in stand net because these emissions are accounted for due, biomass recovered during salvage oper- carbon accumulation at maturity results when the effects of bioenergy demand on ations, thinnings and residue from thinning from the death of individual trees with on- carbon in forest stocks are evaluated operations, and mill processing residue (e.g., going growth distributed among the re- (Figure 2C). sawdust and wood chips); here and through- maining live trees. When forest bioenergy displaces energy out the text, biofuel and bioenergy refer to Figure 2A shows the accumulation of from a fossil fuel, it eliminates GHG emis- fuel produced from live or dead biomass and carbon in live trees in the absence of harvest. sions from producing and burning the fossil to energy derived from burning of biofuel, Harvesting a stand for bioenergy removes fuel (the reference fossil fuel scenario). The respectively. Forest carbon is contained in most live tree carbon, leaving unutilized bio- LCA for a fossil fuel includes all GHG emis- live trees, understory vegetation, and in mass on site, which in traditional harvesting sions from obtaining and processing the aboveground (standing dead trees, down includes stumps, branches and tops, and fuel, but, unlike bioenergy, the fossil fuel woody debris, and forest floor) and below- roots. In temperate and boreal forests, recov- LCA also includes all GHG emissions from ground dead organic matter (mineral soil ery of live tree carbon stocks takes decades combustion (Figure 2C). The difference in and dead roots). The processes determining because of slow stand regrowth after harvest LCA emissions between forest bioenergy changes in carbon pools include growth and (Figure 2B). Forest carbon stocks following and a fossil fuel constitutes the GHG benefit mortality of live trees, decomposition of harvest for bioenergy constitute a forest bio- of displacing this fossil fuel with forest bio- dead organic matter, and its combustion if energy scenario (black line in Figure 2B). For- energy (Figure 2C and D). burned. Tree growth and mortality are the main driving forces determining changes in carbon pools. Live trees transfer carbon to dead organic matter pools through self- Management and Policy Implications pruning and mortality; in turn, dead organic A growing market for energy produced from forest biomass has arisen because of the potential to mitigate matter pools release carbon to the atmo- climate change by replacing fossil fuel energy. However, managers who want to access this market should sphere through decomposition. In temperate and boreal forests, the largest amount of be aware that the benefits of forest bioenergy depend on evaluation of forest management options carbon in a forest is typically contained in against a baseline scenario considering what happens to carbon stocks if biomass is not harvested for live trees and mineral soil, followed by forest energy. Among the more favorable options are the use of residue from ongoing harvest operations for floor, with other pools normally accounting traditional wood products (lumber and pulp) and application of intensive silviculture to regeneration of for less than 15% of total forest carbon (Pan harvested stands. Establishment of new bioenergy-designated plantations on abandoned/degraded lands et al. 2011). requires more time for forest biomass to become available for harvest but has the advantage of a low Given the large amounts of woody bio- carbon stock value baseline. The least favorable options include harvest of standing live trees, both in mass that stands accumulate, it is intuitive addition to and in lieu of ongoing harvest operations for traditional wood products. Policies for bioenergy that carbon accrues as they mature (Figure use also need to recognize that accounting for emission benefits when fossil fuels are replaced requires 1). After a stand-replacing disturbance, accounting for forest carbon (either in forest or in traditional wood products) that would have continued stand-level forest carbon stocks usually de- to exist if fossil fuels were not replaced by bioenergy. crease, because carbon losses from decom-

58 Journal of Forestry • January 2015 Thus, accounting for the GHG emission reduction potential of forest bioenergy must include the following:

A. Forest carbon following biomass harvest for energy production (the forest bioenergy scenario); B. Forest carbon in the absence of demand for bioenergy (the forest baseline scenario); C. Life cycle GHG emissions (upstream fossil fuel emissions) from producing forest bioenergy (excluding GHG combustion emissions); and D. Life cycle GHG emissions (including those from combustion) for the fossil fuel displaced by forest biomass (the reference fossil fuel scenario).

Components A and B are required to assess

CO2 emissions to the atmosphere or lost potential CO2 sequestration resulting from ex- tracting biomass from the forest to meet the demand for bioenergy, relative to that without bioenergy demand (i.e., no harvest). Component C (LCA of bioenergy production) includes GHG emissions from producing the biofuel and its use in place of a

fossil fuel; it includes non-CO2 emissions from biomass combustion but not CO2 emissions, which are accounted for in components A and B. Finally, component D (LCA of the reference fossil fuel) is required to assess the GHG emission benefits of displacing fossil fuel use with forest bioenergy. Component A should include losses of forest carbon stocks due to the construction of access roads to harvest sites. Similarly, upstream emissions for fossil fuel-based energy (component D) may require accounting for changes in forest carbon stocks if extraction of fossil fuels is associated with forestland cover changes due to mining and road construction. While such losses of forested area in North America may be small at the regional and national scales (e.g., Sleeter et al. Figure 2. Effect of harvest for bioenergy used to replace coal on forest carbon stock changes 2012, Natural Resources Canada 2013), and total greenhouse gas (GHG) emissions (stand level, from Ter-Mikaelian et al. 2014b). their local effect on forest carbon stocks can A. Accumulation of carbon in an unharvested forest stand. B. Carbon in the stand regen- be significant (e.g., Campbell et al. 2012, erating after harvest. C. Harvested biomass is used to produce wood pellets; life cycle GHG Drohan et al. 2012). emissions from obtaining and producing wood pellets are lower than life cycle and It should be noted that this review fo- combustion emissions of coal, resulting in a GHG benefit of using wood pellets to replace coal. D. Carbon sequestration parity is achieved when the sum of carbon in the regener- cuses primarily on solid biofuels used for ating stand and the GHG benefits of using wood pellets to replace coal reaches the amount combustion for heat and electricity genera- of carbon in the stand if it had remained unharvested; carbon debt repayment is achieved tion. Although second-generation biofuels when the sum of carbon in the regenerating stand and GHG benefits of using wood pellets (e.g., bioethanol for vehicular use, and bio- to replace coal reaches the preharvest amount of carbon in the stand. gas) made from wood are currently not commercial energy sources (Naik et al. 2010, Bonin and Lal 2012), early research suggests that wood has a potential to become the

