land use, land-use change, forestry, and agricultural activities in the clean development mechanism:...

LAND USE, LAND-USE CHANGE, FORESTRY, AND AGRICULTURALACTIVITIES IN THE CLEAN DEVELOPMENT MECHANISM:

ESTIMATES OF GREENHOUSE GAS OFFSET POTENTIAL

JANINE BLOOMFIELD and HOLLY L. PEARSONEnvironmental Defense, 257 Park Avenue South, New York, NY 10010, USA

(Received 10 May 1999; accepted in final form 21 December 1999)

Abstract. Activities involving land use, land-use change, forestry, and agriculture (LUCF) can helpreduce greenhouse gas (GHG) concentrations in the atmosphere by increasing biotic carbon storage,by decreasing GHG emissions, and by producing biomass as a substitute for fossil fuels. Potentialactivities include reducing rates of deforestation, increasing land devoted to forest plantations, regen-erating secondary forest, agroforestry, improving the management of forests and agricultural areas;and producing energy crops. Policymakers debating the inclusion of a variety of LUCF activities inthe Clean Development Mechanism (CDM) of the Kyoto Protocol need to consider the magnitude ofthe carbon contribution these activities could make. Existing estimates of the cumulative GHG offsetpotential of LUCF activities often take a global or regional approach. In contrast, land-use decisionsare usually made at the local level and depend on many factors including productive capacity ofthe land, financial considerations of the landowner, and environmental concerns. Estimates of GHGoffset potential made at a local, or at most country, level that incorporate these factors may be lower,as well as more useful for policy analyses, than global or large regional estimates. While country-level estimates exist for forestry activities, similar estimates utilizing local information need to begenerated for agricultural activities and biofuels, as well as for the cumulative potential of all LUCFactivities in a particular location.

Keywords: agroforestry, biofuels, carbon sequestration, Clean Development Mechanism, climatechange, deforestation, Kyoto Protocol, tree plantations

1. Introduction

The burning of fossil fuels in vehicles, power plants, and factories and large-scaledeforestation have substantially increased the concentrations of greenhouse gases(GHGs) in the atmosphere relative to pre-industrial levels. Atmospheric concentra-tions of carbon dioxide (CO2), the dominant GHG, are now 30% higher than 200years ago (Houghtonet al. 1995). Increased GHG concentrations are projectedto lead to regional and global changes in climate resulting in potentially seriousimpacts on human societies and natural systems including sea level rise, increasedincidence of droughts and floods, and higher temperatures (Watsonet al. 1995).In response, policymakers are devising programs for reducing emissions of GHGsand for removing them from the atmosphere.

The Kyoto Protocol on Climate Change, adopted in 1997 by the Conference ofParties to the United Nations Framework Convention on Climate Change

Mitigation and Adaptation Strategies for Global Change5: 9–24, 2000.© 2000Kluwer Academic Publishers. Printed in the Netherlands.

10 J. BLOOMFIELD AND H.L. PEARSON

(UNFCCC), established caps on the overall allowable levels of anthropogenic GHGemissions from industrialized (Annex I) nations for the period 2008–2012(UNFCCC 1997). Several provisions of the Protocol provide flexibility in the meansby which Annex I nations can reduce emissions to meet their commitments. One ofthese, the Clean Development Mechanism (CDM), as defined in Article 12 of theProtocol, allows Annex I nations to earn credits to meet domestic GHG quotas byinvesting in projects in developing (non-Annex I) countries that reduce emissionsbelow what would have occurred in the absence of the projects (UNFCCC 1997;Dudeket al.1998). Which activities would be creditable under the CDM and manyof the details necessary for implementation have yet to be clarified (Trexler andKosloff 1998).

