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Available online at www.sciencedirect.com Biomass and Bioenergy 24 (2003) 285 – 296 Negative emissions from BioEnergy use, carbon capture and sequestration (BECS)—the case of biomass production by sustainable forest management from semi-natural temperate forests Florian Kraxner, Sten Nilsson, Michael Obersteiner International Institute for Applied Systems Analysis, Schlossplatz 1, A-2361 Laxenburg, Austria Received 1 December 2001; received in revised form 3 June 2002; accepted 10 September 2002 Abstract In this paper, we show how nature oriented forestry measures in a typical temperate forest type in combination with bioenergy systems could lead to continuous and permanent removal of CO2 from the atmosphere. We employ a forest growth model suited for modeling uneven-aged mixed temperate stands and analyze the interaction with biomass energy systems that allow for CO2 removal and long-term sequestration in geological formations. On global scales this technological option to convert the global energy system from a CO2 emitter to a CO2 remover has been overlooked by both the science and policy communities. Removal of the major Greenhouse Gas (GHG) CO2 from the atmosphere is possible using biomass energy to produce both carbon neutral energy carriers (e.g., electricity and hydrogen) and, at the same time, oer a permanent CO2 sink by capturing carbon at the conversion facility and permanently storing it in geological formations. This technological option resolves the issues of permanence and saturation of biological sinks while at the same time this option respects the multiple benets of sustaining diverse, healthy, and resilient forests. Our results indicate that a typical temperate forest in combination with capturing and long-term storage can permanently remove and on a continuous basis about 2:5 t C yr 1 ha 1 on a sustainable basis respecting the ecological integrity of the ecosystem. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: Semi-natural forests; Bioenergy; Scrubbing; Sequestration; Permanence; Saturation; Adaptation; Sustainability 1. Introduction There seems to be general agreement within the scientic community that sinks cannot be counted on to be maintained steadily into the future (see, e.g., [15]). Contrary to this generally held view of sinks being Corresponding author. Tel.: +43-2236-807460; fax: +43- 2236-807599. E-mail address: [email protected] (M. Obersteiner). limited by permanence and saturation, we can show that forest sinks can be counted on to operate steadily into the future. The major drawback of natural bio- spheric carbon sinks is that the rate of decomposition is so high that most of the net primary production (NPP) eventually ends up as atmospheric CO 2 . There- fore, terrestrial biota appear to be limited due to satu- ration and permanence. In this perspective, statements by for example Schimel et al. [1] that the net terres- trial sink may disappear altogether in the future are 0961-9534/03/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII:S0961-9534(02)00172-1

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Page 1: Negative emissions from BioEnergy use, carbon capture and sequestration (BECS)—the case of biomass production by sustainable forest management from semi-natural temperate forests

Available online at www.sciencedirect.com

Biomass and Bioenergy 24 (2003) 285–296

Negative emissions from BioEnergy use, carbon capture andsequestration (BECS)—the case of biomass productionby sustainable forest management from semi-natural

temperate forestsFlorian Kraxner, Sten Nilsson, Michael Obersteiner∗

International Institute for Applied Systems Analysis, Schlossplatz 1, A-2361 Laxenburg, Austria

Received 1 December 2001; received in revised form 3 June 2002; accepted 10 September 2002

Abstract

In this paper, we show how nature oriented forestry measures in a typical temperate forest type in combination withbioenergy systems could lead to continuous and permanent removal of CO2 from the atmosphere. We employ a forest growthmodel suited for modeling uneven-aged mixed temperate stands and analyze the interaction with biomass energy systems thatallow for CO2 removal and long-term sequestration in geological formations. On global scales this technological option toconvert the global energy system from a CO2 emitter to a CO2 remover has been overlooked by both the science and policycommunities. Removal of the major Greenhouse Gas (GHG) CO2 from the atmosphere is possible using biomass energy toproduce both carbon neutral energy carriers (e.g., electricity and hydrogen) and, at the same time, o<er a permanent CO2