Journal of Forestry • January 2015 59 main feedstock for production of liquid and gaseous biofuels (Hedegaard et al. 2008, Havlik et al. 2011). However, the principles for assessing the GHG effects of liquid and gaseous biofuels, in particular the methodology to account for changes in forest carbon stocks are the same as those described above. The difference between components A and B constitutes the change in forest carbon stocks resulting from biomass harvest for bioenergy; the difference between components C and D indicates the GHG benefit of replacing a reference fossil fuel with forest bioenergy (Figure 2C). The estimated total GHG emissions caused by demand for bioenergy to replace fossil fuel are given by Figure 3. Changes in forest landscape carbon stocks (dotted line), cumulative total GHG emissions (solid line), and GHG benefits (dashed line) from displacing coal with bioenergy Total GHG emissions generated from harvest of standing live trees (modified from McKechnie et al. 2011). ϭ Positive values correspond to emissions, whereas negative values show removals (seques- Change in forest carbon stocks tration) of carbon from the atmosphere. ϩ GHG benefit of replacing fossil fuel with forest bioenergy (1) traditional wood products (lumber and point” (e.g., Jonker et al. 2014, p. 371), For a detailed mathematical form of Equa- pulpwood). This is also true when bioenergy “break-even period” (e.g., Ter-Mikaelian et tion 1, see McKechnie et al. (2011). This replaces fossil fuel energy: replacement of al. 2011, p. 644), or “time to carbon neutral- numerical approach is used for an individual fossil fuels means harvest for bioenergy, ity” (Domke et al. 2012, p. 146). We prefer stand. The same approach is used for a forest whereas no replacement of fossil fuels means the term carbon sequestration parity rather landscape in which the annual biomass har- no harvest for bioenergy. This link results in than carbon neutrality because the latter has vest is used to produce energy by integrating an inextricable connection between the ref- been defined in a variety of ways (National Equation 1 over time, starting from the first erence fossil fuel and forest baseline scenar- Council for Air and Stream Improvement year of biomass collection. ios: accounting for GHG benefits when [NCASI] 2013). The LCA of bioenergy and fossil fuel- fossil fuels are replaced requires account- Time to carbon sequestration parity de- based energy production usually includes ing for forest carbon losses (either in forest pends on factors such as the source of forest emissions of CO2 and two other GHGs: or in traditional wood products) that biomass (e.g., standing live trees versus har- methane (CH4) and nitrous oxide (N2O) would not have occurred if use of fossil vest residue), growth of regenerating stands (Intergovernmental Panel on Climate fuels continued. after harvest, and emissions from the refer-

Change [IPCC] 2006). Non-CO2 GHG At the onset of biomass harvesting for ence fossil fuel. The peer-reviewed literature emissions are converted into CO2 equiva- bioenergy, the total GHG emissions in contains many studies with estimates of time lents based on their global warming poten- Equation 1 are usually negative because the to carbon sequestration parity for forest bio- tial (GWP) (IPCC 2007). Despite growing reductions in forest carbon outweigh the energy replacing coal (e.g., McKechnie et al. criticism (e.g., Shine 2009, Fuglestvedt et al. GHG benefits of displacing fossil fuel with 2011, Ter-Mikaelian et al. 2011, Holtsmark 2010), GWP factors remain the standard forest bioenergy. Over time, however, net 2012, Repo et al. 2012, Jonker et al. 2014, approach for assessing the effects of GHGs GHG emissions in the forest bioenergy sce- Lamers et al. 2014), natural gas (Domke et on climate change (IPCC 2007). The nario become smaller as harvested stands real. 2012), oil (Repo et al. 2012), and auto- amount of CH4 and N2O (in units of mass) generate and sequester carbon (Figure 2D). motive gasoline (Hudiburg et al. 2011). released during combustion of biofuels and The point at which the change in forest car- These studies consistently show that har- fossil fuels is several orders of magnitude bon (the difference between forest carbon in vesting live trees to produce bioenergy ini- lower than that of CO2 (IPCC 2006). Re- the bioenergy and baseline scenarios) equals tially increases GHG emissions, which may lease of these GHGs may also result from the accumulated GHG benefit of using for- take decades to centuries to offset. However, nitrogen fertilizer application (N2O emis- est bioenergy in place of fossil fuel is called it has also been shown that intensive forest sions) and organic matter decomposition in carbon sequestration parity (Mitchell et al. management of areas harvested for bioen- soil (CH4 and N2O emissions) (Cherubini 2012). Consequently, the time from begin- ergy may substantially reduce time to carbon et al. 2009). ning biomass harvest to carbon sequestra- sequestration parity (e.g., Jonker et al. 2014, Accounting for changes in forest carbon tion parity is called time to carbon sequestra- Ter-Mikaelian et al. 2014b). stocks relative to the baseline scenario is par- tion parity. Only after passing the time to Figure 3 presents carbon stock changes amount for proper assessment of bioenergy carbon sequestration parity does forest bio- and GHG emissions for the scenario of an- GHG emissions: without demand for bioenergy reduce atmospheric GHG compared nual demand for bioenergy being met by energy, harvesting either does not occur and with the reference fossil fuel scenario. harvesting standing live trees on a landscape the forest continues growing and sequester- Time to carbon sequestration parity is scale to displace coal-fired power generation ing additional carbon or it is harvested for also referred to as the “carbon offset parity (from McKechnie et al. 2011). The study