Land use, land-use change, forestry and agricultural (LUCF) activities are oneway by which atmospheric CO2 concentrations can be decreased – by increasingcarbon storage in forests and on agricultural lands (i.e., carbon sequestration), bydecreasing emissions of GHGs from deforestation, forest harvesting, and otheractivities (i.e., avoided emissions), and by producing biomass substitute for fossilfuels (i.e., biofuels). Land can be evaluated for current carbon content, its potentialfor storing additional carbon, and the rate at which additional carbon could bestored or biofuels could be produced. Policy measures can provide incentives toencourage these activities. However, to support human society and meet a varietyof goals such as biodiversity protection and sustainable development, land is oftenused in ways that lead to less carbon storage than the theoretical maximum.

In this paper we examine the various options and trade-offs that landownersand managers in developing (non-Annex I), primarily tropical, countries face inundertaking LUCF activities. We then look at existing estimates of offset potentialfor LUCF activities and assess how realistically these estimates capture existingconstraints and driving forces. Finally, we discuss how LUCF offsets estimatescould be improved. This analysis will help policy makers better understand thecumulative offset potential for LUCF activities and will identify needs for futureanalyses.

2. Options for LUCF Activities

While some early studies looked only at planting trees to offset carbon emissions(e.g., Dyson 1977), there is no one best way to increase biotic carbon globally. Car-bon management must go hand-in-hand with existing land use and land cover andlocal social, economic, and ecological goals and constraints. In many cases, thesefactors, while ancillary to increasing carbon sequestration, may be the primarymotivation for participant involvement by non-Annex I countries in the CDM.

ACTIVITIES IN THE CLEAN DEVELOPMENT MECHANISM 11

Figure 1.Choosing a LUCF option for a given site depends on the quality of the available land, socialand economic factors, and the amount of carbon that could be sequestered or conserved.

2.1. FORESTRY

Carbon-enhancing options on forested lands depend on land-use history and sitequality (Figure 1). We consider management options that will increase carbonsequestration or decrease carbon dioxide emissions from mature and managedforests, including actively managed secondary forests and regenerating forests ondegraded or abandoned land.

2.1.1. Mature forestsMature forests can yield carbon benefits through their conservation – leaving theforests standing prevents the CO2 emissions that would have occurred throughdeforestation. Avoiding deforestation also offers many environmental benefits interms of biodiversity, water and air quality, and maintenance of local climate. Forinstance, mature forests are often multi-layered and multi-aged, with large amountsof dead wood, both standing and on the forest floor, increasing the area and di-versity of habitats and food sources available to species (Heywood and Watson1995). In forest conservation pilot projects, carbon credit has been assigned bydividing the standing stock of carbon by the number of years that the project willrun and subtracting the baseline, or without-project, case (e.g., MacDicken 1997;Brownet al.2000).


There has been concern that crediting LUCF projects within the CDM will leadto a replacement of mature forest with fast-growing tree plantations (Brown 1998).Plantations generally have higher rates of carbon sequestration than mature forests;that is, the amount of carbon in trees increases rapidly in plantations, particularlyin those managed for maximum biomass production, while in mature forests theuptake may be approximately balanced by mortality. However, as long as carbondioxide emissions associated with deforestation are taken into account (i.e., a fullcarbon accounting), replacing mature forests with plantations will generally notyield a net carbon benefit. Although mature forests, in a given climatic zone, oftensequester carbon at a slower rate than plantations, they tend to store more carbon(Brown et al.1989; Harmonet al.1990; Dixonet al.1991; Putz and Pinard 1993;Cairns and Meganck 1994). Even in cases where plantation forests are allowed tomature until their carbon storage at the end of the rotation equals the amount ofcarbon in the mature forest, average carbon storage over the length of the rotationis still higher in the mature forest because mature forest maintains carbon storage ata maximum indefinitely, whereas plantations contain plots growing from minimalcarbon to maximum over the rotation length (Vitousek 1991).