sink by capturing carbon at the conversion facility and permanently storing it in geological formations. This technologicaloption resolves the issues of permanence and saturation of biological sinks while at the same time this option respects themultiple bene>ts of sustaining diverse, healthy, and resilient forests. Our results indicate that a typical temperate forest incombination with capturing and long-term storage can permanently remove and on a continuous basis about 2:5 t C yr−1 ha−1

on a sustainable basis respecting the ecological integrity of the ecosystem.? 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Semi-natural forests; Bioenergy; Scrubbing; Sequestration; Permanence; Saturation; Adaptation; Sustainability

1. Introduction

There seems to be general agreement within thescienti>c community that sinks cannot be counted onto be maintained steadily into the future (see, e.g., [1–5]). Contrary to this generally held view of sinks being

∗ Corresponding author. Tel.: +43-2236-807460; fax: +43-2236-807599.

E-mail address: [email protected] (M. Obersteiner).

limited by permanence and saturation, we can showthat forest sinks can be counted on to operate steadilyinto the future. The major drawback of natural bio-spheric carbon sinks is that the rate of decompositionis so high that most of the net primary production(NPP) eventually ends up as atmospheric CO2. There-fore, terrestrial biota appear to be limited due to satu-ration and permanence. In this perspective, statementsby for example Schimel et al. [1] that the net terres-trial sink may disappear altogether in the future are

0961-9534/03/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved.PII: S0961 -9534(02)00172 -1

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286 F. Kraxner et al. / Biomass and Bioenergy 24 (2003) 285–296

correct. However, terrestrial ecosystems when com-bined with the use of biomass energy can o<er a per-manent carbon sink by the technological option ofcapturing carbon from biomass conversion facilitiesand permanently store carbon in geological formations(BECS). This technological possibility could, as aco-bene>t to energy supply, enable mankind to signif-icantly change the aggregated rate of decomposition.If designed with care terrestrial ecosystems togetherwith bioenergy systems, including capturing and stor-ing of carbon, may even neutralize unsustainable his-torical carbon emissions in the course of a century [6].In order to enable the global energy system to trans-

form itself into a sink technology a correct assessmentof the global biomass potential for bioenergy use is ofutmost importance. Many biomass potential estima-tions are based on uncertain data, are incomplete and,in some cases, even ignore biological sustainabilityboundaries. In particular uncertain are biomass supplypotential from existing forests by applying sustainableforest management.Obersteiner et al. [7] di<erentiate between sustain-

able and technological supply potentials. They showthat di<erence between these two concepts of esti-mating global biomass supply potentials is in excessof 200 EJ p.a. It has to be acknowledged that bychoosing to mitigate climate through high productivebiological sinks and biomass production one also de-cides on other values. Basic ecological services, likecarbon >xation, can be produced by simple ecosys-tems [8] such as high productive energy plantations.However, an elimination of more complex ecosys-tems by this approach may reduce the Jexibility andrange of ecological services generated globally. Sim-pli>cation of ecological systems may also reduce theecosystems’ capacity to respond to novel conditionsin the future, as diversity is a fundamental principleof survival in nature. Although humans depend uponecological products and services, there is limited un-derstanding on how these are produced, maintained,enhanced, or degraded [9]. Despite the increasing mo-bility of biomass, bioenergy systems are (still) tied toland. Thus, the spatial component of biomass produc-tion and bioenergy supply is very important. There isstill an unresolved discussion on whether, from an eco-logical point of view, it is better to produce biomassintensively or extensively. Noss [10] argues, basedon an extensive literature review, that well managed

natural forests have a reasonable chance of survivingand adapt to climate change by contributing to diverse,healthy, and resilient forests.Literature on bioenergy and wider sustainable de-

