influences of global change on carbon sequestration by agricultural and forest soils

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161 Influences of global change on carbon sequestration by agricultural and forest soils Ole Hendrickson Abstract: Global change — including warmer temperatures, higher CO 2 concentrations, increased nitrogen deposition, increased frequency of extreme weather events, and land use change — affects soil carbon inputs (plant litter), and carbon outputs (decomposition). Warmer temperatures tend to increase both plant litter inputs and decomposition rates, making the net effect on soil carbon sequestration uncertain. Rising atmospheric carbon dioxide levels may be partly offset by rising soil carbon levels, but this is the subject of considerable interest, controversy, and uncertainty. Current land use changes have a net negative impact on soil carbon. Desertification and erosion associated with overgrazing and excess fuelwood harvesting, conversion of natural ecosystems into cropland and pasture land, and agricultural intensification are causing losses of soil carbon. Losses increase in proportion to the severity and duration of damage to root systems. Strategic landscape-level deployment of plants through agroforestry systems and riparian plantings may represent an efficient way to rebuild total ecosystem carbon, while also stabilizing soils and hydrologic regimes, and enhancing biodiversity. Many options exist for increasing carbon sequestration on croplands while maintaining or increasing production. These include no-till farming, additions of nitrogen fertilizers and manure, and irrigation and paddy culture. Article 3.4 of the Kyoto Protocol has stimulated intense interest in accounting for land use change impacts on soil carbon stocks. Most Annex I parties are attempting to estimate the potential for increased agricultural soil carbon sequestration to partly offset their growing fossil fuel greenhouse gas emissions. However, this will require demonstrating and verifying carbon stock changes, and raises an issue of how stringent a definition of verification will be adopted by parties. Soil carbon levels and carbon sequestration potential vary widely across landscapes. Wetlands contain extremely important reservoirs of soil carbon in the form of peat. Clay and silt soils have higher carbon stocks than sandy soils, and show a greater and more prolonged response to carbon sequestration measures such as afforestation. Increased knowledge of soil organisms and their activities can improve our understanding of how soil carbon will respond to global change. New techniques using soil organic matter fractionation and stable C isotopes are also making major contributions to our understanding of this topic. Key words: climate change, carbon dioxide (CO 2 ), nitrogen, soil respiration, land use change, plant roots, afforestation, no-till. Received 12 September 2003. Accepted 5 January 2004. Published on the NRC Research Press Web site at http://er.nrc.ca/ on 16 March 2004. O. Hendrickson. Environment Canada, Gatineau, QC K1A 0H3, Canada (e-mail: [email protected]). Environ. Rev. 11: 161–192 (2003) doi: 10.1139/A04-001 © 2003 NRC Canada

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Page 1: Influences of global change on carbon sequestration by agricultural and forest soils

161

Influences of global change oncarbon sequestration by agriculturaland forest soils

Ole Hendrickson

Abstract: Global change — including warmer temperatures, higher CO2 concentrations,increased nitrogen deposition, increased frequency of extreme weather events, and landuse change — affects soil carbon inputs (plant litter), and carbon outputs (decomposition).Warmer temperatures tend to increase both plant litter inputs and decomposition rates,making the net effect on soil carbon sequestration uncertain. Rising atmospheric carbondioxide levels may be partly offset by rising soil carbon levels, but this is the subject ofconsiderable interest, controversy, and uncertainty. Current land use changes have a netnegative impact on soil carbon. Desertification and erosion associated with overgrazing andexcess fuelwood harvesting, conversion of natural ecosystems into cropland and pasture land,and agricultural intensification are causing losses of soil carbon. Losses increase in proportionto the severity and duration of damage to root systems. Strategic landscape-level deploymentof plants through agroforestry systems and riparian plantings may represent an efficient wayto rebuild total ecosystem carbon, while also stabilizing soils and hydrologic regimes, andenhancing biodiversity. Many options exist for increasing carbon sequestration on croplandswhile maintaining or increasing production. These include no-till farming, additions ofnitrogen fertilizers and manure, and irrigation and paddy culture. Article 3.4 of the KyotoProtocol has stimulated intense interest in accounting for land use change impacts on soilcarbon stocks. Most Annex I parties are attempting to estimate the potential for increasedagricultural soil carbon sequestration to partly offset their growing fossil fuel greenhouse gasemissions. However, this will require demonstrating and verifying carbon stock changes, andraises an issue of how stringent a definition of verification will be adopted by parties. Soilcarbon levels and carbon sequestration potential vary widely across landscapes. Wetlandscontain extremely important reservoirs of soil carbon in the form of peat. Clay and siltsoils have higher carbon stocks than sandy soils, and show a greater and more prolongedresponse to carbon sequestration measures such as afforestation. Increased knowledge ofsoil organisms and their activities can improve our understanding of how soil carbon willrespond to global change. New techniques using soil organic matter fractionation and stableC isotopes are also making major contributions to our understanding of this topic.

Key words: climate change, carbon dioxide (CO2), nitrogen, soil respiration, land use change,plant roots, afforestation, no-till.

Received 12 September 2003. Accepted 5 January 2004. Published on the NRC Research Press Web site athttp://er.nrc.ca/ on 16 March 2004.

O. Hendrickson. Environment Canada, Gatineau, QC K1A 0H3, Canada (e-mail: [email protected]).

Environ. Rev. 11: 161–192 (2003) doi: 10.1139/A04-001 © 2003 NRC Canada

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Résumé : Le changement global – incluant des températures plus élevées, de plus fortesteneurs en CO2, des dépositions accrues d’azote, une augmentation des fréquences desévènements météorologiques extrêmes, et l’utilisation des terres – affectent l’immobilisationdu carbone dans les sols (litières végétales) et la libération du carbone (décomposition). Lestempératures plus élevées ont tendance à augmenter à la fois les taux d’immobilisation dansles litières et ceux de la décomposition, rendant incertain l’effet sur la séquestration nettede carbone dans les sols. L’augmentation des teneurs en dioxyde de carbone pourrait enpartie contrebalancer l’augmentation du carbone dans les sols, mais ceci est sujet à beaucoupd’intérêt, de controverse et d’incertitude. Les changements actuels de l’utilisation des terresont un impact négatif sur le carbone du sol. La désertification et l’érosion associées ausurpâturage et à l’excès de récolte du bois de feu, la conversion des écosystèmes naturelsen cultures et en pâturages, et l’intensification de l’agriculture entraînent des pertes nettesen carbone du sol. Les pertes augmentent en proportion de la sévérité et de la durée desdommages occasionnés aux systèmes racinaires. Un déploiement stratégique de plantes auniveau du paysage, dans les systèmes agro-forestiers et les plantations riveraines, peuventconstituer une manière efficace de reconstruire le carbone écosystémique total, tout enstabilisant les sols et les régimes hydrologiques, et en augmentant la biodiversité. Plusieursoptions se présentent pour augmenter la séquestration du carbone dans les terres en culture,tout en maintenant ou en augmentant la production. Celles-ci comprennent la culture sanslabour, l’addition de fertilisants azotés et de fumiers, ainsi que l’irrigation et la culture enrizières. L’article 3.4 du protocole de Kyoto a provoqué un intérêt marqué pour tenir comptedes impacts du changement de l’utilisation des terres sur les réserves en carbone du sol.La plupart des participants inscrits à l’Annexe 1 tentent d’évaluer le potentiel d’augmenterla séquestration de carbone dans les sols agricoles afin de contrebalancer leurs émissionscroissantes en gaz à effet serre. Cependant, ceci va demander des démonstrations et desvérifications sur le changement des réserves en carbone, et soulève la question, à savoircomment les participants adopteront une définition contraignante de la vérification. Lesteneurs en carbone du sol et le potentiel de séquestration varient largement à travers lespaysages. Les terres humides contiennent des réservoirs de carbone du sol extrêmementimportants sous forme de tourbe. Les sols argileux et limoneux ont des réserves en carboneplus élevées que les sols sablonneux, et montrent une réaction plus importante et plusprolongée suite aux mesures de séquestration du carbone, telles que l’afforestation. Uneaugmentation de la connaissance des organismes du sol et de leurs activités peut améliorernotre compréhension sur la façon aves laquelle le carbone du sol réagira au changementglobal. De nouvelles techniques utilisant le fractionnement de la matière organique dusol et les isotopes stables du C apportent également une contribution majeure à notrecompréhension sur ce sujet.

Mots clés : changement climatique, dioxyde de carbone (CO2), azote, respiration du sol,changement de l’utilisation des terres, racines des plantes, afforestation, culture sans labour.

[Traduit par la Rédaction]

Introduction

The ability of agricultural and forest soils to sequester carbon depends on the balance betweencarbon inputs and carbon outputs. Inputs to soil are mainly in the form of above- and below-groundplant litter derived from photosynthesis. Carbon outputs arise mainly from the respiratory activity ofsoil decomposer organisms.

Both photosynthesis and respiration are stimulated by higher temperatures, making the net carbonbalance in ecosystems affected by global warming uncertain. Predictions of future carbon stocks arealso rendered imprecise by uncertainty about the magnitude and rate of impending changes in theenvironment. Various aspects of global change — higher CO2, warmer temperatures, modified nutrient

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Table 1. Synergies in meeting multiple political, environmental, economic and social objectives: a broadercontext for carbon sequestration projects.

Political Environmental Economic Social

U.N. FrameworkConvention onClimate Change;Kyoto Protocol

Limiting increase ofgreenhouse gases to alevel compatible withlife

Least cost approachesto meeting nationaltargets

Public engagementin implementingmitigation andadaptation measures

Ramsar Conventionon Wetlands

Integrated waterresources management;sustaining habitat foraquatic life

“Free” ecosystemservices: waterpurification, floodcontrol, etc.

Reduction of adversehealth impactsassociated with lack ofaccess to clean water

U.N. Conventionto CombatDesertification

Restoring productivity ofdegraded lands

Decreasing reliance onglobal aid and relief

Sustainable livelihoodapproaches; reductionof refugee influxes

Convention onBiologicalDiversity

Linking conservationareas across landscapes

Sustainable use inresource sectors:fisheries, agriculture,forestry, tourism, etc.

“Ecosystem approach”:human communitiesembedded withinecosystems

cycles, and altered disturbance regimes — can each have negative or positive effects on soil carbonpools.

Climate variation is a dominant influence on biodiversity in agricultural and forest ecosystems.Different genotypes and species show different adaptive responses to climate-mediated phenomenasuch as extreme high and low temperatures, droughts, and episodic plant litter inputs arising from icestorms, fires, or windstorms. Our understanding of how individual genotypes and species respond toclimate variation is limited and imperfect. However, it is also key to predicting how different ecosystemswill respond to global change and to designing mitigation measures appropriate to a particular site.

Human activities are the ultimate drivers of global change (Millennium Ecosystem Assessment2003). Carbon sequestration projects are implemented in a particular political, environmental, economic,and social context. Climate change is only one of several global change issues addressed by multilateralenvironmental agreements (Table 1). Others include lack of clean water, desertification, and biodiversityloss. Actions to increase soil carbon sequestration can simultaneously address several of these issues. Agrowing view is that projects that provide “synergies” can maximize return on investment and deservepriority attention.

The nature of soil carbon

Carbon stocks in above-ground portions of ecosystems are easier to measure than below-groundcarbon stocks. While above-ground carbon is concentrated in living plants, below-ground carbon isdispersed in a complex mixture of plant parts, soil animals, fungi, and bacteria, mostly in variousstages of decay. The bulk of soil carbon can be considered nonliving, but it is completely permeatedand continuously reprocessed (and excreted as wastes) by living organisms. Owing to this continuousreprocessing activity, soil carbon is composed of highly complex biochemical forms with widely varyingresidence times. In addition to the activities of organisms, erosion (wind and water), and leaching oforganic compounds contribute to soil carbon displacement and (or) dispersal.

Soil organic matter can be grouped by its residence, or turnover time, into three general classes —labile (active), stable (slow release), and inert (recalcitrant) (Schlesinger 1986; Smith et al. 1997a; Batjes1999). Labile or active soil organic matter largely consists of recently deposited plant litter (includingroots), living and dead soil microorganisms and soil animals, and their immediate breakdown products.

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It has a cycling or residence time of 1–10 years. Roots are a particularly important carbon sourcein many soils (e.g., Balesdent and Balabane 1996). Stable soil organic matter consists of polymericsubstances formed after considerable processing of the active pool. These polymers are extremelydiverse in composition (depending on litter sources and soil-forming conditions) and have a residencetime of between 10 and 50 years or more (Baldock and Nelson 1999). Inert or “recalcitrant” SOM,which is also diverse in composition, may be stable for up to 500 years.

The extent to which humic substances are stabilized against microbial mineralization largely dependson the type of bonding with clay minerals (Tate and Theng 1980; Six et al. 2002). Coarse-textured soilshave higher proportions of total soil carbon bound in microbial biomass, making them susceptible tocarbon loss with environmental change (Santruckova et al. 2003). Agricultural practices that involvehigher soil disturbance result in decreased fungal activity, lower ratios of fungi to bacteria, and lessstored soil C compared with less intrusive practices (Bailey et al. 2002). Physical fractionation of soilsand soil organic matter by size and density can provide useful information about stability and persistenceof carbon in soil aggregates (Christensen 1992; Balesdent et al. 1998), particularly when combined withstable carbon isotope analysis (Balesdent et al. 1987; del Galdo et al. 2003).

Well-developed forest soils tend to show a vertical sequence of layers (FAO/ISRIC 1990) anda progressive decline in carbon concentration with depth (Nakane 1976). At the top is an organicsurface layer or “forest floor” (O horizon) with fresh, undecomposed plant debris (Oi horizon); semi-decomposed, fragmented organic matter (Oe horizon); and amorphous, well-humified organic matterlargely resulting from the activity of the soil microfauna (Oa horizon). Below this surface layer is amineral surface horizon (A); a leached subsurface mineral horizon (E); a subsurface mineral horizon thatoften shows accumulation of leached minerals and (or) organic matter (B horizon); a mineral horizonpenetrable by roots (C); and underlying bedrock (R). The E, B, C, and R horizons may be lacking, orthe B horizon may be modified by groundwater or stagnant water. Some forests have large amounts ofrelatively stable organic matter arising from inputs of coarse woody debris (Harmon et al. 1986), whicharrives at the soil surface highly depleted in nutrients owing to internal retranslocation processes duringwood formation.

Agricultural soils associated with rangelands and grasslands often have similar vertical sequences.However, if they are being cultivated (or have been in the past) they may lack the O horizon and theA horizon may be mixed with parts of the E and even the B horizon, resulting in a plow layer (Aphorizon). The B and (or) C horizons may have been broken up by deep cultivation. Soils may havebeen so degraded by past human actions that they can no longer be cultivated. Such soils may still beclassified as agricultural soils and used, for example, for grazing or noncropping production.

Soil carbon is spatially variable at both fine scales (millimetres to metres) and coarse scales (kilo-metres). Below-ground carbon stocks vary greatly across the landscape (Sombroek et al. 1999) and arehighly influenced by topography and climate. Surface soil has higher total amounts of organic carbon,which is dominantly in forms with short residence times. There are also significant amounts of long-lived organic carbon compounds in deeper soil horizons. Deeper soil carbon may include charcoal fromfires and consolidated carbon in the form of iron-humus pans or concretions. Many soils, particularlyin arid and semi-arid regions, also contain large amounts of inorganic carbon in the form of calciumcarbonate (Schlesinger 1982).

Of particular importance are wetlands, which generally have low above-ground plant carbon stocksbut significant accumulations of long-lived soil organic carbon as peat. Some forests and some agricul-tural areas (e.g., rice paddies) are themselves wetlands. Wetlands are subject to drainage for afforestationor agricultural development. Hence, they warrant attention in the context of understanding the influencesof global change on carbon sequestration by forest and agricultural soils.

Pools and fluxes of above-ground carbon are easier to measure than below-ground carbon. Measur-ing root litter inputs, a major influx of carbon in most forest and agricultural soils, is a difficult technicalchallenge. Gaseous carbon efflux from the soil surface represents a combination of autotrophic respi-

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ration of plant roots (plus associated symbiotic microorganisms) and heterotrophic respiration of soildecomposer organisms (Boone et al. 1998). There is no satisfactory method to separate autotrophic andheterotrophic respiration in soils. Leaching of carbon compounds, another potential efflux pathway,varies greatly in time and space and is also difficult to measure. Post et al. (1999) review the prospectsfor monitoring and verifying changes in soil carbon. Meentemeyer et al. (1985), Eswaran et al. (1993),and Batjes (1999) present estimates of global soil carbon stocks, while Sombroek et al. (1993) andBruce et al. (1999) discuss soil carbon sequestration in general terms.

Climate change models cannot predict future events at the site level, yet climate-related disturbancesthat result in carbon losses are highly localized. Land use change and other aspects of global change canexhibit either negative or positive synergistic effects with climate change. This is key to understandingthe potential for using carbon sequestration by agricultural and forest soils as a climate mitigation tool.Mitigation measures have a dual nature. First, they provide insurance that existing carbon stocks willbe protected. Second, they afford opportunities for carbon stock enhancement. In agriculture, thesetwo aspects of mitigation can be illustrated by soil conservation (e.g., through use of cover crops)and rehabilitation of degraded lands (e.g., through planting of multipurpose trees in an agroforestrysystem), respectively. Corresponding examples from forestry are conservation of primary forests andreestablishment of forest cover in previously deforested areas.