To reduce the possibility of intentional harvesting of mature forest for the expli-cit goal of obtaining carbon credits for plantations or regrowth, historical baselines(e.g., since 1990) could be used to ensure that deforestation emissions are takeninto account. A measure of this type has been proposed and advanced by a groupof organizations, including the Institute for Environmental Research in the Amazon(IPAM), the Woods Hole Research Center, the Environmental Defense Fund (EDF),and the Vitae Civilis Institute for Development, Environment and Peace, in col-laboration with the National Council of Rubber Tappers (CNS) and the Centerfor Sustainable Development of the University of Braslia (CDS), participating inthe ‘Seminar on Climate Change and Brazilian Ecosystems’ (Vitae Civilis 1998).The net carbon benefits of various project options will depend ultimately on CDMrules on baselines, wood products, and other issues relevant to LUCF projects(Schlamadinger and Marland 1998).

2.1.2. Managed forestsIn managed forest lands, there is often a large potential to improve stand manage-ment, yielding returns on both carbon and productivity (Figure 1). For example,a study in Sabah, Malaysia, found that improved harvesting methods, includingplanning and marking of skid trails, directional felling, creating a specific harvestplan, cutting climber vines before harvesting, and road and skid trail drainage,decreased carbon loss by 30% (Putz and Pinard 1993).

Options for management of forests that have been degraded through previ-ous logging or agricultural use include natural regeneration (i.e., secondary suc-cession), actively restoring the land to native forest, or planting native or exoticspecies for plantation forestry (Figure 1). Both plantations and naturally regener-ated forests may benefit mature forests by relieving pressure to harvest on mature


forest land. They may also be carbon beneficial compared to the original land use(e.g., degraded pasture) and could potentially earn credits. Moreover, plantationscan be designed to minimize soil erosion, improve water quality, and lead to thereintroduction of native plants and animals (Lugo 1997; Parrottaet al.1997).

One concern that has been voiced is that the planting of permanent mono-cultures of native or exotic tree species will be favored in sites where natural orassisted restoration of indigenous forests is feasible (Frumhoffet al.1998). Whilesuch plantations could yield eventual economic advantages, decisions to initiatesuch projects would depend heavily on demand for timber at local to global scales(Frumhoffet al.1998). Natural regeneration is a cheaper and easier option in manycases and could be favored on those grounds (Brownet al.1996).

Natural or assisted regeneration is likely to be more desirable than monoculturesof exotic species from an ecological perspective. In addition to loss of biodiversity,poorly managed monoculture plantations can produce myriad ecological problemsincluding declines in soil fertility, soil compaction, disturbances in the hydrologicalcycle, and increased risk for forest fires compared to naturally regenerated forests(Putz and Pinard 1993). In addition, use of exotic species have potentially negativeenvironmental consequences including their ability to invade, compete with, andalter native ecosystems (Vitouseket al.1987).

Wood removed from plantation forests may be used for durable wood products,pulp, or biofuels. The net carbon benefit of plantations will depend heavily onthe end use of wood products (Fearnside 1999). When the choice must be madebetween increasing carbon storage or using wood for biofuels at a given site, thebetter option in terms of carbon offset potential may depend on biomass growthrates, the efficiency of displacing fossil fuels with biomass, and the time horizonunder consideration (Marland and Schlamadinger 1997). Many factors other thancarbon will also need to be considered.

2.2. AGRICULTURE

Only half of the land that is converted from tropical forest to agriculture actuallyincreases the productive agricultural area; the other half replaces previously cul-tivated land that has been degraded and abandoned from production (Houghton1994). Thus, if existing agricultural land can be used more effectively, less forestand savanna land will need to be converted to cropland and pasture, reducing thegreenhouse gas emissions associated with land conversion (Brown 1993). In ad-dition, there are significant opportunities to increase carbon sequestration on landused for agricultural production.