velopment nexus is massive (see, e.g., [11–14]) andshall not be repeated here as we only want to addsome speci>c points to this discussion. Despite thefact that there are large potentials for sustainabledevelopment, biomass production is not free fromsocial and environmental costs. In the assessment ofbiomass projects a number of synergies and potentialtrade- o<s need to be considered. Miranda and Hale[15] conclude, based on calculations of social costsof various energy production systems, that bioenergymay constitute a reasonable replacement for fossilfuel based systems, but that environmental cost cal-culations are very site speci>c and it is diLcult toexpress all environmental impacts in monetary terms.Therefore, biomass projects must be appraised inthe context of wider land management and industrialproduction systems that balance the local environmen-tal, social, and economic impacts including food se-curity; biodiversity; poverty, employment and equity;water production and Jood control; soil degradation;waste management and amenity values. There are stilla number of issues to be solved to fully clarify thebioenergy and sustainable development nexus. In par-ticular large- scale contributions of land-use, land-usecover and forestry (LULUCF) activities under theKyoto Protocol to create a joint bene>t of mitigationand adaptation to climate change are challenges thatrequire strong institutional embedding, local partici-pation, and the development, transfer and adaptationof technology.The goal of this paper is twofold. First, to illustrate

the potential supply stream of biomass from sustain-able management of temperate forests and second, toshow that this stream can be permanent and escapesink saturation when combined with biomass energytechnologies involving carbon capture and long-termsequestration.

2. Increased productivity of sinks using natureoriented silvicultural measures

Policies for mitigating global warming by o<er-ing credits for carbon sequestration have neglected

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F. Kraxner et al. / Biomass and Bioenergy 24 (2003) 285–296 287

the e<ects of forest management on the integrity ofecosystems. Silvicultural practices o<er options forenhancing the resistance and resilience to environmen-tal change while at the same time allows satisfying thedemand for wood >bers. Good forest management, ina continental European context, is the manipulationof forest stands based on centuries of accumulatedknowledge on how to manage forests in a nature ori-ented manner and has the primary objective to securethe sustainable use and maintenance of forest ecosys-tems within the frame of a multiple use forestry. Thepurpose of supplying biomass for sequestration pur-poses is only one of multiple silvicultural goals. Forestmanagement options comprise a wide range of activ-ities of silvicultural treatments within stand regenera-tion, tending, and to the sanitation and reconstructionof forest ecosystems based on the synopsis of ecolog-ical, socioeconomic, and technical knowledge.Silvicultural measures in temperate forests are usu-

ally extensive and most of the necessary infrastructurefor forest management is already in place. There area number of silvicultural measures that (de-)increaseproductivity in terms of the carbon balance.The most important are:

• thinning;• amelioration;• species change and intra-species genetic tree im-provement;

• change in rotation length including overlapping ro-tations;

• disturbances (including pest/>re/storm/snow riskmanagement); and

• forest conservation measures.

In this paper we will appraise the e<ects of thin-ning, species change, overlapping rotations, and pre-ventive risk management on gross growth and its in-teraction with a bioenergy system including carboncapture and sequestration. We will restrict our anal-ysis on gross growth of stem volume due to the factthat (1) data for other biomass components is of lim-ited reliability [16,17], (2) good forest managementdoes not allow the harvest of biomass componentsother than stem wood, and (3) the carbon pool of allother components under current forest management ismost likely not decreasing, but rather increasing (see,e.g., [18]).

3. Carbon sequestration using biomass energy CO2

removal and long-term sequestration (BECS)

Carbon removal is an end-of-pipe technology.Technologies that prevent CO2 from escaping to theatmosphere were originally developed for fossil-fuelcombustion facilities. However, the same basic CO2

capture and sequestration (BECS) technologies canbe applied to the conversion of biomass for bioenergyproduction (Fig. 1). While it is impossible for fossilfuel based conversion technologies, due to parasiticconsumption, to achieve carbon neutral cycles BECSbased technologies act as insatiable sinks. MNollerstenand Yan [19] have illustrated, for the whole processchain of fuel upgrading, CO2 removals, compression,transportation, and injection of CO2 at the >nal stor-age site, that BECS in biofuel-based energy systemsenables energy utilization with a negative CO2 bal-ance. Hence, such energy systems can lead to netreductions of CO2 in the atmosphere and constitutean important option for climate mitigation. This tech-nological option might become very valuable whennon-linear self-reinforcing climate change regimesare expected. In such cases BECS could become amajor risk containing mitigation option [6].While there are a number of di<erent technologies

