Climate Change and...

Annotated Bibliography

Carbon Dynamics

Carbon Sequestration

Adams, A. B., Harrison, R. B., Sletten, R. S., Strahm, B. D., Turnblom, E. C., Jensen, C. M. (2005). Nitrogen-fertilization impacts on carbon sequestration and flux in managed coastal Douglas-fir Stands of the Pacific Northwest. Forest Ecology and Management 220 (1-3): 313-325

ABSTRACT: We examined whether N-fertilization and soil origin of Douglas-fir [Psuedotsuga menziesii (Mirb.) Franco] stands in western Washington state could affect C sequestration in both the tree biomass and in soils, as well as the flux of dissolved organic carbon (DOC) through the soil profile. This study utilized four forest sites that were initially established between 1972 and 1980 as part of Regional Forest Nutrition Research Project (RFNRP). Two of the soils were derived from coarse-textured glacial outwash and two from finer-textured volcanic-source material, primarily tephra, both common soil types for forestry in the region. Between 1972 and 1996 fertilized sites received either three or four additions of 224 kg N ha-1 as urea (672-896 kg N ha-1 total). Due to enhanced tree growth, the N-fertilized sites (161 Mg C ha-1 ) had an average of 20% more C in the tree biomass compared to unfertilized sites (135 Mg C ha-1 ). Overall, N-fertilized soils (260 Mg C ha-1 ) had 48% more soil C compared to unfertilized soils (175 Mg C ha-1 ). The finer-textured volcanic-origin soils (348 Mg C ha-1 ) had 299% more C than glacial outwash soils (87.2 Mg C ha-1 ), independent of N-fertilization. Soil-solution DOC collected by lysimeters also appeared to be higher in N-fertilized, upper soil horizons compared to unfertilized controls but it was unclear what fraction of the difference was lost from decomposition or contributed to deep-profile soil C by leaching and adsorption. When soil, understory vegetation and live-tree C compartments are pooled and compared by treatment, N-fertilized plots had an average of 110 Mg C ha-1 more than unfertilized controls. These results indicate these sites generally responded to N-fertilization with increased C sequestration, but differences in stand and soil response to N-ferfilization might be partially explained by soil origin and texture.

Backeus, S., Wikstrom, P., Lamas, T. (2006). Modeling carbon sequestration and timber production in a regional case study. Silva Fennica 40 (4): 615-629

ABSTRACT: Forests make up large ecosystems and by the uptake of carbon dioxide can play an important role in mitigating the greenhouse effect. In this study, mitigation of carbon emissions through carbon uptake and storage in forest biomass and the use of forest biofuel for fossil fuel substitution were considered. The analysis was performed for a 3.2 million hectare region in northern Sweden. The objective was to maximize net present value for harvested timber, biofuel production and carbon sequestration. A carbon price for build-up of carbon storage and for emissions from harvested forest products was introduced to achieve an economic value for carbon sequestration. Forest development was simulated using an optimizing stand-level planning model, and the solution for the whole region was found using linear programming. A range of carbon prices was used to study the effect on harvest levels and carbon sequestration. At a zero carbon price, the mean annual harvest level was 5.4 million m3 , the mean annual carbon sequestration in forest biomass was 1.48 million tonnes and the mean annual replacement of carbon from fossil fuel with forest biofuel was 61,000 tonnes. Increasing the carbon price led to decreasing harvest levels of timber and decreasing harvest levels of forest biofuel. Also, thinning activities decreased more than clear-cut activities when the carbon prices increased. The level of carbon sequestration was governed by the harvest level and the site productivity. This led to varying results for different parts of the region.

Bangsund, D.A., Leistritz, F.L. (2008). Review of literature on economics and policy of carbon sequestration in agricultural soils. Management of Environmental Quality 19 (1): 85-99

ABSTRACT: Abstract: Purpose – The purpose of this paper is to identify and describe key economic and policy-related issues with regard to terrestrial C sequestration and provide an overview of the economics of C sequestration on agricultural soils in the USA.

Design/methodology/approach – Recent economic literature on carbon sequestration was reviewed to gather insights on the role of agriculture in greenhouse gas emissions mitigation. Results from the most salient studies were presented in an attempt to highlight the general consensus on producer-level responses to C sequestration incentives and the likely mechanisms used to facilitate C sequestration activities on agricultural soils.

Findings – The likely economic potential of agriculture to store soil C appears to be considerably less than the technical potential. Terrestrial C sequestration is a readily implementable option for mitigating greenhouse gas emissions and can provide mitigation comparable in cost to current abatement options in other industries. Despite considerable research to date, many aspects of terrestrial C sequestration in the USA are not well understood.

Originality/value – The paper provides a useful synopsis of the terms and issues associated with C sequestration, and serves as an informative reference on the economics of C sequestration that will be useful as the USA debates future greenhouse gas emissions mitigation policies.

Bernacchi, C. J., Hollinger, S. E., Meyers, T. (2005). The conversion of the corn/soybean ecosystem to no-till agriculture may result in a carbon sink.. Global Change Biology 11 (11): 1867-1872

ABSTRACT: Mitigating or slowing an increase in atmospheric carbon dioxide concentration ([CO2 ]) has been the focus of international efforts, most apparent with the development of the Kyoto Protocol. Sequestration of carbon (C) in agricultural soils is being advocated as a method to assist in meeting the demands of an international C credit system. The conversion of conventionally tilled agricultural lands to no till is widely accepted as having a large-scale sequestration potential. In this study, C flux measurements over a no-till corn/soybean agricultural ecosystem over 6 years were coupled with estimates of C release associated with agricultural practices to assess the net biome productivity (NBP) of this no-till ecosystem. Estimates of NBP were also calculated for the conventionally tilled corn/soybean ecosystem assuming net ecosystem exchange is C neutral. These measurements were scaled to the US as a whole to determine the sequestration potential of corn/soybean ecosystems, under current practices where 10% of agricultural land devoted to this ecosystem is no-tilled and under a hypothetical scenario where 100% of the land is not tilled. The estimates of this analysis show that current corn/soybean agriculture in the US releases ~7.2 Tg C annually, with no-till sequestering ~2.2 Tg and conventional-till releasing ~9.4 Tg. The complete conversion of land area to no till might result in 21.7 Tg C sequestered annually, representing a net C flux difference of ~29 Tg C. These results demonstrate that large-scale conversion to no-till practices, at least for the corn/soybean ecosystem, could potentially offset ca. 2% of annual US carbon emissions.

Bernoux, M., Cerri, C. C., Volkoff, B., Carvalho, M. Da Conceição S., Feller, C., Cerri, C. E. P., Eschenbrenner, V., Piccolo, M. De C., Feigl, B. (2005). Greenhouse gas fluxes and carbon storage from soil: The Brazilian inventory. Cahiers Agricultures 14 (1): 96-100

ABSTRACT: Rising levels of atmospheric CO2 have focused attention on potential CO2 emissions from terrestrial ecosystems of the world, notably from soils and biomass. The world’s mineral soils represent a large reservoir of C of about 1500 Pg C. Under the United Nations Framework Convention on Climate Change (UNFCCC) each country is required to develop, update and publish a national inventories of anthropogenic emissions (implementation of the National Communications), as well as to compile the inventories by comparable methodologies. For the last point, guidelines were developed and published as IPCC Guidelines for National Greenhouse Gas Inventories. Also, the land use, land-use changes and forestry (LULUCF) sector should be included in the national inventories. The CO2 fluxes from soils are discussed in chapter 5 for agricultural soils under the category 5D: CO2 emissions and removals from soils. These emissions are calculated from three subcategories : i) net changes in C storage in mineral soils; ii) emissions from organic soils; and iii) emissions from liming of agricultural soils. In a first step the soil organic carbon stocks up to a depth of 30 cm were estimated for Brazil based on a map of different soil-vegetation associations combined with results from a soil database. The soil-vegetation associations map was derived by intersecting soil and vegetation maps. The original soil and vegetation classification were reduced to 6 soil and 15 vegetation categories. Because this data represents sites with native vegetation in the absence of significant disturbances, it constitutes a valuable baseline for evaluating the effect of land-use change on soil C stocks for Brazil. Overall, about 36 400 million tons of carbon would be stored in the 0-30 cm soil layer under native conditions. The Brazilian Amazon region would account for 22,000 million tons. The CO2 emission from mineral soils following land-cover change in Brazil for the period 1975-1995 was estimated by Bernoux et al. who showed that the annual fluxes for Brazil indicate a net emission of CO2 to the atmosphere of 46.4 million tons of CO2 for the period 1975-1995. Intermediary calculation used to derive these annual fluxes estimated that 34 400 million tons of carbon were stored in the Brazilian soil for the year 1995. The annual CO2 emission for Brazil from liming varied from 4.9 to 9.4 million tons of CO2 per year with a mean annual CO2 emission of about 7.2 million tons. The South, Southeast and Center region accounted for a least 92% of total emission. Finally it could be calculated that the total CO2 fluxes from soils reached around 51.9 million tons of CO2 per year for the period 1975-1995.

Bert, D., Danjon, F. (2006). Carbon concentration variations in the roots, stem and crown of maturePinus pinaster (Ait.). Forest Ecology and Management 222 (1-3): 279-295

ABSTRACT: Stands of maritime pine (Pinus pinaster Ait.) cover about one million hectares of land in south-western France and produce 19% of all French timber, thanks to the intensive management methods employed. Evaluations of carbon fixation and storage in this forest are facilitated by its general homogeneity with respect to soil, climate and tree genetics. However, initial assessments were based on basic values for expansion factors and carbon concentration in the biomass, and more accurate results could be obtained.

The aim of the present study was to estimate the carbon concentration in the 13 main compartments of matureP. pinaster shoots and roots, describing sources of variation within these compartments and quantifying precisely the corresponding carbon contents.

The biomass distribution per compartment in the shoots and roots of 12 trees with a range of social status is given. It was obtained by joint architecture and dry weight measurements. The root systems were uprooted with a mechanical shovel and measured by 3D digitizing. Biomass allometric prediction equations per compartment according to girth at breast height were developed. The carbon concentration was analysed in 300 samples from four trees, taking into account their architecture.

The carbon concentration varied largely between compartments and showed a quadratic relationship with relative height in the four stem compartments and in branches and buds. It showed a negative exponential relation with root diameter. The carbon concentration of needles was not related to their age or their relative height in the crown. Carbon concentration variations were in accordance with the tissue chemical composition found in literature. The biochemical concentration of softwoods organs is extensively reviewed in the paper. The weighted mean carbon concentration reached 53.6% in the shoots and 51.7% in the roots. This resulted to 53.2% at tree level. The carbon content in the pine stand was 74 t C per hectare.

Between and within compartment variations in carbon concentration should be considered in carbon content evaluations and in structural–functional models. The underestimation of carbon storage in matureP. pinaster stands and sawnwood products reaches 6% when the usual 50% conversion factor is used.

Birdsey, R.A., Lewis, G.M., Kimble, J.M., Birdsey, R.A., Lal, R., Heath, L.S. (2003). Current and historical trends in use, management, and disturbance of U.S. forestlands. CRC Press: 15-33

ABSTRACT: These tables present current and historical area estimates of land use, land use change, forest management, and natural disturbance for forest lands of the U.S. We reconstruct portions of the history of U.S. forests of the 20th century using readily available and sometimes obscure public information collected by the U.S. Government, principally the U.S. Departments of Agriculture and Commerce. Much of the information is highly aggregated from large electronic data bases containing detailed records for recent decades, and some is summarized from printed tables of information contained in hundreds of government reports from earlier decades. The quality, consistency, and available detail of the information decrease back through time.

Where possible we follow the definitions published in Smith et al. (2001), also available on the internet at http://fia.fs.fed.us/. When combining data from different sources, we use a term “land use/land cover” to acknowledge that the available data sets are themselves based on somewhat inconsistent definitions. Many of the definitions have changed over time. Periodically, analysts revise older data sets to be consistent with changing definitions and standards for data collection. The most recent compilation of U.S. forest statistics by Smith et al. (2001) is an excellent example of the presentation of consistent historical estimates. In other cases where possible we have adjusted historical estimates to current standards to account for methodology changes.

The USDA Forest Service, Forest Inventory and Analysis (FIA) has conducted a comprehensive U.S. forest inventory since 1928. The USDA Natural Resources Conservation Service (NRCS) periodically estimates “land cover/use” for private lands of the U.S. in their National Resources Inventory (NRI) (Natural Resources Conservation Service 2000). The USDA Economic Research Service “Census of Agriculture” program has produced estimates of land use by State for various categories since 1945 (e.g. Daugherty 1995). Some relevant historical data are contained in a Bureau of Census compilation (U.S. Bureau of the Census, 1975), while other data are available in periodic reports by Agencies or special compilations requested by Congress (for example, USDA 1928).

Errors became evident in reconciling the different sources of information because of inconsistency in definitions, independent sampling frames, uncoordinated timing of data collection, and gaps and overlaps in scope of data collection. We estimate that we are missing information on about 6 million ha of Federal nonforest land, and that there is a double counting of about 13 million ha of private forest land and rangeland. These errors amount to about 2% of the total land area of the U.S.

Bricklemyer, R. S., Lawrence, R. L., Miller, P.R., Battogtokh, N. (2007). Monitoring and verifying agricultural practices related to soil carbon sequestration with satellite imagery. Agriculture, Ecosystems & Environment 118 (1-4): 201-210

ABSTRACT: The Kyoto Protocol entering into force on 16 February 2005 continues to spur interest in development of carbon trading mechanisms internationally and domestically. Critical to the development of a carbon trading effort is verification that carbon has been sequestered, and field level measurement of C change is likely cost prohibitive. Estimating C change based on agricultural management practices related to carbon sequestration seems more realistic, and analysis of satellite imagery could be used to monitor and verify these practices over large areas. We examined using Landsat imagery to verify crop rotations and quantify crop residue biomass in north central Montana. Field data were collected using a survey of farms. Standard classification tree analysis (CTA) and boosted classification and regression tree analysis (BCTA) were used to classify crop types. Linear regression (LM), regression tree analysis (RTA), and stochastic gradient boosting (SGB) were used to estimate crop residue. Six crop types were classified with 97% accuracy (BCTA) with class accuracies of 88–99%. Paired t-tests were used to compare the difference between known and predicted mean crop residue biomass. The difference between known and predicted mean residues using SGB was not different than 0 (p-value = 0.99); however root mean square error (RMSE) was large (1981 kg ha−1 ), implying that SGB accurately predicted regional crop residue biomass but not local predictions (i.e., field or farm level). The results of this study, and previous research classifying tillage practices and estimating soil disturbance, supports using satellite imagery as an effective tool for monitoring and verifying agricultural management practices related to carbon sequestration over large areas.