As with forestry, carbon-enhancing options on agricultural lands depend on sitecharacteristics and previous land-use (Figure 1). In some non-Annex I countries,the same practices that increase soil carbon sequestration in temperate Annex Icountries could be employed. Minimizing tillage, using crop rotations that includesmall grains, hay, or other high biomass-producing crops, planting cover crops,


eliminating fallow, and other practices can increase soil carbon content and, con-sequently, soil fertility (Lalet al. 1998). In addition, multi-species agriculturalsystems that include woody plants (agroforests) are well-suited to the climate andsoils in many tropical regions (Ewel 1986, Vandermeeret al. 1998). Agroforestrysystems can help maintain soil structure, reduce rates of erosion and decompositionof the litter layer, and increase inputs to the soil, thereby sequestering carbon in soilas well as trees (Coleet al.1996). In the case of productive agricultural land, someportion of it could be used for production of dedicated energy crops, dependingon a region’s food production needs. Pastures can also be managed in ways thatincrease soil carbon (Coleet al.1996). If the land is severely degraded or marginaland in surplus, forestation, as discussed above, could produce relatively large andrapid carbon increases.

2.3. BIOFUELS

On either agricultural or forest land, plant biomass may be harvested and eitherburned to generate energy or used to produce fuels such as ethanol. Biomass maycome from a variety of sources, including conventional food crops, crops that aregrown and harvested specifically for biofuel use (so-called dedicated biofuels),crop residues, and agricultural and forestry by-products. Given current technology,burning of whole-plant biomass – instead of, or in combination with, fossil fuels –offers the greatest CO2 offset potential (Coleet al.1996). Technology is changingrapidly, however, and liquid biofuels could substantially increase in importance(see, for example, Abelson 1995; Lynd 1996; Lugar and Woolsey 1999).

Widespread use of biomass for energy in tropical countries has been evaluatedin terms of environmental, social, and economic costs and benefits (e.g., Rosillo-Calle and Cortez 1998). Centralized processing of biomass for energy could allevi-ate some of the human health concerns associated with the burning of herbaceouscrops (e.g., sugarcane), wood, or charcoal for energy (Hall and Scrase 1998). Whilepoorly managed short-rotation plantations can create environmental damage, com-pared to degraded or under-utilized agricultural land, short-rotation woody cropsmay decrease soil erosion and runoff once the trees are established (Kortet al.1998; Thorntonet al.1998).

3. Estimates of LUCF Offset Potential

In the past decade, a variety of estimates have been made of the mitigation potentialof forestry, agriculture, and biofuels activities. To use these estimates in CDMpolicy assessments, several factors must be kept in mind. First, studies are oftenindependent analyses focusing on a particular sector of interest (e.g., agriculture)without regard to potential overlap between sectors. Second, studies may not con-sider the same ecosystem carbon pools. For instance, some count aboveground


trees only, while others include above- and below-ground vegetation as well assoil, so simplifying assumptions about unmeasured pools are required to compareor sum estimates.

Finally, there is a wide range of uncertainties – political, institutional, socio-economic, demographic, environmental, and scientific – associated with using es-timates of the mitigation potential as indicators of how much credit could be earnedthrough LUCF activities. Which pools are potentially creditable within the CDMhas not been decided (see Schlamadinger and Marland 1998; Goldberg 1998). Forinstance, a decision on whether wood products will be creditable may affect thechoice of forest regeneration versus tree plantations on some parcels of degradedland as well as actual credit awards. Socio-economic and demographic factors inspecific non-Annex I countries, or regions within countries, may play a large rolein determining how much land is available for biofuel versus food production. Interms of environmental uncertainties, studies to date have assumed current envir-onmental conditions, but future changes in atmospheric CO2 levels and climateconditions could cause sequestration rates or storage potential to change (Brownetal. 1993; Brown 1996). In addition, each estimate made in offset analyses has errorassociated with it, but the magnitude of these combined errors is unknown (Brown1996).

3.1. FORESTRYACTIVITIES

Early LUCF offset potential estimates focused on increasing the uptake of carbonthrough tree planting (Dyson 1977) or reforestation of degraded pasture and grasslands (Houghton 1990). These estimates considered only the amount and suitabil-ity of the land available, not the practicality of implementing such programs, thelikelihood of landowner participation, or the time period over which such ratescould be maintained. In a later analysis, Houghtonet al. (1993) compared current,satellite-derived land cover with historical vegetation maps. Areas were assigneda plausible combination of reforestation, plantations, and agroforestry activities toderive an estimate of the total carbon sequestration potential in vegetation for thetropics of 160–170 Pg C (Houghtonet al.1993) (Table I). This amount is equivalentto 42–45 years of CO2 emissions from fossil fuel combustion in Annex I nations at1990 levels (UNFCCC 1998).