Impacts of global change on photosynthesis and carbon inputs to soil

Warmer temperatures will increase plant productivityCold temperatures are the major factor limiting plant growth in high-latitude (Antarctic, Arctic,

boreal, cool temperate) ecosystems. Rapid warming associated with increasing atmospheric greenhousegas concentrations has already been observed in some high-latitude regions such as continental NorthAmerica. This is expected to increase crop yields in high-latitude agricultural zones by virtue of longergrowing seasons (e.g., Cantagallo et al. 1997). Global warming is also expected to increase the growthof existing boreal forests and to allow the northward spread of forests into areas currently occupied bytundra.

This picture is complicated by the prospect of increased frequency of insect outbreaks and firesand by the collapse of forests into sedge- and grass-dominated areas in thermokarst areas (areas ofpermafrost melting and soil subsidence). Microbial communities in far northern areas may be adaptedto cold conditions and show net negative growth and enhanced C mineralization even with modestwarming (Santruckova et al. 2003). In general, however, stimulation of plant productivity by warmertemperatures will increase plant litter inputs and soil carbon pools.

Precipitation trends and their effects on plant productivity are uncertainPrecipitation trends will affect the ability of plants to respond to global warming. Although there is

a high probability that average precipitation amounts will increase, global circulation models indicateconsiderable regional variability in predicted trends. At any given point on the Earth’s surface, thereis greater uncertainty about precipitation trends than temperature trends. For example, some globalcirculation models predict that warming trends in the northern interior portions of North America willnot be matched by increasing precipitation, resulting in conversion of boreal forest to grassland acrossmuch of the region.

More extreme weather, and associated disturbance events, may decrease carbon stocks andecosystem productivity

A higher frequency of droughts, floods, and violent storms will likely have a negative impact on long-term average carbon stocks, both below- and above-ground. This magnitude of these negative impactsdepends in part on the degree to which management practices incorporate high levels of biodiversity.

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For example, grasslands with higher species diversity maintain higher overall levels of ecosystemproductivity, and this advantage increases during droughts (Tilman et al. 1996). Longer and moresevere droughts increase the probability of episodic disturbance events such as dust storms or severefires.

Changes in weather are inherently abrupt, even at hourly and daily time scales, and ecosystemsrespond to these changes in complex and nonlinear fashion. Both soil organisms and plants are highlyresponsive to wetting and drying cycles. A prolonged drought, followed by a precipitation event, andthen by warm and drier conditions, will trigger rapid decay of labile soil organic matter, spurring a boutof competition between soil microorganisms and plant roots for newly available nutrients (Griffiths andBirch 1961).

Disturbance events in forests have several impacts on the carbon budget (Apps and Kurz 1993).First, they redistribute the existing carbon by transferring carbon from living material, above and belowground, to nonliving organic matter pools, mostly near the soil surface. Second, disturbances transfercarbon out of the ecosystem (e.g., into the atmosphere as combustion products, in the case of fire). Third,disturbances change the species composition and micro-environment of the site, resetting vegetationsuccession and carbon uptake rates. Pre-disturbance species composition has a great impact on post-disturbance recovery, including the fate of soil organic matter pools. For example, post-harvest aspenstands retain extensive root networks capable of rapid nutrient uptake and resprouting of above-groundtissues (Hendrickson et al. 1989). Retention of intact root systems minimizes mineralization of soilorganic matter pools (Hendrickson and Robinson 1984).

Major disturbances in forests include forest fires, ice storms, harvesting, wind-throw, landslides,and severe insect and disease outbreaks. All these have the potential to cause large pulses of CO2 tobe released into the atmosphere — either through direct oxidation of organic matter or through deathand subsequent decomposition of once-living tissues. Stand-replacing disturbances such as crown firesare associated with the sudden death of large cohorts of trees near one another (Pickett and White1985; Kurz et al. 1995a, 1995b; Kurz and Apps 1999). Other disturbance agents, such as pollutionand some insect and disease outbreaks, may result in widespread productivity decline but only localmortality (Hall and Moody 1994). Other factors being equal, during periods of reduced disturbance(e.g., with increasing fire suppression effort), C stocks tend to increase as biomass accumulates andlitter production increases: forests act as a sink for atmospheric C (Bhatti et al. 2001).

Croplands and pastures are also exposed to fires, biomass removal, and outbreaks of insects anddiseases. However, lower above-ground carbon stocks in these systems make these disturbances lesssignificant in terms of CO2 losses. Desertification and erosion — associated with droughts, high winds,and intense rain events (Valentin 1996; Gregory et al. 1999) — are more serious threats in these systems.They cause significant losses of soil carbon, reducing the productive capacity of agricultural systemsand their long-term carbon storage capacity (Lal et al. 1999). Some carbon may simply be redepositedelsewhere as opposed to being released to the atmosphere (Lal 1995; van Noordwijk et al. 1997; Lal etal. 1998; Stallard 1998).

In recognition of the negative impacts of desertification and erosion, the Third Assessment Report ofIPCCWorking Group III (IPCC 2001b) places considerable emphasis on both soil conservation measuresand rehabilitation of severely degraded lands (those where past management activities have caused adrastic decline or disruption of productivity). Degradation is widespread in areas previously used foragriculture but then abandoned after excessive erosion, over-grazing, desertification, or salinization(Oldeman 1994; Lal and Bruce 1999). Approximately 23% of the world’s agricultural land, permanentpastures, forests, and woodland have been degraded (as defined by the United Nations EnvironmentProgramme) since the end of World War II (Oldeman et al. 1991). There is considerable scope forrebuilding carbon stocks on these lands (e.g., Dormaar and Smoliak 1985; Lal et al. 1999). Wheredegradation was caused by social and economic pressures, land rehabilitation may depend on theamelioration of the underlying causes of degradation.

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Higher carbon dioxide levels will increase plant productivity

Increasing CO2 levels will increase plant productivity (Eamus and Jarvis 1989; Ceulemans andMousseau 1994; Hättenschwiler et al. 1997) and thereby enhance the amount of C added to soils(Schimel 1995; Woodwell et al. 1998). This is partly a direct effect on photosynthesis (Medlyn etal. 1999) and partly the result of higher water use efficiency. Plant stomates open less to acquire thesame amount of CO2, and water losses are reduced. Photosynthesis will saturate at a particular CO2level, which varies with the type of plant photosynthetic metabolism. Plants (e.g., grasses) with a C4metabolism are adapted to maximize photosynthesis at current atmospheric CO2 levels. They willrespond to further increases in CO2 mainly through increased water use efficiency, whereas C3 plantswill benefit both directly from increased CO2 and from increased water use efficiency.

There has been considerable attention to the need to “filter out” the CO2 fertilization effect whencounting measures eligible for carbon credits under the Kyoto Protocol. At current rates of increase ofCO2 in the atmosphere, van Ginkel et al. (1999) estimate the magnitude of this effect at0.036 t ha−1 year−1 in temperate grassland, even after the effect of rising temperature on decom-position is deducted. However, as data from experiments with in situ field CO2 enrichment studiesbecome available, results suggest that the gains in productivity may be smaller than previous estimates(Walker et al. 1999), owing in part to limitations of soil nutrient availability (Oren et al. 2001). Con-versely, there is considerable evidence that plants grown at high nutrient supply respond more stronglyto elevated CO2 than nutrient-stressed plants (Poorter 1998).

Even given the likelihood that elevated CO2will increase plant productivity and plant litter inputsto soils, the magnitude and fate of this “new C” is very much a matter of debate. One promising newapproach for addressing this question is analysis of stable carbon isotopes. By following the fate of13C-depleted CO2 added at elevated levels (570 ppm) to beech–spruce model ecosystems in open-topchambers, Hagedorn et al. (2003) concluded that only a small fraction of new C inputs to soils willbecome long-term soil C.

Higher nitrogen inputs may increase ecosystem productivity

Manufacture of nitrogen (N) fertilizers (e.g., ammonia production from N2 gas and methane via theHaber process) and the oxidation of N2 gas to N oxides (associated with high temperatures of fossilfuel combustion) have doubled annual inputs of plant-available N — a massive change in the global Nbudget. Increasing N deposition increases plant productivity on many sites where nitrogen is a limitingnutrient (Schindler and Bayley 1993; Vitousek et al. 1997). As a general rule, soil N supply is oftenlimiting in temperate and boreal forests and grasslands, while plant growth in tropical regions is limitedby other elements.

Where plant growth is now limited by nitrogen deficiencies, increased atmospheric N depositionand applications of fertilizer N may accelerate plant growth. This tends to increase plant litter inputsand enhance the carbon stock of the soil (Wedin and Tilman 1996). Nadelhoffer et al. (1999) caution,however, that the global impact of N deposition may be comparatively small. Nitrogen saturation — theinability of ecosystems to retain added N — is increasingly common. Moreover, while N fertilizationmay increase growth, as in N-deficient northern forests, it may also delay the hardening-off process,resulting in increased winter damage, and thus negating some of the growth enhancement (Makipaa etal. 1999).

While increased nitrogen inputs stimulate growth in some regions, they may aggravate shortagesof other essential nutrients. Increased emissions of N oxides are a major contributor to acid loadsin precipitation. Leaching of the highly mobile, negatively charged nitrate anion is accompanied byincreased loss of metal cations such as magnesium, calcium, and potassium. Losses of these essentialmineral nutrients from plant canopies and soil can reduce ecosystem productivity and partly offset gainsowing to increased N availability.

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Other atmospheric pollutants tend to reduce ecosystem productivitySulfur oxides released during combustion of fossil fuels — especially coal — are the major contrib-

utor to human-derived acid loading in many regions (Fowler et al. 1989). While sulfur is an essentialplant nutrient, pollutant loads in some regions vastly exceed plant demand and may in some cases reachlevels that are directly toxic to plants. In addition to direct toxic effects, leaching of the sulfate anionis accompanied by loss of essential mineral nutrients from plant canopies and soils (Last and Watling1991).

Ground-level ozone is a serious and widespread pollutant. Current levels are high enough to reduceplant productivity in many industrialized parts of the world. For example, increased surface ozoneconcentrations may have caused grain yields to decline by 20% in some parts of Europe (Semenov et al.1997). Trees in rural areas may be more susceptible to ozone damage than those in urban areas, wherescavenging by nitrogen oxides limits damage (Gregg et al. 2003). Higher CO2 levels can also compensatefor ozone damage. In cotton, higher CO2 compensates for growth suppression resulting from elevatedO3 levels (Heagle et al. 1999). With wheat, elevated CO2 fully protects against the detrimental effects ofO3 on biomass but not grain yield (McKee et al. 1997). Similar results have been reported with soybean(Fiscus et al. 1997).

Substances such as methyl bromide and chlorofluorocarbons that deplete the stratospheric ozonelayer may be having an indirect negative effect on ecosystem productivity, owing to the increasedlevels of ultraviolet (UV-B) radiation reaching the Earth’s surface. Elevated CO2 and temperature maycompensate for growth losses. Growing seedlings of sunflower and maize at a 4 ◦C higher daily maximumtemperature, with or without higher CO2, compensates for losses from enhanced UV-B (Mark and Tevini1997). Yield increases with elevated CO2 are suppressed by UV-B more in cereals than in soybean; ricealso loses its CO2-enhanced water use efficiency (Teramura et al. 1990). However, Unsworth and Hogsett(1996) assert that many research studies from the preceding decade used unrealistic UV-B exposuresand that UV-B does not pose a threat to crops alone or in combination with other stressors.

Land use change is reducing plant and soil carbon stocks, but significant potential exists toreverse this trend

Land use change is in itself a component of global change. This has been the subject of an entireIPCC special report, Land Use, Land Use Change and Forestry (IPCC 2000). Carbon stock enhancementin forests and agricultural areas to mitigate climate change is also discussed in detail in the ThirdAssessment Reports of IPCC Working Group II (IPCC 2001a, Chapter 5) and IPCC Working Group III(IPCC 2001b, Chapter 4).

Increasing global populations have increased the pace of land use change in recent decades. Green-house gas emissions resulting from land use change remain high, although the rapid increase in fossilfuel use has meant that the proportion of total human-induced greenhouse gas emissions attributableto land use change has fallen (Houghton et al. 1983). Overall, land use change accounts for roughly20% of the global warming attributable to increasing atmospheric greenhouse gases. Land use changeincludes conversion of forests to agricultural, industrial, and urban uses; cultivation of native grasslands,conversion of primary forests to secondary forests and plantations; flooding of native ecosystems byconstruction of dams and reservoirs; drainage of wetlands; loss of hedgerows, riparian vegetation, andscattered trees due to agricultural intensification; and fragmentation of ecosystems by linear corridorsfor pipelines, power lines, highways, etc.

Among these land use changes, conversion of natural ecosystems to agricultural croplands makesthe largest single contribution to greenhouse gas emissions. Such disruptions typically result in a largereduction of vegetation biomass and a loss of about 30% of the carbon in the surface 1 m of soil (Mann1986; Detwiler 1986; Davidson and Ackermann 1993; Anderson 1995; Houghton 1995a; Kolchugina etal. 1995). Globally, conversion to arable agriculture has resulted in losses of about 50 Gt of C from soils(Harrison et al. 1993; Scharpenseel and Becker-Heidmann 1994; Houghton 1995a; Cole et al. 1996;

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Paustian et al. 2000). Total emissions of C from land use change, including that from biomass loss, haveamounted to about 122 ± 40 Gt C (Houghton 1995b; Schimel 1995).

Impacts of global change on soil respiration and carbon outputs fromsoil

Warmer temperatures will increase soil respiration

Warmer temperatures are a strong stimulus for soil respiration (Schimel 1995; Townsend and Rastet-ter 1996; Trumbore et al. 1996; Woodwell et al. 1998). Warming increases litter turnover rates and mayaccelerate decomposition of carbon already stored in soils (Jenkinson 1991; MacDonald et al. 1999;Niklinska et al. 1999; Scholes et al. 1999). Failure to account for the decay resistance of “older” soilcarbon with long residence times can lead to an overestimate of this global warming effect (Liski et al.1998; 1999; Giardina and Ryan 2000). Furthermore, while soil warming accelerates soil organic matterdecay and carbon dioxide fluxes to the atmosphere, it also increases the availability of mineral nitrogento plants, which may indirectly stimulate enough carbon storage in plants to compensate for the carbonlosses from soils (Melillo et al. 2002).

The consensus of the scientific community is that increasing carbon losses via respiration will bea major factor in diminishing the strength of existing terrestrial C sinks over time (Bolin et al. 2000;Prentice et al. 2001).The balance between photosynthesis and respiration (the “P/R ratio”, in ecology)determines whether total ecosystem carbon stocks increase or decrease. Direct observation of changesin below-ground carbon stocks may be possible through repeated intensive soil sampling in benchmarkareas within about 20 years (Conen et al. 2003).

Organic matter decomposition tends to be more responsive to temperature than photosynthesis,especially at low temperatures (Kirschbaum 2000). Global circulation models predict greater increasesin minimum than maximum temperatures, so the balance of respiration and production in winter maybe significantly affected. Warming in winter will tend to stimulate respiration (carbon loss) more thanplant production (carbon gain), resulting in a loss of soil carbon. Significant decomposition activityoccurs at low temperatures in northern regions, even under snow cover (Coxson and Parkinson 1987;Sommerfield et al.,1993). A major flush of soil respiration occurs after leaf abscission in the fall, andoften as well in spring, while soils remain frozen and above-ground tissues remain dormant. Trendstowards higher maximum temperatures in summer may also influence the P/R ratio, as the upperthreshold temperature for stimulus of plant photosynthesis is lower than for soil respiration.

Precipitation trends and their effects on soil carbon turnover are uncertain

While there is consideration uncertainty about how climate change will affect regional precipitationtrends, overall predictions are for increasing precipitation. There may be regions where increases inprecipitation do not keep pace with temperature-driven increases in potential evapo-transpiration. Inthis context it is worth noting that soil respiration continues at lower moisture potentials than doesphotosynthesis. Fungi, for example, are capable of continued metabolic activity under relatively dryconditions when plant root activity is adversely affected (Griffin 1969). Hence, if significant dryingoccurs, soil carbon stocks will likely decrease.

Other regions may experience precipitation increases that outpace potential evapo-transpiration.When soil is at or above its moisture holding capacity, soil respiration falls off rapidly (Hendrickson1985), as evidenced by peat accumulations in wetlands. Soil respiration is highly stimulated by wettingand drying (Griffiths and Birch 1961), and changes in frequency and intensity of precipitation may havemore importance for the fate of soil carbon stocks than trends in mean annual precipitation.

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Effects of higher carbon dioxide levels on decomposition rates are uncertain

Plants grown under elevated CO2 generally increase their allocation of photosynthates to roots(Rogers et al. 1996; Murray 1997). This increases the capacity and (or) activity of belowground carbonsinks (Rogers et al. 1994; Canadell et al. 1996; Körner 1996) and enhances root turnover (Pregitzeret al. 1995; Loiseau and Soussana 1999a; 1999b), rhizodeposition (Cardon 1996), and mycorrhizaldevelopment (Dhillion et al. 1996) in some but not all systems. Some measurements also have shown anincrease in soil N cycling in response to short-term enrichment in CO2 (Hungate et al. 1997), althoughother studies have shown no detectable change (Prior et al. 1997). The relationships between C and Nturnover in soils after exposure to elevated CO2 are not fully understood.