for CO2 removals available, absorption is the mostcommonly used technology for removing CO2 fromgas streams. Chemical or physical solvents are usedto scrub the gases and collect the CO2. Chemical ab-sorption is a proven end-of-pipe method for removingCO2 from Jue gases. Gas separation membranes is an-other promising technology for CO2 removals, whichcan lead to energy and cost savings. However, muchfurther research and development is needed before thistechnology can be used in large-scale applications.MNollersten and Yan [19] conclude that, due to the

low additional cost for CO2 removals, bioenergy withend-of-pipe scrubbing technology might turn out tobe a cost-e<ective BECS option. For several reasonsgasi>cation of black liquor in chemical pulp mills isalso an interesting option. The combustion of blackliquor in pulp mills gives rise to large single-sourceemissions of CO2. There are also strong incentives forthe development of black liquor gasi>cation due toproduct-, process-, and energy-related reasons. Otherbiomass-integrated gasi>cation systems that are inter-esting are systems for the production of gas or liquid

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Energy Products

Bio-mass

CO2

Carbon in Underground

Storage

Forest Products

Fig. 1. The carbon cycle of bioenergy with carbon capture and sequestration.

fuels, e.g., biomass-based methanol, where suggestedprocess designs include CO2 removal from the gasi->ed biomass based on improved process economy andeLciency. A promising new method for the capture ofcarbon is the hydrocarb process [20], which was orig-inally designed to produce methanol and carbon frombiomass and fossil fuels with subsequent storage of(very large volumes of) carbon in elementary form.A recent method developed by Steinberg [21] is theCarnol system, which consists of methanol productionwith CO2 recovered from coal->red power plants and

natural gas and the methanol produced is used as al-ternative automotive fuel.Traditionally, CO2 releases from the consumption

of carbon-based fuels have been emitted to the airrather than returning the carbon to the earth’s crust.The most widely discussed options for sequestrationof captured CO2 include injection into deep geologi-cal formations and disposal in deep oceans [22]. Deepunderground disposal is regarded as the most maturestorage option today [23]. There are four main geo-logical settings appropriate for deep storage: oil and

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Table 1Low and high estimated potential of CO2 utilization and storageoptions [38,27]

Utilizationa 0.2 1 Gt C/yrExhausted gas wells 90 400 Gt COil wells 40 100 Gt CUnminable coal measures 40 Gt CSaline aquifers 90 ¿ 1000 Gt COcean disposal 400 ¿ 1200 Gt C

aMainly for the use of enhanced oil recovery. Minor contributionfor the production of chemicals.

gas >elds, deep rocks containing saline waters and un-mineable coal formations. Disposal of CO2 in deepoceans has been suggested [24], but there are consid-erable uncertainties regarding potential environmentaldamage, especially with respect to the e<ects on ma-rine life due to increased acidity, and regarding thelong-term isolation and permanence of the CO2 se-questration [25]. A large potential reservoir for car-bon disposal, in the form of solid CO2 ice, is the deepocean ice, which currently stores about 36; 000 Gt C.Table 1 presents an overview of storage potentials

as discussed in the literature. These storage potentialsalso include aquifers and ocean disposal not discussedabove. Further discussion on the economics andenvironmental aspects of these storage reservoirscan be found in Hendricks and Turkenburg [26] andIPCC [27].There are a number of recent studies that appraise