Canadell, Josep G., Pataki, Diane E., Gifford, Roger, Houghton, Richard A., Luo, Yiqi, Raupach, Michael R., Smith, Pete, Steffen, Will, Anonymous (2007). Saturation of the terrestrial carbon sink. 24: 59-78

FIRST PARAGRAPH: There is strong evidence that the terrestrial biosphere has acted as a net carbon (C) sink over the last two and half decades. Its strength is highly variable year-to-year ranging from 0.3 to 5.0 Pg C yr–1 ; an amount of significant magnitude compared to the emission of about 7 Pg C yr–1 from fossil fuel burning (Prentice et al. 2001; Schimel et al. 2001; Sabine et al. 2004). Uncertainties associated with C emissions from land-use change are large. On average, the terrestrial C sink is responsible for removing from the atmosphere approximately one third of the CO2 emitted from fossil fuel combustion, thereby slowing the build-up of atmospheric CO2 . The ocean sink is of similar magnitude (Sabine et al. 2004). Given the international efforts to stabilize atmospheric CO2 concentration and climate (i.e., Kyoto Protocol, C trading markets), the terrestrial C sink can be viewed as a subsidy to our global economy worth trillions of dollars. Because many aspects of the terrestrial C sink are amenable to purposeful management, its basis and dynamics need to be well understood.

Cao,M., Zhang,Q., Shugart,H. H. (2001). Dynamic responses of African ecosystem carbon cycling to climate change. Climate Research 17 (2): 183-193

ABSTRACT: Global climate change has been modifying ecosystem carbon cycling, which has produced feedbacks on climate by affecting the concentration of atmospheric CO2 . The importance of biospheric CO2 uptake or release to climate change has generated great interest in quantifying the dynamic responses of terrestrial ecosystem carbon cycling to climate change. However, less attention has been given to Africa, although it accounts for about one-fifth of the global net primary production and is one of the regions that have the greatest climate change. Here we use a biogeochemical model to simulate the dynamic variations in the carbon fluxes and stocks of African ecosystems caused by changes in climate and atmospheric CO2 from 1901 and 1995. We estimate that climate change reduces plant production and soil carbon stocks and causes net CO2 release, but the fertilization effect of increasing atmospheric CO2 on photosynthesis reverses the reduction and leads to carbon accumulation in vegetation. Therefore, the combined effect of climate change and increasing atmospheric CO2 causes net CO2 uptake, particularly in central Africa. The mean rate of the carbon sequestration in the period 1981-1995 is calculated to be 0.34 Gt C yr-1 . Nevertheless, Africa is not necessarily a significant carbon sink, because a large part of the carbon sequestration is offset by the carbon release arising from land use changes.

Cao, M. K., Prince, S. D., Shugart, H. H. (2002). Increasing terrestrial carbon uptake from the 1980s to the 1990s with changes in climate and atmospheric CO2 . Global Biogeochemical Cycles 16 (4): 1069, doi:10.1029/2001GB001553

ABSTRACT: Atmospheric measurements suggest that the terrestrial carbon sink increased from the 1980s to the 1990s, but the causes of the increase are not well understood yet. In this study we investigated the responses of global net primary production in (NPP), soil heterotrophic respiration (HR), and net ecosystem production (NEP) to atmospheric CO2 increases and climate variation in the period 1981-1998. Our results show that the unusual climate variability in this period associated with strong warming and El Niño caused high interannual variations in terrestrial ecosystem carbon fluxes; nevertheless NPP and NEP increased consistently from the 1980s to 1990s. Annual global NPP and HR varied with a similar magnitude and contributed about equally to the interannual variations in NEP. Global NEP fluctuated between -0.64 and 1.68 Gt C yr-1 with a mean value of 0.62 Gt C yr-1 , its decadal means increased from 0.23 Gt C yr-1 in the 1980s to 1.10 Gt C yr-1 in the 1990s. Total and vegetation carbon storage increased with increases of NPP, but soil carbon storage declined because of higher HR than litter inputs. The tropics (20°N-20°S) had higher mean NEP than the north (>20°N), however, they contributed similarly to the global NEP increase from the 1980s and 1990s. Our estimated terrestrial ecosystem carbon uptake, in response to climate variation and atmospheric CO2 increase, accounted for only about 15 to 30% of the total terrestrial carbon sink but contributed 73% of its increase from the 1980s to the 1990s.

Cao, M. K., Woodward, F. I. (1998). Net primary and ecosystem production and carbon stocks of terrestrial ecosystems and their responses to climate change. Global Change Biology 4 (2): 185-198

ABSTRACT: Evaluating the role of terrestrial ecosystems in the global carbon cycle requires a detailed understanding of carbon exchange between vegetation, soil, and the atmosphere. Global climatic change may modify the net carbon balance of terrestrial ecosystems, causing feedbacks on atmospheric CO2 and climate. We describe a model for investigating terrestrial carbon exchange and its response to climatic variation based on the processes of plant photosynthesis, carbon allocation, litter production, and soil organic carbon decomposition. The model is used to produce geographical patterns of net primary production (NPP), carbon stocks in vegetation and soils, and the seasonal variations in net ecosystem production (NEP) under both contemporary and future climates. For contemporary climate, the estimated global NPP is 57.0 Gt C y–1 , carbon stocks in vegetation and soils are 640 Gt C and 1358 Gt C, respectively, and NEP varies from –0.5 Gt C in October to 1.6 Gt C in July. For a doubled atmospheric CO2 concentration and the corresponding climate, we predict that global NPP will rise to 69.6 Gt C y–1 , carbon stocks in vegetation and soils will increase by, respectively, 133 Gt C and 160 Gt C, and the seasonal amplitude of NEP will increase by 76%. A doubling of atmospheric CO2 without climate change may enhance NPP by 25% and result in a substantial increase in carbon stocks in vegetation and soils. Climate change without CO2 elevation will reduce the global NPP and soil carbon stocks, but leads to an increase in vegetation carbon because of a forest extension and NPP enhancement in the north. By combining the effects of CO2 doubling, climate change, and the consequent redistribution of vegetation, we predict a strong enhancement in NPP and carbon stocks of terrestrial ecosystems. This study simulates the possible variation in the carbon exchange at equilibrium state. We anticipate to investigate the dynamic responses in the carbon exchange to atmospheric CO2 elevation and climate change in the past and future.

Carney, K. M., Hungate, B. A., Drake, B. G., Megonigal, J. P. (2007). Altered soil microbial community at elevated CO2 leads to loss of soil carbon. Proceedings of the National Academy of Sciences: PNAS 104 (12): 4990-4995

ABSTRACT: Increased carbon storage in ecosystems due to elevated CO2 may help stabilize atmospheric CO2 concentrations and slow global warming. Many field studies have found that elevated CO2 leads to higher carbon assimilation by plants, and others suggest that this can lead to higher carbon storage in soils, the largest and most stable terrestrial carbon pool. Here we show that 6 years of experimental CO2 doubling reduced soil carbon in a scrub-oak ecosystem despite higher plant growth, offsetting ≈52% of the additional carbon that had accumulated at elevated CO2 in aboveground and coarse root biomass. The decline in soil carbon was driven by changes in soil microbial composition and activity. Soils exposed to elevated CO2 had higher relative abundances of fungi and higher activities of a soil carbon-degrading enzyme, which led to more rapid rates of soil organic matter degradation than soils exposed to ambient CO2 . The isotopic composition of microbial fatty acids confirmed that elevated CO2 increased microbial utilization of soil organic matter. These results show how elevated CO2 , by altering soil microbial communities, can cause a potential carbon sink to become a carbon source.

Catovsky, S., Bradford, M. A., Hector, A. (2002). Biodiversity and ecosystem productivity: implications for carbon storage. Oikos 97 (3): 443-448

ABSTRACT: Recent experiments have found that Net Primary Productivity (NPP) can often be a positive saturating function of plant species and functional diversity. These findings raised the possibility that more diverse ecosystems might store more carbon as a result of increased photosynthetic inputs. However, carbon inputs will not only remain in plant biomass, but will be translocated to the soil via root exudation, fine root turnover, and litter fall. Thus, we must consider not just plant productivity (NPP), but also net productivity of the whole ecosystem (NEP), which itself measures net carbon storage. We currently know little about how plant diversity could influence soil processes that return carbon back to the atmosphere, such as heterotrophic respiration and decomposition of organic matter. Nevertheless, it is clear that any effects on such processes could make NPP a poor predictor of whole-ecosystem productivity, and potentially the ability of the ecosystem to store carbon. We examine the range of mechanisms by which plant diversity could influence net ecosystem productivity, incorporating processes involved with carbon uptake (productivity), loss (autotrophic and heterotrophic respiration), and residence time within the system (decomposition rate). Understanding the relationship between plant diversity and ecosystem carbon dynamics must be made a research priority if we wish to provide information relevant to global carbon policy decisions. This goal is entirely feasible if we utilize some basic methods for measuring the major fluxes of carbon into and out of the ecosystem.

Chastain, Jr., R. A., Currie, W. S., Townsend, P. A. (2006). Carbon sequestration and nutrient cycling implications of the evergreen understory layer in Appalachian forests. Forest Ecology and Management 231 (1-3): 63-77

ABSTRACT: Evergreen understory communities dominated by mountain laurel (Kalmia latifolia L.) and/or rosebay rhododendron (Rhododendron maximum L.) are an important but often overlooked component of Appalachian forests. In the dense thickets in which these species often occur, they have high carbon sequestration potential and play important roles in nutrient storage and cycling. We used allometric modeling of the aboveground biomass to quantify the importance ofK. latifolia andR. maximum , relative to overstory tree species, in driving biogeochemical cycling in the Central Appalachian mountains. Carbon sequestration and nitrogen and phosphorus storage potentials were investigated by running 50-year simulations of the ecosystem accounting model NuCSS for two situations: forests comprising the canopy overstory layer with or without the evergreen understory layer. When simulating forests in several test watersheds based only on the composition and biomass of the overstory canopy, these forests contain between 1631 and 4825 kg/ha less in overall C content and 41–224 kg/ha less N content than if the evergreen understory layer is included. Additional N uptake by evergreen understory vegetation was estimated to amount to between 6 and 11 kg N ha−1 yr−1 at year 50 for the overstory-with-understory forest compared to the overstory-only forest. Vegetation pool nutrient storage was higher by 2–4% for N, and by 2–14% for P at year 50 whenR. maximum andK. latifolia were included in the model. Aboveground standing biomass ofR. maximum andK. latifolia accounted for only a modest portion of the C sequestered and N stored in the forest ecosystems at the watershed scale. In contrast, notably higher amounts of C and N were simulated as stored in the forest floor and soil pools when the understory was included. N storage predominated in the forest floor compared to the soil pool when a larger amount ofR. maximum was present in a watershed, most likely due to the larger amounts of recalcitrant litter produced annually by this species compared toK. latifolia . In addition, storage of P inK. latifolia andR. maximum exceeded expectations compared to their watershed-scale standing biomass.

Chojnacky, D.C., Amacher, M.C., Perry, C.H., K.M. Reynolds (2006). A model for monitoring forest floor duff and litter carbon sequestration. USDA Forest Service, Pacific Northwest Research Station

ABSTRACT: The forest floor is an important part of carbon storage, biodiversity, nutrient cycling, and fire fuel hazard. This paper reports on a study of litter and duff layers of the forest floor for eastern U.S. forests. The U. S. Department of Agriculture (USDA) Forest Service, Forest Inventory Analysis (FIA) program currently measures variables related to duff and litter on a subsample of plots covering all U.S. forest lands regardless of ownership. The FIA soils protocol includes duff and litter thickness measurement and sample collection followed by lab measurement of mass and carbon content. We examined these lab data to test a model of duff and litter carbon storage based upon simple measurements of forest floor depth. Duff and litter data were compiled from 1,468 plots sampled in 2001 and 2002 from most states in the eastern U.S. These data were combined with other available FIA data for regression modeling to predict duff and litter carbon from depth of duff and litter layer and several other classification variables (R2 =0.56). Results on duff and litter model predictions show that duff and litter are an important carbon sink in eastern U.S. forests by containing about 50 percent of the forest floor carbon or 10 percent of total forest carbon (excluding mineral soil).

Cornelissen, J. H. C., van Bodegom, P. M., Aerts, R., Callaghan, T. V., van Logtestijn, R. S. P., Alatalo, J., Stuart C. F., Gerdol, R., Gudmundsson, J., Gwynn-Jones, D., Hartley, A. E., Hik, D. S., Hofgaard, A., Jonsdottir, I. S., Karlsson, S., Klein, J. A., Laundre, J., Magnusson, B., Michelsen, A., Molau, U., Onipchenko, V. G., Quested, H. M., Sandvik, S. M., Schmidt, I. K., Shaver, G. R., Solheim, B., Soudzilovskaia, N. A., Stenstrom, A., Tolvanen, A., Totland, O., Wada, N., Welker, J. M., Zhao, X. (2007). Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes. Ecology Letters 10 (7): 619-627

ABSTRACT: Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide. Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth-form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.

Davi, H., Dufrene, E., Francois, C., Le Maire, G., Loustau, D., Bosc, A., Rambal, S., Granier, A., Moors, E. (2006). Sensitivity of water and carbon fluxes to climate changes from 1960 to 2100 in European forest ecosystems. Agricultural and Forest Meteorology 141 (1): 35-56

ABSTRACT: The effects of climate changes on carbon and water fluxes are quantified using a physiologically multi-layer, process-based model containing a carbon allocation model and coupled with a soil model (CASTANEA). The model is first evaluated on four EUROFLUX sites using eddy covariance data, which provide estimates of carbon and water fluxes at the ecosystem scale. It correctly reproduces the diurnal fluxes and the seasonal pattern. Thereafter simulations were conducted on six French forest ecosystems representative of three climatic areas (oceanic, continental and Mediterranean areas) dominated by deciduous species (Fagus sylvatica ,Quercus robur ), coniferous species (Pinus pinaster ,Pinus sylvestris ) or sclerophyllous evergreen species (Quercus ilex ). The model is driven by the results of a meteorological model (ARPEGE) following the B2 scenario of IPCC. From 1960 to 2100, the average temperature increases by 3.1 °C (30%) and the rainfall during summer decreases by 68 mm (-27%). For all the sites, between the two periods, the simulations predict on average a gross primary production (GPP) increase of 513 g(C) m-2 (+38%). This increase is relatively steep until 2020, followed by a slowing down of the GPP rise due to an increase of the effect of water stress. Contrary to GPP, the ecosystem respiration (Reco) raises at a constant rate (350 g(C) m-2 i.e. 31% from 1960 to 2100). The dynamics of the net ecosystem productivity (GPP minus Reco) is the consequence of the effect on both GPP and Reco and differs per site. The ecosystems always remain carbon sinks; however the sink strength globally decreases for coniferous (-8%), increases for sclerophyllous evergreen (+34%) and strongly increases for deciduous forest (+67%) that largely benefits by the lengthening of the foliated period. The separately quantified effects of the main variables (temperature, length of foliated season, CO2 fertilization, drought effect), show that the magnitude of these effects depends on the species and the climatic zone.