60 Journal of Forestry • January 2015 area covered a total of 52,494 km2 in the changes on the land where bioenergy feed- opportunity cost baseline” (Johnson and Great Lakes-St. Lawrence forest region (On- stock production occurs, such as a change Tschudi 2012, p. 12), and a “natural relax- tario, Canada); the supply of biomass came from farmland to bioenergy plantation. In- ation baseline” (Helin et al. 2013, p. 477). from clearcut harvesting of low-intensity direct LUC refers to changes in land use that We prefer the term no-harvest baseline be- managed stands composed of a mix of hard- take place elsewhere as a consequence of har- cause it intuitively suggests what happens to wood (sugar maple, yellow birch, and red vesting for bioenergy. An example of indi- the forest in the absence of harvest for bio- oak) and softwood (jack pine, black spruce, rect LUC is conversion in another country energy. Other baselines considered in the lit- and balsam ﬁr) species. Emissions from re- of natural forest to farmland in response to erature, such as the comparative baseline duced forest carbon stocks initially outweigh the above direct LUC, where farmland in (US Environmental Protection Agency GHG beneﬁts, resulting in positive GHG the study area was converted to a bioenergy 2011) and the marginal fossil fuel baseline emissions overall (solid line above zero in plantation. Here, we focus on forest land- (Johnson and Tschudi 2012), combine for- Figure 3, indicating increased atmospheric scapes managed for bioenergy production; est and reference fossil fuel baselines to esti-

CO2). The trend is reversed by continued indirect LUC associated with forest bioen- mate net atmospheric balance. accumulation of GHG beneﬁts from fossil ergy production is discussed in a section of As noted by Helin et al. (2013), there fuel displacement and plateauing of land- this review devoted to that topic. are no scientiﬁc criteria governing what the scape losses in forest carbon, although car- Bioenergy LCAs can be attributional or time frame for assessing GHG effects of for- bon sequestration parity (and net atmo- consequential (Brander et al. 2008, Lippke est bioenergy must be, because it depends on spheric reduction of GHG) is not reached et al. 2011, Helin et al. 2013). An attribu- the aims of the assessment. Typically, studies until 38 years after harvesting begins (the tional LCA provides information about the cover at least one silvicultural rotation, with time at which the solid line crosses below the direct effects of processes used for a given the time horizon ranging from several de- zero line), beyond which total GHG emis- product (e.g., production, consumption, cades to hundreds of years. Unlike tradi- sions are negative (solid line below zero in and disposal) but does not consider indirect tional LCA studies, in which results are pre-

Figure 3), indicating net removal of CO2 effects arising from changes in the output of sented as one estimate covering the entire from the atmosphere. a product (Brander et al. 2008). Studies in- time frame, studies on the GHG effects of The approach we describe is based on cluded in this review use a consequential forest bioenergy often provide a temporal counting carbon fluxes between the bio- LCA approach, because they assess the con- profile of GHG emissions (Helin et al. sphere and atmosphere, referred to as a mass sequences of changes in the level of output of 2013). It is worth noting, however, that balance or carbon balance approach (Sathre a product, including effects both inside and short- and long-term effects of bioenergy and Gustavsson 2011). For approaches that outside the life cycle of the product (Brander emissions are likely to be different (Sedjo enhance the mass balance approach by ac- et al. 2008). Some reports (e.g., NCASI 2011). Miner et al. (2014) correctly point counting for the timing of GHG emissions 2013) erroneously suggest that the conse- out that use of short time frames for assess- and radiative forcing, the reader is referred quential LCA approach is appropriate only ing the GHG effects of bioenergy is incon- to Sathre and Gustavsson (2011), Cherubini for large-scale evaluations of forest carbon sistent with application of GWP factors es- et al. (2011), Repo et al. (2012), and Agos- policies. In reality, all bioenergy studies re- timated over a 100-year period (GWP-100). tini et al. (2013). viewed here, regardless of their scale and ob- Using a fixed time frame of 100 years is ac- jective, use a consequential LCA approach, ceptable as long as it is clearly understood Review Scope at least partially. Indeed, it is most common that such estimates of GHG effects will be Studies accounting for the GHG effects to include reference fossil fuel scenarios to realized 100 years after the beginning of bio- of forest bioenergy are characterized by spa- demonstrate the GHG benefits of using for- energy production. However, using only a tial and temporal boundaries, type of LCA, est bioenergy. This inclusion automatically 100-year time frame would obscure time to and forest baseline and reference fossil fuel places such studies in the category of a con- carbon sequestration parity, which is an im- scenarios (Helin et al. 2013). This review sequential LCA approach, because fossil fuel portant indicator of how long it takes forest pertains spatially to studies of forest land- displacement occurs as a consequence of for- bioenergy to start yielding climate mitiga- scapes managed for bioenergy production. est bioenergy use. tion benefits. In addition, the GWP factor