Higher CO2 concentrations may suppress decomposition of stored C, because C/N ratios in residuesmay increase (Torbert et al. 1995; Henning et al. 1996) and because more C may be allocated belowground (Owensby 1993; Morgan et al. 1994; Van Ginkel et al. 1996; Torbert et al. 1997). This may leadto an increment in ecosystem carbon stocks in croplands similar to that observed in fertilized grasslands(Casella and Soussana 1997; Loiseau and Soussana 1999a). Reduced decomposition associated withlower litter quality caused by CO2 fertilization may offset the expected temperature-induced increasein decomposition (Moore et al. 1999). However, other studies (Ross et al. 1996, Hungate et al. 1997)suggest higher carbon turnover rather than a net increase in soil carbon under elevated CO2. In a free airCO2 enrichment study of forest plots, Schlesinger and Lichter (2001) observed fast turnover of litter Cand absence of mineral soil C accumulation, suggesting that significant long-term net C sequestrationin forest soils is unlikely. Predicting the long-term influence of elevated CO2 concentrations on the Cstocks of ecosystems remains a research challenge (Bolin et al. 2000; Prentice et al. 2001).

Other things being equal, increasing CO2 levels by themselves tend to inhibit the activity of de-composer organisms. Owing to slow diffusion of gases in many soils, CO2 levels in soil already tendto exceed CO2 levels in the atmosphere many-fold. It may therefore be difficult to detect any inhibitoryeffects directly attributable to increased atmospheric CO2 levels.

Higher nitrogen inputs may increase soil carbon storage

As discussed earlier, where plant growth is now limited by nitrogen (N) supply, increased depositionof N will likely increase plant growth. This will in turn tend to enhance the carbon stock of the soil(Wedin and Tilman 1996). Assuming a typical C:N ratio of 15:1 in surface organic horizons, a soilreceiving an increment of 10 kg ha−1 year−1 of N (a typical pollutant load) could in theory sequester upto 0.15 t ha−1 year−1 of carbon. This requires the rather unrealistic assumption that none of the nitrogenis lost from the site or incorporated in above-ground plant biomass.

Nitrogen additions to soil tend to result in increased microbial biomass and are not a direct stimulusto soil respiration in the short term (Hendrickson 1985; Mikan et al. 2000). However, microbial biomassis a labile soil carbon pool, and the processes by which it is converted into forms with longer residencetimes are complex and poorly understood. A related issue is the degree to which N-induced soil carbongains may be reversed if N inputs (e.g., cessation of fertilization, replacement of N-fixing legumes withnonfixing species, reduction of nitrogen oxides as pollutant inputs) subsequently decline.

Owing to continuing elevated anthropogenic N inputs (global N inputs are now twice natural back-ground), the potential for carbon accumulation owing to N fertilization is steadily declining. Whileproductivity in many ecosystems currently responds to N inputs, continuing N additions shorten thetime until other factors become limiting. The phenomenon of nitrogen saturation, manifested by leach-ing of excess nitrogen inputs in forms such nitrate, is becoming increasingly widespread in naturalforests and grasslands in the Northern Hemisphere (Vitousek et al. 1997; Aber et al. 1998).

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More frequent extreme weather events may increase desertification and soil erosion andreduce soil carbon storage

Desertification should not be thought of as a process wholly controlled by water inputs in precipi-tation. In addition to climatic factors, it is influenced by unsustainable land use (such as overgrazing orover-harvesting of fuelwood), physiological responses of vegetation to climatic variation, and changesin soil physical properties that influence infiltration and erosion. The higher frequencies of extremeweather events (drought, intense rainstorms, high winds) predicted by climate models are likely to actin concert with these other factors to worsen the problem of desertification (Bullock and Le Houérou1996; Gitay and Noble 1998; Canziani and Diaz 1998).

Erosion control practices play a key role by preventing losses of sequestered carbon during wind-storms (often combined with drought), intense rains, and floods. Calculating soil carbon losses associatedwith erosion (or gains associated with erosion control practices) is very difficult. Lal and Bruce (1999)estimate that total soil organic carbon displaced by erosion annually is approximately 0.5 Gt, of which20% may be emitted into the atmosphere (the remainder is re-located on the landscape). Preventingwind erosion is a particularly serious challenge. Use of soil conservation measures in the Loess Plateauregion of China was estimated to prevent 10.6 × 109 t of soil loss in 1995 alone (Nie 1996; cited inIPCC 2000, Section 4.4.2.3).

In arid and semi-arid regions, where loss of woody plant cover is advancing (Kharin 1996) andleading to carbon loss (Duan et al. 1995), afforestation and proper management of existing secondaryforests can help combat desertification (Cony 1995; Kuliev 1996).Afforestation of desertified lands maybe limited, however, by costs and insufficient knowledge of ecology, genetics, and physiology (Cony1995). In relatively arid regions, fuelwood plantations may reduce pressure on natural woodlands,thereby retarding deforestation (Kanowski et al. 1992). By reducing runoff, forests control erosion andsalinity, and reduce mud slides, maintaining sites in a productive state. Afforestation activities in aridregions will become more feasible with rising atmospheric CO2 levels, given their positive effect onthe water use efficiency of photosynthesis (Grunzweig et al. 2003).

Land use change impacts on soil carbon vary according to specificmanagement practices in croplands, grazing lands, wetlands, andforests

General concepts regarding land use change and soil carbon

Land use change, as part of global change, plays a key role in carbon sequestration. Deforestationand conversion of forests to agriculture or other land uses reduce soil carbon levels and represent a majorglobal source of greenhouse gases (e.g., Balesdent et al. 1998). Losses may be transient if permanentvegetation cover such as pasture grasses is restored (Lugo et al. 1986; Cerri et al. 1991; Brown andLugo 1990). Afforestation and conversion from row crop agriculture to forages or agroforestry systemsincrease soil carbon levels.

Most of the soil C losses occur within a few years or decades of forest conversion, so that in temperatezones, where there is little expansion of agricultural lands now, losses of C have largely abated (Cole etal. 1993; Anderson 1995; Janzen et al. 1998; Larionova et al. 1998; but see Sleutel et al. 2003). Tropicalareas, however, remain an important source of CO2 because of widespread clearing of new lands andreduced duration of “fallow” periods in shifting agriculture systems (Paustian et al. 1997b; Scholes andvan Breemen 1997; Woomer et al. 1997; Mosier 1998).

There is considerable scope for land use changes that enhance soil carbon sequestration. In the past,land management has often resulted in reduced C pools, but in many regions like Western Europe, Cpools have now stabilized and are recovering. In most countries in temperate and boreal regions, forestsare expanding, although current C pools are still smaller than those in pre-industrial or pre-historictimes. While complete recovery of pre-historic C pools is unlikely, there is potential for substantial

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increases in carbon stocks. Most of the world’s agricultural soils have not reached saturation of theircarbon stocks; therefore, most are potential carbon sinks (Kern and Johnson 1993; Donigian et al. 1995).Rebuilding terrestrial carbon stocks to help offset fossil fuel emissions is a major focus of Article 3.4of the Kyoto Protocol and the special IPCC report on Land Use, Land Use Change and Forestry (IPCC2000).

As the carbon reservoir is depleted or enhanced by some change in an ecosystem, it tends to approacha threshold — some minimum or maximum level (Odum 1969; Johnson 1995). Thus, an ecosystemwith a large carbon pool may have a high potential for carbon loss, while one depleted of carbon by pastevents may have a high potential rate of carbon accumulation. As ecosystems approach their maximumcarbon pool, the sink strength (i.e., the rate of increase of the pool) will diminish. Eventually, soil Cstorage will reach a new equilibrium where C gains equal C losses (Paustian et al. 2000). Althoughboth the sequestration rate and pool of carbon may be relatively high at some stages, they cannot bemaximized simultaneously.

Consequently, additional carbon storage in response to any management shift is of limited magnitudeand duration (Greenland 1995; Scholes 1999). Rates of carbon gain often are highest in the first fewdecades after adoption of carbon-sequestering land use and management practices (Dumanski et al.1998; IGBP 1998; Smith et al. 1998).

Impacts of land use change on soil carbon sequestration must be addressed in the context of specificagricultural and forestry practices. For example, harvesting timber in secondary forests may lead tosmall gains in soil carbon if harvest residues are deposited on site. However, “whole-tree harvesting”(tree removal and chipping off site) followed by “site preparation” (mechanical disturbance of soil inpreparation for tree planting) increases soil carbon losses.

Cropland management and soil carbon

The conversion of natural systems to cultivated agriculture results in losses of soil organic carbon onthe order of 20–50% from the pre-cultivation stocks in the surface 1 m (Davidson and Ackerman 1993;Cole et al. 1997; Paustian, et al. 1997a; 1998; Lal and Bruce 1999). Loss rates are fastest immediatelyafter cultivation begins and gradually decline until soil carbon reaches a new plateau after severaldecades (Díaz-Raviña et al. 1997; Lal et al. 1998). Conversely, when cropland management practiceschange in such a way as to promote carbon sequestration, gains are fastest initially and decline as amaximum threshold is approached. In calculating net carbon changes, samples must be taken from thelower soil profile because accumulations of carbon in surface horizons may be balanced by losses ofcarbon at depth (Powlson and Jenkinson 1981; Ismail et al. 1994; McCarty et al. 1998).

The broad category of cropland management includes practices such as conservation tillage, im-proved fertilization and irrigation water management, and use of cover crops. Conservation tillagesystems were originally developed to address water quality, soil erosion, and soil nutrient retentionissues, but they also lead to higher soil carbon and increased efficiency of fossil fuel use (Lal 1989;1997; Blevins and Frye 1993; Kern and Johnson 1993; Dalal and Mayer 1996).

Increased use of cover crops can lead to significant soil carbon sequestration. In the Canadianprairies, for example, conversion of “bare fallow” (fallow with no vegetation cover) to forages resultsin initial carbon gains in the top 30 cm of soil of 0.48–0.76 t ha−1 year−1 ; conversion to cereal cropsyields lower initial carbon gains of 0.17–0.52 t ha−1 year−1 (Dumanski et al. 1998). Cover croppingprovides environmental benefits similar to conservation tillage, including reduced soil erosion andsurface water runoff. Carbon sequestration from the use of cover crops plus conservation tillage isgreater than that from conservation tillage alone (Donigian et al. 1995; Grant et al. 1997; Paustian etal. 1997 b; Buyanovsky and Wagner 1998). Creating permanent cover, or “set-asides”, further reducessoil disturbance and allocates more carbon below ground (Barker et al. 1995; Cole et al. 1997; Fellerand Beare 1997; Grace et al. 1997; Paustian et al. 1997b; Smith et al. 1997b; 1998; Carter et al. 1998;Huggins et al. 1998).

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Estimated carbon gains with improved cropland management practices depend on continued use ofthese practices. Increased carbon pools from management of terrestrial ecosystems can only partiallyoffset fossil fuel emissions. Moreover, larger C stocks may pose a risk for higher carbon dioxideemissions in the future, if the C-conserving practices are discontinued (Bremner et al. 2002). Forexample, reverting to intensive tillage in agriculture may result in rapid loss of at least part of the Caccumulated during previous years (Dick et al. 1998; Lindstrom et al. 1999; Stockfisch et al. 1999).

Management practices that enhance carbon sequestration may also increase fluxes of non-CO2greenhouse gases — notably N2O and CH4. Increased applications of fertilizers, animal manure, andsewage sludge directly contribute substrates for anaerobic microbial decay processes; no-till farming,permanent cover set-asides, and irrigated and paddy land uses tend to increase soil water content andreadily available carbon substrates.

Fertilization with nitrogen creates a potential to sequester significant amounts of soil organic matter.For example, assuming that humus is formed at a C:N ratio of 15:1, adding one part of N could sequesteras much as 15 parts of C. However, this makes several unrealistic assumptions: no leaching, no gaseouslosses, no harvest removals. Furthermore, about 1.2 t of carbon is oxidized and released as CO2 in theprocess of manufacturing, distributing, and applying 1 t of N fertilizer (Schlesinger 2000).

Additions of fertilizer N or animal manure are susceptible to gaseous loss via microbial deni-trification, particularly if these applications are accompanied by irrigation, which creates anaerobicmicrohabitats suitable for denitrifying bacteria. Denitrification can lead to release of either N2 or N2Oas gaseous end products. If significant N2O releases occur they can negate the benefits of sequesteringcarbon in soil, as N2O has 130 times the global warming potential of CO2 on a mass basis. Smith et al.(2001) have shown that including increased N2O fluxes in a full greenhouse gas accounting scenariocan significantly reduce the carbon sequestration benefits for several agricultural land use change sce-narios, including de-intensification, manure additions, and no-till farming. These authors noted that fewdata are available to quantify the effect of these scenarios on CH4 production and oxidation. Aerobicagricultural soils are thought to be methane sinks via microbial oxidation, but manure additions maydecrease the strength of the sink. It is extremely difficult to quantify net fluxes of methane and nitrousoxide. Anaerobic decomposition processes vary greatly over space and time, and high rates of N2O orCH4 production in localized microsites can easily be missed without an intensive sampling program(Hendrickson 1981).

When arid or semi-arid soils are brought under irrigation, increased organic matter input from rootsand crop residues may increase soil carbon stocks (Leuking and Schepers 1985). Estimates of carbongains range from 0.05–0.15 t ha−1 year−1, with a modal rate of 0.10 t ha−1 year−1 (Lal et al. 1998).However, expansion of irrigation may lead to higher fossil fuel use, and soil carbon gains may bepartially offset by associated N2O emissions (Schlesinger 1999, 2000).

These uncertainties could affect accounting for agricultural soils as a carbon sink under Article 3.4of the Kyoto Protocol. Smith et al. (2001) concluded that agricultural management options still showconsiderable potential for carbon mitigation after allowing for increased trace gas fluxes. But Parties tothe Protocol may find it difficult to prepare standard methodologies for calculating sources and removalsby sinks of greenhouse gases in agricultural soils given the limits in scientific knowledge and samplingdifficulties.

Agroforestry — the introduction of multi-purpose trees into food production systems — is recog-nized as having a considerable potential to increase soil carbon sequestration, particularly in tropical re-gions (Huxley 1999). Overall, agroforestry can sequester carbon at time-averaged rates of 0.2–3.1 t ha−1

(IPCC 2000, Section 4.4.4). As with other management practices, there is an upper limit to the addi-tional carbon that can be sequestered. In temperate regions, the maximum potential carbon storage withagroforestry ranges from 15–198 t ha−1 (Dixon et al. 1994), with a modal value of 34 t ha−1 (Dixon etal. 1993). Where soil N is not limiting, planting trees in strips rather than blocks is the most efficient

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way of sequestering C per unit area of woodland, owing to the increased active canopy area providedby the edges of the strips (Poulton et al. 2003).

Agroforestry represents a more stable and sustainable production system, providing increased socialand environmental benefits for local communities, as well as diversification of economic opportunities(Sanchez 1995; Leakey 1996; Fay et al. 1998). Trees in agroforestry systems improve soil productivitythrough maintenance of soil physical properties such as porosity and infiltration, fixation of nitrogen,extraction of nutrients from deep soil horizons, and promotion of more closed nutrient cycling (Young1997). These benefits, and appropriate enabling policies, are key to ensuring that carbon gains aresustained and that reversion to crop monocultures does not occur (Izac and Sanchez 2000).

Grazing lands management and soil carbon

Grazing lands — which include grassland, pasture, rangeland, shrubland, savanna, and arid grass-lands — occupy 1900 to 4400 Mha, depending on definitions (Ojima et al. 1993a). A recent globalestimate places the area of grazing lands at 3200 Mha (FAO/UNEP 1999). Grazing lands contain10–30% of the world’s soil carbon (Anderson 1991; Eswaran et al. 1993)—including approximately200–420 Gt organic C (Ojima et al. 1993a; Scurlock and Hall 1998; Batjes 1999) and 470–550 Gt ofcarbonate C to a depth of 1 m (Batjes 1999). These soil C pools will be affected by climate change andincreasing CO2 concentrations (Ojima et al. 1993b) as well as by changing land use practices.

Available means for increasing carbon sequestration in grazing lands include introduction of im-proved species and legumes, reducing grazing pressure by livestock, fire management, fertilization,irrigation, and conservation reserves (or “set-asides”). The introduction of N-fixing legumes increasesproductivity, thereby enhancing soil C storage (Fisher et al. 1997; Conant et al. 2001). Large increases insoil C have been also reported from the introduction of deep-rooted grasses in South American savannas(e.g., Fisher et al. 1994), though the area over which these findings apply is still uncertain (Davidsonet al. 1995). Numerous studies have shown benefits of better management of grazing intensity andfrequency (Manley et al. 1995; Ash et al. 1996; Burke et al. 1997; 1998); however, grazing has lessnegative impact on soil C than tillage (Kelly et al. 1996). Fire control is also an option for increasingsoil C in pastures (Burke et al. 1997).

Fertilization and irrigation are also options for increasing productivity of grazing lands. Growthresponses to phosphorus additions (Barrett and Gifford 1999) are common, especially in tropical ar-eas. Nitrogen fertilization can result in large growth responses, as well as increased biomass and soilcarbon pools (e.g., Schwab et al. 1990; Haynes and Williams 1992; Huggins et al. 1998; Schnabel etal. 2000). This effect will increase if legumes are introduced in conjunction with fertilizers (Barrow1969). Although response to increased fertility is generally greater where grazing is either reduced orremoved (Cameron and Ross 1996; McIntosh et al. 1997), normal management practice is to increasethe harvesting intensity of the additional biomass produced (e.g., Winter et al. 1989), potentially leadingto little change in carbon stocks. Fertilization and irrigation also have certain disadvantages — they en-tail significant fossil fuel consumption, tend to increase releases of non-CO2 greenhouse gases (nitrousoxide, methane), and may result in salinization or nutrient leaching problems (IPCC 2000, Table 4.6).