De Vries, W., G.J. Reinds, P. Gundersen, H. Sterba (2006). The impact of nitrogen deposition on carbon sequestration in European forests and forest soils. Global Change Biology 12 (7): 1151-1173

ABSTRACT: An estimate of net carbon (C) pool changes and long-term C sequestration in trees and soils was made at more than 100 intensively monitored forest plots (level II plots) and scaled up to Europe based on data for more than 6000 forested plots in a systematic 16 km × 16 km grid (level I plots). C pool changes in trees at the level II plots were based on repeated forest growth surveys At the level I plots, an estimate of the mean annual C pool changes was derived from stand age and available site quality characteristics. C sequestration, being equal to the long-term C pool changes accounting for CO2 emissions because of harvest and forest fires, was assumed 33% of the overall C pool changes by growth. C sequestration in the soil were based on calculated nitrogen (N) retention (N deposition minus net N uptake minus N leaching) rates in soils, multiplied by the C/N ratio of the forest soils, using measured data only (level II plots) or a combination of measurements and model calculations (level I plots). Net C sequestration by forests in Europe (both trees and soil) was estimated at 0.117 Gton yr−1 , with the C sequestration in stem wood being approximately four times as high (0.094 Gton yr−1 ) as the C sequestration in the soil (0.023 Gton yr−1 ). The European average impact of an additional N input on the net C sequestration was estimated at approximately 25 kg C kg−1 N for both tree wood and soil. The contribution of an average additional N deposition on European forests of 2.8 kg ha−1 yr−1 in the period 1960–2000 was estimated at 0.0118 Gton yr−1 , being equal to 10% of the net C sequestration in both trees and soil in that period (0.117 Gton yr−1 ). The C sequestration in trees increased from Northern to Central Europe, whereas the C sequestration in soil was high in Central Europe and low in Northern and Southern Europe. The result of this study implies that the impact of forest management on tree growth is most important in explaining the C pool changes in European forests.

Dell, C. J., Sharpley, A. N. (2006). Spatial variation of soil organic carbon in a northeastern U.S. watershed. Journal of Soil and Water Conservation 61 (3): 129-136

ABSTRACT: Increasing the accumulation of organic carbon (C) in agricultural soils provides one means to reduce atmospheric carbon dioxide (CO2 ) concentrations, but detection of the relatively small changes in soil organic C is complicated by spatial variability. Soil organic C variation was assessed at various scales within a small (40 ha; 98 ac), mixed-use watershed in central Pennsylvania to determine sampling requirement for possible C credit programs. Composite soil samples (0 to 5 cm; 0 to 2 in deep) were collected on 30-m (98-ft) grid intervals across the watershed and at 10- and 0.6-m (33- and 2-ft) intervals at selected locations, and descriptive- and geo-statistical analysis utilized. Concentrations of soil organic C in pasture and forest soils were approximately two times greater than cultivated fields, where means ranged from 15 to 24 g C kg−1 (1.5 to 2.4 percent) and coefficients of variation were typically 15 to 20 percent. Soil organic C was spatially dependent over a range of approximately 200 m (660 ft) when sampled at 30-m (98-ft) intervals, and high nugget variances indicated spatially-dependent variability over lag distances shorter than 30 m (98ft). However, sampling at 10-m (33 ft) intervals appeared to adequately describe variation. Estimates of sample size requirement showed that, with the observed coefficient variances for individual fields, two- to five-fold increases in sample numbers would be required to verify statistically significant soil organic C changes ≤ 10 percent. Given the large number of samples required to provide representative measurements and the concurrent cost for labor and analysis, participation by farmers in a C credit program could be low if measured verification of soil organic C increases are required. Basing payments on modeled, rather than measured C sequestration rates, should be considered.

R. K. Dixon, A. M. Solomon, S. Brown, R. A. Houghton, M. C. Trexier, J. Wisniewski (1994). Carbon pools and flux of global forest ecosystems. Science 263 (5144): 185-190

ABSTRACT: Forest systems cover more than 4.1 x 109 hectares of the Earth's land area. Globally, forest vegetation and soils contain about 1146 petagrams of carbon, with approximately 37 percent of this carbon in low-latitude forests, 14 percent in mid-latitudes, and 49 percent at high latitudes. Over two-thirds of the carbon in forest ecosystems is contained in soils and associated peat deposits. In 1990, deforestation in the low latitudes emitted 1.6 ± 0.4 petagrams of carbon per year, whereas forest area expansion and growth in mid- and high-latitude forest sequestered 0.7 ± 0.2 petagrams of carbon per year, for a net flux to the atmosphere of 0.9 ± 0.4 petagrams of carbon per year. Slowing deforestation, combined with an increase in forestation and other management measures to improve forest ecosystem productivity, could conserve or sequester significant quantities of carbon. Future forest carbon cycling trends attributable to losses and regrowth associated with global climate and land-use change are uncertain. Model projections and some results suggest that forests could be carbon sinks or sources in the future.

Eliseev, A. V., Mokhov, I. I. (2007). Carbon cycle-climate feedback sensitivity to parameter changes of a zero-dimensional terrestrial carbon cycle scheme in a climate model of intermediate complexity. Theoretical and Applied Climatology 89 (1): 9-24

ABSTRACT: A series of sensitivity runs have been performed with a coupled climate–carbon cycle model. The climatic component consists of the climate model of intermediate complexity IAP RAS CM. The carbon cycle component is formulated as a simple zero-dimensional model. Its terrestrial part includes gross photosynthesis, and plant and soil respirations, depending on temperature viaQ 10 -relationships (Lenton, 2000). Oceanic uptake of anthropogenic carbon is formulated is a bi-linear function of tendencies of atmospheric concentration of CO2 and globally averaged annual mean sea surface temperature. The model is forced by the historical industrial and land use emissions of carbon dioxide for the second half of the 19th and the whole of the 20th centuries, and by the emission scenario SRES A2 for the 21st century. For the standard set of the governing parameters, the model realistically captures the main features of the Earth’s observed carbon cycle. A large number of simulations have been performed, perturbing the governing parameters of the terrestrial carbon cycle model. In addition, the climate part is perturbed, either by zeroing or artificially increasing the climate model sensitivity to the doubling of the atmospheric CO2 concentration. Performing the above mentioned perturbations, it is possible to mimic most of the range found in the C4MIP simulations. In this way, a wide range of the climate–carbon cycle feedback strengths is obtained, differing even in the sign of the feedback. If the performed simulations are subjected to the constraints of a maximum allowed deviation of the simulated atmospheric CO2 concentration (p CO2( ) ) from the observed values and correspondence between simulated and observed terrestrial uptakes, it is possible to narrow the corresponding uncertainty range. Among these constraints, consideringp CO2( ) and uptakes are both important. However, the terrestrial uptakes constrain the simulations more effectively than the oceanic ones. These constraints, while useful, are still unable to rule out both extremely strong positive and modest negative climate–carbon cycle feedback.

Eliseev, A.V., Mokhov, I.I., Karpenko, A.A. (2007). Climate and carbon cycle variations in the 20th and 21st centuries in a model of intermediate complexity. Izvestiya - Atmospheric and Ocean Physics 43 (1): 1-14

ABSTRACT: The climate model of intermediate complexity developed at the Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM), has been supplemented by a zero-dimensional carbon cycle model. With the carbon dioxide emissions prescribed for the second half of the 19th century and for the 20th century, the model satisfactorily reproduces characteristics of the carbon cycle over this period. However, with continued anthropogenic CO2 emissions (SRES scenarios A1B, A2, B1, and B2), the climate-carbon cycle feedback in the model leads to an additional atmospheric CO2 increase (in comparison with the case where the influence of climate changes on the carbon exchange between the atmosphere and the underlying surface is disregarded). This additional increase is varied in the range 67–90 ppmv depending on the scenario and is mainly due to the dynamics of soil carbon storage. The climate-carbon cycle feedback parameter varies nonmonotonically with time. Positions of its extremes separate characteristic periods of the change in the intensity of anthropogenic emissions and of climate variations. By the end of the 21st century, depending on the emission scenario, the carbon dioxide concentration is expected to increase to 615–875 ppmv and the global temperature will rise by 2.4–3.4 K relative to the preindustrial value. In the 20th–21st centuries, a general growth of the buildup of carbon dioxide in the atmosphere and ocean and its reduction in terrestrial ecosystems can be expected. In general, by the end of the 21st century, the more aggressive emission scenarios are characterized by a smaller climate-carbon cycle feedback parameter, a lower sensitivity of climate to a single increase in the atmospheric concentration of carbon dioxide, a larger fraction of anthropogenic emissions stored in the atmosphere and the ocean, and a smaller fraction of emissions in terrestrial ecosystems.

Fang, J.Y., Guo, Z.D., Piao, S.L., Chen, A.P. (2007). Terrestrial vegetation carbon sinks in China, 1981-2000. Science in China, Series D: Earth Sciences 50 (9): 1341-1350

ABSTRACT; Using China’s ground observations, e.g., forest inventory, grassland resource, agricultural statistics, climate, and satellite data, we estimate terrestrial vegetation carbon sinks for China’s major biomes between 1981 and 2000. The main results are in the following: (1) Forest area and forest biomass carbon (C) stock increased from 116.5×106 ha and 4.3 Pg C (1 Pg C = 1015 g C) in the early 1980s to 142.8×106 ha and 5.9 Pg C in the early 2000s, respectively. Forest biomass carbon density increased form 36.9 Mg C/ha (1 Mg C = 106 g C) to 41.0 Mg C/ha, with an annual carbon sequestration rate of 0.075 Pg C/a. Grassland, shrub, and crop biomass sequestrate carbon at annual rates of 0.007 Pg C/a, 0.014–0.024 Pg C/a, and 0.0125–0.0143 Pg C/a, respectively. (2) The total terrestrial vegetation C sink in China is in a range of 0.096–0.106 Pg C/a between 1981 and 2000, accounting for 14.6%–16.1% of carbon dioxide (CO2 ) emitted by China’s industry in the same period. In addition, soil carbon sink is estimated at 0.04–0.07 Pg C/a. Accordingly, carbon sequestration by China’s terrestrial ecosystems (vegetation and soil) offsets 20.8%–26.8% of its industrial CO2 emission for the study period. (3) Considerable uncertainties exist in the present study, especially in the estimation of soil carbon sinks, and need further intensive investigation in the future.

Godbold, D.L., Brunner, I. (2007). The platform for European root science, COST action E38: An introduction and overview. Plant Biosystems 141 (3): 390-393

ABSTRACT: Globally, forests cover 4 billion ha or 30% of the Earth's land surface and account for more that 75% of carbon stored in terrestrial ecosystem. However, 20 - 40% of the forest biomass is roots. Roots play a key role in acquisition of water and nutrients from the soil, the transfer of carbon to soil, as well as providing physical stabilisation. In temperate forests of Europe, average biomass of trees is estimated to be ca. 220 t ha-1 , of which 52 t ha-1 are coarse roots and 2.4 t ha-1 are fine roots. Thus, forests and their soils belong to the planets largest reservoirs of carbon. As an outcome of a recently established European platform for scientists working on woody roots, COST action E38, a series of papers has been initiated in order to review the current knowledge on processes in and of roots of woody plants and to identify possible knowledge gaps. These reviews concentrate on aspects of roots as indicators of environmental change, biomass of fine roots, and modelling of course root systems. The reviews of roots as indicators of environmental change cover a number of aspects including, specific root length, the calcium to aluminium ratio, root electrolyte leakage, and ectomycorrhiza community composition.

Gough, C. M., Vogel, C. S., Kazanski, C., Nagel, L., Flower, C. E., Curtis, P. S. (2007). Coarse woody debris and the carbon balance of a north temperate forest. Forest Ecology and Management 244 (1-3): 60-67

ABSTRACT: Comprehensive estimates of forest carbon (C) mass and respiration require measurements of all C pools, including coarse woody debris (CWD). We used inventory and chamber-based methods to quantify C mass and the annual respiratory C loss from CWD and other major ecosystem components for a deciduous forest in the upper Great Lakes region. Coarse woody debris mass (MCWD , 2.2 Mg C ha−1 ) was less than that of soils (104.1 Mg C ha−1 ) and boles (71.7 Mg C ha−1 ), but similar to that of leaves (1.8 Mg C ha−1 ). Coarse woody debris respiration (RCWD ) increased with temperature and water content, with differences in RCWD among decay classes due to variation in water content rather than to variable sensitivity to environmental conditions. Sensitivity of RCWD to changing temperature, evaluated as Q10 , ranged from 2.20 to 2.57 and was variable among decay classes. Annual CWD respiration (FCWD , 0.21 Mg C ha−1 year−1 ) was 12% of bole respiration, 8% of leaf respiration, and 2% of soil respiration. The CWD decomposition rate-constant (FCWD /MCWD ) in 2004 was 0.09 year−1. When compared to the average annual ecosystem C storage of 1.53 Mg C ha−1 year−1 , FCWD represents a small, but substantial flux that is expected to increase over the next several decades in this maturing forest.

T. Grϋnwald, C. Bernhofer (2007). A decade of carbon, water and energy flux measurements of an old spruce forest at the Anchor Station Tharandt. Tellus B 59 (3): 387-396

ABSTRACT: At Tharandt/Germany eddy covariance (EC) measurements of carbon dioxide and heat fluxes are performed above an old spruce forest since 1996. The last ten years cover almost all meteorological extremes observed during the last 45 years: the coldest and warmest year with mean air temperature of 6.1°C (1996) and 9.6°C (2000) as well as the fourth wettest and the driest year with a precipitation of 1098 mm (2002) and 501 mm (2003), respectively. In general, the observed annual carbon net ecosystem exchange (NEE) indicates a high net sink from −395 g C m−2 a−1 (2003) to −698 g C m−2 a−1 (1999) with a coefficient of variation cv= 16.6% . The yearly evapotranspiration (ET) has a lower interannual variability (cv= 9.5%) between 389 mm (2003) and 537 mm (2000). The influence of flux correction and gap filling on the amount of annual NEE and ET is considerable. Using different methods of gap filling (non-linear regressions, mean diurnal courses) yields annual NEE totals that differ by up to 18%.

Consistency analysis regarding energy balance closure, comparisons with independent soil respiration and biomass increment measurements indicate reliability of the fluxes. The average gap of the energy balance is 15% of the available energy based on regression slope with an intercept of 3 to 16 W m−2 , but around zero for annual flux ratios. Between 47% and 63% of the net ecosystem productivity was fixed above ground according to up-scaled tree ring data and forest inventories, respectively. Chamber measurements of soil respiration yield up to 90% of nighttime EC based total ecosystem respiration. Thus, we conclude that the EC based flux represents an upper limit of the C sink at the site.

Hagedorn, F., Maurer, S., Egli, P., Blaser, P., Bucher, J. B., Siegwolf, R. (2001). Carbon sequestration in forest soils: effects of soil type, atmospheric CO2 enrichment, and N deposition. European Journal of Soil Science 52 (4): 619-628

ABSTRACT: Soil contains the major part of carbon in terrestrial ecosystems, but the response of this carbon to enriching the atmosphere in CO2 and to increased N deposition is not completely understood. We studied the effects of CO2 concentrations at 370 and 570μmolCO2 mol−1 air and increased N deposition (7 against 0.7 g N m−2 year−1 ) on the dynamics of soil organic C in two types of forest soil in model ecosystems with spruce and beech established in large open-top chambers containing an acidic loam and a calcareous sand. The added CO2 was depleted in13 C and thus the net input of new C into soil organic carbon and the mineralization of native C could be quantified.