We focus primarily on accounting for the This review considers three potential for N2O is reasonably constant over the ﬁrst carbon effects of harvesting standing live forest baseline scenarios: the no-harvest base- 100 years (e.g., GWP-20 and GWP-100 are trees for bioenergy, because this biomass line, constituting the natural evolution of equal to 289 and 298, respectively) (IPCC source has the greatest potential to produce the forest in the absence of harvest for bio- 2007). The GWP factor for CH4 estimated large, long-lasting effects on the atmospheric energy; the traditional wood products base- over shorter periods would be higher than carbon concentration. Nevertheless, the line, in which forest in the absence of harvest that for 100 years (e.g., GWP-20 and GWP- same basic premises for determining the at- for bioenergy is harvested for traditional 100 are 72 and 25, respectively) (IPCC mospheric effects of bioenergy apply to wood products (lumber and pulpwood); and 2007). However, the numerical error in es- other sources of biomass and are also dis- the reference point baseline, which will be in- timating time to carbon sequestration parity cussed. troduced later in this review. Of the three introduced by applying GWP-100 to CH4 is The spatial boundary used in bioenergy baselines, the no-harvest baseline appears to small because of the relatively low amounts GHG accounting is interrelated with the is- be at the core of many misconceptions dis- produced during both bioenergy and fossil sue of land-use change (LUC), which can be cussed in this review. This baseline is also fuel energy production (e.g., Zhang et al. either direct or indirect (Berndes et al. 2010, referred to as an “anticipated future base- 2010; also see the sensitivity analysis in Ter- Bird et al. 2011). Direct LUC involves line” (e.g., AEBIOM 2013, p. 5), a “biomass Mikaelian et al. 2014b). Next, we examine

Journal of Forestry • January 2015 61 Table 1. Main types of errors in approaches used to assess the carbon effects of forest bioenergy.

Category Rationale for approach Errors in approach

Renewable equals carbon neutral Forest bioenergy is carbon neutral because harvested forest will grow Disregards the length of time required for the forest to grow back back and compensate for carbon losses incurred during harvest and effects of elevated atmospheric carbon concentration during this period Sustained yield equals carbon Carbon losses from harvesting a fraction of a sustainably managed Fails to account for changes in forest carbon stocks in the absence neutral landscape are compensated for by tree growth in the remaining of harvest for bioenergy (no-harvest baseline scenario) landscape, removing the need to account for forest carbon stock Commits a methodological error of using only “one-half” of the changes reference fossil fuel scenario Direct diversion from traditional In the absence of demand for bioenergy, the forest would be Fails to account for lost carbon storage in traditional wood wood products harvested for traditional wood products, removing the need to products and substitution of these products with more carbon account for forest carbon stock changes emission-costly materials (traditional wood products baseline) Dividend-then-debt Harvest releases carbon previously sequestered from the atmosphere, Disregards the fact that each stand is preceded by another stand therefore beginning the carbon accounting framework when the and thus ignores carbon released by previous harvest, while forest stand starts to grow “eliminates” the carbon deficit created crediting the current sequestration by stand harvest (usually proposed in conjunction with sustained Also involves the errors outlined for the sustained yield approach yield approach described above) (described above) Plantations for bioenergy Forest carbon stock changes need not be accounted for when Currently associated with a largely hypothetical case in the plantations are established purposely for harvest for bioenergy United States; few plantations were established on nonforested land for bioenergy; also a partial case of the dividend-then- debt approach (see above) Abandoned plantations carry no Forest carbon stock changes need not be accounted for when Fails to consider the appropriate baseline scenarios that include carbon debt plantations established for traditional wood products are either