Avoiding deforestation has offset potential because the CO2 and other GHGemissions associated with deforestation are avoided and carbon remains on theland in vegetation and soils. During the 1980s, an estimated 20% of the annual at-mospheric buildup of carbon dioxide, equivalent to 1.6± 0.4 Pg C/yr, was releasedfrom tropical forests through deforestation (Brownet al.1993, 1996). According toUN Food and Agriculture Organization (1997) estimates, deforestation rates rosefrom 11.3 Mha/yr in the late 1970s to 15.5 Mha/yr in the 1980s – an increase of36%. The rate of deforestation has slowed to 13.7 Mha/yr during the first part of the1990s (1990–1995) (UN Food and Agriculture Organization 1997). However, the


TABLE I

Regional and country-level estimates of LUCF offset potential

Reference Region Carbon pools Activities Offset potential

Houghtonet al. Tropical America, Above & belowground Reforestation, plantations, 160–170 Pg C1

1993 Africa, Asia biomass agroforestry

Houghton 1996 Tropical forests Above & belowground Halting deforestation 400–500 Pg C2

biomass and soil

Trexler and 52 tropical countries Aboveground biomass Pg C, by 2050

Haugen 1994 (non-Annex I) in Plantations 2–5

in Africa, Latin America, Agroforestry 0.7–1.6

and Asia3 Natural & assisted 9–23

regeneration

Slowing deforestation 9–17

Brown et al. Tropical non-Annex I Above & belowground Pg C, by 2050

19964 countries biomass and soil Plantations 16.4

Agroforestry 6.3

Regeneration 11.5–28.7

Slow Deforestation 10.8–20.8

Brown et al. Temperate non-Annex I Above & belowground Plantations Pg C, by 2050

19965 countries6 biomass and soil 5.35

Brown 19967 Asia Above & belowground Pg C, by 2050

(tropical and temperate) biomass and soil Slowing deforestation 4.5

Forest regeneration 5.7

Tropical plantations 7.5

Tropical agroforestry 2.6

Plantations – temperate, 3.9

inc. China

Total 24.2

Paustianet al. Tropics Soil Improved management of 9–12 Pg C, by

19988 cultivated land 2050–2100

Coleet al.1996 Tropics Fossil fuel offset Production of dedicated 0.2–0.7 Pg C/yr

energy crops, agroforestry

1 No time period was specified. Lands were assumed to sequester different amounts of carbon basedon activities and forest classification.2 The amount of carbon held in forests at present which would be lost with deforestation, includingcarbon lost from soils due to cultivation.3 Only countries considered too small or too arid for substantial carbon sequestration were excluded.4 Using Nilsson and Schopfhauser (1995) and Trexler and Haugen (1994) and assuming that below-ground biomass and soil is equivalent to 25% of aboveground biomass.5 Using Nilsson and Schopfhauser (1995).6 Includes China, Asia, South Africa and South America. Japan, an Annex I country, is included inAsia. Non-Annex I countries that are part of the FSU are not included in this estimate.7 Using analyses of Trexler and Haugen (1994) and Nilsson and Schopfhauser (1995).8 An estimated 17.7 Pg C have been lost from tropical forest and grassland/savanna soils due tocultivation. We assumed that 1/2 - 2/3 of this carbon could be restored within 50–100 years, as inColeet al. (1996) and Paustianet al. (1998).


total amount of carbon lost could be substantially higher than previously thoughtwhen the effects of ground-level fires and logging (without complete deforestation)are included (Nepstadet al.1999).