the economic competitiveness of BECS based tech-nologies. Obersteiner et al. [28] illustrate the poten-tial relative competitiveness of BECS during the 21stcentury by scenario analysis using the IIASA- MES-SAGE model and analyses from Azar and Lindgren[29]. More detailed cost analysis is outlined in Azaret al. [30], which analyze the potential for CO2 se-questration from fossil fuels and biomass energy ona comparative basis. Barreto et al. [31] focus on hy-drogen production from biomass with carbon captureand sequestration and derive detailed cost functions,that are inter alia dependent on transportation distanceand scale of production. Barreto et al. [31] assess thehydrogen production potential from BECS in a widerscenario of the hydrogen economy in the 21st century.From these studies it can be concluded that, given bestavailable technologies of BECS, a carbon price in the

range of 200–300US$ per t C would be suLcient tomake BECS fully commercial on large scales. How-ever, there are particular technologies as describedabove for the pulp and paper sector that are commer-cial at lower carbon prices in the range of 25US$ pert C. All authors also agree that there is still potentialfor technological learning, which could improve thecost competitiveness of BECS.

4. Simulation of carbon sequestration options inuneven-aged mixed Beech-spruce stands with(out)BECS

We analyzed around 100 di<erent silvicultural andbioenergy scenarios for various stand types represen-tative for the main temperate forest types. In Fig. 2,two examples with two baseline scenarios illustratethe possible interaction between two types of forestmanagement regimes and the use of BECS over tworotation periods (2×100 years). The simulations wereassumed to take place in common mixed stands of ex-isting temperate forests (no plantations).Forest stand growth was modeled by using MOSES

(MOdelling Stand rESponse), a single tree simulatorof stem wood for uneven-aged mixed forest stands[33]. The MOSES forest stand simulator allows forgrowth and yield modeling of uneven-aged foreststands composed of Norway spruce (Picea abies L.Karst) mixed with Scots pine (Pinus sylvestris L.)stands, and Common beech (Fagus sylvatica L.)with Norway spruce stands. MOSES is a single treesimulator and the associated data are based on 22real existing permanent long-term experimental plots.For each 5-year period, this program provides infor-mation on species, diameter breast height (DBH),height, crown height, height/diameter (H=D) ratio,plus tree, time and cause of extraction. For the standthe program o<ers data on site class, current annualincrement, top height, Lorey’s mean height, diame-ter of the mean basal area tree, volume lost due tonatural mortality or snow damage, regeneration, har-vested volume and volume of the growing stock. Alldata provided varies due to di<erences in forest man-agement regime that was applied. By this we couldaccount for certi>cation criteria as they are de>nedby, e.g., the Forest Stewardship Council or the PanEuropean Forest Certi>cation scheme.

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Fig. 2. Carbon sequestration trajectories under various forest management regimes and use of BECS. Scenario I: Selective cutting withBECS, Scenario II: Selective cutting without BECS, Scenario III: Single regeneration cut with BECS, and Scenario IV: Single regenerationcut without BECS.

Natural mortality and snow damage, which signif-icantly depended on the type of forest management,was modeled by MOSES. However, the decomposi-tion of coarse woody debris was assumed by us tohave a 20-year cycle.Table 2 provides an overview of the various scenar-

ios analyzed. While all four scenarios start from thesame initial stand condition, Scenarios I and II show

the implementation of active forest tending in the formof three thinnings, a regeneration planting mimick-ing the amount of natural regeneration of spruce, anda >nal regeneration cut (selective cut) at the end ofeach rotation period (after 100 years). Scenarios IIIand IV describe the same forest stand without tend-ing and planting, but also with a regeneration cutafter 100 years. All data shown in Fig. 2 and Table 2

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Fig. 2. continued.

are expressed in tons of carbon (t C). For the calcu-lation from m3 wood to t C, conversion factors fromthe Austrian Carbon Database were used [34]. In thefollowing text we provide more details on the variousforest management regimes that were assumed.Scenario I: The composition of the simulated for-

est is a mixed beech-spruce stand where, at the start,

the amount of spruce trees is four times higher than forbeech. At the beginning of the simulation, spruce is 20years of age, reaching a productivity index for standsof 37.5 [35]. Beech is 30 years of age and reaches theproductivity index for stands of 22.0 [36].MOSES starts the stand simulation at a total stock

of 43 m3 ha−1. After 15 years of simulation, a >rst

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Table 2Overview of scenarios