Protection of previously over-grazed lands and reversion of cultivated lands to perennial grasslands(e.g., in “set-aside” programs) generally increases aboveground and below-ground carbon. The rate ofcarbon sequestration is fastest initially and then declines with time over a period of 50 years (McConnelland Quinn 1988) or longer (Burke et al. 1995). Additional carbon sinks may be available if afforestationis promoted in such lands (Burke et al. 1995).

It has been suggested that if one considers only the soil component, converting forests to well-managed pastures could increase carbon storage in Amazonian soils (e.g., Cerri et al. 1996; Batjes andSombroek 1997). Forest conversion, however, can lead to losses of carbon from above-ground biomassthat more than offset any gains in soil (Neill et al. 1997). The same consideration applies to the question

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of whether conversion of natural savannas to improved pastures increases (Fisher et al. 1994; 1995) ordecreases carbon stocks (Nepstad et al. 1995).

There is growing evidence that, even within the soil sphere, improved pasture management inAmazonia may result in substantial losses of soil carbon (Fearnside and Barbosa 1998). If deep soillayers (below 1-m depth) are included in analyses, conversion of forests to pasture can result in largeemissions of deep soil carbon even if the stock in the surface soil has increased. In tropical moist forestswith a pronounced dry season, trees have much deeper roots than pasture grasses and may penetratemore than 8 m (Nepstad et al. 1994). Roots supply carbon to the soil through exudates and root litterinputs. When deep-rooted trees are removed, the soil-carbon equilibrium in the deep soil shifts to a lowerlevel over a period of decades (Trumbore et al. 1995). More recently, Veldkamp et al. (2003) have shownthat even in tropical wet forests (that do not depend upon deep roots to maintain the canopy), clearingof forests for pasture can cause significant losses of deep soil carbon. The source of this relatively labiledeep soil carbon appears to be downward leaching of dissolved organic carbon, rather than root litterinputs.

The question of whether subsidies for improved pasture management in Amazonia will result incarbon benefits is controversial. It illustrates the problem of “leakage”: gains in carbon sequestrationvia activities proposed for one sector may be offset by carbon losses in another sector (IPCC 2001b,Chapter 4). Faminow (1998) suggests that ranchers who switch to improved pasture management willslow their rates of forest clearance, but evidence reviewed by Fearnside (1999) indicates that increasedcapital supply to ranchers (from subsidies and from more profitable pastures) would have the oppositeeffect on deforestation.

Wetlands management and soil carbon

Wetlands contain an estimated 20–25% of the world’s soil carbon in the form of peat (Gorham1995), despite occupying only about 5% of the Earth’s land area (Matthews and Fung 1987; Aselmannand Crutzen 1989). Most of the wetland area is in boreal and temperate regions; roughly 10–30% isin the tropics. Peat accumulations are found where water-saturated conditions limit oxygen penetrationand limit aerobic soil respiration to a thin surface layer. Rates of carbon accumulation in peats vary withage (Armentano and Menges 1986; Tolonen and Turunen 1996) but eventually reach equilibrium wheninputs equal losses (Clymo 1984).

Wetlands represent a major global carbon reservoir. They are also the dominant global source ofmethane, the second most important greenhouse gas after carbon dioxide. The range of CH4emissionsfrom freshwater wetlands ranges from 7 to 40 g CH4 m−2 year−1; carbon accumulation rates range fromsmall losses up to 0.35 t ha−1 year−1 of storage (Gorham 1995; Tolonen and Turunen 1996; Bergkampand Orlando 1999). Using a Global Warming Potential (GWP) of 21 for CH4, emissions of CH4 of∼1.7 g m−2 year−1 will offset a CO2 sink equivalent to a 0.1 t ha−1 year−1 carbon accumulation oforganic matter (IPCC 2000, Section 4.4.6). Most freshwater wetlands therefore are small net greenhousegas sources to the atmosphere. However, some upland forested wetlands are sinks for CH4, and hencerepresent important net greenhouse gas sinks (Moosavi and Crill 1997).

The influence of climate change on wetlands is an important consideration, raising fears about apossible “runaway” greenhouse effect. Wetlands are vulnerable to future climate change (IPCC 1996,Chapter 6). Increased decomposition rates in warmer temperatures — if associated with drier conditions— may lead to large carbon losses to the atmosphere (both CO2 and CH4), particularly from north-ern peatlands (Gorham 1995). Predicted regional trends in precipitation are uncertain, but significantdecreases or increases may cause loss or new growth of wetlands, respectively.

Much is known about the effects of lowered water levels on the carbon balance of northern peatlands,based on studies in areas partially drained for forestry (Glenn et al. 1993; Roulet et al. 1993; Laine et al.1995; Martikainen et al. 1995; Minkkinen and Laine 1998). These studies may be used to predict climatechange impacts, in so far as drainage affects wetland structure and functioning in a manner similar to

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that predicted for climate-change-induced drying (Laine et al. 1996). In most drainage studies, primaryproduction and biomass increased (Laiho and Finér 1996; Laiho and Laine 1997; Sharitz and Gresham1998), litter production increased (Laiho and Fin ér 1996; Laiho and Laine 1997; Finér and Laine1998), and litter was more resistant to decomposition (Meentemeyer 1984; Berg et al. 1993; Couteauxet al. 1998). There is some evidence for increased carbon storage in the upper peat profile (Domisch etal. 1998). The net effect is to maintain the net carbon accumulation rate at or slightly above the pre-drainage level Minkkinen and Laine 1998). However, increased duration and shortened return periodsof droughts may have negative effects on the peat carbon balance (Alm et al. 1997). Furthermore,responses of forested peatlands to drainage may not be representative of responses of nonforestedwetlands. Therefore, it is not clear how soil carbon in various wetland types will respond to a warmer,drier climate.

Drainage of wetlands for agriculture is associated with potentially large and rapid carbon losses as or-ganic matter that has accumulated slowly over centuries to millennia is oxidized (Kasimir-Klemedtssonet al. 1997). When organic soils (Histosols) are drained and brought into cultivation, losses of soilcarbon do not tend to slow with time but may continue at rapid rates as long as the soil is exposed (Lalet al. 1998). Methane emissions from drained wetlands will be reduced (some drained systems may bemethane sinks), offsetting some of the net carbon dioxide emissions (Gorham 1995).

Drainage of forested wetlands, largely concentrated in boreal regions, can enhance tree growthsignificantly, but the net ecosystem carbon changes are less clear. Some studies report large net gainswhile others indicate large net losses of carbon to the atmosphere (Zoltai and Martikainen 1996). Whendrainage and disturbance to establish trees accelerates decomposition, the loss of carbon can exceed thecarbon store created by growing trees (Cannell et al. 1993). A more important mitigation measure, fromthe perspective of atmospheric CO2, is the preservation of the vast carbon reserves already present inpeatlands (van Noordwijk et al. 1997). But with or without climate change, many peatlands in boreal,continental North America may well shift from being sinks to sources of atmospheric C during the 21stcentury (Wieder 2001).

Forest management and soil carbon

Much of the focus on building and maintaining carbon stocks in forests is related to above-groundbiomass — unlike agricultural systems and wetlands, where the focus is mainly on soil organic matter.Carbon sequestration options in forests vary by social and economic conditions. In some regions,slowing or halting deforestation is the major opportunity. In other regions where deforestation rateswere once high but have declined to low levels, the most attractive opportunities are improved naturalforest management practices and afforestation–reforestation of degraded forests and wastelands.

Afforestation can significantly increase soil carbon sequestration. Silver et al. (2000) found thatwhen abandoned tropical croplands and pastures were afforested, carbon accumulated at a rate of0.41 t ha−1 year−1 over a 100-year period and at faster rates during the first 20 years (1.30 t ha−1 year−1).Soil carbon accumulates faster on sites that were cleared but not developed and on former pasture sites.Increased carbon stocks above ground tend to exceed those below ground (e.g., Richter et al. 1999).

For a given type of forest (e.g., as determined by potential mature vegetation composition) thereis generally a good correlation between above- and below-ground carbon. Forest plantations are oftenrelegated to nutrient-poor soils with lower potential for soil C accumulation (Oren et al. 2001). Soilswith higher amounts of clay and available N sequester the largest amounts of carbon, and carbonsequestration persists over longer time periods than in sandy soils.

A fenced-off area of fertile, formerly cultivated soil that was allowed to revert to woodland (Rotham-sted Farm, southeast England) has demonstrated continuing high rates of soil carbon accumulation(0.54 t ha−1 year−1 for 120 years (Poulton et al. 2003). This exceeds previously reported rates of soil Caccumulation for agricultural lands reverting to temperate hardwoods (Post and Kwon 2000). Afforesta-tion with hardwoods and conifers tends to increase soil C in mineral and litter horizons, respectively

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(Vesterdal et al. 2002). In temperate conifer plantations, rates of litter C accumulation can approach1 t ha−1 year−1 (Richter et al. 1999). Following afforestation of a maize field, “old C” was stabilized inphysically protected organic matter fractions, in addition to increases in “new C”, as shown by analysisof stable carbon isotopes (del Galdo et al. 2003).

Conversion of primary forests to secondary forests or forest plantations can result in significant soilcarbon losses, and further losses can occur if forests are converted to agriculture and other land uses.Global estimates of C emissions from deforestation are highly uncertain and show high geographicalvariability. The magnitude of forest degradation and secondary forest regrowth is not well documented.Improving the accuracy of these estimates is an urgent and challenging task. Recent evidence suggeststhat there may be natural sinks in the Amazon basin (Tian et al. 1998) that roughly offset net sourcesof C from land use change (Houghton et al. 2000). Estimates of C emissions from land-use change andforestry activities in the tropics during the 1990s range from 1.1 to 1.7 Gt year−1 with a best estimateof 1.6 Gt year−1 (Brown et al. 1996; Melillo et al. 1993; Bolin et al. 2000).

Carbon losses from human disturbance of forests are site-specific and depend on pre-existing vege-tation composition and natural disturbance regimes. Some primary forests (e.g., temperate rainforests)contain large amounts of carbon in the form of coarse woody debris (Harmon et al. 1990). These carbonstocks are generally not replaced in secondary forests. Other forests, such as much of the boreal forest,have relatively high frequencies of stand-replacing disturbances such as crown fires and major insectoutbreaks. Amounts of woody debris are lower in these forests and their soil carbon pools are lesssusceptible to loss, barring major disturbances such as drainage or tillage. As noted earlier, many forestsretain functional root systems even after disturbances. Roots and associated mycorrhizal fungi — therhizosphere — can exert a protective influence on soil carbon pools (e.g., by exudation of antibioticcompounds) but also contribute much of the labile carbon found in the soil (Hendrickson and Robinson1984). Accordingly, post-disturbance forest soil carbon losses increase in proportion to the severity andduration of damage to root system functioning.

During and after a disturbance such as timber harvest, carbon is transferred from living material,above and below ground, to soil organic matter pools. Disturbed forest stands continue to release soilcarbon into the atmosphere at an accelerated rate, as the newly transferred material is enriched in labilecarbon compounds with higher turnover rates than pre-existing soil carbon pools. Soil carbon turnoveris also accelerated by increased nutrient and moisture availability on disturbed sites. These factorsaffect pre-existing pools as well and may cause total soil carbon to decline roughly 50% below pre-disturbance levels, according to a chronosequence study of temperate hardwood forest floors (Covington1981). However, a recent study of similar stands cast doubt on this conclusion (Yanai et al. 2000). Manystudies of secondary forests in temperate regions indicate that a single timber harvest followed by promptreforestation generally does not result in major changes in forest soil carbon pools (Johnson 1992).

In general, however, short rotation plantations will not sequester and maintain as much carbon aslong rotation plantations in which vegetation and soil carbon is allowed to accumulate, owing to morefrequent opportunities for soil leaching and erosion and reduced overall litter inputs (SCBD 2003). Thepossibility of using biomass energy from short rotation plantations to displace fossil fuel energy canincrease their overall mitigation potential (Ericsson 2003), but it is also necessary to account for fossilfuels consumed in plantation establishment, maintenance, and harvesting.

If cleared forest land in tropical regions is not cultivated or degraded, surface soil carbon stocksmay show little change over decades (e.g., Lugo and Brown 1993; Christopher et al. 1997). However,in some studies soil carbon losses of up to 30% have also been reported (e.g., García-Oliva et al. 1999).The outcome may be influenced more by retention of permanent vegetation cover in deforested areasthan by cover type (Trumbore et al. 1995).

Undisturbed primary forests represent major carbon reservoirs, but there is debate as to whetherthey continue to act as carbon sinks. There is some evidence that mature tropical forests are not incarbon equilibrium but continue to act as carbon sinks (Tian et al. 1998), although the reasons for this

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are unclear. This may be related to continuing small increases in soil carbon levels, or to formation andexport of labile soil organic matter (e.g., humic acids), which is abundant in many rivers (Schlesingerand Melack 1981). Within the soil profile itself there can be leaching, and subsequent lateral transportthrough groundwater, of dissolved organic carbon. For example, the waters of the Rio Negro in theAmazon region are acid and deep-brown colored, containing high amounts of dissolved carbon (Sioli1984). This carbon may end up in sedimentary deposits where the river meets with other, silt-laden riverwaters, or where discharge into the ocean takes place (Richey et al. 1980; Meybeck 1982).

There is stronger evidence that temperate and boreal regions represent carbon sinks (Janssens etal. 2003; Nilsson et al. 2003), with an increasing contribution of soil relative to above-ground biomassat higher latitudes (Liski et al. 2002). Carbon continues to accumulate in young soils that developedfollowing deglaciation in the northern hemisphere (Harden et al. 1992). In these soils, carbon lossesfrom decomposition of organic matter (which are slow owing to low temperatures) are exceeded bythe inputs of carbon in fresh organic debris (Liski et al. 1999). However, it should be noted that borealforests are experiencing some of the most rapid warming of any region on the globe, which alreadyis causing widespread melting of permafrost. Changes that promote permafrost melting appear to becausing a net efflux of carbon dioxide from the soil carbon pool in these forests, more than offsettingany gains that occur in moss and wood (Goulden et al. 1998; Santruckova et al. 2003).

Political, social, and economic context for soil carbon sequestration

The Kyoto Protocol has greatly stimulated carbon sequestration research, particularly studies of landuse change. The cumulative global mitigation potential of carbon sequestration options is in the rangeof 10–20% of projected fossil fuel emissions by the year 2050, or approximately 100 Gt C (IPCC 2002).Soil carbon sequestration could account for 30–60 Gt C of the total and help “buy time” while nonfossilfuel energy sources and conservation measures are implemented (Lal 2003). Pursuant to Article 3.4of the Kyoto Protocol, Annex I parties are investigating the role that carbon sequestration could playto achieving their national targets, with a particular focus on agricultural soils. This requires couplingeconomic cost analyses of different farming scenarios to realistic estimates of soil carbon storage underthese scenarios (Antle et al. 2002). It also requires knowledge of baseline carbon stocks in 1990 andchanges in subsequent years.

Article 3.4 clearly poses significant measurement challenges. Sleutel et al. (2003) observed thatmany countries are facing a serious shortage of historic as well as current soil C data. They observedthat in regions where agricultural production is very intense, soil carbon may still be decreasing andC sequestration has very limited potential for reducing net greenhouse gas emissions. Inherent spatialvariability of soil carbon limits the precision of measurement of changes in soil carbon and hence, theability to detect changes (Conant et al. 2003). After reviewing issues related to non-CO2 greenhousegases, Smith et al. (2002) concluded that if parties decide on a stringent definition of verifiability,Article 3.4 is at present, and is likely to remain in the future, unverifiable. They added, however, thatless stringent levels of verifiability could be adopted that might be achieved by most parties.

Another provision of the Kyoto Protocol, the Clean Development Mechanism, allows Annex Icountries to invest in carbon mitigation projects in the developing world. Projects with a sole focuson maximum carbon sequestration are unlikely to be most cost effective, and they can also createnegative environmental (reduced water quality and quantity, loss of biodiversity) and social impacts.This can undermine the security of carbon credits for the investor and cause loss of sustainable livelihoodopportunities for local communities (SCBD 2003).

There are significant opportunities to create synergies between activities to mitigate climate change,such as enhancing soil C sinks, and activities to conserve biodiversity and provide related social benefitssuch as poverty alleviation (SCBD 2003). Revegetation of eroded or severely degraded lands has a highpotential to increase carbon sequestration and enhance biodiversity. Agroforestry projects are partic-ularly attractive from a synergies perspective, as they can be used to link forest fragments and other

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critical habitats as part of a broader strategy of landscape management and biodiversity conservation.Such holistic approaches contrast with intensive afforestation of limited areas in an attempt to maximizeabove-ground production. Strategic landscape-level deployment of plants, as through agroforestry sys-tems and riparian plantings, may be the most efficient way to rebuild total ecosystem carbon in degradedzones, and also warrants consideration in the context of agricultural de-intensification.

Acknowledgements

Research assistance provided by Jean-François Bélanger and Marie Jetten is gratefully acknowl-edged.

References

Aber, J., McDowell, W., Nadelhoffer, K., Magill, A., Berntson, G., Kamakea, M., McNulty, S., Currie, W.,Rustad L., and Fernandez, I. 1998. Nitrogen saturation in temperate forest ecosystems. Bioscience, 48:921–934.