Soil type was the greatest determining factor in carbon dynamics. After 4 years, the net input of new C in the acidic loam (670 ± 30 g C m−2 ) exceeded that in the calcareous sand (340 ± 40 g C m−2 ) although the soil produced less biomass. The mineralization of native organic C accounted for 700 ± 90 g C m−2 in the acidic loam and for 2800 ± 170 g C m−2 in the calcareous sand. Unfavourable conditions for mineralization and a greater physico-chemical protection of C by clay and oxides in the acidic loam are probably the main reasons for these differences. The organic C content of the acidic loam was 230 g C m−2 more under the large than under the small N treatment. As suggested by a negligible impact of N inputs on the fraction of new C in the acidic loam, this increase resulted mainly from a suppressed mineralization of native C. In the calcareous sand, N deposition did not influence C concentrations. The impacts of CO2 enrichment on C concentrations were small. In the uppermost 10 cm of the acidic loam, larger CO2 concentrations increased C contents by 50–170 g C m−2 . Below 10 cm depth in the acidic loam and at all soil depths in the calcareous sand, CO2 concentrations had no significant impact on soil C concentrations. Up to 40% of the 'new' carbon of the acidic loam was found in the coarse sand fraction, which accounted for only 7% of the total soil volume. This suggests that a large part of the CO2 -derived 'new' C was incorporated into the labile and easily mineralizable pool in the soil.

Han, F., Plodinec, M., Su, Y., Monts, D., Li, Z. (2007). Terrestrial carbon pools in southeast and south-central United States. Climatic Change 84 (2): 191-202

ABSTRACT: Analyses of regional carbon sources and sinks are essential to assess the economical feasibility of various carbon sequestration technologies for mitigating atmospheric CO2 accumulation and for preventing global warming. Such an inventory is a prerequisite for regional trading of CO2 emissions. As a U.S. Department of Energy Southeast Regional Carbon Sequestration Partner, we have estimated the state-level terrestrial carbon pools in the southeast and south-central US. This region includes: Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Texas, and Virginia. We have also projected the potential for terrestrial carbon sequestration in the region. Texas is the largest contributor (34%) to greenhouse gas emission in the region. The total terrestrial carbon storage (forest biomass and soils) in the southeast and south-central US is estimated to be 130 Tg C/year. An annual forest carbon sink (estimated as 76 Tg C/year) could compensate for 13% of the regional total annual greenhouse gas emission (505 Tg C, 1990 estimate). Through proper policies and the best land management practices, 54 Tg C/year could be sequestered in soils. Thus, terrestrial sinks can capture 23% of the regional total greenhouse emission and hence are one of the most cost-effective options for mitigating greenhouse emission in the region.

Han, F. X. X., Lindner, J. S., Wang, C. J. (2007). Making Carbon Sequestration a Paying Proposition. Naturwissenschaften 94 (3): 170-182

ABSTRACT: Atmospheric carbon dioxide (CO2 ) has increased from a preindustrial concentration of about 280 ppm to about 367 ppm at present. The increase has closely followed the increase in CO2 emissions from the use of fossil fuels. Global warming caused by increasing amounts of greenhouse gases in the atmosphere is the major environmental challenge for the 21st century. Reducing worldwide emissions of CO2 requires multiple mitigation pathways, including reductions in energy consumption, more efficient use of available energy, the application of renewable energy sources, and sequestration. Sequestration is a major tool for managing carbon emissions. In a majority of cases CO2 is viewed as waste to be disposed; however, with advanced technology, carbon sequestration can become a value-added proposition. There are a number of potential opportunities that render sequestration economically viable. In this study, we review these most economically promising opportunities and pathways of carbon sequestration, including reforestation, best agricultural production, housing and furniture, enhanced oil recovery, coalbed methane (CBM), and CO2 hydrates. Many of these terrestrial and geological sequestration opportunities are expected to provide a direct economic benefit over that obtained by merely reducing the atmospheric CO2 loading. Sequestration opportunities in 11 states of the Southeast and South Central United States are discussed. Among the most promising methods for the region include reforestation and CBM. The annual forest carbon sink in this region is estimated to be 76 Tg C/year, which would amount to an expenditure of $11.1-13.9 billion/year. Best management practices could enhance carbon sequestration by 53.9 Tg C/year, accounting for 9.3% of current total annual regional greenhouse gas emission in the next 20 years. Annual carbon storage in housing, furniture, and other wood products in 1998 was estimated to be 13.9 Tg C in the region. Other sequestration options, including the direct injection of CO2 in deep saline aquifers, mineralization, and biomineralization, are not expected to lead to direct economic gain. More detailed studies are needed for assessing the ultimate changes to the environment and the associated indirect cost savings for carbon sequestration.

Harper, R.J., Beck, A.C., Ritson, P., Hill, M.J., Mitchell, C.D., Barrett, D.J., Smettem, K.R.J., Mann, S.S. (2007). The potential of greenhouse sinks to underwrite improved land management. Ecological Engineering 29 (4): 329-341

ABSTRACT: The current agricultural systems of broad areas of Australia are unsustainable, with large projected increases in salinization, decreases in water quality, wind erosion, and losses of biodiversity. It is well known that these problems can be partially resolved by farmland reforestation; however, a major issue is financing the scale of activity required. The international response to global warming, the United Nations Framework Convention on Climate Change and its Kyoto Protocol, includes provisions that enable greenhouse sinks (sequestration of carbon in soils and vegetation) to be used by parties to fulfil their obligations. The Kyoto Protocol also allows for trading in emission reductions, and this opens the possibility that investment in carbon sinks may help underwrite broader natural resource management objectives. This paper examines the possibilities for improved land management in Western Australia arising from the development of carbon sinks by considering: (a) the likelihood of a carbon market developing and the likely depth of that market as a result of current national and international policies, (b) the data available to provide estimates on different types of sinks, and (c) the likely benefits of wide-scale sink investment.

It was estimated that the total amount of carbon that could be sequestered by reforesting 16.8 Mha of cleared farmland is 2200 Mt CO2 -e, and between 290 and 1170 Mt CO2 -e by destocking 94.8 Mha of rangelands. There were insufficient data to produce estimates of sequestration following changes in tillage practice in cropping systems or the revegetation of already salinized land. We conclude that carbon sinks are only likely to become profitable as a broad-scale stand-alone enterprise when carbon prices reach AUD$15/t CO2 -e, with this threshold value varying with carbon yield and project costs. Below this price, their value can be significant as an adjunct to reforestation schemes that are aimed at providing other products (wood, pulp, bioenergy) and land and water conservation benefits. Irrespective of this, carbon sinks provide an opportunity to both sequester carbon in a least-cost fashion and improve soil and watershed management.

Hill, P., Marshall, C., Harmens, H., Jones, D., Farrar, J. (2005). Carbon sequestration: Do N inputs and elevated atmospheric CO2 alter soil solution chemistry and respiratory C losses?. Water Air and Soil Pollution 4 (6): 177-186

ABSTRACT: Soil respiration is a large C flux which is of primary importance in determining C sequestration. Here we ask how it is altered by atmospheric CO2 concentration and N additions. Swards ofLolium perenne L. were grown in a Eutric cambisol under controlled conditions with and without the addition of 200 kg NO3 –N ha–1 , at either 350 ppm or 700 ppm CO2 , for 3 months. Soil respiration and net canopy photosynthesis were both increased by added N and elevated CO2 , but soil respiration increased proportionately less than fixation by photosynthesis. Thus, both elevated CO2 and N appeared to increase potential C sequestration, although adding N at elevated CO2 reduced the C sequestered as a proportion of that fixed relative to elevated CO2 alone. Across all treatments below-ground respiratory C losses were predicted by root biomass, but not by soil solution C and N concentrations. Specific root-dependent respiration was increased by elevated CO2 , such that belowg-round respiration per unit biomass and per unit plant N was increased.

Hoover, C.M., Kimble, J.M., Heath, L.S., Birdsey, R.A., Lal, R. (2003). Soil carbon sequestration and forest management: challenges and opportunities. CRC Press: 211-238

DESCRIPTION: The subject of the effects of forest management activities on soil carbon is a difficult one to address, but ongoing discussions of carbon sequestration as an emissions offset and the emergence of carbon-credit-trading systems necessitate that we broaden and deepen our understanding of the response of forest-soil carbon pools to forest management. There have been several reviews of the literature, but hard-and-fast conclusions are still difficult to draw, since many of the studies reviewed were not designed specifically to address management effects on soil carbon, were conducted on a short timescale, and differ in the methodology employed.

Janzen, H. H. (2004). Carbon Cycling in Earth Systems - a Soil Science Perspective. 104 (3): 399-417

ABSTRACT: The carbon cycle binds together earth’s ecosystems and their inhabitants. My intent is to review the global carbon cycle, examine how humans have modified it, and contemplate (from a soil science bias) the new questions that await us on a changing earth. These thoughts are proffered, not to propose a way forward, but to invite conversation about opportunities that await us.

Terrestrial ecosystems hold a lot of carbon—about 500 Pg C in plant biomass, and 2000 Pg C in soil organic matter. Oceans contain even more. And the atmosphere, now with about 785 Pg C, connects all of these pools. The flows of carbon between the pools, and their feedbacks, have kept atmospheric CO2 reasonably constant for millennia. But humans have increasingly distorted the balance, by changing land use and by injecting fossil C back into the cycle. Consequently, atmospheric CO2 has increased recently by more than 3 Pg C per year and, by century’s end, its concentration may be twice pre-industrial levels, or more.

The changing carbon cycle poses new questions for scientists. Now we will be asked, not how things are, but how they will be. For example: How will changes in CO2 alter flows of carbon through biological carbon stocks? Can we manage ecosystems to hold more carbon? Are current carbon stores vulnerable should the earth warm, or water cycles shift, or nitrogen flows be altered? What will the C cycle look like a century from now; and will it then still provide all that we expect from it? These and other new questions may elicit from us fresh insights and approaches.We may learn to look more broadly at the C cycle, seeing all the ‘ecosystem services’ (not just C sequestration). We may insist on studies yielding deeper understanding of the C cycle, relevant beyond current issues. We may further emphasize ‘time’ in our studies, looking more at flows and changes than at describing what is—and looking long enough to see even subtle shifts.We may learn to follow C beyond the usual boundaries set by arbitrary disciplines. And we may come to see, more than before, how the carbon cycle weaves through our fields and skies and forests—and find new ways to reveal its grandeur to those who have not yet seen it. And then, it may happen that
our successors, a century from now, will look back, almost in envy, at the urgent, enticing questions we were given to solve.

Jiménez, J. J., Lal, R. (2006). Mechanisms of C sequestration in soils of Latin America. Critical Reviews in Plant Sciences 25 (4): 337-365

ABSTRACT: Carbon (C) sequestration, defined as the process whereby atmospheric CO2 is transferred into a long-lived C pool, is an important issue not only in the scientific community but also in the society at large because of its potential role in off-setting fossil fuel emissions. Through photosynthesis this C is stored in plants and through decomposition, trunks, branches, leaves and roots are incorporated in the soil via the action of different soil organisms, i.e., bacteria, fungi and invertebrates. This, together with the C exudates from roots that are utilized by microbial populations, constitutes the natural pathways of incorporating biomass-C into the soil. The amount of C stored in terrestrial ecosystems is the third largest among the global C pools. Soil organic carbon (SOC) up to 3 m is 2,344 Pg C (1 Petagram = 1015 g), and the SOC pool in tropical soils is approximately 30% of the global pool. Abiotic factors, which moderate C sequestration in soils are clay content, mineralogy, structural stability, landscape position, and soil moisture and temperature regimes. On the other hand, biotic factors involved in soil C sequestration are determined by the activities of soil organisms. However, models do not include the formation, stabilization and lifespan of the aggregates that have been biologically produced, including roots. This is not only due to the lack of studies on this subject, but also to overlooking the role of soil organisms in soil aggregation. Furthermore, there is a lack of comprehensive knowledge regarding the processes that control dissolved organic carbon (DOC) fluxes in soils and its role in the global budget of C sequestration. The boundaries of ecosystems are not considered in the studies of the subject, as it may be the case for terrestrial C sequestration, since the borders around the sites under study constitute pathways for the flow of C between sites and through the landscape. The concentrations of DOC in deep soil horizons and the contribution to DOC fluxes (exports) are relatively small, from 4 to 37 g DOC m−2 yr−1 retained in the mineral subsoil. In South America, although substantial research has been done under different ecosystems and land use systems in some countries, like Brazil, Colombia, Argentina, there is a need to conduct more studies with agreed standard methodologies in natural ecosystems and agricultural systems, and in other areas of Central America few studies have been undertaken to date. The principal objective of this review was to address the main mechanisms that determine SOC and SIC sequestration in soils of Latin America, and include: physical aggregate protection, SOC-clay interaction, DOC transport, bioturbation by soil organisms, and the formation of secondary carbonates. All of these mechanisms are generally explained by physical and chemical processes. In contrast, this review takes a soil ecological approach to describe the mechanisms listed above.

Kirby, K. R., Potvin, C. (2007). Variation in carbon storage among tree species: Implications for the management of a small-scale carbon sink project. Forest Ecology and Management 246 (2-3): 208-221

ABSTRACT: Despite growing evidence for an effect of species composition on carbon (C) storage and sequestration, few projects have examined the implications of such a relationship for forestry and agriculture-based climate change mitigation activities. We worked with a community in Eastern Panama to determine the average above- and below-ground C stocks of three land-use types in their territory: managed forest, agroforests and pasture. We examined evidence for a functional relationship between tree-species diversity and C storage in each land-use type, and also explored how the use of particular tree species by community members could affect C storage. We found that managed forests in this landscape stored an average of 335 Mg C ha−1 , traditional agroforests an average of 145 Mg C ha−1 , and pastures an average of 46 Mg C ha−1 including all vegetation-based C stocks and soil C to 40 cm depth. We did not detect a relationship between diversity and C storage; however, the relative contributions of species to C storage per hectare in forests and agroforests were highly skewed and often were not proportional to species’ relative abundances. We conclude that protecting forests from conversion to pasture would have the greatest positive impact on C stocks, even though the forests are managed by community members for timber and non-timber forest products. However, because several of the tree species that contribute the most to C storage in forests were identified by community members as preferred timber species, we suggest that species-level management will be important to avoiding C-impoverishment through selective logging in these forests. Our data also indicate that expanding agroforests into areas currently under pasture could sequester significant amounts of carbon while providing biodiversity and livelihood benefits that the most common reforestation systems in the region – monoculture teak plantations – do not provide.

Lal, R. (2005). Forest soils and carbon sequestration. Forest Ecology and Management 220 (1-3): 242-258

ABSTRACT: Soils in equilibrium with a natural forest ecosystem have high carbon (C) density. The ratio of soil:vegetation C density increases with latitude. Land use change, particularly conversion to agricultural ecosystems, depletes the soil C stock. Thus, degraded agricultural soils have lower soil organic carbon (SOC) stock than their potential capacity. Consequently, afforestation of agricultural soils and management of forest plantations can enhance SOC stock through C sequestration. The rate of SOC sequestration, and the magnitude and quality of soil C stock depend on the complex interaction between climate, soils, tree species and management, and chemical composition of the litter as determined by the dominant tree species. Increasing production of forest biomass per se may not necessarily increase the SOC stocks. Fire, natural or managed, is an important perturbation that can affect soil C stock for a long period after the event. The soil C stock can be greatly enhanced by a careful site preparation, adequate soil drainage, growing species with a high NPP, applying N and micronutrients (Fe) as fertilizers or biosolids, and conserving soil and water resources. Climate change may also stimulate forest growth by enhancing availability of mineral N and through the CO2 fertilization effect, which may partly compensate release of soil C in response to warming. There are significant advances in measurement of soil C stock and fluxes, and scaling of C stock from pedon/plot scale to regional and national scales. Soil C sequestration in boreal and temperate forests may be an important strategy to ameliorate changes in atmospheric chemistry.