Sequestration of carbonForestmanagement BECS No BECS

Thinning Scenario I Scenario II1 time planting Total sequestered Total sequestered

C: 2:5 t C ha−1 yr−1 C: 0:85 t C ha−1 yr−1

No Thinning Scenario III Scenario IVNo planting Total sequestered Total sequestered

C: 1:7 t C ha−1 yr−1 C: 1:0 t C ha−1 yr−1

thinning is carried out, followed by two further thin-nings in the years 40 and 65 (spruce is at that moment80 years of age and beech 90 years).The simulation program allows for di<erent man-

ual or automatic thinning methods after each 5-yearperiod. For this modeling we used an automaticK-value-thinning according to Johann [37], wherethe period of thinning, the level of thinning, the plustree characteristics and its desired H=D ratio is setby the user. Additionally, spruce was given priorityfor the automatic plus tree selection. All three thin-nings during one rotation period were given the samesettings.After the second thinning, when spruce is 60 years

of age, planting is simulated with spruce (4000 treesper hectare), substituting natural regeneration. Beechregeneration is assumed to be natural due to site con-ditions and stand characteristics. At the end of therotation period (after 100 years), a >nal regenerationcut is carried out without crucial harming the under-growth (i.e. by using cable logging), which is used asfuture stock for the second rotation.As mentioned, this scenario is simulated over two

rotation periods, in which the same managementregime and environmental conditions are assumed(Fig. 2, Scenario I).The total yield of the three thinnings during one

rotation period is about 300 m3 ha−1 of timber har-vested. The yield of the regeneration cut at the end ofthe rotation is about 400 m3 ha−1 of timber harvested,while the total growing stock at that time reaches about440 m3 ha−1.As there is suLcient undergrowth and regeneration

(taking into consideration a high mortality rate of re-generation) so as to receive a similar growing stock in

the second rotation period, the conditions and forestrymeasures of the second rotation are assumed to be thesame as in the >rst rotation.During each rotation we assumed the occurrence

of 20 stand damaging incidents (disturbances) dueto snow impact on spruce, randomly distributed byMOSES. These stand damages can also be assumed tobe damage caused by wind or pests. The program alsocalculates a natural rate of tree mortality. Mortality anddisturbances together reach a volume of 195 m3 ha−1

in 100 years. For the coarse woody debris on groundwe assumed a decomposition rate of 20 years, whichis added to the total sequestered carbon curve (Fig. 2).At the end of each rotation period the total accumu-lated gross growth reaches 925 m3 ha−1.Scenario II: The basic stand data and forest man-

agement measure is identical to Scenario I. Scenario IIincludes two simulated rotation periods, producing thegross growth, yielding approximately the same woodvolume in the three thinnings, a regeneration plant-ing and one regeneration cut at the end of each rota-tion period. Fig. 2 illustrates identical growing stockcurves (t C ha−1) and also the same development ofwoody debris on the ground for Scenarios I and II.The di<erences in the total carbon sequestration willbe discussed later.Scenario III: In this case the stand composition

and the structure of the growing stock at the beginningof each rotation period is also identical to Scenario I.Due to di<erent forest management measures, di<er-ent stand development can be generated. There is nothinning and no replanting simulated in this scenario,but a >nal regeneration cut still occurs after 100 years.The yield of these harvests at the end of each rotationperiod reaches 440 m3 ha−1 of timber harvested. Notending (thinnings) during 100 years creates a higherrate of woody debris from natural mortality and snowdamage. Also, the growing stock volume at the endof each rotation period is slightly higher than in Sce-narios I and II, reaching 485 m3 ha−1 compared to440 m3 ha−1. However, the total accumulated grossgrowth in this scenario is about 10 percent lower thanthat in Scenarios I and II. The second rotation of thisscenario is also assumed to have a similar develop-ment as the >rst rotation period and the basic data re-mained the same.Scenario IV: As for the >rst two scenarios there is

no di<erence between Scenarios III and IV regarding

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F. Kraxner et al. / Biomass and Bioenergy 24 (2003) 285–296 293

forest management measures and stand data. Thereare two identical rotation periods simulated in order toshow the development of carbon sequestration through200 years.