Alm, J., Talanov, A., Saarnio, S., Silvola, J., Ikkonen, E., Aaltonen, H., Nykänen, H., and Martikainen, P.J.1997. Reconstruction of the carbon balance for microsites in a boreal oligotrophic pine fen, Finland.Oecologia, 110: 423–431.

Anderson, D.W. 1995. Decomposition of organic matter and carbon emissions from soils. In Soils and globalchange. Edited by R. Lal, J. Kimble, E. Levine, and B.A. Stewart. CRC Lewis Publishers, Boca Raton,Fla., pp. 165–175.

Anderson, J.M. 1991. The effects of climate change on decomposition processes in grassland and coniferousforests. Ecol. Appl. 1: 326–347.

Antle, J, Capalbo, S., Mooney, S., Elliott, E.T., Paustian, K.H., Mickler, R.A., and McNulty, S.G. 2002.Sensitivity of carbon sequestration costs to soil carbon rates. Environ. Pollut. 116: 413–422.

Apps, M.J., and Kurz, W.A. 1993. The Role of Canadian Forests in the Global Carbon Balance. In Carbonbalance on world’s forested ecosystems: Towards a global assessment. Edited by M. Kannien. ProceedingsIntergovernmental Panel on Climate Change Workshop, Joensuu, Finland, 11–15 May 1992, Publications ofthe Academy of Finland, Helsinki, Finland, pp. 14–28.

Armentano, T.V., and Menges, E.S. 1986. Patterns of change in the carbon balance of organic soil-wetlands ofthe temperate zone. J. Ecol. 74: 755–774.

Aselmann, I., and Crutzen, P.J. 1989. Global distribution of natural freshwater wetlands and rice paddies, theirnet primary productivity, seasonality, and possible methane emissions. J. Atmos. Chem. 8: 307–358.

Ash, A.J., Howden, S.M., and McIvor, J.G. 1996. Improved rangeland management and its implications forcarbon sequestration. In Proceedings of the Fifth International Rangeland Congress, Salt Lake City, Utah,23–28 July 1995. Society for Range Management, Denver, Colorado. Vol. 1, pp. 19–20.

Bailey, V.L., Smith, J.L., and Bolton, H., Jr. 2002. Fungal-to-bacterial ratios in soils investigated for enhancedC sequestration. Soil Biol. Biochem. 34: 997–1007.

Baldock, J.A., and Nelson, P.N. 1999. Soil organic matter. In Handbook of soil science. Edited byM.E. Sumner. CRC Press, Washington, D.C., pp. B25–B84.

Balesdent, J., and Balabane, M. 1996. Major contribution of roots to soil carbon storage inferred from maizecultivated soils. Soil Biol. Biochem. 28(9): 1261–1263.

Balesdent, J., Mariotti, A., and Guillet, B. 1987. Natural 13C abundance as a tracer for studies of soil organicmatter dynamics. Soil Biol. Biochem. 19: 25–30.

Balesdent, J., Besnard, E., Arrouays, D., and Chenu, C. 1998. The dynamics of carbon in particle-sizefractions of soil in a forest-cultivation sequence. Plant Soil, 201: 49–57.

Barker, J.R., Baumgardner, G.A., Turner, D.P., and Lee, J. 1995. Potential carbon benefits of the ConservationReserve Program in the United States. J. Biogeogr. 22: 743–751.

Barrett, D.J., and Gifford, R.M. 1999. Increased C-gain by an endemic Australian pasture grass at elevatedatmospheric CO2 concentration when supplied with non-labile inorganic phosphorus. Aust. J. Plant Physiol.26: 443–451.

Barrow, N.J. 1969. The accumulation of soil organic matter under pasture and its effect on soil properties.Aust. J. Exp. Agric. Anim. Husb. 9: 437–444.

© 2003 NRC Canada

Page 20: Influences of global change on carbon sequestration by agricultural and forest soils

180 Environ. Rev. Vol. 11, 2003

Batjes, N.H. 1999. Management options for reducing CO2 concentrations in the atmosphere by increasingcarbon sequestration in the soil. International Soil Reference and Information Centre, Wageningen, TheNetherlands, 114 pp.

Batjes, N.H., and Sombroek, W.G. 1997. Possibilities for carbon sequestration in tropical and subtropicalsoils. Global Change Biol. 3(2): 161–173.

Berg, B., Berg, M.P., Bottner, P., Box, E., Breymeyer, A., Calvo de Anta, R., Couteaux, M.M., Escudero,A., Gallardo, A., Kratz, W., Madeira, M., Mälkönen, E., McClaugherty, C., Meentemeyer, V., Munoz, F.,Piussi, P., Remacle, J., and Virzo de Santo, A. 1993. Litter mass loss rates in pine forests of Europe andeastern United States: some relationships with climate and litter quality. Biogeochemistry, 20: 127–159.

Bergkamp, G., and Orlando, B. 1999. Wetlands and climate change — exploring collaboration between theConvention on Wetlands and the UNFCCC. Ramsar Bureau, Geneva, Switzerland.

Bhatti, J.S., Apps M.J., and Jiang, H. 2001. Examining the carbon stocks of boreal forest ecosystems at standand regional scales. In Assessment of methods for soil C pools. Edited by R. Lal, M. Kimble, R.F. Follett,and B.A. Stewart. Advances in soil science, Lewis Publishers, Boca Raton, Fla., pp. 513–532.

Blevins, R.L., and Frye, W.W. 1993. Conservation tillage: An ecological approach to soil management. Adv.Agron. 51: 33–78.

Bolin, B., Sukumar, R., Ciais, P., Cramer, W., Jarvis, P., Kheshgi, H., Nobre, C., Semenov, S., and Steffen, W.2000. Global perspective. In Land use, land use change and forestry. Edited by R.T. Watson, I.R. Noble,B. Bolin, N.H. Ravindranath, D.J. Verardo, and D.J. Dokken. Special report of the IPCC, CambridgeUniversity Press, Cambridge, U.K., pp. 23–51.

Boone, R.D., Nadelhoffer, K.J., Canary, J.D., and Kaye, J.P. 1998. Roots exert a strong influence on thetemperature sensitivity of soil respiration. Nature, 396: 570–572

Bremner, E., Janzen, H.H., and McKenzie, R.H. 2002. Short-term impact of fallow frequency and perennialgrass on soil organic carbon in a Brown Chernozem in southern Alberta. Can. J. Soil Sci. 82: 481–488.

Brown, S., and Lugo, A. 1990. Effects of forest clearing and succession on the carbon and nitrogen content ofsoils in Puerto Rico and U.S. Virgin Islands. Plant Soil, 124, 53–64.

Brown, S., Sathaye, J., Cannell, M., and Kauppi, P.E. 1996. Management of forests for mitigation ofgreenhouse gas emissions. In Climate change 1995 — Impacts, adaptations and mitigation of climatechange: Scientific-Technical analyses. Edited by R.T. Watson, M.C. Zinyowera, R.H. Moss, andD.J. Dokken. Contribution of Working Group II to the Second Assessment Report of the IntergovernmentalPanel on Climate Change, Cambridge University Press, Cambridge, U.K., pp. 773–797.

Bruce, J.P., Frome, M., Haites, E., Janzen, H., Lal, R., and Paustian, K. 1999. Carbon sequestration in soils.J. Soil Water Conserv. 54: 381–389.

Bullock, P., and Le Houérou, H. 1996. Land degradation and desertification. In Climate change 1995 —Impacts, adaptions, and mitigation of climate change: Scientific-Technical analyses. Edited byR.T. Watson, M.C. Zinyowera, and R.H. Moss. Contribution of Working Group II to the SecondAssessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press,Cambridge, U.K., pp. 171–190.

Burke, I.C., Lauenroth, W.K., and Coffin, D.P. 1995. Soil organic matter recovery in semiarid grasslands:implications for the Conservation Reserve Program. Ecol. Appl. 5(3): 793–801.

Burke, I.C., Lauenroth, W.K., and Milchunas. D.G. 1997. Biogeochemistry of managed grasslands in centralNorth America. In soil organic matter in temperate agroecosystems: Long-term experiments in NorthAmerica. Edited by E.A. Paul, E.T. Elliott, K. Paustian, and C.V. Cole. CRC Press, Boca Raton, Fla.,pp. 85–102.

Burke, I.C., Lauenroth, W.K., Vinton, M.A., Hook, P.B., Kelly, R.H., Epstein, H.E., Aguiar, M.R., Robles,M.D., Aguilera, M.O., Murphy, K.L., and Gill, R.A. 1998. Plant–soil interactions in temperate grasslands.Biogeochemistry, 42: 121–143.

Buyanovsky, G.A., and Wagner, G.H. 1998. Carbon cycling in cultivated land and its global significance.Global Change Biol. 4: 131–141.

Cameron, A.G., and Ross, B.J. 1996. Fertilizer responses of established grass pastures in the NorthernTerritory. Trop. Grassl. 30: 426–429.

Canadell, J.G., Pitelka, L.F., and Ingram, J.S.I. 1996. The effects of elevated CO2 concentration on plant-soilcarbon below-ground — a summary and synthesis. Plant Soil, 187(2): 391–400.

Cannell, M.G.R., Dewar, R.C., and Pyatt, D.G. 1993. Conifer plantations on drained peatlands in Britain: a

© 2003 NRC Canada

Page 21: Influences of global change on carbon sequestration by agricultural and forest soils

Hendrickson 181

net gain or loss of carbon? Forestry, 66: 353–369.Cantagallo, J.E., Chimenti, C.A., and Hall, A.J. 1997. Number of seeds per unit area in sunflower correlates

well with a photothermal quotient. Crop Sci. 37: 178–1786.Canziani, O.F., and Diaz, S. 1998. Latin America. In The regional impacts of climate change: An assessment

of vulnerability. Edited by R.T. Watson, M.C. Zinyowera, and R.H. Moss. Special Report of IPCC WorkingGroup II, Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, U.K.,pp. 187–230.

Cardon, Z.G. 1996. Influence of rhizodeposition under elevated CO2 on plant nutrition and soil organicmatter. Plant Soil, 187: 277–288.

Carter, M.R., Gregorich, E.G., Angers, D.A., Donald, R.G., and Bolinder, M.A. 1998. Organic C and Nstorage, and organic C fractions, in adjacent cultivated and forested soils of eastern Canada. Soil andTillage Research, 47: 253–261.

Casella, E., and Soussana, J.F. 1997. Long-term effects of CO2 enrichment and temperature increase on thecarbon balance of a temperate grass sward. J. Exp. Bot. 48: 1309–1321.

Cerri, C.C., Volkoff, B., and Andreaux, F. 1991. Nature and behavior of organic matter in soils under naturalforest, and after deforestation, burning and cultivation near Manaus. For. Ecol. Manage. 38: 247–257.

Cerri, C.C., Bernoux, M., and Feigl, B.J. 1996. Deforestation and use of soil as pasture: Climatic impacts.In Interdisciplinary research on the conservation and sustainable use of the Amazonian rain forest and itsinformation requirements. Edited by R. Lieberei, C. Reisdorff, and A.D. Machado. ForschungszentrumGeesthacht GmbH (GKSS), Bremen, Germany, pp. 323.

Ceulemans, R., and Mousseau, M. 1994. Effects of elevated atmospheric CO2 on woody plants. New Phytol.127: 425–446.

Christensen, B.T. 1992. Physical fractionation of soil and organic matter in primary particles and densityseparates. Adv. Soil Sci. 20: 2–90.

Christopher, N., Melillo, J.M., Steudler, P.A., Cerri, C.C., de Moreaes, J.F.L., Piccolo, M.C., and Brito, M.1997. Soil carbon and nitrogen stocks following forest clearing for pasture in the southwestern BrazilianAmazon. Ecol. Appl. 7: 1216–1226.

Clymo, R.S. 1984. The limits to peat bog growth. Philos. Trans. R. Soc. London, 303: 605–654.Cole, C.V., Flach, K., Lee, J., Sauerbeck, D., and Stewart, B. 1993. Agricultural sources and sinks of carbon.

Water, Air, Soil Pollut. 70: 111–122.Cole, C.V., Duxbury, J., Freney, J., Heinemeyer, O., Minami, K., Mosier, A., Paustian, K., Rosenberg, N.,

Sampson, N., Sauerbeck, D., and Zhao, Q. 1996. Agricultural options for mitigation of greenhouse gasemissions. In Climate change 1995 — Impacts, adaptations, and mitigation of climate change: Scientific-Technical analyses. Edited by R.T. Watson, M.C. Zinyowera, R.H. Moss, and D.J. Dokken. CambridgeUniversity Press, Cambridge, U.K., pp. 745–771.

Cole, C.V., Duxbury, J., Freney, J., Heinemeyer, O., Minami, K., Mosier, A., Paustian, K., Rosenburg, N.,Sampson, N., Sauerbeck, D., and Zhao, Q. 1997. Global estimates of potential mitigation of greenhousegas emissions by agriculture. Nutr. Cycling Agroecosyst. 49: 221–228.

Conant, R.T., Paustian, K., and Elliot, E.T. 2001. Grassland management and conversion into grassland:Effects on soil carbon. Ecol. Appl. 11: 343–355.

Conant, R.T., Smith, G.R., and Paustian, K. 2003. Spatial variability of soil carbon in forested and cultivatedsites: implications for change detection. J. Environ. Qual. 32: 278–286.

Conen, F., Yakutin, M.V., and Sambuu, A.D. 2003. Potential for detecting changes in soil organic carbonconcentrations resulting from climate change. Global Change Biol. 9: 1515–1520.

Cony, M.A. 1995. Rational afforestation of arid and semiarid lands with multipurpose trees. Interciencia, 2(5):249–253.

Couteaux, M.M., McTiernan, K.B., Berg, B., Szuberla, D., Dardenne, P., and Bottner, P. 1998. Chemicalcomposition and carbon mineralisation potential of Scots pine needles at different stages of decomposition.Soil Biol. Biochem. 30: 583–595.

Covington, W.W. 1981. Changes in forest floor organic matter and nutrient content following clear cutting innorthern hardwoods. Ecology, 62(1): 41–48.

Coxson, D.S., and Parkinson, D. 1987. Winter respiratory activity in aspen woodland forest floor litter andsoil. Soil Biol. Biochem. 19: 49–59.

Dalal, R.C., and Mayer, R.J. 1996. Long-term trends in fertilization of soils under continuous cultivation and

© 2003 NRC Canada

Page 22: Influences of global change on carbon sequestration by agricultural and forest soils

182 Environ. Rev. Vol. 11, 2003

cereal cropping in Southern Queensland. II. Total organic carbon and its rate of loss from the soil profile.Aust. J. Soil Res. 24: 281–292.

Davidson, E.A., and Ackerman, I.L. 1993. Changes in soil carbon inventories following cultivation ofpreviously untilled soils. Biogeochemistry, 20: 161–193.

Davidson, E.A., Nepstad, D.C., Klink, C., and Trumbore, S.E. 1995. Pasture soils as carbon sink. Nature,376: 472–473.

del Galdo, I., Six, J., Peressotti, A., and Francesca Cotrufo, M. 2003. Assessing the impact of land-use changeon soil C sequestration in agricultural soils by means of organic matter fractionation and stable C isotopes.Global Change Biol. 9: 1204–1213.

Detwiler, R.P. 1986. Land use change and global carbon cycle: The role of tropical soils. Biogeochemistry, 2:67–93.

Dhillion, S.S., Roy, J., and Abrams, M. 1996. Assessing the impact of elevated CO2 on soil microbial activityin a Mediterranean model ecosystem. Plant Soil, 187: 333–342.

Díaz-Raviña, R.A., Magrin, G.O, Travasso, M.I., and Rodr íguez, R.O. 1997. Climate change and its impacton the properties of agricultural soils in the Argentinean Rolling Pampas. Clim. Res. 9: 25–30.

Dick, W.A., Blevins, R.L., Frye, W.W., Peters, S.E., Christenson, D.R., Pierce, F.J., and Vitosh, M.L. 1998.Impacts of agricultural management practices on C sequestration in forest-derived soils of the eastern CornBelt. Soil Tillage Res. 47: 235–244.

Dixon, R.K., Winjum, J.K., and Schroeder, P.E. 1993. Conservation and sequestration of carbon: the potentialof forest and agroforest management practices. Global Environ. Change, 3(2): 159–173.

Dixon, R.K., Wimjum, J.K., Andrasko, K.J., Lee, J.J., and Schroeder, P.E. 1994. Integrated systems:assessing of promising agroforest and alternative land use practices to enhance carbon conservation andsequestration. Clim. Change, 30: 1–23.

Domisch, T., Finér, L., Karsisto, M., Laiho, R., and Laine, J. 1998. Relocation of carbon from decaying litterin drained peat soils. Soil Biol. Biochem. 30: 1529–1536.

Donigian, A.S., Partwardhan, A.S., Jackson, R.V., Barnwell, T.O., Weinrich, K.B., and Rowell, A.L.1995. Modeling the impacts of agricultural management practices on soil carbon in the central U.S. InSoil Management and Greenhouse Effect. Edited by R. Lal, J. Kimble, E. Levine, and B.A. Stewart.CRC-Lewis Publishers, Boca Raton, Fla., pp. 121–135.

Dormaar, J.F., and Smoliak, S. 1985. Recovery of vegetative cover and soil organic matter during revegetationof abandoned farmland in a semiarid climate. J. Range Manage. 38: 487–91.

Duan, Z., Liu., X., and Qu, J. 1995. Effect of land desertification on CO2 content of atmosphere in China.Agric. Input Environ. 1995: 279–302.