R. Lal (2007). Carbon management in agricultural soils. Mitigation and Adaptation Strategies for Global Change 12 (2): 303-322

ABSTRACT: World soils have been a major source of enrichment of atmospheric concentration of CO2 ever since the dawn of settled agriculture, about 10,000 years ago. Historic emission of soil C is estimated at 78 ± 12 Pg out of the total terrestrial emission of 136 ± 55 Pg, and post-industrial fossil fuel emission of 270 ± 30 Pg. Most soils in agricultural ecosystems have lost 50 to 75% of their antecedent soil C pool, with the magnitude of loss ranging from 30 to 60 Mg C/ha. The depletion of soil organic carbon (SOC) pool is exacerbated by soil drainage, plowing, removal of crop residue, biomass burning, subsistence or low-input agriculture, and soil degradation by erosion and other processes. The magnitude of soil C depletion is high in coarse-textured soils (e.g., sandy texture, excessive internal drainage, low activity clays and poor aggregation), prone to soil erosion and other degradative processes. Thus, most agricultural soils contain soil C pool below their ecological potential. Adoption of recommend management practices (e.g., no-till farming with crop residue mulch, incorporation of forages in the rotation cycle, maintaining a positive nutrient balance, use of manure and other biosolids), conversion of agriculturally marginal soils to a perennial land use, and restoration of degraded soils and wetlands can enhance the SOC pool. Cultivation of peatlands and harvesting of peatland moss must be strongly discouraged, and restoration of degraded soils and ecosystems encouraged especially in developing countries. The rate of SOC sequestration is 300 to 500 Kg C/ha/yr under intensive agricultural practices, and 0.8 to 1.0 Mg/ha/yr through restoration of wetlands. In soils with severe depletion of SOC pool, the rate of SOC sequestration with adoption of restorative measures which add a considerable amount of biomass to the soil, and irrigated farming may be 1.0 to 1.5 Mg/ha/yr. Principal mechanisms of soil C sequestration include aggregation, high humification rate of biosolids applied to soil, deep transfer into the sub-soil horizons, formation of secondary carbonates and leaching of bicarbonates into the ground water. The rate of formation of secondary carbonates may be 10 to 15 Kg/ha/yr, and the rate of leaching of bicarbonates with good quality irrigation water may be 0.25 to 1.0 Mg C/ha/yr. The global potential of soil C sequestration is 0.6 to 1.2 Pg C/yr which can off-set about 15% of the fossil fuel emissions.

Lal, R., Kimble, J. M. (1997). Conservation tillage for carbon sequestration. Nutrient Cycling in Agroecosystems 49 (1-3): 243-253.

ABSTRACT: World soils represent the largest terrestrial pool of organic carbon (C), about 1550 Pg compared with about 700 Pg in the atmosphere and 600 Pg in land biota. Agricultural activities (e.g., deforestation, burning, plowing, intensive grazing) contribute considerably to the atmospheric pool. Expansion of agriculture may have contributed substantially to the atmospheric carbon pool. However, the exact magnitude of carbon fluxes from soil to the atmosphere and from land biota to the soil are not known. An important objective of the sustainable management of soil resources is to increase soil organic carbon (SOC) pool by increasing passive or non-labile fraction. Soil surface management, soil water conservation and management, and soil fertility regulation are all important aspects of carbon sequestration in soil. Conservation tillage, a generic term implying all tillage methods that reduce runoff and soil erosion in comparison with plow-based tillage, is known to increase SOC content of the surface layer. Principal mechanisms of carbon sequestration with conservation tillage are increase in micro-aggregation and deep placement of SOC in the sub-soil horizons. Other useful agricultural practices associated with conservation tillage are those that increase biomass production (e.g., soil fertility enhancement, improved crops and species, cover crops and fallowing, improved pastures and deep-rooted crops). It is also relevant to adopt soil and crop management systems that accentuate humification and increase the passive fraction of SOC. Because of the importance of C sequestration, soil quality should be evaluated in terms of its SOC content.

R. D. Lasco, M. M. Cardinoza (2007). Baseline carbon stocks assessment and projection of future carbon benefits of a carbon sequestration project in East Timor. Mitigation and Adaptation Strategies for Global Change 12 (2): 243-257

ABSTRACT: Climate change is one of the most pressing environmental problems humanity is facing today. Forest ecosystems serve as a source or sink of greenhouse gases, primarily CO2 . With support from the Canadian Climate Change Fund, the Community-based Natural Resource Management for Carbon Sequestration project in East Timor (CBNRM-ET) was implemented to “maintain carbon (C) stocks and increase C sequestration through the development of community-based resource management systems that will simultaneously improve livelihood security”. Project sites were in the Laclubar and Remexio Sub-districts of the Laclo watershed. The objective of this study was to quantify baseline C stocks and sequestration benefits of project components (reforestation with fast-growing species, primarilyCasuarina equisetifolia , and agroforestry involving integration ofParaserianthes falcataria ). Field measurements show that mature stands (=30 years) ofP. falcataria andC. equisetifolia contain up to 200 Mg C ha-1 in above ground biomass, indicating the vast potential of project sites to sequester carbon. Baseline C stocks in above ground biomass were very low in both Laclubar (6.2 Mg C ha-1 for reforestation sites and 5.2 Mg C ha-1 for agroforestry sites and Remexio (3.0 Mg C ha-1 for reforestation and 2.5 Mg C ha-1 for agroforestry). Baseline soil organic C levels were much higher reaching up to 160 Mg C ha-1 in Laclubar and 70 Mg C ha-1 in Remexio. For the next 25 years, it is projected that 137 671 Mg C and 84 621 Mg C will be sequestered under high- and low C stock scenarios, respectively.

Lee, H.-C., McCarl, B. A., Gillig, D. (2005). The dynamic competitiveness of U.S. agricultural and forest carbon sequestration. Canadian Journal of Agricultural Economics 53 (4): 343-357

ABSTRACT: Society is increasingly turning attention toward greenhouse gas emission control with for example the Kyoto Protocol has entered into force. Since many of the emissions come from energy use, high cost strategies might be required until new technological developments reduce fossil fuel dependency or increase energy utilization efficiency. On the other hand biologically based strategies may be used to offset energy related emissions. Agricultural soil and forestry are among the largest carbon reservoirs on the planet; therefore, agricultural and forest activities may help to reduce the costs of greenhouse gas emission mitigation. However, sequestration exhibits permanence related characteristics that may influence this role. We examine the dynamic role of carbon sequestration in the agricultural and forest sectors can play in mitigation. A 100-year mathematical programming model, depicting U.S. agricultural and forest sectoral activities including land transfers and greenhouse gas consequences is applied to simulate potential mitigation response. The results show that at low cost and in the near term agricultural soil and forest management are dominant sectoral responses. At higher prices and in the longer term biofuels and afforestation take over. Our results reveal that the agricultural and forest sector carbon sequestration may serve as an important bridge to the future helping to hold costs down until energy emissions related technology develops.

Lehmann, J., Gaunt, J., Rondon, M. (2006). Bio-char sequestration in terrestrial ecosystems - A review. Mitigation and Adaptation Strategies for Global Change 11 (2): 395-419

ABSTRACT: The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is proposed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver immediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (< 10–20% after 5–10 years), therefore yielding more stable soil C than burning or direct land application of biomass. This efficiency of C conversion of biomass to bio-char is highly dependent on the type of feedstock, but is not significantly affected by the pyrolysis temperature (within 350–500 ∘C common for pyrolysis). Existing slash-and-burn systems cause significant degradation of soil and release of greenhouse gases and opportunies may exist to enhance this system by conversion to slash-and-char systems. Our global analysis revealed that up to 12% of the total anthropogenic C emissions by land use change (0.21 Pg C) can be off-set annually in soil, if slash-and-burn is replaced by slash-and-char. Agricultural and forestry wastes such as forest residues, mill residues, field crop residues, or urban wastes add a conservatively estimated 0.16 Pg C yr−1 . Biofuel production using modern biomass can produce a bio-char by-product through pyrolysis which results in 30.6 kg C sequestration for each GJ of energy produced. Using published projections of the use of renewable fuels in the year 2100, bio-char sequestration could amount to 5.5–9.5 Pg C yr−1 if this demand for energy was met through pyrolysis, which would exceed current emissions from fossil fuels (5.4 Pg C yr−1 ). Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable.

Litynski, J., Klara, S., McIlvried, H., Srivastava, R. (2006). An overview of terrestrial sequestration of carbon dioxide: the United States department of energy's fossil energy R&D program. Climatic Change 74 (1-3): 81-95

ABSTRACT: Increasing concentrations of CO2 and other greenhouse gases (GHG) in the Earth's atmosphere have the potential to enhance the natural greenhouse effect, which may result in climatic changes. The main anthropogenic contributors to this increase are fossil fuel combustion, land use conversion, and soil cultivation. It is clear that overcoming the challenge of global climate change will require a combination of approaches, including increased energy efficiency, energy conservation, alternative energy sources, and carbon (C) capture and sequestration. The United States Department of Energy (DOE) is sponsoring the development of new technologies that can provide energy and promote economic prosperity while reducing GHG emissions. One option that can contribute to achieving this goal is the capture and sequestration of CO2 in geologic formations. An alternative approach is C sequestration in terrestrial ecosystsems through natural processes. Enhancing such natural pools (known as natural sequestration) can make a significant contribution to CO2 management strategies with the potential to sequester about 290 Tg C/y in U.S. soils. In addition to soils, there is also a large potential for C sequestration in above and belowground biomass in forest ecosystems.

A major area of interest to DOE's fossil energy program is reclaimed mined lands, of which there may be 0.63 ×106 ha in the U.S. These areas are essentially devoid of soil C; therefore, they provide an excellent opportunity to sequester C in both soils and vegetation. Measurement of C in these ecosystems requires the development of new technology and protocols that are accurate and economically viable. Field demonstrations are needed to accurately determine C sequestration potential and to demonstrate the ecological and aesthetic benefits in improved soil and water quality, increased biodiversity, and restored ecosystems.

The DOE's research program in natural sequestration highlights fundamental and applied studies, such as the development of measurement, monitoring, and verification technologies and protocols and field tests aimed at developing techniques for maximizing the productivity of hitherto infertile soils and degraded ecosystems.

Luo, Y., Hui, D., Zhang, D. (2006). Elevated CO2 stimulates net accumulations of carbon and nitrogen in land ecosystems: A meta-analysis. Ecology 87 (1): 53-63

ABSTRACT: The capability of terrestrial ecosystems to sequester carbon (C) plays a critical role in regulating future climatic change yet depends on nitrogen (N) availability. To predict long-term ecosystem C storage, it is essential to examine whether soil N becomes progressively limiting as C and N are sequestered in long-lived plant biomass and soil organic matter. A critical parameter to indicate the long-term progressive N limitation (PNL) is net change in ecosystem N content in association with C accumulation in plant and soil pools under elevated CO2 . We compiled data from 104 published papers that study C and N dynamics at ambient and elevated CO2 . The compiled database contains C contents, N contents, and C:N ratio in various plant and soil pools, and root:shoot ratio. Averaged C and N pool sizes in plant and soil all significantly increase at elevated CO2 in comparison to those at ambient CO2 , ranging from a 5% increase in shoot N content to a 32% increase in root C content. The C and N contents in litter pools are consistently higher in elevated than ambient CO2 among all the surveyed studies whereas C and N contents in the other pools increase in some studies and decrease in other studies. The high variability in CO2 -induced changes in C and N pool sizes results from diverse responses of various C and N processes to elevated CO2 . Averaged C:N ratios are higher by 3% in litter and soil pools and 11% in root and shoot pools at elevated relative to ambient CO2 . Elevated CO2 slightly increases root:shoot ratio. The net N accumulation in plant and soil pools at least helps prevent complete down-regulation of, and likely supports, long-term CO2 stimulation of C sequestration. The concomitant C and N accumulations in response to rising atmospheric CO2 may reflect intrinsic nature of ecosystem development as revealed before by studies of succession over hundreds to millions of years.

Luo, Y., Su, B., Currie, W.S., Dukes, J,S., Finzi, A., Hartwig, U., Hungate, B. A., McMurtrie, R.E., Oren, R., Parton, W.J., Pataki, D.E., Shaw, M.R., Zak, D. R., Field, C. B. (2004). Progressive nitrogen limitation of ecosystem responses to rising atmospheric carbon dioxide. BioScience 54 (8): 731-739

ABSTRACT: A highly controversial issue in global biogeochemistry is the regulation of terrestrial carbon (C) sequestration by soil nitrogen (N) availability. This controversy translates into great uncertainty in predicting future global terrestrial C sequestration. We propose a new framework that centers on the concept of progressive N limitation (PNL) for studying the interactions between C and N in terrestrial ecosystems. In PNL, available soil N becomes increasingly limiting as C and N are sequestered in long-lived plant biomass and soil organic matter. Our analysis focuses on the role of PNL in regulating ecosystem responses to rising atmospheric carbon dioxide concentration, but the concept applies to any perturbation that initially causes C and N to accumulate in organic forms. This article examines conditions under which PNL may or may not constrain net primary production and C sequestration in terrestrial ecosystems. While the PNL-centered framework has the potential to explain diverse experimental results and to help researchers integrate models and data, direct tests of the PNL hypothesis remain a great challenge to the research community.

Macedo, M.O., Resende, A.S., Garcia, P.C., Boddey, R.M., Jantalia, C.P., Urquiaga, S., Campello, E.F.C., Franco, A.A. (2008). Changes in soil C and N stocks and nutrient dynamics 13 years after recovery of degraded land using leguminous nitrogen-fixing trees. Forest Ecology and Management 255 (5-6): 1516-1524

ABSTRACT: In tropical forest areas with highly weathered soils, organic matter plays an important role in soil functioning and forest sustainability. When forests are clear-cut, the soil begins almost immediately to lose organic matter, triggering a series of soil degradation processes, the extent and intensity of which depends on soil management. Depending on the level of soil degradation, the rate at which the system can re-establish itself can be slow and may require the use of degraded land restoration techniques. This study aimed at evaluating the potential of pioneer leguminous nitrogen-fixing trees to recuperate degraded land. The area studied – located in the coastal town of Angra dos Reis in the State of Rio de Janeiro, Brazil – was planted with seven species of fast-growing leguminous nitrogen-fixing trees in 1991. The nutrient concentrations (Ca, Mg, P and K) and N and C stocks in the soil and litter were determined, in addition to the free- and occluded-light fractions of soil organic matter. Soil samples were also collected from two reference areas: (1) an area of undisturbed native forest; and (2) a deforested area spontaneously colonised by Guinea grass (Panicum maximum ). The nutrient stocks in the litter of the restored area were similar to those found in native forest. The recuperation technique used was able to re-establish the soil C and N stocks after 13 years. C and N increased by 1.73 and 0.13 Mg ha−1 year−1 , respectively. The free-light fraction was highest in the recuperated area and lowest in the deforested area. The occluded-light fraction of the recuperated area was higher than that of the native forest only in the 0–5 cm layer. Both the free-light and occluded fractions were higher in the native forest and recuperated areas than in the deforested area. Since the free-light and the occluded-light fractions are the result of litterfall and decomposition, these results – combined with the data of litter stocks and soil C and N stocks – indicate that the use of legume trees was efficient in re-establishing the nutrient cycling processes of the systems. These results also show that recovering degraded land with this technique is effective in sequestering carbon dioxide from the atmosphere at high rates.