the no-harvest baseline scenario that could offer a better abandoned because of diminishing market demand for such carbon emission mitigation option than harvest for bioenergy, products and would likely be deforested or the deforestation scenario that includes a single harvest for traditional wood products/bioenergy and carbon stocks in deforested area Carbon debt repayment Changes in forest carbon stocks after harvest for bioenergy are Fails to account for changes in forest carbon stocks in the absence (reference point baseline) compared with carbon losses at the time of harvest (often of demand for bioenergy (no-harvest baseline scenario) proposed in conjunction with sustained yield approach described Involves a methodological error of using only “one-half” of the above) reference fossil fuel scenario common errors in forest bioenergy carbon forest carbon level relative to the no-bioen- Jonker et al. 2014) and non-peer-reviewed accounting using live tree harvest for bioenergy demand scenario. Although the state- (e.g., Strauss 2011, 2013, Ray 2012, ergy, summarized in Table 1. ment is generally correct in that the forest AEBIOM 2013) literature. The common carbon deficit resulting from biomass har- argument is that because biomass removal Common Errors in Accounting vest for energy might be eventually offset by from a fraction of the area in a sustained for Carbon When Using Forest carbon sequestration in regenerating forests, yield landscape is compensated for by Bioenergy it is made implicitly incorrect by not ac- growth in the remaining forest, harvesting knowledging that decades to centuries are causes no net loss of biomass, which leads to Renewable Equals Carbon Neutral needed to erase this deficit. In the meantime, an incorrect claim that there is no carbon One of the earliest misconceptions elevated levels of CO2 in the atmosphere deficit from bioenergy harvest in a sustained about the effects of forest bioenergy is the have numerous potential direct (indepen- yield landscape. erroneous conclusion that forest bioenergy is dent of climate change) and indirect Although sustained yield harvesting is a carbon neutral because forests harvested for (through changes to climate) biological con- valid approach in traditional forestry for bioenergy eventually grow back, reabsorbing sequences (Ziska 2008). providing a steady flow of wood, the claim carbon emitted during energy combustion. Sustained Yield Equals Carbon that it is carbon neutral can only be made by Although the flaw in this assumption has ignoring the principles of carbon mass bal- been identified repeatedly (e.g., Marland Neutral ance accounting (for examples of incorrect 2010, Agostini et al. 2013), some govern- An assumption that bioenergy harvest- accounting, see Strauss and Schmidt 2012, ment documents, forest industry reports, ing in forests managed on a sustained yield AEBIOM 2013). To repeat these principles, and websites claim that forest bioenergy is (also called sustainable yield) basis does not to claim an emissions reduction from using carbon neutral because forests regrow. One create a carbon deficit is one of the most such statement among many found on the common errors in forest bioenergy account- forest biomass to produce energy in place of worldwide web is as follows: ing. This argument is often presented as a a fossil fuel, two scenarios must be accepted: “stand versus landscape” approach, imply- one where fossil fuels are used and forests are The carbon dioxide (CO2) emitted on ing that the accounting principles presented not harvested for bioenergy; and the other combustion of biomass is taken up by new plant growth, resulting in zero net emis- in the previous section of this review are where forests are harvested with the biomass sions of CO2—bioenergy is considered to valid for an individual stand but do not ap- used for energy generation. Stating that sus- be carbon neutral (Sustainable Energy Au- ply to forest landscapes managed for sustained yield management is carbon neutral is thority of Ireland)1 tained yield. The stand versus landscape ap- incorrect because it fails to account for the Statements such as this one disregard the proach has been discussed in both the peer- case involving no harvest for bioenergy in time factor for forests to achieve the same reviewed (e.g., Lamers and Junginger 2013, the reference fossil fuel scenario.