Dumanski, J., Desjardins, R.L., Tarnocai, C., Monreal, C., Gregorich, E.G., Kirkwood, V., and Campbell, C.A.1998. Possibilities for future carbon sequestration in Canadian agriculture in relation to land use changes.Clim. Change, 40: 81–103.

Eamus, D., and Jarvis, P.G. 1989. The direct effects of increase in the global atmospheric CO2 concentrationon natural and commercial trees and forests. Adv. Ecol. Res. 19: 1–55.

Ericsson, E. 2003. Carbon accumulation and fossil fuel substitution during different rotation scenarios. Scand.J. For. Res. 18: 269–278.

Eswaran, H., Van den Berg, E., and Reich, P. 1993. Organic carbon in soils of the world. Soil Sci. Soc. Am.J. 57: 192–194.

Faminow, M.D. 1998. Cattle, deforestation and development in the Amazon: An economic, agronomic andenvironmental perspective. CAB International, Wallingford, United Kingdom, 253 pp.

FAO/ISRIC, 1990. Guidelines for soil description. Food and Agriculture Organization, Rome, Italy.FAO/UNEP, 1999. Terminology for integrated resources planning and management. Food and Agriculture

Organization/United Nations Environmental Programme, Rome, Italy and Nairobi, Kenya.Fay, C., de Foresta, H., Sarait, M., and Tomich, T.P. 1998. A policy breakthrough for Indonesian farmers in

the Krui damar agroforests. Agrofor. Today, 10(2): 25–26.Fearnside, P.M. 1999. Biodiversity as an environmental service in Brazil’s Amazonian forests: Risks, value

and conservation. Environ. Conserv. 26(4): 305–321.Fearnside, P.M., and Barbosa, R.I. 1998. Soil carbon changes from conversion of forest to pasture in Brazilian

Amazonia. For. Ecol. Manage. 108(1–2): 147–166.Feller, C., and Beare, M.H. 1997. Physical control of soil organic matter dynamics in the tropics. Geoderma,

© 2003 NRC Canada

Page 23: Influences of global change on carbon sequestration by agricultural and forest soils

Hendrickson 183

79: 69–116.Finér, L., and Laine, J. 1998. Fine root dynamics at drained peatland sites of different fertility in southern

Finland. Plant Soil, 201: 27–36.Fiscus, E.L., Reid, C.D., Miller, J.E., and Heagle, A.S. 1997. Elevated CO2 reduces O3 flux and O3-induced

yield losses in soybeans: possible implications for elevated CO2 studies. J. Exp. Bot. 48: 307–313.Fisher, M.J., Rao, I.M., Lascano, C.E., Ayarza, M.A., Sanz, J.I., Thomas, R.J., and Vera, R.R. 1995. Pasture

soils as carbon sink. Nature, 376(10): 473.Fisher, M.J., Rao, I.M., Ayarza, M.A., Lascano, C.E., Sanz, J.I., Thomas, R.J., and Vera, R.R. 1994. Carbon

storage by introduced deep-rooted grasses in the South American savannas. Nature, 371(6494): 236–238.Fisher, M.J., Thomas, R.J., and Rao, I.M. 1997. Management of tropical pastures in acid-soil savannas of

South America for carbon sequestration in the soil. In Management of carbon sequestration in soil. Editedby R. Lal, J.M. Kimble, R.F. Follett, and B.A. Stewart. CRC-Lewis Press, Boca Raton, Fla., pp. 405–420.

Fowler, D., Cape, J.N., and Unsworth, M.H. 1989. Deposition of atmospheric pollutants on forests. Philos.Trans. R. Soc., London, 324B: 247–265.

García-Oliva, F., Sanford, R.L., and Kelly, E. 1999. Effects of slash-and-burn management on soil aggregateorganic C and N in a tropical deciduous forest. Geoderma, 88(1–2): 1–12.

Giardina, C.P., and Ryan, M.G. 2000. Evidence that decomposition rates of organic carbon in mineral soils donot vary with temperature. Nature, 404: 858–861.

Gitay, H., and Noble, I.R. 1998. Middle East and arid Asia. In The regional impacts of climate change: Anassessment of vulnerability. Edited by R.T. Watson, M.C. Zinyowera, and R.H. Moss. Special Reportof IPCC Working Group II, Intergovernmental Panel on Climate Change, Cambridge University Press,Cambridge, U.K., pp. 231–252.

Glenn, S., Heyes, A., and Moore, T.R. 1993. Carbon dioxide and methane emissions from drained peatlandsoils, southern Quebec. Global Biogeochem. Cycles, 7: 247–258.

Gorham, E. 1995. The biogeochemistry of northern peatlands and its possible responses to global warming.In Biotic feedbacks in the global climatic system. Edited by G.M. Woodwell and F.T. MacKenzie. OxfordUniversity Press, New York, N.Y., pp. 169–187.

Goulden, M.L., Wofsy, S.C., Harden, J.W., Trumbore, S.E., Crill, P.M., Gower, S.T., Fries, T., Daube, B.C.,Fan, S.M., Sutton, D.J., Bazza, A., and Munger, J.W. 1998. Sensitivity of boreal forest carbon balance tosoil thaw. Science, 279: 214–216.

Grace, P.R., Post, W.M., Godwin, D.C., Bryceson, K.P., Truscott, M.A., and Hennessy, K.J. 1997. Soil carbondynamics in relation to soil surface management and cropping systems in Australian agroecosystems. InManagement of carbon sequestration in soil. Edited by R. Lal, J.M. Kimble, R.F. Follett, and B.A. Stewart.CRC-Lewis Press, Boca Raton, Fla., pp. 175–193.

Grant, R.F., Izaurralde, R.C., Nyborg, M., Malhi, S.S., Soberg, E.D., and Jans-Hammermeister, D. 1997. InSoil processes and the carbon cycle. Edited by R. Lal, J.M. Kimble, R.F. Follett, and B.A. Stewart. CRCPress, Boca Raton, Fla., pp. 527–547.

Greenland, D.J. 1995. Land use and soil carbon in different agroecological zones. In Soil management andgreenhouse effect. Edited by R. Lal, J. Kimble, E. Levine, and B.A. Stewart. Lewis Publishers, BocaRaton, Fla., pp. 9–24.

Gregg, J.W., Jones, C.G., and Dawson, T.D. 2003. Urbanization effects on tree growth in the vicinity of NewYork City. Nature, 424: 183–187.

Gregory, P., Ingram, J., Campbell, B., Goudriaan, J., Hunt, T., Landsberg, J., Linder, S., Stafford-Smith, M.,Sutherst, B., and Valentin, C. 1999. Managed production systems. In The terrestrial biosphere and globalchange. Implications for natural and managed ecosystems. Synthesis Volume B. Edited by B. Walker,W. Steffen, J. Canadell, and J. Ingram. International Geosphere-Biosphere Program Book Series No. 4,Cambridge University Press, Cambridge, U.K., pp. 229–270.

Griffin, D.M. 1969. Soil water in the ecology of fungi. Annu. Rev. Phytopathol. 7: 289–311.Griffiths, E., and Birch, H.F. 1961. Microbiological changes in freshly moistened soil. Nature, 189: 424.Grunzweig, J.M., Lin, T., Rotenberg, E., Schwartz, A., and Yakir, D. 2003. Carbon sequestration in arid-land

forest. Global Change Biol. 19: 791–799.Hagedorn, F., Spinnler, D., Bundt, M., Blas1er, P., and Siegwolf, R. 2003. The input and fate of new C in two

forest soils under elevated CO2. Global Change Biol. 9: 862–872.Hall, P.J., and Moody, B. 1994. Forest depletions caused by insects and diseases in Canada 1982–1987.

© 2003 NRC Canada

Page 24: Influences of global change on carbon sequestration by agricultural and forest soils

184 Environ. Rev. Vol. 11, 2003

Information Report ST-X-8, Natural Resources Canada, Canadian Forest Service, Ottawa, Ont., 14 pp.Harden, J.W., Sundquist, E.T., Stallard, R.F., and Mark, R.K. 1992. Dynamics of soil carbon during

deglaciation of the Laurentide ice sheet. Science, 258: 1921–1924.Harmon, M.E., Franklin, J.F., Swanson, F.J., Sollins, P., Gregory, S.V., Lattin, J.D., Anderson, N.H., Cline,

S.P., Sedell, J.R., Lienkaemper, G.W., Cromack, K., and Cummins, K.W. 1986. Ecology of coarse woodydebris in temperate ecosystems. In Advances in ecological research, Volume 15. Edited by A. Macfadyenand E.D. Ford., Academic Press, London, U.K., pp. 133–302.

Harmon, M.E., Ferrel, W.K., and Franklin, J.F. 1990. Effects on carbon storage of conversion of old-growthforests to young forests. Science, 247(4943): 699–703.

Harrison, K.G., Broecker, W.S., and Bonani, G. 1993. The effect of changing land use on soil radiocarbon.Science, 262: 725–726.

Hättenschwiler, S., Miglietta, F., Raschi, A., and Körner, C. 1997. Thirty years of in situ tree growth underelevated CO2: a model for future forest responses? Global Change Biol. 3: 463–71.

Haynes, R.J., and Williams, P.H. 1992. Accumulation of soil organic matter and the forms, mineralizationpotential and plant-availability of accumulated organic sulfur: effects of pasture improvement and intensivecultivation. Soil Biol. Biochem. 24: 209–217.

Heagle, A.S., Miller, J.E., Booker, F.L., and Pursley, W.A. 1999. Ozone stress, carbon dioxide enrichment,and nitrogen fertility interactions in cotton. Crop Sci. 39: 731–741.

Hendrickson, O.Q. 1981. Flux of nitrogen and carbon gases in bottomland soils of an agricultural watershed.Ph.D. thesis, University of Georgia, Athens, Ga., 210 pp.

Hendrickson, O.Q. 1985. Variation in the C:N ratio of substrate mineralized during forest humusdecomposition. Soil Biol. Biochem. 17: 435–440.

Hendrickson, O.Q., and Robinson, J.B. 1984. Effects of roots and litter on mineralization processes in forestsoil. Plant Soil, 80: 391–405.

Hendrickson, O.Q., Chatarpaul, L., and Burgess, D. 1989. Nutrient cycling following whole-tree andconventional harvest in northern mixed forest. Can. J. For. Res. 19: 725–735.

Henning, F.P., Wood, C.W., Rogers, H.H., Runion, G.B., and Prior, S.A. 1996. Composition anddecomposition of soybean and sorghum tissues grown under elevated atmospheric carbon dioxide. J.Environ. Qual. 25: 822–827.

Houghton, R.A. 1995a. Changes in the storage of terrestrial carbon since 1850. In Soils and global change.Edited by R. Lal, J. Kimble, E. Levine, and B.A. Stewart . Lewis Publishers, Boca Raton, Fla., pp. 45–65.

Houghton, R.A. 1995b. Effects of land-use change, surface temperature, and CO2 concentration on terrestrialstores of carbon. In Biotic feedbacks in the global climate systems. Edited by G.M. Woodwell andE.T. MacKenzie. Oxford University Press, New York, N.Y., pp. 333–350.

Houghton, R.A., Hobbie, J.E., Melillo, J.M., Moore, B., Peterson, B.J., Shave, G.R., and Woodwell, G.M.1983. Changes in the carbon content of the terrestrial biota and soils between 1860 and 1990: a release ofCO2 to the atmosphere. Ecol. Monogr. 53(3): 235–262.

Houghton, R.A., Skole, D.L., Nobre, C.A., Hackler, J.L., Lawrence, K.T., and Chomentowski, W.H. 2000.Annual fluxes of carbon from deforestation and regrowth in the Brazilian Amazon. Nature, 403: 301–304.

Huggins, D.R., Allan, D.L., Gardner, J.C., Karlen, D.L., Bezdicek, D.F., Rosek, M.J., Alms, M.J., Flock, M.,and Staben, M.L. 1998. Enhancing carbon sequestration in CRP-managed lands. In Management of carbonsequestration in soil. Edited by R. Lal, J. Kimble, R.F. Follett, and B.A. Stewart. CRC-Lewis Press, BocaRaton, Fla., pp. 323–334.

Hungate, B.A., Holland, E.A., Jackson, R.B., Chapin, F.S., Mooney, H.A., and Field, C.B. 1997. The fate ofcarbon in grasslands under carbon dioxide enrichment. Nature, 388: 576–579.

Huxley, P. 1999. Tropical Agroforestry. Blackwell Science Publishers, London, U.K., 371 pp.IGBP Terrestrial Carbon Working Group, 1998. The terrestrial carbon cycle: Implications for the Kyoto

Protocol. Science, 280: 1393–1394.IPCC. 1996. Climate change 1995: Impacts, adaptations and mitigation of climate change: Scientific-

Technical analyses. Contribution of working group II to the Second Assessment Report of theIntergovernmental Panel on Climate Change. Edited by R. Watson, M.C. Zinyowera, and R. Moss.Cambridge University Press, Cambridge, U.K., 880 pp.

IPCC. 2000. Land use, land-use change, and forestry. Special Report of the Intergovernmental Panel onClimate Change, Edited by R.T. Watson, I. R. Noble, B. Bolin, N.H. Ravindranath, D.J. Verardo, and

© 2003 NRC Canada

Page 25: Influences of global change on carbon sequestration by agricultural and forest soils

Hendrickson 185

D.J. Dokken. Cambridge University Press, Cambridge, U.K., 375 pp.IPCC. 2001a. Climate change 2001: Impacts, adaptation & vulnerability. Contribution of Working Group

II to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). Edited byJ.J. McCarthy, O.F. Canziani, N. A. Leary, D.J. Dokken and K.S. White. Cambridge University Press,Cambridge, U.K., 1000 pp.

IPCC. 2001b. Climate change 2001: Mitigation. Contribution of Working Group III to the Third AssessmentReport of the Intergovernmental Panel on Climate Change (IPCC), Edited by B. Metz, O. Davidson,R. Swart, and J. Pan. Cambridge University Press, Cambridge, U.K., 700 pp.

IPCC. 2002. Climate change and biodiversity. IPCC Technical Paper no. 5, H. Gitay, A. Suarez andR. Watson (lead authors). Intergovernmental Panel on Climate Change, Geneva, Switzerland, 88 pp.Available from http://www.ipcc.ch/pub/tpbiodiv.pdf [accessed 25 February 2004].

Ismail, I., Bevins, R.L., and Frye, W.W. 1994. Long-term no-tillage effects on soil properties and continuouscorn yields. Soil Sci. Soc. Am. J. 58: 193–198.

Izac, A.M.N., and Sanchez, P.A. 2000. Towards a natural resource management paradigm for internationalagriculture: the example of agroforestry research. Agric. Syst. 69: 5–25.

Janssens, I.A., Freibauer, A., Ciais, P., Smith, P., Nabuurs, G.J., Folberth, G., Schlamadinger, B., Hutjes,R.W.A., Ceulemans, R., Schulze, E.-D., Valentini, R., Dolman, A.J. 2003. Europe’s terrestrial biosphereabsorbs 7 to 12% of European anthropogenic CO2 emissions. Science, 300: 1538–1542.

Janzen, H.H., Campbell, C.A., Izaurralde, R.C., Ellert, B.H., Juma, N., McGill, W.B., and Zentner, R.P. 1998.Management effects on soil C storage on the Canadian prairies. Soil Tillage Res. 47: 181–195.

Jenkinson, D.S. 1991. The Rothamsted long-term experiments: are they still of use? J. Agron. 83: 2–12.Johnson, D.W. 1992. Effects of forest management on soil carbon storage. Water, Air, Soil Pollut. 64: 83–120.Johnson, D.W. 1995. Role of carbon in the cycling of other nutrients in forested ecosystems. In Carbon forms

and functions in forest soils. Edited by J.M. Kelly and W.M. McFee. Soil Science Society of America,Madison, Wis., pp. 299–328.

Kanowski, P.J., Savill, P.S., Adlard, P.G., Burley, J., Evans, J., Palmer, J.R., and Wood, P.J. 1992. Plantationforestry. In Managing the world’s forests, Edited by N.P. Sharma. Kendall-‘Hunt, Dubuque, Ia., pp. 375–401.

Kasimir-Klemedtsson, A., Klemedtsson, L., Berglund, K., Martikainen, P., Silvola, J., and Oenema. O. 1997.Greenhouse gas emissions from farmed organic soils: a review. Soil Use Manage. 13: 245–250.

Kelly, R.H., Burke, I.C., and Lauenroth, W.K. 1996. Soil organic matter and nutrient availability responses toreduced plant inputs in shortgrass steppe. Ecology, 77(8): 2516–2527.

Kern, J.S., and Johnson, M.G. 1993. Conservation tillage impacts on national soil and atmosperic carbonlevels. Soil Sci. Soc. Am. J. 57: 200–210.

Kharin, N. 1996. Strategy to combat desertification in Central Asia. Desertif. Control Bull. 29: 29–34.Kirschbaum, M.U.F. 2000. Will changes in soil organic matter act as a positive or negative feedback on

global warming? Biogeochemistry, 48: 21–51.Kolchugina, T.P., Vinson, T.S., Gaston, G.G., Rozhkov, V.A., and Shwidenko, A.Z. 1995. Carbon pools,

fluxes, and sequestration potential in soils of the former Soviet Union. In Soil management and greenhouseeffect. Edited by R. Lal, J. Kimble, E. Levine, and B.A. Stewart. CRC-Lewis Publishers, Boca Raton, Fla.,pp. 25–40.