5. Results

The results indicate that the most important factordetermining the productivity of sequestration is theeLciency factor of CO2 removal. There are two ma-jor components determining this eLciency. First, theeLciency of the chemical process per se, which canbe assumed to be in the range of 90–95 percent. Thesecond determinant refers to the eLciency of theindustrial metabolism in general. This means howmuch carbon stored in wood >nally ends up at thefacility that removes the carbon from the industrialmetabolism.A minor component determining the overall pro-

ductivity of BECS is the type of forest management,demonstrated in the comparison of Scenario I, wherethe forest is tended during the rotation period, andScenario III where there is only the >nal regenerationcut at the end of the rotation period.Due to the forest management regime employed in

Scenarios I and II, gross growth was larger than inthe baseline scenarios with no tending. In Scenario Iwe assumed a 70 percent eLciency of BECS from thebiomass that was extracted from the forest stand.This means that in addition to the steadily increas-

ing amount of sequestered carbon due to growingstock development, there is only a 30 percent loss ofcarbon that is emitted back to the atmospheric car-bon cycle, through thinning and >nal harvesting (Fig.2, Scenario I). After one rotation period the totalamount of sequestered carbon is about 280 t C ha−1

in 100 years. While most of the growing stock atthat point is harvested and the growing stock curvefalls “back to the starting point”, the total sequesteredcarbon curve only shows a short interruption in theincrement, which is due to the 30 percent of har-vested “carbon” decomposing (decaying) back to theatmospheric cycle (which is not sequestered withBECS). In the second rotation period, there is a sim-ilar development of the growing stock curve, but ata higher level, which is also true for the total car-bon sequestered. At the end of the second rotation

(after 200 years), the amount of sequestered car-bon will reach about 500 t C ha−1, which meansan average of about 2:5 t C ha−1 yr−1 over 200years.In Scenario II the forest management conditions are

the same as in Scenario I, but the harvested amount ofwood from thinning and >nal regeneration cut is notused at BECS. This scenario illustrates what happens,if the harvested wood is only used in traditional forestproducts (e.g., furniture, paper). For traditional forestproducts end use, a carbon reduction period of 10 yearsis assumed. The carbon, sequestered in such productsis steadily decreasing due to waste dumping of theproducts. The e<ect of this decay rate generates a totalsequestered carbon curve that does not fall verticallylike the growing stock curve after thinnings and har-vests (Fig. 2, Scenario II). The total growing stock inScenario II reaches after 200 years an amount of about170 t C ha−1 and an average of 0:85 t C ha−1 yr−1.In Scenario III the BECS method is applied with

a regeneration cut at the end of the rotation period,but without any forest tending (thinning). The com-parison with Scenario I shows that, even if the to-tal growing stock at the end of each rotation periodis slightly higher, the total sequestered carbon rate ismuch lower than in Scenario I, due to the lackingaccumulation by thinnings. However, after 200 yearsthe amount of total and permanent sequestered car-bon is about 340 t C ha−1 with an average rate of1:7 t C ha−1 yr−1 (Fig. 2, Scenario III).In Scenario IV, the stem wood is again only used

in traditional forest products and with an assumedcarbon decomposition period of 10 years withoutany BECS method. As in Scenario II, the amountof sequestered carbon is limited. Compared with thesteadily increasing curve of total sequestered carbonin Scenario III, the amount of sequestered carbon inScenario IV reaches its maximum after 200 with about200 t C ha−1 at an average of about 1 t C ha−1 yr−1

over 200 years (Fig. 2, Scenario IV).If we apply the knowledge gained from the

above-mentioned calculations (Scenario I) to anAustrian scale, we can show through a back-of-an-envelope-calculation that there is a potential between2 and 5 million t C yr−1 to be removed permanentlyfrom the atmosphere. In Austria there are about4 million ha of forest amounting to a total growingstock of 1 billion m3. The annual harvest of wood in