Factors influencing deforestation rates include expansion of subsistence ag-riculture in Africa and Asia, and government-sponsored development programsinvolving resettlement, promotion of agriculture, and infrastructural improvements(e.g., road building, dam construction) in Latin America (UN Food and AgricultureOrganization 1999). Other factors include population growth, use of wood for fuel,unsustainable logging practices, urban expansion, uncontrolled burning during landclearing or harvesting, mining and oil drilling (Dixonet al. 1991; Trexler andHaugen 1994; Brownet al. 1996; Melillo et al. 1996). Houghton (1996) estim-ated that the long-term reduction in emissions could be 400–500 Pg C if tropicaldeforestation were completely halted (Table I), but this is unrealistic given existingsocio-economic, demographic, and political pressures to deforest.

Only one study to date (Trexler and Haugen 1994) has comprehensively evalu-ated the potential of slowing deforestation, natural and assisted forest regeneration,agroforestry, and plantation establishment to sequester carbon in tropical countriesgiven existing (i.e., early 1990s) social, political, and economic constraints andpressures. Thus, unlike the studies described above, this analysis recognized thatphysical availability of land may be quite different from availability of land forforestry intervention (Brownet al. 1993). Trexler and Haugen (1994) used inter-views and questionnaires to qualitatively evaluate the potential for 52 countriesto undertake activities and estimated how a variety of policy mechanisms, such asdiscontinuing cattle subsidies or giving landowners tree tenure and land ownership,could affect carbon storage or sequestration.

For deforestation, Trexler and Haugen (1994) projected a ‘business-as-usual’scenario. Even if demand for forest land continues, rates of deforestation willeventually decline due to the elimination of easily accessible forest and slow fur-ther as all available land in certain countries is deforested. Their estimate of thedeforestation rate for 1990 – 16 Mha/yr – was similar to the FAO estimate of 15.5Mha/yr and slightly higher than some other estimates (see Melliloet al. 1996, fora review). In their analysis, deforestation could be slowed by approximately 20%of the business-as-usual scenario, resulting in cumulative savings of approximately140 Mha of tropical forest and 9–17 Pg C by the year 2050. The impact of slowingdeforestation, as well as implementing other LUCF activities, starts gradually andgains momentum in later decades.

In addition to the CO2 emissions avoided through slowing deforestation, naturaland assisted regeneration activities on 220 Mha of already deforested tropical landcould result in cumulative carbon sequestration of 9–23 Pg C, while agroforestrycould sequester 0.7–1.6 Pg C. Plantation expansion could increase by 67 Mha fora cumulative total of 2–5 Pg C in new vegetation by 2050.

Trexler and Haugen (1994) concluded that the total cumulative potential forcarbon sequestration (aboveground trees only) in the 52 tropical countries included


in the study was 21–47 Pg C by the year 2050 (Table I). The range presented isbased on high and low estimates of biomass carbon stocks per unit area by country.This range represents an upper bound of potential sequestration, based on existingexpert knowledge at the time (M. Trexler 1999, pers. comm.). Only countries thatwere too small or too arid to have substantial offset potential were excluded. Thisamount of carbon is equivalent to 6–12 years of CO2 emissions from fossil fuelcombustion in Annex I nations at 1990 levels (UNFCCC 1998).

The Trexler and Haugen study was combined with a global forestation analysisby Nilsson and Schopfhauser (1995) into the widely accepted IntergovernmentalPanel on Climate Change (IPCC) estimate published in the Second AssessmentReport (Brownet al. 1996) (Table I). Nilsson and Schopfhauser’s analysis, whileglobal in scale, used aggregated regional data and only included land that wasregarded as ‘economically, politically, and technically feasible’ to support new,large-scale plantations. Their global estimate of 345 Mha of land availability forforestation was substantially less than previous estimates of over 1 billion ha. TheIPCC estimates do not include agroforestry, slowing deforestation or regenerationfor temperate non-Annex I countries. An analysis similar to the one Trexler andHaugen performed could be done for temperate non-Annex I countries providingagroforestry, regeneration, and slowing deforestation estimates for these areas.