McGuire, A.D., Melillo, J.M., Kicklighter, D.W., Pan, Y., Xiao, X., Helfrich, J., Moore, B., III, Vorosmarty, C.J., Schloss, A.L. (1997). Equilibrium responses of global net primary production and carbon storage to doubled atmospheric carbon dioxide: Sensitivity to changes in vegetation nitrogen concentration. Global Biogeochemical Cycles 11 (2): 173-189

ABSTRACT: We ran the terrestrial ecosystem model (TEM) for the globe at 0.5° resolution for atmospheric CO2 concentrations of 340 and 680 parts per million by volume (ppmv) to evaluate global and regional responses of net primary production (NPP) and carbon storage to elevated CO2 for their sensitivity to changes in vegetation nitrogen concentration. At 340 ppmv, TEM estimated global NPP of 49.0 1015 g (Pg) C yr−1 and global total carbon storage of 1701.8 Pg C; the estimate of total carbon storage does not include the carbon content of inert soil organic matter. For the reference simulation in which doubled atmosphericCO2 was accompanied with no change in vegetation nitrogen concentration, global NPP increased 4.1 Pg C yr−1 (8.3%), and global total carbon storage increased 114.2 Pg C. To examine sensitivity in the global responses of NPP and carbon storage to decreases in the nitrogen concentration of vegetation, we compared doubled CO2 responses of the reference TEM to simulations in which the vegetation nitrogen concentration was reduced without influencing decomposition dynamics ("lower N" simulations) and to simulations in which reductions in vegetation nitrogen concentration influence decomposition dynamics ("lower N+D" simulations). We conducted three lower N simulations and three lower N+D simulations in which we reduced the nitrogen concentration of vegetation by 7.5, 15.0, and 22.5%. In the lower N simulations, the response of global NPP to doubled atmospheric CO2 increased approximately 2 Pg C yr−1 for each incremental 7.5% reduction in vegetation nitrogen concentration, and vegetation carbon increased approximately an additional 40 Pg C, and soil carbon increased an additional 30 Pg C, for a total carbon storage increase of approximately 70 Pg C. In the lower N+D simulations, the responses of NPP and vegetation carbon storage were relatively insensitive to differences in the reduction of nitrogen concentration, but soil carbon storage showed a large change. The insensitivity of NPP in the N+D simulations occurred because potential enhancements in NPP associated with reduced vegetation nitrogen concentration were approximately offset by lower nitrogen availability associated with the decomposition dynamics of reduced litter nitrogen concentration. For each 7.5% reduction in vegetation nitrogen concentration, soil carbon increased approximately an additional 60 Pg C, while vegetation carbon storage increased by only approximately 5 Pg C. As the reduction in vegetation nitrogen concentration gets greater in the lower N+D simulations, more of the additional carbon storage tends to become concentrated in the north temperate-boreal region in comparison to the tropics. Other studies with TEM show that elevated CO2 more than offsets the effects of climate change to cause increased carbon storage. The results of this study indicate that carbon storage would be enhanced by the influence of changes in plant nitrogen concentration on carbon assimilation and decomposition rates. Thus changes in vegetation nitrogen concentration may have important implications for the ability of the terrestrial biosphere to mitigate increases in the atmospheric concentration of CO2 and climate changes associated with the increases.

Mitra, S., Wassmann, R., Vlek, P. L. G. (2005). An appraisal of global wetland area and its organic carbon stock. Current Science 88 (1): 25-35

ABSTRACT: Wetlands are among the most important natural resources on earth. They are the sources of cultural, economic and biological diversity. With their wealth of stored carbon, wetlands provide a potential sink for atmospheric carbon, but if not managed properly could become sources of greenhouse gases (GHGs) such as carbon dioxide and methane. Two important long-term uncertainties have initiated much debate in the scientific community. These are global wetland area and the amount of carbon stored in it. Compilation of relevant databases could be useful in setting up a long-term strategy for wetland conservation. It has been difficult to estimate the net carbon sequestration potential of a wetland, because the rate of decomposition of organic matter and the abundance of methanogenic micro-organisms and fluxes from the sediment are extremely complex, and there are often gaps in relevant scientific knowledge. The present discussion on density distribution of soil organic C in global wetlands could well be instrumental in formulating efficient strategies related to carbon sequestration and reduction of GHG emissions in wetland ecosystems. Effective assessment of wetlands will only take place when the available information becomes accessible and usable for all stakeholders.

Mu, Q., M. Zhao, S. W. Running, M. Liu, H. Tian (2008). Contribution of increasing CO2 and climate change to the carbon cycle in China's ecosystems. Journal of Geophysical Research - Biogeosciences 113 (G01018)

ABSTRACT: Atmospheric CO2 and China's climate have changed greatly during 1961–2000. The influence of increased CO2 and changing climate on the carbon cycle of the terrestrial ecosystems in China is still unclear. In this article we used a process-based ecosystem model, Biome-BGC, to assess the effects of changing climate and elevated atmospheric CO2 on terrestrial China's carbon cycle during two time periods: (1) the present (1961–2000) and (2) a future with projected climate change under doubled CO2 (2071–2110). The effects of climate change alone were estimated by driving Biome-BGC with a fixed CO2 concentration and changing climate, while the CO2 fertilization effects were calculated as the difference between the results driven by both increasing CO2 and changing climate and those of variable climate alone. Model simulations indicate that during 1961–2000 at the national scale, changes in climate reduced carbon storage in China's ecosystems, but increasing CO2 compensated for these adverse effects of climate change, resulting in an overall increase in the carbon storage of China's ecosystems despite decreases in soil carbon. The interannual variability of the carbon cycle was associated with climate variations. Regional differences in climate change produced differing regional carbon uptake responses. Spatially, reductions in carbon in vegetation and soils and increases in litter carbon were primarily caused by climate change in most parts of east China, while carbon in vegetation, soils, and litter increased for much of west China. Under the future scenario (2071–2110), with a doubling CO2 , China will experience higher precipitation and temperature as predicted by the Hadley Centre HadCM3 for the Intergovernmental Panel on Climate Change Fourth Assessment. The concomitant doubling of CO2 will continue to counteract the negative effects of climate change on carbon uptake in the future, leading to an increase in carbon storage relative to current levels. This study highlights the role of CO2 fertilization in the carbon budget of China's ecosystems, although future studies should include other important processes such as land use change, human management (e.g., fertilization and irrigation), environmental pollution, etc.

Niu, X., Duiker, S. W. (2006). Carbon sequestration potential by afforestation of marginal agricultural land in the Midwestern U.S.. Forest Ecology and Management 223 (1-3): 415-427

ABSTRACT: Carbon sequestration has been well recognized as a viable option to slow the rise in atmospheric greenhouse gas concentration. The main goals of this study were to assess the carbon sequestration potential (CSP) by afforestation of marginal agricultural land (MagLand) and to identify hotspots for potential afforestation activities in the U.S. Midwest region (Michigan (MI), Indiana (IN), Ohio, Kentucky (KY), West Virginia, Pennsylvania (PA) and Maryland (MD)). The 1992 USGS National Land Cover Dataset and the State Soil Geographic (STATSGO) database were used to determine MagLand. Two forest types (coniferous and deciduous) and two management practices (short-rotation versus permanent forest) were combined to form four afforestation scenarios. Simulation models were employed to predict changes in four carbon pools: aboveground biomass, roots, forest floor, and soil organic carbon (SOC). A scenario-generating tool was developed to detect the hotspots. We estimated that there was a total of 6.5 million hectares (Mha) MagLand available in the U.S. Midwest region, which accounts for approximately 24% of the regional total agricultural land. The CSP capacity was predicted to be 508–540 Tg C (1 Tg = 1012 g) over 20 years and 1018–1080 Tg C over 50 years. The results indicate that afforestation of MagLand could offset 6–8% of current CO2 emissions by combustion of fossil fuel in the region. This analysis showed only slight differences in carbon sequestration between forest types or between short-rotation and permanent forest scenarios. Note that this calculation assumed that all suitable MagLand in the U.S. Midwest region was converted to forest and that “best carbon management” was adopted. The actual CSP could be less if the economical and social factors are taken into account. The most preferred locations for implementing the afforestation strategy were found to be concentrated along a west-east axis across the southern parts of Indiana, Ohio, and Pennsylvania, as well as in an area covering southern Michigan and northern parts of Indiana and Ohio. Overall, we conclude that afforestation of MagLand in the Midwest U.S. region offers great potential for carbon sequestration. Future studies are needed to evaluate its economic feasibility, social acceptability, and operation capability.

Nosetto, M.D., Jobbagy, E.G., Paruelo, J.M. (2006). Carbon sequestration in semi-arid rangelands: Comparison ofPinus ponderosa plantations and grazing exclusion in NW Patagonia. Journal of Arid Environments 67 (1): 142-156

ABSTRACT: The large global extension of arid and semi-arid regions together with their widespread degradation give these areas a high potential to sequester carbon. We explored the possibilities of semi-arid ecosystems to sequester carbon by means of rangeland exclusion and afforestation withPinus ponderosa in NW Patagonia (Argentina). We sampled all pools where organic carbon accumulates in a network of five trios of adjacent grazed, non-grazed and afforested stands (age: 12–25 years, density 605–1052 trees ha−1 ). After 15 years since trees were planted, afforestation added 50% more C to the initial ecosystem carbon pool, with annual sequestration rate ranging 0.5–3.3 Mg C ha−1 year−1 . Carbon gains in afforested stands were higher above than below-ground (150% vs. 32%). Root biomass differences (374% more in afforested vs. grazed stands,p =0.0011) explained below-ground carbon contrasts whereas soil organic carbon showed no differences with afforestation. By contrast, grazing exclosures did not result in significant changes in the total carbon storage in comparison with the adjacent grazed stands (p=0.42) suggesting a slow ecosystem recovery in the time frame of this study (15 years of exclusion). Nevertheless, higher litter amount was found in the former (+53%, p=0.07). Neither, soil organic carbon nor root carbon showed significant differences between grazed and non-grazed conditions. Considering that more than 1.1 millions of hectares of the studied ecosystems are highly degraded and suitable for tree planting, afforesting this area could result in a carbon sequestration rate of 1.7 Tg C year−1 , almost 6% of the current fossil fuel emissions of Argentina; however environmental consequences which could emerge from this deep land use shift must be taken into account when afforestation program are being designed.

Petersen, G., Viviani, D., Magrini-Bair, K., Kelley, S., Moens, L., Shepherd, P., DuBois, D. (2005). Nongovernmental valorization of carbon dioxide. Science of The Total Environment 338 (3): 159-182

ABSTRACT: Carbon dioxide (CO2 ) is considered the largest contributor to the greenhouse gas effect. Most attempts to manage the flow of CO2 or carbon into our environment involve reducing net emissions or sequestering the gas into long-lived sinks. Using CO2 as a chemical feedstock has a long history, but using it on scales that might impact the net emissions of CO2 into the atmosphere has not generally been considered seriously. There is also a growing interest in employing our natural biomes of carbon such as trees, vegetation, and soils as storage media. Some amelioration of the net carbon emissions into the atmosphere could be achieved by concomitant large withdrawals of carbon. This report surveys the potential and limitations in employing carbon as a resource for organic chemicals, fuels, inorganic materials, and in using the biome to manage carbon. The outlook for each of these opportunities is also described.

Post, W. M., R. C. Izaurralde, J.D. Jastrow, B. A. McCarl, J. E. Amonette, V. L. Bailey, P. M. Jardine, T. O. West, J. Zhou (2004). Enhancement of carbon sequestration in US Soils. BioScience 54 (10): 895-908

ABSTRACT: Improved practices in agriculture, forestry, and land management could be used to increase soil carbon and thereby significantly reduce the concentration of atmospheric carbon dioxide. Understanding biological and edaphic processes that increase and retain soil carbon can lead to specific manipulations that enhance soil carbon sequestration. These manipulations, however, will only be suitable for adoption if they are technically feasible over large areas, economically competitive with alternative measures to offset greenhouse gas emissions, and environmentally beneficial. Here we present the elements of an integrated evaluation of soil carbon sequestration methods.

Rastetter, E. B., Perakis, S. S., Shaver, G. R., Agren, G. I. (2005). Terrestrial C sequestration at elevated-CO2 and temperature: the role of dissolved organic N loss. 15 (1): 71-86

ABSTRACT: We used a simple model of carbon–nitrogen (C–N) interactions in terrestrial ecosystems to examine the responses to elevated CO2 and to elevated CO2 plus warming in ecosystems that had the same total nitrogen loss but that differed in the ratio of dissolved organic nitrogen (DON) to dissolved inorganic nitrogen (DIN) loss. We postulate that DIN losses can be curtailed by higher N demand in response to elevated CO2 , but that DON losses cannot. We also examined simulations in which DON losses were held constant, were proportional to the amount of soil organic matter, were proportional to the soil C:N ratio, or were proportional to the rate of decomposition. We found that the mode of N loss made little difference to the short-term (<60 years) rate of carbon sequestration by the ecosystem, but high DON losses resulted in much lower carbon sequestration in the long term than did low DON losses. In the short term, C sequestration was fueled by an internal redistribution of N from soils to vegetation and by increases in the C:N ratio of soils and vegetation. This sequestration was about three times larger with elevated CO2 and warming than with elevated CO2 alone. After year 60, C sequestration was fueled by a net accumulation of N in the ecosystem, and the rate of sequestration was about the same with elevated CO2 and warming as with elevated CO2 alone. With high DON losses, the ecosystem either sequestered C slowly after year 60 (when DON losses were constant or proportional to soil organic matter) or lost C (when DON losses were proportional to the soil C:N ratio or to decomposition). We conclude that changes in long-term C sequestration depend not only on the magnitude of N losses, but also on the form of those losses.