62 Journal of Forestry • January 2015 Furthermore, in a regulated forest, har- growth in demand for traditional wood CO2 that was previously absorbed by the vested biomass is maximized on a sustained products both at the national and global trees to the atmosphere. To quote, “carbon yield basis when stands are harvested as they scales (Ince et al. 2011, Daigneault et al. deficit is only real if you ignore the fact that reach the maximum mean annual growth 2012, Nepal et al. 2012, Latta et al. 2013). the trees gobbled up carbon before they were rate, which occurs before they attain maxi- If these issues were addressed and a le- harvested” (Ray 2012). mum yield, i.e., if left unharvested the stand gitimate case was made that forest biomass However, the dividend-then-debt ap- would gain more biomass and consequently was diverted from harvest for traditional proach ignores the fact that, in most cases, increase live tree carbon stocks for a period wood products to bioenergy, then the tradi- new stands replace previously harvested of time (Cooper 1983). A stand may con- tional wood products scenario is the correct stands. Those stands were in turn preceded tinue to accumulate carbon stocks even past forest baseline (Agostini et al. 2013). This by other stands, and so on. Thus, moving the point of maximum fiber yield, because would include accounting for the large and the starting point of carbon accounting carbon from dead trees is transferred to dead long-lasting stock of carbon that is retained backwards in time to when carbon stocks in organic matter pools, which, depending on in some traditional wood products (Chen et a given piece of land were low takes credit for climate, can have slow decomposition rates al. 2008, 2013). Retention of carbon in the latest cycle of carbon accumulation but (Kurz et al. 2009). Therefore, increased har- wood products is characterized by product ignores the fact that over time, on average, vest applied to an existing regulated (i.e., “half-life”: the time it takes half of a type of forests contain substantial amounts of car- sustained yield) forest landscape results in a wood product to be removed from service. bon. The point in question in dividend- loss of potential carbon sequestration. This Estimates of wood product half-life range then-debt comes down to the original natu- may also be the case in old-growth land- from 67 to 100 years for construction lum- ral state of the land, which, for most current scapes (Luyssaert et al. 2008), which may ber in the United States and from 1 to 6 forestland, was forest. In that case, it is in- continue to increase total carbon stocks, al- years for paper (Skog and Nicholson 2000). correct to use dividend-then-debt account- beit slowly, in the absence of harvesting. After wood product use ends, some carbon ing. Thus, in a regulated forest landscape, any may be emitted to the atmosphere through harvest (and harvest for bioenergy in partic- decomposition or burning (with or without Plantations Used for Bioenergy Carry ular) would in all instances result in in- producing energy), or wood products may No Carbon Debt Some studies conclude that forest bio- creased atmospheric CO2 for a period of be recycled or disposed of in landfills. In time due to lost future carbon sequestration. landfills, a fraction of the carbon slowly re- energy obtained from plantations that are already in a sustained yield state carries no Such increases in atmospheric CO2 cannot leases to the atmosphere through decompo- be ignored simply because the landscape is sition, and the rest remains indefinitely due carbon debt because the plantations were being harvested on a sustained yield basis. to its resistance to decomposition (Micales specifically established to be harvested for In summary, it is an error to conclude and Skog 1997). The traditional wood prod- bioenergy, and, therefore, all the biomass in that bioenergy from a sustained yield forest ucts baseline for building materials and such forests can be considered to have been is automatically carbon neutral, because, on other solidwood products should also in- grown for the purpose of burning (e.g., the one hand, it accepts carbon emissions clude the displacement value from using AEBIOM 2013, Jonker et al. 2014). On this basis, it is argued that since carbon in such reductions associated with reduced fossil wood compared with using more CO2 emis- fuel use, but then fails to acknowledge the sion-intensive materials (Richter 1998, forests was sequestered for the purpose of “other half” of the reference fossil fuel sce- Gustavsson et al. 2006), so that accounting burning, without a bioenergy market they nario; i.e., if fossil fuels are used, then forests for wood used for bioenergy in place of use would never have existed in the first place. are not harvested for bioenergy. in traditional wood products must include Sedjo (2011) calls this a forward-looking ap- LCA emissions associated with substitution proach: Diversion from Traditional Wood of wood by nonwood materials (Matthews if trees are planted in anticipation of their Products et al. 2012). future use for biofuels, then the carbon re- An argument can be made that in the leased on the burning of the wood was pre- sustained yield approach the no-harvest Dividend-Then-Debt viously sequestered in the earlier biological growth process (Sedjo 2011, p. 4) baseline does not need to be considered if, in Proponents of the dividend-then-debt the absence of demand for bioenergy, forests approach to forest carbon accounting argue We contend that this is an acceptable inter- would be harvested for traditional wood that studies on the effects of forest bioenergy pretation, but only as long as such planta- products (e.g., lumber and pulp). This argu- are incorrect if they use the moment of har- tions were established on deforested land ment may not be relevant, however, because vest as the starting point for carbon cycle specifically to be harvested for bioenergy. bioenergy is one of the lowest value uses for analysis (e.g., Strauss 2011, Ray 2012). As However, we are unaware of large existing forest biomass and market forces would be stated by Strauss (2013, p. 14), areas of plantations in the United States es- unlikely to result in bioenergy harvest in lieu all of the studies that show that wood-to- tablished specifically for bioenergy (short- of harvest for traditional wood products energy adds to the carbon stock of the at- rotation bioenergy plantations are not un- (Werner et al. 2010, AEBIOM 2013). Fur- mosphere assume a carbon debt is created common in Europe). For these reasons, the thermore, even if the choice was made to that has to be repaid by new growth over concept is largely hypothetical, and it is a 30–80 years (or more in some studies) harvest for bioenergy, this would shift the mistake to apply this premise to plantations harvest for traditional wood products else- The dividend-then-debt approach is based in general. Furthermore, plantations are where (see the section on Indirect LUC), on the idea that harvest does not create a loss usually established on land that historically because many studies predict continued of forest carbon because it merely returns held natural forest, which either was con-