Both the Trexler and Haugen (1994) and Nilsson and Schopfhauser (1995) ana-lyses have also been used for regional assessments. For example, Brown (1996)estimated the offset potential for tropical and temperate Asia (excluding Russia)from 1995–2050 to be 24 Pg C (Table I). With the exception of Japan, all countriesin Asia are non-Annex I.

Some constraints that Trexler and Haugen (1994) cited as reasons why adop-tion of carbon-sequestering activities could be slow in a particular country couldbe equally applicable to CDM projects. For example, investment in new forestryactivities would be unlikely in countries where civil war has destroyed basic hu-man services and physical infrastructure. In other countries, forestry programscould face great difficulty in the face of severe population pressures. While CDMfunding of projects was not specifically examined, Trexler and Haugen’s analysisdid assume that outside money would be available to fund projects. Thus, a newsource of funding through the CDM probably would not fundamentally change theunderlying conclusions of the report. However, an update of the study that reflectsthe changes in political, social, and economic factors since the early 1990s whenthe report was written would be valuable. Such an update could also provide moreaccurate carbon estimates and add a direct estimate of soil carbon. In addition, es-timates of the offset potential from large-scale biomass energy development couldbe included. As discussed above, biofuel technology and implementation is rapidlychanging.


3.2. AGRICULTURAL ACTIVITIES

While forestry offset estimates are generally based on the amount of land availablefor specific activities, current estimates of the potential for carbon sequestrationon cultivated lands are based on the amount of carbon lost historically throughcultivation. The assumption is that all or part of this carbon can be regained throughmanagement practices that sequester carbon (Lalet al.1998). Worldwide estimatesof carbon loss vary by approximately an order of magnitude (Wallace 1994; Coleet al. 1996), however, resulting in substantial uncertainty about the potential toincrease soil carbon content.

One worldwide analysis divided by soil types estimated that 12.2 and 5.5 PgC have been lost from tropical forest and grassland soils, respectively, due to cul-tivation (Paustianet al. 1998). Conversion from forest to well-managed pasturemay result in similar or even increased soil C levels compared with native forest.Assuming as a reasonable upper-limit that one-half to two-thirds of this carboncan be regained over a 50–100 year time period (Coleet al. 1996; Paustianet al.1998), the sequestration potential of cultivated tropical agricultural soils would be8.9–11.8 Pg C by 2050 (Table I). This amount of carbon is equivalent to 2–3 yearsof CO2 emissions from fossil fuel combustion in Annex I nations at 1990 levels(UNFCCC 1998). Several global analyses of sequestration potential are available(Coleet al.1996; Lal and Bruce 1999), but they are not divided regionally.

A more finely resolved estimate of offset potential would require more detailedinformation on current land use and management, soils, and climate. A few regionalanalyses, e.g., in the U.S. Corn Belt and in Canadian agricultural soils, have beendone (Coleet al. 1996), but none are for non-Annex I countries. Even in thesedetailed regional analyses, there is uncertainty in both carbon sequestration ratesand storage capacity.

We are not aware of any agricultural analysis to date for non-Annex I countriesthat has incorporated socio-economic factors as Trexler and Haugen did in theirforestry analysis. Consideration of these factors, as well as expected demographicchanges, could reduce estimates. However, unlike in forestry where gaining carbonon-site may require a decrease or cessation of harvesting, carbon sequestrationand productivity increases will often go hand-in-hand in agriculture. Agriculturalpractices that increase the amount of soil carbon lessen soil erosion and improvesoil quality: soils that contain more organic carbon (humus) are better able to holdwater and nutrients, which increases their productivity while protecting water qual-ity and minimizing flooding (Lalet al.1998). Higher-quality soils also help cropswithstand drought, cut irrigation needs, and increase the long-term productivity offarmed land. Thus, overcoming transaction costs and information barriers associ-ated with improved management practices may be the most important factors inrealizing the substantial offset potential of agriculture.