Saurette, D. D., Chang, S. X., Thomas, B. R. (2006). Some characteristics of soil respiration in hybrid poplar plantations in northern Alberta. Canadian Journal of Soil Science 86 (2): 257-268

ABSTRACT: Fast-growing hybrid poplars are being planted in the Canadian prairies to meet the increasing demand for fibre and environmental services of trees and forests; however, the impact of hybrid poplars on C dynamics and storage on previously farmed land is largely unknown for the boreal region. We measured soil CO2 efflux along a chronosequence (3-, 9-, and 11-yr-old stands) of hybrid poplar (Populus deltoides ×Populus ×petrowskyana var. Walker) plantations and a control agricultural field from June to August 2004. Measurements were made between 0800 and 1800 with a portable Li-Cor 6400-09 system and were based on 4–5 min averaging. We also measured the response to simulated rainfall and the diurnal fluctuation of soil CO2 efflux. Soil CO2 efflux ranged from 1.30 µmol CO2 m-2 s-1 in the 3-yr old plantation to 5.41 µmol CO2 m-2 s-1 in the agricultural control field, or from 0.17 ìmol CO2 m-2 s-1 kg-1 C (based on soil organic C content to a 0.4 m depth) in the 3-yr-old plantation to 1.09 µmol CO2 m-2 s-1 kg-1 C in the 11-yr-old plantation. Simulated rainfall applied in the 3-yr-old plantation and a newly planted site resulted in an immediate pulse of CO2 efflux, 2.90 and 2.54 µmol CO2 m-2 s-1 , respectively, followed by an efflux rate sustained slightly above pre-irrigation levels. No secondary pulse of soil respiration was observed in the 2-h period following water application. Diurnal variation of soil respiration was found to be small between 0600 and 1900 in the agricultural control field, with values that varied from 2.66 to 3.17 µmol CO2 m-2 s-1 . Continued monitoring of soil respiration and other C cycling processes in the chronosequence will improve our understanding of the potential for C sequestration in hybrid poplar plantations in northern Alberta. Key words: Carbon sequestration, greenhouse gas emissions, biomass, boreal forest, land-use change, hybrid poplar

Schmid, S., Thurig, E., Kaufmann, E., Lischke, H., Bugmann, H. (2006). Effect of forest management on future carbon pools and fluxes: A model comparison. Forest Ecology and Management 237 (1-3): 65-82

ABSTRACT: Currently, there is a strong demand for estimates of the current and potential future carbon sequestration in forests, the role of management practices, and the temporal duration of biotic carbon sinks. Different models, however, lead to different projections. Model comparisons allow us to assess the range of potential ecosystem responses, and they facilitate the detection of the strengths and weaknesses of particular models. In this study, the empirical, individual-based forest models MASSIMO, the semi-empirical individual-based forest models SILVA – both combined with the soil model YASSO – and the process-based, biogeochemical model Biome-BGC were used to assess the above- and belowground carbon pools and net fluxes of several forested regions in Switzerland for the next 100 years under four different management scenarios: (1) the current harvest amounts were used, (2) harvest was intensified by reducing the amount of large tree dimensions, (3) harvest was reduced to a minimum by only maintaining the protection function in mountain forests and avoiding pests and diseases, and (4) harvest was adjusted to achieve maximum sustainable growth. The results show that the three models projected similar patterns of net carbon fluxes. The models estimated that in the absence of large-scale disturbances the forest biomass and soil carbon can be increased, particularly under scenario 2, and therefore, forests can be used as carbon sinks. These sinks were estimated to last for a maximum of 100 years. Differences between the management scenarios depend on the time period considered: either net carbon fluxes are maximized at a short term (30–40 years) or at a longer term (100 years or more). In contrast to the similar carbon fluxes, some carbon pools projected by the models differed strongly. These differences in model behaviour can be attributed to model-specific responses to the strongly heterogeneous Swiss climate conditions and to different model assumptions. To find the optimum strategy in terms of not only maximizing carbon sequestration but climate protection, it is essential to account for wood-products and particularly substitution of fossil fuel in the model simulations.

Schulze, E., Wirth, C., Heimann, M. (2000). Managing forests after Kyoto. Science 289 (5487): 2058-2059

ABSTRACT: The Kyoto protocol aims to reduce carbon emissions into the atmosphere. Part of the strategy is the active management of terrestrial carbon sinks, principally through afforestation and reforestation. In their Perspective, Schulze et al. argue that the preservation of old-growth forests may have a larger positive effect on the carbon cycle than promotion of regrowth.

Singh, B. R., Lal, R. (2005). The potential of soil carbon sequestration through improved management practices in Norway. Environment, Development and Sustainability 7 (1): 161-184

ABSTRACT: The study was conducted to assess the potential of Norwegian agricultural ecosystems to sequester carbon (C) based on the data from some long-term agronomic and land use experiments. The total emission of CO2 in Norway in 1998 was 41.4 million metric ton (MMT), of which agriculture contributed only 0.157 MMT, or <0.4% of the total emissions. With regards to methane (CH4) and nitrous oxide (N2 O) gases, however, agricultural activities contributed 32.5% and 51.3% of their respective emissions in Norway. The soil organic carbon (SOC) losses associated with accelerated soil erosion in Norway are estimated at 0.475 MMTC yr–1 . Land use changes and soil/crop management practices with potential for SOC sequestration include conservation tillage methods, judicious use of fertilizers and manures, use of crop residues, diverse crop rotations, and erosion control measures. The potential for SOC sequestration is 0.146 MMTC yr–1 for adopting conservation tillage, 0.011–0.035 MMTC yr–1 for crop residue management, 0.026 MMTC yr–1 for judicious use of mineral fertilizer, 0.016–0.135 MMTC yr–1 for manure application, and 0.036 MMTC yr–1 for adopting crop rotations. The overall potential of these practices for SOC sequestration ranges from 0.591 to 1.022 MMTC yr–1 with an average value of 0.806 MMTC yr–1 . Of the total potential, 59% is due to adoption of erosion control measures, 5.8% to restoration of peat lands, 21% to conversion to conservation tillage and residue management, and 14% to adoption of improved cropping systems. Enhancing SOC sequestration and improving soil quality, through adoption of judicious land use and improved system of soil and crop management, are prudent strategies for sustainable management of soil, water and environment resources.

Smith, P. .. (2004). Soils as carbon sinks: the global context. Soil Use and Management 20 (2): 212-218

ABSTRACT: Soil carbon sequestration could meet at most about one-third of the current yearly increase in atmospheric CO2 -carbon, but the duration of the effect would be limited, with significant impacts lasting only 20–50 years. Coupled with this limited duration, increases in population and per-capita energy demand mean that soil carbon sequestration could play only a minor role in closing the difference between predicted and target carbon emissions by 2100. However, if atmospheric CO2 concentrations are to be stabilized at reasonable levels (450–650 ppm), drastic reductions in carbon emissions will be required over the next 20–30 years. Given this, carbon sequestration should form a central role in any portfolio of measures to reduce atmospheric CO2 concentrations over this crucial period, while new energy technologies are developed and implemented. International agreements, such as the Kyoto Protocol, encourage soil carbon sequestration and could be used to formulate soil carbon sequestration polices. Such policies need to take account of other environmental impacts as well as political, economic and societal needs, so that they form part of a raft of measures encouraging sustainable development. Of the carbon sequestration options available, those of a 'win–win' nature, that is, those that increase carbon stocks at the same time as improving other aspects of the environment, and those that protect or enhance existing stocks ('no regrets' implementation) show the greatest promise in meeting these goals.

Sperow, M. (2007). The marginal costs of carbon sequestration: Implications of one greenhouse gas mitigation activity. Journal of Soil & Water Conservation 62 (6): 367-375

ABSTRACT: This paper provides a method for estimating the marginal cost of soil carbon (C) derived from setting aside highly erodible cropland in the United States. Increases in soil carbon are estimated using a modified Intergovernmental Panel on Climate Change soil organic carbon inventory method and National Resources Inventory data. Marginal costs of soil carbon sequestration activities are based on the opportunity cost of removing highly erodible land from crop production using land rental rates adjusted to account for the productivity of cropland and Conservation Reserve Program rental rates. Total soil carbon sequestration from setting aside highly erodible land is over 10 Tg C yr−1 (11.0 Mtn C yr−1 ) on the 21.9 Mha (54.1 Mac) where corn, cotton, sorghum, soybean, wheat, or fallow were grown in 1997. The marginal cost of stored carbon based on these estimates range from $11 to $4,492 Mg−1 C ($10 to $4,075 tn−1 C) with a US weighted average of $288 Mg−1 C ($261tn−1 C). Changes in US crop production levels from removing land from crop production are also estimated.

Trettin, C.C., Jurgensen, M.F., Kimble, J.M., Heath, L.S., Birdsey, R.A., Lal, R. (2003). Carbon cycling in wetland forest soils. CRC Press: 311-331

ABSTRACT; Wetlands comprise a small proportion (i.e., 2 to 3%) of earth's terrestrial surface, yet they contain a significant proportion of the terrestrial carbon (C) pool. Soils comprise the largest terrestrial C pool (ca. 1550 Pg C in upper 100 cm; Eswaran et al., 1993; Batjes, 1996), and wetlands contain the single largest component, with estimates ranging between 18 and 30% of the total soil C. In addition to being an important C pool, wetlands contribute approximately 22% of the annual global methane emissions (Bartlett and Harris, 1993; Matthews and Fung, 1987). Despite the importance of wetlands in the global C budget, they are typically omitted from large-scale assessments because of scale, inadequate models, and limited information on C turnover and temporal dynamics.

van Groenigen, K. J., Six, J., Hungate, B. A., De Graaff, M. A., Van Breemen, N., Van Kessel, C. (2006). Element interactions limit soil carbon storage. Proceedings Of The National Academy Of Sciences Of The United States Of America 103 (17): 6571-6574

ABSTRACT: Rising levels of atmospheric CO2 are thought to increase C sinks in terrestrial ecosystems. The potential of these sinks to mitigate CO2 emissions, however, may be constrained by nutrients. By using metaanalysis, we found that elevated CO2 only causes accumulation of soil C when N is added at rates well above typical atmospheric N inputs. Similarly, elevated CO2 only enhances N2 fixation, the major natural process providing soil N input, when other nutrients (e.g., phosphorus, molybdenum, and potassium) are added. Hence, soil C sequestration under elevated CO2 is constrained both directly by N availability and indirectly by nutrients needed to support N2 fixation.

Van Kessel, C., Horwath, W. R., Hartwig, U., Harris, D., Luscher, A. (2000). Net soil carbon input under ambient and elevated CO2 concentrations: isotopic evidence after 4 years. Global Change Biology 6 (4): 435-444

SUMMARY: Elevation of atmospheric CO2 concentration is predicted to increase net primary production, which could lead to additional C sequestration in terrestrial ecosystems. Soil C input was determined under ambient and Free Atmospheric Carbon dioxide Enrichment (FACE) conditions forLolium perenne L. andTrifolium repens L. grown for four years in a sandy-loam soil. The13 C content of the soil organic matter C had been increased by 5‰ compared to the native soil by prior cropping to corn (Zea mays) for > 20 years. Both species received low or high amounts of N fertilizer in separate plots. The total accumulated above-ground biomass produced by L. perenne during the 4-year period was strongly dependent on the amount of N fertilizer applied but did not respond to increased CO2 . In contrast, the total accumulated above-ground biomass of T. repens doubled under elevated CO2 but remained independent of N fertilizer rate. The C:N ratio of above-ground biomass for both species increased under elevated CO2 whereas only the C:N ratio ofL. perenne roots increased under elevated CO2 . Root biomass ofL. perenne doubled under elevated CO2 and again under high N fertilization. Total soil C was unaffected by CO2 treatment but dependent on species. After 4 years and for both crops, the fraction of new C (F-value) under ambient conditions was higher (P= 0.076) than under FACE conditions: 0.43 vs. 0.38. Soil underL. perenne showed an increase in total soil organic matter whereas N fertilization or elevated CO2 had no effect on total soil organic matter content for both systems. The net amount of C sequestered in 4 years was unaffected by the CO2 concentration (overall average of 8.5 g C kg−1 soil). There was a significant species effect and more new C was sequestered under highly fertilizedL. perenne . The amount of new C sequestered in the soil was primarily dependent on plant species and the response of root biomass to CO2 and N fertilization. Therefore, in this FACE study net soil C sequestration was largely depended on how the species responded to N rather than to elevated CO2 .

Vetter, M., Wirth, C., Bottcher, H., Churkina, G., Schulze, E. D., Wutzler, T., Weber, G. (2005). Partitioning direct and indirect human-induced effects on carbon sequestration of managed coniferous forests using model simulations and forest inventories. Global Change Biology 11 (5): 810-827

ABSTRACT: Temperate forest ecosystems have recently been identified as an important net sink in the global carbon budget. The factors responsible for the strength of the sinks and their permanence, however, are less evident. In this paper, we quantify the present carbon sequestration in Thuringian managed coniferous forests. We quantify the effects of indirect human-induced environmental changes (increasing temperature, increasing atmospheric CO2 concentration and nitrogen fertilization), during the last century using BIOME-BGC, as well as the legacy effect of the current age-class distribution (forest inventories and BIOME-BGC). We focused on coniferous forests because these forests represent a large area of central European forests and detailed forest inventories were available.

The model indicates that environmental changes induced an increase in biomass C accumulation for all age classes during the last 20 years (1982–2001). Young and old stands had the highest changes in the biomass C accumulation during this period. During the last century mature stands (older than 80 years) turned from being almost carbon neutral to carbon sinks. In high elevations nitrogen deposition explained most of the increase of net ecosystem production (NEP) of forests. CO2 fertilization was the main factor increasing NEP of forests in the middle and low elevations.

According to the model, at present, total biomass C accumulation in coniferous forests of Thuringia was estimated at 1.51 t C ha−1 yr−1 with an averaged annual NEP of 1.42 t C ha−1 yr−1 and total net biome production of 1.03 t C ha−1 yr−1 (accounting for harvest). The annual averaged biomass carbon balance (BCB: biomass accumulation rate-harvest) was 1.12 t C ha−1 yr−1 (not including soil respiration), and was close to BCB from forest inventories (1.15 t C ha−1 yr−1 ). Indirect human impact resulted in 33% increase in modeled biomass carbon accumulation in coniferous forests in Thuringia during the last century. From the forest inventory data we estimated the legacy effect of the age-class distribution to account for 17% of the inventory-based sink. Isolating the environmental change effects showed that these effects can be large in a long-term, managed conifer forest.

G. Marland, Garten, C.T., Jr., W. M. Post, T. O. West (2004). Studies on enhancing carbon sequestration in soils. Energy 29 (9-10): 1643-1650

ABSTRACT: Studies of carbon and nitrogen dynamics in ecosystems are leading to an understanding of the factors and mechanisms that affect the inputs to and outputs from soils and how these might be manipulated to enhance C sequestration. Both the quantity and the quality of soil C inputs influence C storage and the potential for C sequestration. Changes in tillage intensity and crop rotations can also affect C sequestration by changing the soil physical and biological conditions and by changing the amounts and types of organic inputs to the soil. Analyses of changes in soil C and N balances are being supplemented with studies of the management practices needed to manage soil carbon and the implications for fossil-fuel use, emission of other greenhouse gases (such as N2 O and CH4 ), and impacts on agricultural productivity. The Consortium for Research on Enhancing Carbon Sequestration in Terrestrial Ecosystems (CSiTE) was created in 1999 to perform fundamental research that will lead to methods to enhance C sequestration as one component of a C management strategy. Research to date at one member of this consortium, Oak Ridge National Laboratory, has focused on C sequestration in soils and we begin here to draw together some of the results.