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294 F. Kraxner et al. / Biomass and Bioenergy 24 (2003) 285–296

Austria is 19:5 million m3 and in addition to that thereis a reserve of another 7:8 million m3 to be harvestedon a sustainable basis [38].Active forest management carries a number of ben-

e>ts additional to increased sequestration using BECS.Due to the silvicultural measures employed, the grossgrowth in Scenarios I and II was 10 percent highercompared thus with the baseline scenario of no foresttending measures (Scenarios III and IV). The timbervalue of the >nal standing stock using current pricesdi<ers by some 15 percent. The value of the totalharvest is two times higher in Scenarios I and II com-pared to the baseline case, mainly due to the di<er-ences in mortality. Mortality in the tended stand is halfof the untended, and damages and losses by snow aremuch lower. This results from the forestry measuresemployed in Scenarios I and II leading to increasesof the average H=D factor. A high H=D ratio can beassociated with higher stability of stands including im-proved resistance against storms, and enhanced capac-ity of protection functions such as erosion and rockfalls [39,40].In all the presented scenarios, the harvest at the end

of the periods is also important to open the canopyto regeneration. In a selection forest system [41] thee<ect of overlapping generations would become moreapparent [42]. The overlapping generation due tosimulated regeneration would allow for progressivegroup felling at the end of the rotation periods, whichmight further minimize the decrease period of the totalsequestered carbon curve.

6. Conclusion

Society’s response to climate change is determinedthrough the political process on di<erent levels of ag-gregation. If educated to understand the multiple ben-e>ts of sustaining diverse, healthy, resilient forests inaddition to mitigation bene>ts of carbon sequestration,people will value the ensemble of bene>ts. In this pa-per we have shown that in temperate forest ecosystemsit is possible to achieve the dual goal of maintain-ing the natural structure, dynamics and resilience ofthe ecosystem while at the same time providing con-siderable climate mitigation bene>ts. The economicsof the BECS technology indicate that conditional onhow the European emissions trading system will be

designed the pulp and paper industry will most likelybe able to implement this technology and start to geton the technological learning curve. This will be the>rst step towards a transformation of the global en-ergy system from a net emitter to a net sink operatingwithin ecological safety boundaries. Timely prepara-tion and preservation of suLcient absorptive capacityis crucial to improve the expected ecological integrityof many ecosystems, mitigate climate, and deliver sus-tainable energy on global scales.In the absence of governmental intervention BECS

might not be able to expand its market share in the nearor medium future as energy investment decisions arebased on strict cost minimization calculations givena particular demand pattern. BECS will only be ableto win the support of governments and ultimately ofthe mass of consumers if BECS can contribute tosustainable development in general and climate miti-gation in particular. Only if the full social and environ-mental costs of energy producing technologies (fromcradle to grave) are taken into account, the long-termcompetitiveness of BECS will increase and therebythe socioeconomic potential of bioenergy can be fullyutilized.Obersteiner et al. [6] argue that certi>cation pro-

cedures for sustainable forest management that arecurrently used for certifying timber products couldhelp to solve some of the sustainability questions andsite-speci>city issues related to biomass production incombination with revenues from carbon markets. In anumber of countries, e.g., Sweden, green energy cer-ti>cates are starting to win the hearts of consumers.These countries are just making their >rst experienceswith auditing the production of green energy. E<ortsto improve, be it national or international, should notmiss the bandwagon of green energy auditing and cer-ti>cation as such audits are usually conducted under awider sustainable development concept. These are farfrom perfect, but maybe a good start.

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