Journal of Forestry • January 2015 63 verted to plantation forest or was deforested carbon stocks in deforested areas determined Indirect LUC and converted to another land use before the by the new land use. As noted earlier, indirect LUC refers to plantation forest was established. In such To conclude, the correct baseline sce- changes in land use outside the area man- cases, bioenergy plantations would be sub- narios for abandoned plantations are either aged for bioenergy that occur as a conse- ject to the criticisms made of the dividend- the no-harvest scenario or, where this is quence of harvesting for bioenergy (Berndes then-debt approach if they replace planta- deemed unrealistic, a deforestation scenario et al. 2010, Bird et al. 2011). For this reason, tions for traditional wood products. that accounts for the fate of forest biomass the spatial scale of bioenergy studies where In conclusion, existing plantations used carbon due to deforestation and carbon indirect LUC is considered typically are re- for bioenergy cannot be considered exempt stocks in deforested land. gional or national in scope (for examples, see from the need to account for carbon using Abt et al. 2010, 2012, Ince et al. 2011, Galik the mass balance approach described in this Use of the Carbon Debt Repayment and Abt 2012, Daigneault et al. 2012, Nepal review, although it may be the case in future Approach to Carbon Accounting et al. 2012, Sedjo and Tian 2012, Latta et al. for bioenergy plantations established on The concept of carbon debt repayment 2013). long-deforested land. (Mitchell et al. 2012, Jonker et al. 2014) The above cited studies share in com- calls for calculation of the forest carbon def- mon the use of econometric models to ana- Abandoned Plantations Carry No icit relative to the amount of forest carbon at lyze the effects of market prices and wood Carbon Debt time of harvest. Unlike carbon sequestration products and bioenergy demand scenarios Several studies (e.g., Lamers and parity, carbon debt repayment, referred to as on forest growing stock and/or carbon. Car- Junginger 2013, Jonker et al. 2014) discuss “atmospheric carbon parity” by Agostini et bon accounting in these studies often has plantations established for traditional wood al. (2013, p. 33), assumes that a forest car- products but “abandoned” due to diminish- serious shortcomings; for example, some do bon deficit created by harvest is completely not account for LCA emissions, whereas ing fiber demand (referring primarily to the repaid once the combined balance of carbon southeastern United States). They suggest others do not consider forest carbon pools stocks in the postharvest forest and LCA beyond those in harvested wood. Such that protection (no harvest) of such planta- benefits from substituting for fossil fuel tions is an unlikely scenario, and more real- shortcomings can potentially alter whether equals carbon stocks in the preharvest forest or when forest biomass produces a net atmo- istic alternatives are conversion to agricul- (Figure 2D). ture or urban development. Lamers and spheric carbon benefit. Generally, and with Recent defense of the carbon debt re- these caveats in mind, such studies conclude Junginger (2013) argue that these planta- payment approach was made in a report tions should therefore be considered a “free” that greater bioenergy demand would in- published by AEBIOM (2013). In its dis- source of bioenergy, since deforestation crease biomass supply and that growth in cussion of harvest for bioenergy of standing would be the baseline in the fossil fuel sce- forest carbon due to indirect land use effects, live trees in southeastern US forests, the no- nario, whereas Jonker et al. (2014) propose such as increased planting or silviculture, harvest baseline is called “completely inap- using the carbon debt repayment approach may outpace forest carbon stock reductions propriate” and “unrealistic” and is listed discussed later in this review. Here we note caused by bioenergy harvest. among the that such an approach is in error because it In the event that indirect LUC is ac- ignores the fate of forest carbon in the base- fundamental flaws in key assumptions and counted for, the estimation of GHG emis- line scenario where there is no harvest for methodology that underlie prominent sions attributed to forest bioenergy still re- bioenergy. studies that have found forest-based bioen- quires quantification of forest carbon stocks ergy to be associated with significant carbon in an appropriate forest baseline, as well as Although production of certain tradi- deficits (AEBIOM 2013, p. 5–6) tional wood products (e.g., pulp and paper) LCA emissions for the bioenergy and refer- has indeed been declining since 2000 (Hu- Instead, the report advocates using the so- ence fossil fuel scenarios. This is because di- jala et al. 2013), the likelihood of there being called “reference point baseline” (p. 36), rect LUC associated with forest bioenergy large numbers of abandoned plantations which is identical to carbon debt repayment. (forest landscape managed for bioenergy) is contradicts national and global projections Proponents of carbon debt repayment “nested” in indirect LUC (changes to forest of increasing demand for traditional wood (such as AEBIOM 2013, Jonker et al. 2014) and/or nonforested areas outside of the products (Ince et al. 2011, Daigneault et al. make the fundamental error of ignoring the landscape managed for forest bioenergy) 2012, Nepal et al. 2012, Latta et al. 2013). fate of forests in the reference fossil fuel sce- (Berndes et al. 2010). In other words, inclu- If, however, there are plantations abandoned nario. As noted earlier, in the fossil fuel sce- sion of indirect LUC may alter the time to due to regional deviations from global trends nario, when GHG emissions from fossil fuel carbon sequestration parity for a given for- for which the no-harvest baseline is an unre- combustion occur, they do so in lieu of bio- estry system, but it does not alter the meth- alistic scenario, then for such plantations the energy, and so carbon stored in forests in- odology of assessing the forest bioenergy appropriate baseline for forest bioenergy sce- creases over time. To claim emissions reduc- contribution to GHG emissions from this nario is deforestation followed by LUC. Be- tions from avoided fossil fuel use, it is system. In addition, it is important to verify cause it is highly unlikely that the act of de- logically required that forest growth be ac- that potential indirect LUC does in practice forestation results in disposal of standing live counted for in the case where fossil fuels are occur, taking note of Rabl et al. (2007), who trees as waste, the deforestation baseline used (no harvest for bioenergy is needed). recommend that emissions and removals of should include a single harvest of standing Therefore, use of the carbon debt repayment CO2 be accounted for explicitly during each live trees and their utilization for either tra- method results in incorrect estimates of bio- stage of the bioenergy life cycle. We consider ditional wood products or bioenergy, with energy GHG emissions. the recommendation by Rabl et al. (2007)