Körner, C. 1996. The response of complex multispecies systems to elevated CO2. In Global Changeand Terrestrial Ecosystems. Edited by B. Walker, W. Steffen, J. Canadell, and J. Ingram. InternationalGeosphere-Biosphere Program Book Series No. 4, Cambridge University Press, Cambridge, U.K.,pp. 20–42.

Kuliev, A. 1996. Forests — an important factor in combatting desertification. Probl. Desert Dev. 4: 29–31.Kurz, W.A., Apps, M.J., Stocks, B.J., and Volney, W.J.A. 1995a. Global climatic change: disturbance regimes

and biospheric feedbacks of temperate and boreal forests. In Biotic feedbacks in the global climaticsystem: Will the warming speed the warming? Edited by G.M. Woodwell and F.T. Mackenzie. OxfordUniversity Press, New York, N.Y., pp. 119–133.

Kurz, W.A., Apps, M.J., Beukema, S.J., and Lekstrum, T. 1995b. Twentieth century carbon budget ofCanadian forests. Tellus, 47B: 170–177.

Kurz, W.A., and Apps, M.J. 1999. A 70-year retrospective analysis of carbon fluxes in the Canadian forestsector. Ecol. Appl. 9: 526–547.

© 2003 NRC Canada

Page 26: Influences of global change on carbon sequestration by agricultural and forest soils

186 Environ. Rev. Vol. 11, 2003

Laiho, R., and L. Finér, 1996. Changes in root biomass after water-level drawdown on pine mires in SouthernFinland. Scand. J. For. Res. 11: 251–260.

Laiho, R., and Laine, J. 1997. Tree stand biomass and carbon content in an age sequence of drained pinemires in southern Finland. For. Ecol. Manage. 93: 161–169.

Laine, J., Vasander, H., and Laiho, T. 1995. Long-term effects of water level drawdown on the vegetation ofdrained pine mires in southern Finland. J. Appl. Ecol. 32: 785–802.

Laine, J., Silvola, J., Tolonen, K., Alm, J., Nykänen, H., Vasander, H., Sallantaus, T., Savolainen, I., Sinisalo,J., and Martikainen, P.J. 1996. Effect of water-level drawdown in northern peatlands on the global climaticwarming. Ambio, 25: 179–184.

Lal, R. 1989. Conservation tillage for sustainable agriculture. Adv. Agron. 42: 85–197.Lal, R. 1995. Global soil erosion by water and carbon dynamics. In Soils and global change. Advances in

soil science. Edited by R. Lal, J. Kimble, E. Levine, and B.A. Stewart. Lewis Publishers, Chelsea, Mich.,pp. 131–142.

Lal, R. 1997. Residue management conservation tillage and soil restoration for mitigating greenhouse effectby CO2-enrichment. Soil Tillage Res. 43: 81–107.

Lal, R. 2003. Global potential of soil carbon sequestration to mitigate the greenhouse effect. Crit. Rev. PlantSci. 22: 151–184.

Lal, R., and Bruce, J.P. 1999. The potential of world cropland soils to sequester C and mitigate thegreenhouse effect. Environ. Sci. Policy, 2: 177–185.

Lal, R., Kimble, J.M., Follett, R.F., and Cole, C.V. 1998. The potential of US cropland to sequester carbonand mitigate the greenhouse effect. Ann Arbor Press, Chelsea, Mi., 128 pp.

Lal, R., Hassan, H.M., and Dumanski, J. 1999. Desertification control to sequester C and mitigate thegreenhouse effect. In Carbon sequestration in soils: Science, monitoring and beyond. Edited byR.J. Rosenberg, R.C. Izaurralde, and E.L. Malone. Battelle Press, Columbus, Oh., pp. 83–107.

Larionova, A.A., Yermolayev, A.M., Blagodatsky, S.A., Rozanova, L.N., Yevdokimov, I.V., and Orlinsky, D.B.1998. Soil respiration and carbon balance of gray forest soils as affected by land use. Biol. Fertil. Soils,27: 251–257.

Last, F.T., and Watling, R. (Editors). 1991. Acidic deposition: Its nature and impacts. Proc. R. Soc.Edinburgh, Sect. B, 97.

Leakey, R.R.B. 1996. Definition of agroforestry revisited. Agrofor. Today, 8(1): 5–7.Leuking, M.A., and Schepers, J.S. 1985. Changes in soil carbon and nitrogen due to irrigation development in

Nebraska’s sand hill soils. Soil Sci. Soc. Am. J. 49: 626–630.Lindstrom, M.J., Schumacher, T.E., Reicosky, D.C., and Beck, D.L. 1999. Soil quality: Post conservation

reserve changes with tillage and cropping. In Soil quality and soil erosion. Edited by R. Lal. CRC Press,Boca Raton, Fla., pp. 143–151.

Liski, J., Ilvesniemi, H., Mäkelä, A., and Starr, M. 1998. Model analysis of the effects of soil age, fires andharvesting on the carbon storage of boreal forest soils. Eur. J. Soil Sci. 49(3): 407–416.

Liski, J., Ilvesniemi, H., Makela, A., and Westman, C.J. 1999. CO2 emissions from soil in response toclimatic warming are overestimated — the decomposition of old soil organic matter is tolerant oftemperature. Ambio, 28(2): 171–174.

Liski, J., Perruchoud, D., and Karjalainen, T. 2002. Increasing carbon stocks in the forest soils of westernEurope. For. Ecol. Manage. 169: 159–175.

Loiseau, P., and Soussana, J.-F. 1999a. Effects of elevated CO2, temperature and N fertilizer on theaccumulation of below-ground carbon in a temperate grassland ecosystem. Plant Soil, 212: 123–134.

Loiseau, P., and Soussana, J.-F. 1999b. Effect of elevated CO2, temperature and N fertilizer on the turnover ofbelow-ground carbon in a temperate grassland ecosystem. Plant Soil, 212: 233–247.

Lugo, A.E., and Brown, S. 1993. Management of tropical soils as sinks or sources of atmospheric carbon.Plant Soil, 149: 27–41.

Lugo, A.E., Sanchez, M.J., and Brown, S. 1986. Land use and organic carbon content of some subtropicalsoils. Plant Soil, 96: 185–196.

MacDonald, N.W., Randlett, D.L., and Zak, D.R. 1999. Soil warming and carbon loss from a Lake StatesSpodosol. Soil Sci. Soc. Am. J. 63: 211–218.

Makipaa, R., Karjalainen, T., Pussinen, A., and Kellomaki, S. 1999. Effects of climate change and nitrogendeposition on the carbon sequestration of a forest ecosystem in the boreal zone. Can. J. For. Res. 29:

© 2003 NRC Canada

Page 27: Influences of global change on carbon sequestration by agricultural and forest soils

Hendrickson 187

1490–1501.Manley, J.T., Schuman, G.E., Reeder, J.D., and Hart, R.H. 1995. Rangeland soil carbon and nitrogen

responses to grazing. J. Soil Water Conserv. 50: 294–298.Mann, L.K. 1986. Changes in soil carbon storage after cultivation. Science, 142(5): 279–288.Mark, U., and Tevini, M. 1997. Effects of solar ultraviolet-B radiation, temperature and CO2 on growth and

physiology of sunflower and maize seedlings. Plant Ecol. 128: 224–234.Martikainen, P.J., Nykänen, H., Alm, J., and Silvola, J. 1995. Change in fluxes of carbon dioxide, methane

and nitrous oxide due to forest drainage of mire sites of different trophy. Plant Soil, 168–169: 571–577.Matthews, E., and Fung, I. 1987. Methane emission from natural wetlands: global distribution, area, and

environmental characteristics of sources. Global Biogeochem. Cycles, 1: 61–86.McCarty, G.W., Lyssenko, N.N. and Starr, J.L. 1998. Short-term changes in soil carbon and nitrogen pools

during tillage management transition. Soil Sci. Soc. Am. J. 62: 1564–1571.McConnell, S.G., and Quinn, M.L. 1988. Soil productivity of four land use systems in southeastern Montana.

Soil Sci. Soc. Am. J. 52: 500–506.McIntosh, P.D., Allen, R.B., and Scott, N. 1997. Effects of exclosure and management on biomass and soil

nutrient pools in seasonally dry high country, New Zealand. J. Environ. Manage. 51: 169–186.McKee, I.F., Bullimore, J.F., and Long, S.P. 1997. Will elevated CO2 concentrations protect the yield of

wheat from O3 damage? Plant, Cell Environ. 20: 77–84.Medlyn, B.E., Badeck, F.-W., De Pury, D.G.G., Barton, C.V.M., Broadmeadow, M., Ceulemans, R., De

Angelis, P., Forstreuter, M., Jach, M.E., Kellomaki, S., Laitat, E., Marek, M., Philippot, S., Rey, A.,Strassemeyer, J., Laitinen, K., Liozon, R., Portier, B., Roberntz, P., Wang, K., and Jarvis, P.G. 1999.Effects of elevated [CO2] on photosynthesis in European forest species: a meta-analysis of modelparameters. Plant, Cell Environ. 22: 1475–1495.

Meentemeyer, V. 1984. The geography of organic decomposition rates. Ann. Assoc. Am. Geogr. 74: 551–560.Meentemeyer, V., Gardner, J., and Box, E.O. 1985. World patterns and amounts of detrital soil carbon. Earth

Surf. Proc. Landforms, 10(6): 557–567.Melillo, J.R., McGuire, A.D., Kicklighter, D.W., Moore, B., Vorosmarty, C.J., and Schloss, A.L. 1993. Global

climate change and terrestrial net primary production. Nature, 363: 234–240.Melillo, J.M., Steudler, P.A., Aber, J.D., Newkirk, K., Lux, H., Bowles, F.P., Catricala, C., Magill, A., Ahrens

T., and Morrisseau, S. 2002. Soil warming and carbon-cycle feedbacks to the climate system. Science, 298:2173–2176.

Meybeck, D.J.D. 1982. Carbon, nitrogen and phosphorous transport by world rivers. Am. J. Sci. 282:410–450.

Mikan, C.J., Zak, D.R., Kubiske, M.E., and Pregitzer, K.S. 2000. Combined effects of atmospheric CO2 andN availability on the below ground carbon and nitrogen dynamics of aspen mesocosms. Oecologia, 124:432–445.

Millennium Ecosystem Assessment, 2003. Ecosystems and human well-being: A framework for assessment.Island Press, Washington, D.C., 245 pp.

Minkkinen, K., and Laine, J. 1998. Long-term effect of forest drainage on the peat carbon stores of pinemires in Finland. Can. J. For. Res. 28: 1267–1275.

Moore, T.R., Trofymow, T.A., Taylor, B., Prescott, C., Camire, C., Duschene, L., Fyles, J., Kozak, L.,Kranabetter, M., Morrison, I., Siltanen, M., Smith, S., Titus, B., Visser, S., Wein, R., and Zoltai, S. 1999.Rates of litter decomposition in Canadian forests. Global Change Biol. 5: 75–82.

Moosavi, S.C., and Crill, P.M. 1997. Controls on CH4 and CO2 emissions along two moisture gradients in theCanadian boreal zone. J. Geophys. Res. 102: 29, 261–229, 277.

Morgan, J.A., Knight, W.G., Dudley, L.M., and Hunt, H.W. 1994. Enhanced root system C-sink activity,water relations and aspects of nutrient acquisition in mycotrophic Bouteloua gracilis subjected to CO2

enrichment. Plant Soil, 165: 139–146.Mosier, A.R. 1998. Soil processes and global change. Biol. Fertil. Soils, 27: 221–229.Murray, D.R. 1997. Carbon dioxide and plant response. Research Studies Press Ltd., John Wiley and Sons,

New York, N.Y., 275 pp.Nadelhoffer, K.J., Emmett, B.A., Gundersen, P., Kjonaas, O.J., Koopmans, C.J., Schleppi, P., Tietema, A., and

Wright, R.F. 1999. Nitrogen deposition makes a minor contribution to carbon sequestration in temperateforests. Nature, 398(6723): 145–148.

© 2003 NRC Canada

Page 28: Influences of global change on carbon sequestration by agricultural and forest soils

188 Environ. Rev. Vol. 11, 2003

Nakane, K. 1976. An empirical formulation of the vertical distribution of carbon concentration in forest soils.Jpn. J. Ecol. 26: 171–174.

Neill, C., Melillo, J.M., Steudler, P.A., Cerri, C.C, Moraes, J.F.L., Piccolo, M.C., and Brito, M. 1997. Soilcarbon and nitrogen stocks following forest clearing for pasture in the southwestern Brazilian Amazon.Ecol. Appl. 7(4): 1216–1225.

Nepstad, D.C., Decarvalho, C.R., Davidson, E.A., Jipp, P.H., Lefebvre, P.A., Negreiros, G.H., Dasilva, E.D.,Stone, T.A., Trumbore, S.E., and Vieira, S. 1994. The role of deep roots in the hydrological and carboncycles of Amazonian forests and pastures. Nature, 372(6507): 666–669.

Nepstad, D.C., Klink, C., and Trumbore, S.E. 1995. Pasture soils as carbon sink. Nature, 376: 472–473.Nie, X. 1996. The water and soil conservation and Loess Plateau farming. J. Sci. Tech. Shangxi Water Soil

Conserv. 6–8. [In Chinese.]Niklinska, M., Maryanski, M., and Laskowski, R. 1999. Effect of temperature on humus respiration rate and

nitrogen mineralization: Implications for global climate change. Biogeochemistry, 44: 239–257.Nilsson, S., Jonas, M., Stolbovoi, V., Shivdenko, A., Obersteiner, M., and McCallum, I. 2003. The missing

“missing sink”. For. Chron. 79: 1071–1074.Odum, E.P. 1969. The strategy of ecosystem development. Science, 164: 262–270.Ojima, D.S., Dirks, B.O.M., Glenn, E.P., Owensby, C.E., and Scurlock, J.O. 1993a. Assessment of C budget

for grasslands and drylands of the world. Water, Air, Soil Pollut. 70, 95–109.Ojima, D.S., Parton, W.J., Schimel, D.S., Scurlock, J.M.O., and Kittel, T.G.F. 1993b. Modeling the effects of

climatic and CO2 changes on grassland storage of soil C. Water, Air, Soil Pollut. 70: 643–657.Oldeman, L.R. 1994. The global extent of soil degradation. In Soil resilience and sustainable land use. Edited

by D.J. Greenland and I. Szaboles. CAB International, Wallingford, U.K., pp. 99–118.Oldeman, R.L., Hakkeling, T.A., and Sombroek, W.G. 1991. World map of the status of human-induced

soil degradation, 2nd rev. ed. International Soil Reference and Information Centre, Wageningen, TheNetherlands.

Oren, R., Ellsworth, D.S., Johnsen, K.H., Phillips, N., Ewers, B.E., Maier, C., Schafer, K.V.R., McCarthy,H., Hendrey, G., McNulty, S.G., and Katul, K.K. 2001. Soil fertility limits carbon sequestration by forestecosystems in a CO2-enriched atmosphere. Nature, 411: 469–472.

Owensby, C.E. 1993. Potential impacts of elevated CO2 and above- and belowground litter quality of atallgrass prairie. Water, Air, Soil Pollut. 70: 413–424.

Paustian, K., Andren, O., Janzen, H.H., Lal, R., Smith, P., Tian, G., Tiessen, H., Van Noordwijk, M., andWoomer, P.L. 1997a. Agricultural soils as a sink to mitigate carbon dioxide emissions. Soil Use Manage.13(4): 230–244.

Paustian, K., Elliot, E.T., and Killian, K. 1997b. Modeling soil carbon in relation to management and climatechange in some agroecosystems in central North America. In Soil processes and the carbon cycle. Editedby R. Lal, J.M. Kimble, R.F. Follett, and B.A. Stewart. CRC Press, Boca Raton, Fla., pp. 459–471.

Paustian, K., Cole, C.V., Sauerbeck, D., and Sampson, N. 1998. CO2 mitigation by agriculture: an overview.Clim. Change, 40: 135–162.

Paustian, K., Six, J., Elliott, E.T., and Hunt, H.W. 2000. Management options for reducing CO2 emissionsfrom agricultural soils. Biogeochemistry, 48: 147–163.

Pickett, S.T.A., and White, P.S. 1985. The ecology of natural disturbance and patch dynamics. AcademicPress Inc., San Diego, Calif., 472 pp.

Poorter, H. 1998. Do slow-growing species and nutrient stressed plants respond relatively strongly to elevatedCO2? Global Change Biol. 4: 639–697.

Post, W.M., and Kwon, K.C. 2000. Soil carbon sequestration and land use: processes and potential. GlobalChange Biol. 6: 317–328.

Post, W.M., Izaurralde, R.C., Mann, L.K., and Bliss, N. 1999. Monitoring and verifying soil carbonsequestration. In Carbon sequestration in soils. Edited by N. Rosenberg, R.C. Izaurralde, and E.L. Malone.Batelle Press, Columbus, Oh., pp. 41–82.

Poulton, P.R., Pye, E., Hargreaves, P.R., and Jenkinson, D.S. 2003. Accumulation of carbon and nitrogen byold arable land reverting to woodland. Global Change Biol. 9, 942–955.

Powlson, D.S., and Jenkinson, D.S. 1981. A comparison of the organic matter, biomass, adenosinetriphosphate and mineralizable nitrogen contents of ploughed and direct-drilled soils. J. Agric. Sci. 97:713–721.

© 2003 NRC Canada

Page 29: Influences of global change on carbon sequestration by agricultural and forest soils

Hendrickson 189

Pregitzer, K.S., Zak, D.R., Curtis, P.S., Kubiske, M.E., Teeri, J.A., and Vogel, C.S. 1995. Atmospheric CO2,soil nitrogen and turnover of fine roots. New Phytol. 129: 579–585.