3.3. BIOFUELS

Estimating the potential of biofuels to substitute for fossil fuels requires assump-tions about land availability, crop choice and productivity, transport of biomass,the fossil fuel being replaced, and conversion efficiencies. Although some country-level studies of offset potential have been done, for example, for the United States(Wright and Hughes 1993), analyses are not available for most non-Annex I coun-tries or for the group as a whole.

The IPCC analysis (Coleet al.1996) separated tropical and temperate regions.Assuming that 10–15% of the world’s cropland area could be made available forproduction of biofuel crops, Coleet al. (1996) estimated that CO2 emissions couldbe reduced by 0.3–1.3 Pg C/yr. Of this total, 0.2–0.7 Pg C/yr would occur intropical regions, through production of dedicated energy crops and agroforestry(Coleet al.1996) (Table I). If these rates were achieved annually during a 50-yearperiod (as was used in the carbon sequestration estimates above), the amount ofGHG offset would be equivalent to 3–9 years of CO2 emissions from fossil fuelcombustion in Annex I nations at 1990 levels (UNFCCC 1998). An additional 0.2–0.3 Pg C/yr could be offset through worldwide use of crop residues as biofuels(assuming a 25% residue recovery rate for the world’s wheat, rice, corn, barley,and sugarcane) (Paustianet al.1998), some of which would occur in non-Annex Icountries.

The estimate in Cole et al. (1996) assumes current conversion efficiencies, but,as discussed above, technological innovations could raise the offset potential. Onthe other hand, the estimate assumes that 10 to 15% of current cropland in trop-ical regions would be available for production of biofuel crops or increased agro-forestry. Given projected population increases and the recent deceleration in grainyields per unit area (Brown 1999), many developing countries may not be able toconvert land from crop to biofuel production. An analysis that included projectionsof cropland surplus for various developing countries would be useful for assess-ments of the potential to grow dedicated biofuel crops as part of LUCF activitiesin the CDM.

3.4. TOWARDS MORE ACCURATEESTIMATES OFLUCF OFFSET POTENTIAL

Because of the methods used to generate GHG offset potential estimates for forestry,agriculture, and biofuels activities, some overlap will necessarily occur, resulting inan overestimate for the total offset potential if all estimates were simply summed.This occurs because the same land area could potentially be used for foresta-tion (natural regeneration or plantations), agroforestry, or biofuels production (Fig-ure 1). For example, the biofuels estimate assumed that 10–15% of agriculturallands could be used for production of bioenergy crops, but both Coleet al. (1996)and Brownet al.(1996) count agroforestry in their respective estimates for agricul-ture and forestry activities. All of these activities, potentially, could be assumed tooccur on the same piece of available land, which would result in multiple counting


if the totals were simply summed (Table I). Analysis at the country level or smallerscale would enable a more realistic assessment of the proportion of each activity.One approach would be to design multiple management scenarios at the country orregional level, assign land to different activities, and assess carbon as well as social,economic, and environmental consequences of each scenario. In some cases, morethan one mitigation activity could occur on a single parcel of land. For example,a biofuel crop could be produced in a manner that increases soil carbon storage(Schroeder 1992), so two types of offsets could be realized.

4. Conclusions

Crediting for biotic carbon sequestration and storage in the CDM has the poten-tial to offset significant amounts of fossil fuel emissions, help slow deforestation,and provide many important ecological and social benefits. Land-use decisions arecomplex, however, and are based on many conflicting economic, social, political,and environmental factors in addition to the amount of carbon that could be creditedfor a particular project. When selecting between different possible LUCF activitiesfor a given site, socio-economic and ecological benefits, as well as carbon credits,should be considered. Often, but not always, projects with greater amounts ofcarbon credits will also have important socio-economic and ecological benefits.Detailed country and regional level analyses including land-management plans areneeded for more accurate estimates of LUCF offset potential.

Acknowledgements

The authors would like to thank Sandra Brown, Mark Trexler, Peter Vitousek, andAnnie Petsonk for their constructive comments on manuscript drafts.

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