64 Journal of Forestry • January 2015 key, given some highly uncertain potential composition varies by region, but it is not the characteristics of the forest harvested and consequences to indirect LUC resulting instantaneous. Second, even where harvest the fossil fuel replaced by bioenergy. Even from increased bioenergy demand. residue is burned, a substantial fraction does when bioenergy from live tree biomass from not get burned for logistical reasons (e.g., temperate forests replaces coal, a CO2-in- Other Sources of Forest insufficient staffing and weather condi- tensive fossil fuel, the time to obtain a net Biomass tions). Analysis of annual forest management reduction in atmospheric CO2 can be de- Residue from ongoing harvest opera- reports by Ter-Mikaelian et al. (2014b) re- cades; if it is replacing a less CO2-intensive tions is the second most common potential vealed that fewer than 50% of slash piles fossil fuel, the time to achieve an atmo- source of biomass considered in the litera- were burned in northwestern Ontario, Can- spheric benefit may be more than 100 years. ture on forest bioenergy. The GHG effects ada. Differences in slash burning rates are Nevertheless, as correctly pointed out of using harvest residue for bioenergy have also apparent among the administrative re- by AEBIOM (2013) and NCASI (2013), been studied by several authors (e.g., Mc- gions of British Columbia, Canada (Lamers biomass combustion for bioenergy emits Kechnie et al. 2011, Domke et al. 2012, et al. 2014). Even in the case of slash burn- carbon that is part of the biogenic carbon Repo et al. 2012). The key difference being, the net effect of collecting it for bioen- cycle. Despite delays that may occur in tween assessing GHG effects of using har- ergy is not zero, contrary to the suggestion achieving a net reduction in atmospheric vest residue versus live trees as a source of by Miner et al. (2014), because of incom- carbon, as long as forests regrow, the total biomass is in the baseline scenario: in the plete combustion, with between 5 and 25% amount of carbon in the biosphere-atmo- case of harvest residue, the baseline scenario of residue in piles remaining after burning sphere system remains approximately the must include a projection of the amount of (e.g., Hardy 1996). Incomplete combustion same, with small increases due to consump- carbon stored in harvest residue if it were not of slash when burned produces black car- tion of fossil fuels to obtain, process, and transport the biofuel. It is considerably more collected because of an absence of demand bon, which resists biological and chemical damaging when energy is generated from for bioenergy (an exception to the need to degradation (Forbes et al. 2006). Although fossil fuels because this increases total carbon account for the fate of harvest residue is if it the black carbon pool is relatively small, its in the biosphere-atmosphere system and is came from plantations established specifi- stability makes it an important component essentially permanent. We also note that the cally for bioenergy production). Conse- of total forest carbon. Thus, the baseline for long-term GHG benefits of substituting fos- quently, studies not including an analysis of harvest residue is not straightforward and sil fuels with forest bioenergy will greatly a residue baseline scenario are bound to should reflect local conditions and practices. surpass those of carbon sequestration in for- show shorter periods to reach a net reduc- Sawmill residue (sawdust and wood ests (e.g., see Miner et al. 2014) because net tion in GHG emissions (e.g., Yoshioka et al. chips), because it is a by-product of tradi- carbon accumulation in the no-harvest base- 2005, Froese et al. 2010, Gustavsson et al. tional wood products, has a substantially line scenario will slow substantially as forests lower GHG baseline scenario compared 2011). reach maturity, whereas the benefits of sub- with that of other sources of biomass because Studies accounting for the fate of resi- stituting fossil fuels with forest bioenergy its LCA emissions include only those from dues in the event they are not used for bio- will keep accumulating at a steady pace. In production and transportation of biofuel energy are consistent in concluding that an addition, forest bioenergy may be needed as and non-CO GHGs from its combustion. overall reduction in GHG emissions is 2 a stopgap until sufficient nonfossil fuel en- However, according to Gronowska et al. achieved within the first few years of biomass ergy generation methods, with better atmo- collection. Based on literature reports re- (2009), in the United States about 98 and spheric CO2 consequences than forest bio- viewed by Lamers and Junginger (2013), the 60% of primary and secondary mill residue, mass, can be implemented. Until then, even time required to achieve the reduction in to- respectively, is already used for energy or a century-long increase in atmospheric CO2 tal GHG emissions ranges from 0 to 16 years other value-added products; in Canada, caused by using forest bioenergy may be from the onset of harvest residue collection 70% of mill residue is currently used. Prop- preferable to burning fossil fuels. As stated for bioenergy. A variation in the time to erly assessing the GHG effects of mill resi- by Dehue (2013), mitigation of climate overall GHG emission reduction is caused due used for bioenergy thus requires knowl- change may not be possible without broad- by assumptions about the fate of residue in edge of the existing fate of mill residue to scale use of forest bioenergy; in other words, the baseline scenario (e.g., decomposition correctly define its baseline scenario in the human society is probably going to require rate and rate of slash burning) and the refer- absence of use for bioenergy. use of all available options to mitigate cli- ence fossil fuel. mate change, whether such options provide The assumption that harvest residue is a Is Forest Bioenergy “Bad” for a short- or long-term GHG reduction ben- carbon “free” source of biomass for energy Climate? efit. because otherwise it would be burned is an The aim of this review is to promote There may be reasons beyond climate exaggeration of its fate (for example, in accurate accounting of the atmospheric ef- change to harvest forests to produce bioen- AEBIOM 2013, p. 18: “the majority of the fects of bioenergy, not to argue against using ergy, such as the opportunity for forest land- biomass left following harvest is burned as a forest biomass for energy generation. When owners to receive economic benefits (as waste management measure”). The reality of correctly accounted for, GHG emissions mentioned in AEBIOM 2013), the eco- the residue baseline scenario is more com- from live tree forest biomass used for energy nomic benefits to society overall of reducing plex. First, in some regions, all harvest resi- exceed those from fossil fuels for periods of a dependence on imported fossil fuels (US due is left on site to decompose; i.e., none is few years to more than a century, and the Department of Energy 2013), or achieve- burned (e.g., McKechnie et al. 2011). De- difference can be substantial, depending on ment of ecological objectives for which for-

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