Prentice, I.C., Farquhar, G.D., Fasham, M.J.R., Goulden, M.L., Heimann, M., Jaramillo, V.J., Kheshgi, H.S.,Le Quéré, C., Scholes, R.J., Wallace, D.W.R. 2001. The carbon cycle and atmospheric CO2. In Climatechange 2001: The scientific basis. Contribution of Working Group I to the IPCC Third Assessment Report,Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, U.K., 892 pp.

Prior, S.A., Torbert, H.A., Runion, G.B., Rogers, H.H., Wood, C.W., Kimball, B.A., LaMorte, R.L., Pinter,P.J., and Wall, G.W. 1997. Free-air carbon dioxide enrichment of wheat: soil carbon and nitrogendynamics. J. Environ. Qual. 26: 1161–1166.

Richey, J.E., Brock, J.T., Naiman, R.J., Wissmar, R.C., and Stallart, R.R. 1980. Organic carbon: oxidation andtransport in the Amazon River. Science, 207: 1348–1351.

Richter, D.D., Markewitz, D., Trumbore, S.E., and Wells, C.G. 1999. Rapid accumulation and turnover of soilcarbon in an aggrading forest. Nature, 400: 56–58.

Robles, M.D., and Burke, I.C. 1998. Soil organic matter recovery on Conservation Reserve Program fields insoutheastern Wyoming. Soil Sci. Soc. Am. J. 62: 725–730.

Rogers, G., Milham, P.J., Thibaud, M.C., and Conroy, J.P. 1996. Interactions between rising CO2

concentration and nitrogen supply in cotton, I: Growth and leaf nitrogen concentration. Aust. J. PlantPhysiol. 23: 119–125.

Rogers, H.H., Runion, G.B., and Krupa, S.V. 1994. Plant responses to atmospheric CO2 enrichment withemphasis on roots and the rhizosphere. Environ. Pollut. 83: 155–189.

Ross, D.J., Saggar, S., Tate, K.R., Feltham, C.W., and Newton, P.C.D. 1996. Elevated CO2 effects on carbonand nitrogen cycling in grass/clover turves of a Psammaquent soil. Plant Soil, 182: 185–198.

Roulet, N.T., Ash, R., Quinton, W., and Moore, T.R. 1993. Methane flux from drained northern peatland:effect of persistent water table lowering on flux. Global Biogeochem. Cycles, 7: 749–769.

Sanchez, P.A. 1995. Science in agroforestry. Agrofor. Syst. 30: 5–55.Santruckova, H., Bird, M.I., Kalaschnikov, Y.N., Grund, M., Elhottova, D., Simek, M., Grigoryev, S.,

Gleixner, G., Arneth, A., Schulze, E.-D., and Lloyd, J. 2003. Microbial characteristics of soils on alatitudinal transect in Siberia. Global Change Biol. 9: 1106–1117.

SCBD, 2003. Interlinkages between biological diversity and climate change: Advice on the integration ofbiodiversity considerations into the implementation of the United Nations Framework Convention onClimate change and its Kyoto Protocol. CBD Technical Series no. 10. Secretariat of the Convention onBiological Diversity, Montreal, Que. Available from http://www.biodiv.org/doc/publications/cbd-ts-10.pdf[accessed 25 February 2004].

Scharpenseel, H.W., and Becker-Heidmann, P. 1994. Sustainable land use in the light of resilience/elasticity tosoil organic matter fluctuations. In Soil resilience and sustainable land use. Edited by D.J. Greenland andI. Szabolcs. CAB International, Wallingford, U.K., pp. 249–264.

Schimel, D.S. 1995. Terrestrial ecosystems and the carbon cycle. Global Change Biol. 1: 77–91.Schindler, D.W., and Bayley, S.E. 1993. The biosphere as an increasing sink for atmospheric carbon:

Estimates from increased nitrogen deposition. Global Biogeochem. Cycles, 7: 717–733.Schlesinger, W.H. 1982. Carbon storage in the caliche of arid soils: a case study from Arizona. Soil Sci. 133:

247–255.Schlesinger, W.H. 1986. Changes in soil carbon storage and associated properties with disturbance and

recovery. In The changing carbon cycle: A global analysis. Edited by J.R. Trabalka and D.E. Reichle.Springer-Verlag, New York, N.Y., pp. 194–220.

Schlesinger, W.H. 1999. Carbon and agriculture — carbon sequestration in soils. Science, 284(5423): 2095.Schlesinger, W.H. 2000. Carbon sequestration in soils: some cautions amid optimism. Agric. Ecosyst.

Environ. 82: 121–127.Schlesinger, W.H., and Melack, J.M. 1981. Transport of organic carbon in the world’s rivers. Tellus, 33:

172–187.Schlesinger, W.H., and Lichter, J. 2001. Limited carbon storage in soil and litter of experimental forest plots

under increased atmospheric CO2. Nature, 411: 466–469.Schnabel, R.R., Franzluebbers, A.J., Stout, W.L., Sanderson, M.A., and Stuedemann, J.A. 2000. Pasture

management effects on soil carbon sequestration. In Carbon sequestration potential of U.S. grazinglands.Edited by R.F. Follett, J.M. Kimble, and R. Lal. CRC Press, Boca Raton, Fla., pp. 291–322.

© 2003 NRC Canada

Page 30: Influences of global change on carbon sequestration by agricultural and forest soils

190 Environ. Rev. Vol. 11, 2003

Scholes, R.J. 1999. Will the terrestrial carbon sink saturate soon? Global Change Newsl. 37: 2–3.Scholes, R.J., and van Breemen, N. 1997. The effects of global change on tropical ecosystems. Geoderma,

79: 9–24.Scholes, R.J., Schulze, E.-D., Pitelka, L.F., and Hall, D.O. 1999. Biogeochemistry of terrestrial ecosystems.

In The terrestrial biosphere and global change. Edited by B. Walker, W. Steffen, J. Canadell, and J. Ingram.International Geosphere-Biosphere Program Book Series No. 4, Cambridge University Press, Cambridge,U.K., pp. 271–303.

Schwab, A.P., Owensby, C.E., and Kulyingyong, S. 1990. Changes in soil chemical properties due to 40 yearsof fertilization. Soil Sci. 149(1): 35–43.

Scurlock, J.M.and Hall, D.O. 1998. The global carbon sink: a grassland perspective. Global Change Biol. 4:229–233.

Semenov, S.M., Kukhta, B.A., and Rudkova, A.A. 1997. Assessment of the tropospheric ozone effect onhigher plants. Meteorol. Hydrol. 12: 36–40.

Sharitz, R.R., and Gresham, C.A. 1998. Pocosins and Carolina bays. In Southern forested wetlands: Ecologyand management. Edited by M.G. Messina and W.H. Conner. Lewis Publishers, Boca Raton, Fla.,pp. 343–377.

Silver, W.L., Ostertag, R., and Lugo, A.E. 2000. The potential for carbon sequestration through reforestationof abandoned tropical agricultural and pasture lands. Restor. Ecol. 8: 394–407.

Sioli, H. 1984. The Amazon — Limnology and landscape ecology of a mighty tropical river and its basin:Wildlife planning glossary. US Department of Agriculture Forest Service, Boston, Mass., 736 pp.

Six, J., Conant, R.T., Paul, E.A., and Paustian, K. 2002. Stabilization mechanisms of soil organic matter:implications for C-saturation of soils. Plant Soil, 241: 155–176.

Sleutel, S., de Neve, S., Hofman, G., Boeckx, P., Beheydt, D., van Cleemput, O., Mestdagh, I., Lootens, P.,Carlier, L., Van Camp, N., Verbeeck, H., Vande Walle, I., Samson, R., Lust, N., and Lemeur, R. 2003.Carbon stock changes and carbon sequestration potential of Flemish cropland soils. Global Change Biol. 9:1193–1203.

Smith, P., Powlson, D.S., Glendining, M.J., and Smith, J.U. 1997a. Potential for carbon sequestration inEuropean soils — preliminary estimates for five scenarios using results from long-term experiments.Global Change Biol. 3(1): 67–79.

Smith, P., Powlson, D.S., Glendining, M.J., and Smith, J.U. 1997b. Opportunities and limitations for Csequestration in European agricultural soils through changes in management. In Management of carbonsequestration in soil. Edited by R. Lal, J.M. Kimble, R.F. Follett, and B.A. Stewart. RC Press, Boca Raton,Fla., pp. 143–152.

Smith, P., Powlson, D.S., Glendining, M.J., and Smith, J.U. 1998. Preliminary estimates of the potential forcarbon mitigation in European soils through no-till farming. Global Change Biol. 4(6): 679–685.

Smith, P., Goulding, K.W., Smith, K.A., Powlson, D.S., Smith, J.U., Falloon, P.D., and Coleman, K. 2001.Enhancing the carbon sink in European agricultural soils: Including trace gas fluxes in estimates of carbonmitigation potential. Nutr. Cycling Agroecosyst. 60: 237–252.

Smith, P., Peterson, S.O., and Oleson, J.E. 2002. Effects of cultivation practice on carbon storage in arablesoils and grassland. In Greenhouse gas inventories for agriculture in the Nordic Countries. DIAS ReportNo.81, Danmarks Jordbrugs Forskning; Tjele; Denmark, pp. 64–69.

Sombroek, W.G., Nachtergaele, F.O., and Hebel, A. 1993. Amounts, dynamics and sequestering of carbon intropical and subtropical soils. Ambio, 22(7): 417–426.

Sombroek, W.G., Fearnside, P.M., and Cravo, M. 1999. Geographic assessment of carbon stored inAmazonian terrestrial ecosystems and their soils in particular. In Global climate change and tropicalecosystems. Edited by R. Lal, J.M. Kimble, and B.A. Stewart. CRC Lewis, Boca Raton, Fla., pp. 375–389.

Sommerfield, R.A., Mosier, A.R., and Musselman, R.C. 1993. CO2, CH4 and N2O flux through a Wyomingsnowpack and implications for global budgets. Nature, 361: 140–142.

Stallard, R.F. 1998. Terrestrial sedimentation and the carbon cycle: Coupling weather and erosion to carbonburial. Global Biogeochem. Cycles, 12: 231–257.

Stockfisch, N., Forstreuter, T., and Ehlers, W. 1999. Ploughing effects on soil organic matter after twentyyears of conservation tillage in Lower Saxony, Germany. Soil Tillage Res. 52: 91–101.

Tate, K.R., and Theng, B.K.G. 1980. Organic matter and its interactions with inorganic soil constituents. InSoils with variable change. Edited by B.K.G. Theng. New Zealand Society of Soil Science, Lower Hutt,

© 2003 NRC Canada

Page 31: Influences of global change on carbon sequestration by agricultural and forest soils

Hendrickson 191

New Zealand.Teramura, A.H., Sullivan, J.H., and Ziska, L.H. 1990. Interactions of ultraviolet B radiation and CO2 on

productivity and photosynthetic characteristics in wheat, rice, and soybean. Plant Physiol. 94: 470–475.Tian, H., Melillo, J.M., Kicklighter, D.W., McGuire, A.D., Helfrich, J.V.K., Moore, B., Vörösmarty, C.J.

1998. Effect of interannual climate variability on carbon storage in Amazonian ecosystems. Nature, 396:664–667.

Tilman, D., Wedin D., and Knops, J. 1996. Productivity and sustainability influenced by biodiversity ingrassland ecosystems. Nature, 379: 718–720.

Tolonen, K., and Turunen, J. 1996. Accumulation rates of carbon in mires in Finland and implications forclimate change. The Holocene, 6: 171–178.

Torbert, H.A., Prior, S.A., and Rogers, H.H. 1995. Elevated atmospheric carbon dioxide effects on cottonplant residue decomposition. Soil Sci. Soc. Am. J. 59: 1321–1328.

Torbert, H.A., Rogers, H.H., Prior, S.A., Schlesinger, W.H., and Runion, G.B. 1997. Effects of elevatedatmospheric CO2 in agro-ecosystems on soil carbon storage. Global Change Biol. 3: 513–521.

Townsend, A.R., and Rastetter, E.B. 1996. Nutrient constraints on carbon storage in forested ecosystems. InForest ecosystems, forest management and the global carbon cycle. Edited by M.J. Apps and D.T. Price.NATO ASI Series I (Global Environmental Change), Number 40, Springer-Verlag Academic Publishers,Heidelberg, Germany, pp. 35–46.

Trumbore, S.E., Davidson, E.A., de Camargo, P.B., Nepstad, D.C., and Martinelli, L.A. 1995. Belowgroundcycling of carbon in forests and pastures of Eastern Amazonia. Global Biogeochem. Cycles, 9: 515–528.

Trumbore, S.E., Chadwick, O.A., and Amundson, R. 1996. Rapid exchange between soil carbon andatmospheric carbon dioxide driven by temperature change. Science, 272: 393–396.

Unsworth, M.H., and Hogsett, W.E. 1996. Combined effects of changing CO2, temperature, UV-B radiation,and O3 on crop growth. In Global climate change and agricultural production. Edited by F. Bazzaz andW. Sombroek. John Wiley and Sons, West Sussex, U.K., 345 pp.

Valentin, C. 1996. Soil erosion under global change. In Global change and terrestrial ecosystems. Edited byB.H. Walker and W.L. Steffen. International Geosphere-Biosphere Program Book Series No. 2, CambridgeUniversity Press, Cambridge, U.K., pp. 317–338.

van Ginkel, J.H., Gorissen, A., and van Veen, J.A. 1996. Long-term decomposition of grass roots as affectedby elevated atmospheric carbon dioxide. J. Environ. Qual. 25: 1122–1128.

van Ginkel, J.H., Whitmore, A.P., and Gorissen, A. 1999. Lolium perene grasslands may function as a sinkfor atmospheric carbon dioxide. J. Environ. Qual. 28: 1580–1584.

van Noordwijk, M., Cerri, C., Woomer, P.L., Nugroho, K., and Bernoux, M. 1997. Soil carbon dynamicsin the humid tropical forest zone. In The management of carbon in tropical soils under global change:Science, practice and policy. Edited by E.T. Elliott, J. Kimble, and M.J. Swift. Geoderma, 79: 187–225.

Veldkamp, E., Becker, A., Schwendenmann, L., Clark, D.A., and Schulte-Bisping, H. 2003. Substantial labilecarbon stocks and microbial activity in deeply weathered soils below a tropical wet forest. Global ChangeBiol. 9: 1171–1184.

Vesterdal, L., Ritter, E., Gundersen, P., and Karjalainen, T. 2002. Change in soil organic carbon followingafforestation of former arable land. For. Ecol. Manage. 169: 137–147.

Vitousek, P.M., Aber, J.D., Howarth, R.W., Likens, G.E., Matson, P.A., Schindler, D.W., Schlesinger, W.H.,and Tilman, D.G. 1997. Human alteration of the global nitrogen cycle: sources and consequences. Ecol.Appl. 7: 737–750.

Walker, B.H., Steffen, W.L., and Langridge, J. 1999. Interactive and integrated effects of global changeon terrestrial ecosystems. In The terrestrial biosphere and global change: Implications for natural andmanaged ecosystems. Synthesis volume. Edited by B. Walker, W. Steffen, J. Canadell, and J. Ingram.International Geosphere-Biosphere Program Book Series No. 4, Cambridge University Press, Cambridge,U.K., pp. 329–375.

Wedin, D.A., and Tilman, D. 1996. Influence of nitrogen loading and species composition on the carbonbalance of grasslands. Science, 274: 1720–1723.

Wieder, R.K. 2001. Past, present and future peatland carbon balance: an empirical model based on 210-Pb-dated cores. Ecol. Appl. 11: 327–342.

Winter, W.H., Mott, J.J., McLean, R.W., and Ratcliff, D. 1989. Evaluation of management options forincreasing the productivity of tropical savanna pastures 1. Fertilizer. Aust. J. Exp. Agric. 29: 613–622.

© 2003 NRC Canada

Page 32: Influences of global change on carbon sequestration by agricultural and forest soils

192 Environ. Rev. Vol. 11, 2003

Woodwell, G.M., MacKenzie, F.T., Houghton, R.A., Apps, M., Gorham, E., and Davidson, E. 1998. Bioticfeedbacks in the warming of the earth. Climatic Change, 40: 495–518.

Woomer, P.L., Palm, C.A., Qureshi, J.N., and Kotto-Same, J. 1997. Carbon sequestration organic and resourcemanagement in African smallholder agriculture. In Management of Carbon Sequestration in Soil. Edited byR. Lal, J.M. Kimble, R.F. Follett, and B.A. Stewart. CRC Press, Boca Raton, Fla., pp. 153–173.

Yanai, R.D., Arthur, M.A., Siccama, T.G., and Federer, C.A. 2000. Challenges of measuring forest floororganic matter dynamics: repeated measures from a chronosequence. For. Ecol. Manage. 138: 273–283.

Young, A. 1997. Agroforestry for soil management. 2nd ed. CAB International, Oxford, U.K. 320 pp.Zoltai, S.T., and Martikainen, P.J. 1996. Estimated extent of forested peatlands and their role in the global

carbon cycle. In Forest ecosystems, forest management and the global carbon cycle. Edited by M.J. Appsand D.T. Price. NATO ASI Series I (Global Environmental Change), Number 40, Springer-VerlagAcademic Publishers, Heidelberg, Germany, pp. 47–58.

© 2003 NRC Canada