E. A. H. Smithwick, M. E. Harmon, S. M. Remillard, S. A. Acker, J. F. Franklin (2002). Potential upper bounds of carbon stores in forests of the Pacific Northwest. Ecological Applications 12 (5): 1303-1317

ABSTRACT: Placing an upper bound to carbon (C) storage in forest ecosystems helps to constrain predictions on the amount of C that forest management strategies could sequester and the degree to which natural and anthropogenic disturbances change C storage. The potential, upper bound to C storage is difficult to approximate in the field because it requires studying old-growth forests, of which few remain. In this paper, we put an upper bound (or limit) on C storage in the Pacific Northwest (PNW) of the United States using field data from old-growth forests, which are near steady-state conditions. Specifically, the goals of this study were: (1) to approximate the upper bounds of C storage in the PNW by estimating total ecosystem carbon (TEC) stores of 43 old-growth forest stands in five distinct biogeoclimatic provinces and (2) to compare these TEC storage estimates with those from other biomes, globally. Finally, we suggest that the upper bounds of C storage in forests of the PNW are higher than current estimates of C stores, presumably due to a combination of natural and anthropogenic disturbances, which indicates a potentially substantial and economically significant role of C sequestration in the region. Results showed that coastal Oregon stands stored, on average, 1127 Mg C/ha, which was the highest for the study area, while stands in eastern Oregon stored the least, 195 Mg C/ha. In general, coastal Oregon stands stored 307 Mg C/ha more than coastal Washington stands. Similarly, the Oregon Cascades stands stored 75 Mg C/ha more, on average, than the Washington Cascades stands. A simple, area-weighted average TEC storage to 1 m soil depth (TEC100 ) for the PNW was 671 Mg C/ha. When soil was included only to 50 cm (TEC50 ), the area-weighted average was 640 Mg C/ha. Subtracting estimates of current forest C storage from the potential, upper bound of C storage in this study, a maximum of 338 Mg C/ha (TEC100 ) could be stored in PNW forests in addition to current stores.

B. A. Hungate, K. van Groenigen, J. Six, J.D. Jastrow, Y. Luo, M. de Graaff, C. van Kessel, C.W. Osenberg (2009). Assessing the effect of elevated carbon dioxide on soil carbon: a comparison of four meta-analyses. Global Change Biology 15 (8): 2020-2034

ABSTRACT: Soil is the largest reservoir of organic carbon (C) in the terrestrial biosphere and soil C has a relatively long mean residence time. Rising atmospheric carbon dioxide (CO2) concentrations generally increase plant growth and C input to soil, suggesting that soil might help mitigate atmospheric CO2 rise and global warming. But to what extent mitigation will occur is unclear. The large size of the soil C pool not only makes it a potential buffer against rising atmospheric CO2 , but also makes it difficult to measure changes amid the existing background. Meta-analysis is one tool that can overcome the limited power of single studies. Four recent meta-analyses addressed this issue but reached somewhat different conclusions about the effect of elevated CO2 on soil C accumulation, especially regarding the role of nitrogen (N) inputs. Here, we assess the extent of differences between these conclusions and propose a new analysis of the data. The four meta-analyses included different studies, derived different effect size estimates from common studies, used different weighting functions and metrics of effect size, and used different approaches to address nonindependence of effect sizes. Although all factors influenced the mean effect size estimates and subsequent inferences, the approach to independence had the largest influence. We recommend that meta-analysts critically assess and report choices about effect size metrics and weighting functions, and criteria for study selection and independence. Such decisions need to be justified carefully because they affect the basis for inference. Our new analysis, with a combined data set, confirms that the effect of elevated CO2 on net soil C accumulation increases with the addition of N fertilizers. Although the effect at low N inputs was not significant, statistical power to detect biogeochemically important effect sizes at low N is limited, even with meta-analysis, suggesting the continued need for long-term experiments.

R. Lal (2004). Soil carbon sequestration to mitigate climate change. Geoderma 123 (1-2): 1-22

ABSTRACT: The increase in atmospheric concentration of CO2 by 31% since 1750 from fossil fuel combustion and land use change necessitates identification of strategies for mitigating the threat of the attendant global warming. Since the industrial revolution, global emissions of carbon (C) are estimated at 270±30 Pg (Pg=petagram=1015 G=1 billion ton) due to fossil fuel combustion and 136±55 Pg due to land use change and soil cultivation. Emissions due to land use change include those by deforestation, biomass burning, conversion of natural to agricultural ecosystems, drainage of wetlands and soil cultivation. Depletion of soil organic C (SOC) pool have contributed 78±12 Pg of C to the atmosphere. Some cultivated soils have lost one-half to two-thirds of the original SOC pool with a cumulative loss of 30–40 Mg C/ha (Mg=megagram=106 G=1 ton). The depletion of soil C is accentuated by soil degradation and exacerbated by land misuse and soil mismanagement. Thus, adoption of a restorative land use and recommended management practices (RMPs) on agricultural soils can reduce the rate of enrichment of atmospheric CO2 while having positive impacts on food security, agro-industries, water quality and the environment. A considerable part of the depleted SOC pool can be restored through conversion of marginal lands into restorative land uses, adoption of conservation tillage with cover crops and crop residue mulch, nutrient cycling including the use of compost and manure, and other systems of sustainable management of soil and water resources. Measured rates of soil C sequestration through adoption of RMPs range from 50 to 1000 kg/ha/year. The global potential of SOC sequestration through these practices is 0.9±0.3 Pg C/year, which may offset one-fourth to one-third of the annual increase in atmospheric CO2 estimated at 3.3 Pg C/year. The cumulative potential of soil C sequestration over 25–50 years is 30–60 Pg. The soil C sequestration is a truly win–win strategy. It restores degraded soils, enhances biomass production, purifies surface and ground waters, and reduces the rate of enrichment of atmospheric CO2 by offsetting emissions due to fossil fuel.

Lal, R. (2008). Carbon sequestration. Philosophical Transactions of the Royal Society B: Biological Sciences 363 (1492): 815-830

ABSTRACT: Developing technologies to reduce the rate of increase of atmospheric concentration of carbon dioxide (CO2 ) from annual emissions of 8.6 Pg C yr–1 from energy, process industry, land-use conversion and soil cultivation is an important issue of the twenty-first century. Of the three options of reducing the global energy use, developing low or no-carbon fuel and sequestering emissions, this manuscript describes processes for carbon (CO2 ) sequestration and discusses abiotic and biotic technologies. Carbon sequestration implies transfer of atmospheric CO2 into other long-lived global pools including oceanic, pedologic, biotic and geological strata to reduce the net rate of increase in atmospheric CO2 . Engineering techniques of CO2 injection in deep ocean, geological strata, old coal mines and oil wells, and saline aquifers along with mineral carbonation of CO2 constitute abiotic techniques. These techniques have a large potential of thousands of Pg, are expensive, have leakage risks and may be available for routine use by 2025 and beyond. In comparison, biotic techniques are natural and cost-effective processes, have numerous ancillary benefits, are immediately applicable but have finite sink capacity. Biotic and abiotic C sequestration options have specific nitches, are complementary, and have potential to mitigate the climate change risks.

Nabuurs, G.J., O. Masera, K. Andrasko, P. Benitez-Ponce, R. Boer, M. Dutschke, E. Elsiddig, J. Ford Robertson, P. Frumhoff, T. Karjalainen, O. Krankina, W.A. Kurz, M. Matsumoto, W. Oychantcabal, N.H. Ravindranath, M.J. Sanz Sanchez, X. Zhang, B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (2007). Forestry. Cambridge University Press: 541-584

FIRST PARAGRAPH: During the last decade of the 20th century, deforestation in the tropics and forest regrowth in the temperate zone and parts of the boreal zone remained the major factors responsible for emissions and removals, respectively. However, the extent to which the carbon loss due to tropical deforestation is offset by expanding forest areas and accumulating woody biomass in the boreal and temperate zones is an area of disagreement between land observations and estimates by top-down models. Emissions from deforestation in the 1990s are estimated at 5.8 GtCO2 /yr (medium agreement, medium evidence).

D. Schimel, J. Melillo, H. Tian, A. D. McGuire, D. Kicklighter, T. Kittel, N. Rosenbloom, S. Running, P. Thornton, D. Ojima, W. Parton, R. Kelly, M. Sykes, R. Neilson, B. Rizzo (2000). Contribution of increasing CO2 and climate to carbon storage by ecosystems in the United States. Science 287 (5460): 2004-2006

ABSTRACT: The effects of increasing carbon dioxide (CO2 ) and climate on net carbon storage in terrestrial ecosystems of the conterminous United States for the period 1895-1993 were modeled with new, detailed historical climate information. For the period 1980-1993, results from an ensemble of three models agree within 25%, simulating a land carbon sink from CO2 and climate effects of 0.08 gigaton of carbon per year. The best estimates of the total sink from inventory data are about three times larger, suggesting that processes such as regrowth on abandoned agricultural land or in forests harvested before 1980 have effects as large as or larger than the direct effects of CO2 and climate. The modeled sink varies by about 100% from year to year as a result of climate variability.

Lal, R., Follett, R. F., Kimble, J. M. (2003). Achieving soil carbon sequestration in the United States: a challenge to the policy makers. Soil Science 168 (12): 827-845

ABSTRACT: Carbon (C) sequestration in soil implies enhancing the concentrations/pools of soil organic matter and secondary carbonates. It is achieved through adoption of recommended management practices (RMPs) on soils of agricultural, grazing, and forestry ecosystems, and conversion of degraded soils and drastically disturbed lands to restorative land use. Of the 916 million hectares (Mha) comprising the total land area in the continental United States and Alaska, 157 Mha (17.1%) are under cropland, 336 Mha (36.7%) under grazing land, 236 Mha (25.8%) under forest, 14 Mha (1.5%) under Conservation Reserve Programs (CRP), and 20 Mha (2.2%) are under urban land use. Land areas affected by different soil degradative processes include 52 Mha affected by water erosion, 48 Mha by wind erosion, 0.2 Mha by secondary salinization, and more than 4 Mha affected by mining. Adoption of RMPs can lead to sequestration of soil organic carbon (SOC) at an annual rate of 45 to 98 Tg (teragram = 1 × 1012 g = 1 million metric tons or MMT) in cropland, 13 to 70 Tg in grazing land, and 25 to 102 Tg in forestlands. In addition, there is an annual soil C sequestration potential of 21 to 77 Tg by land conversion, 25 to 60 Tg by land restoration, and 15 to 25 Tg by management of other land uses. Thus, the total potential of C sequestration in soils of the United States is 144 to 432 Tg/y or an average of 288 Tg C/y. With the implementation of suitable policy initiatives, this potential is realizable for up to 30 years or when the soil C sink capacity is filled. In comparison, emission by agricultural activities is estimated at 43 Tg C/y, and the current rate of SOC sequestration is reported as 17 Tg C/y. The challenge the policy makers face is to be able to develop and implement policies that are conducive to realization of this potential.

Depro, B.M., B.C. Murray, R.J. Alig, A. Shanks (2008). Public land, timber harvests, and climate mitigation: Quantifying carbon sequestration potential on U.S. public timberlands. Forest Ecology and Management 255 (3-4): 1122-1134

ABSTRACT: Scientists and policy makers have long recognized the role that forests can play in countering the atmospheric buildup of carbon dioxide (CO2 ), a greenhouse gas (GHG). In the United States, terrestrial carbon sequestration in private and public forests offsets approximately 11% of all GHG emissions from all sectors of the economy on an annual basis. Although much of the attention on forest carbon sequestration strategy in the United States has been on the role of private lands, public forests in the United States represent approximately 20% of the U.S. timberland area and also hold a significantly large share (30%) of the U.S. timber volume. With such a large standing timber inventory, these forested lands have considerable impact on the U.S. forest carbon balance. To help decision makers understand the carbon implications of potential changes in public timberland management, we compared a baseline timber harvest scenario with two alternative harvest scenarios and estimated annual carbon stock changes associated with each. Our analysis found that a “no timber harvest” scenario eliminating harvests on public lands would result in an annual increase of 17–29 million metric tonnes of carbon (MMTC) per year between 2010 and 2050—as much as a 43% increase over current sequestration levels on public timberlands and would offset up to 1.5% of total U.S. GHG emissions. In contrast, moving to a more intense harvesting policy similar to that which prevailed in the 1980s may result in annual carbon losses of 27–35 MMTC per year between 2010 and 2050. These losses would represent a significant decline (50–80%) in anticipated carbon sequestration associated with the existing timber harvest policies. If carbon sequestration were valued in the marketplace as part of a GHG offset program, the economic value of sequestered carbon on public lands could be substantial relative to timber harvest revenues.

K. Richards, K. Andersson (2001). The leaky sink: persistent obstacles to a forest carbon sequestration program based on individual projects. Climate Policy 1 (1): 41-54

ABSTRACT: One strategy for mitigating the increase in atmospheric carbon dioxide is to expand the size of the terrestrial carbon sink, particularly forests, essentially using trees as biological scrubbers. Within relevant ranges of carbon abatement targets, augmenting carbon sequestration by protecting and expanding biomass sinks can potentially make large contributions at costs that are comparable or lower than for emission source controls. The Kyoto protocol to the framework convention on climate change includes many provisions for forest and land use carbon sequestration projects and activities in its signatories’ overall greenhouse gas mitigation plans. In particular, the protocol provides a joint implementation provision and a clean development mechanism that would allow nations to claim credit for carbon sequestration projects undertaken in cooperation with other countries. However, there are many obstacles for implementing an effective program of land use change and forestry carbon credits, especially measurement challenges. This paper explains the difficulty that even impartial analysts have in assessing the carbon offset benefits of projects. When these measurement challenges are combined with self-interest, asymmetries of information, and large numbers, it prevents to a project-based forest and land use carbon credit program may be insurmountable.

K. Caldeira, G.H. Rau (2000). Accelerating carbonate dissolution to sequester carbon dioxide in the ocean: Geochemical implications. Geophysical Research Letters 27 (2): 225-228

ABSTRACT: Various methods have been proposed for mitigating release of anthropogenic CO2 to the atmosphere, including deep-sea injection of CO2 captured from fossil-fuel fired power plants. Here, we use a schematic model of ocean chemistry and transport to analyze the geochemical consequences of a new method for separating carbon dioxide from a waste gas stream and sequestering it in the ocean. This method involves reacting CO2 -rich power-plant gases with seawater to produce a carbonic acid solution which in turn is reacted on site with carbonate mineral (e.g., limestone) to form Ca2+ and bicarbonate in solution, which can then be released and diluted in the ocean. Such a process is similar to carbonate weathering and dissolution which would have otherwise occurred naturally, but over many millennia. Relative to atmospheric release or direct ocean CO2 injection, this method would greatly expand the capacity of the ocean to store anthropogenic carbon while minimizing environmental impacts of this carbon on ocean biota. This carbonate-dissolution technique may be more cost-effective and less environmentally harmful, and than previously proposed CO2 capture and sequestration techniques.

R. Lal (2004). Soil carbon sequestration impacts on global climate change and food security. Science 304 (5677): 1623-1627

ABSTRACT: The carbon sink capacity of the world's agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossilfuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.

K. S. Lackner (2002). A guide to CO2 sequestration. Science 300 (5636): 1677-1678

ABSTRACT: Carbon capture and storage (or sequestration) is receiving increasing attention as one tool for reducing carbon dioxide concentrations in the atmosphere. In his Perspective, Lackner discusses the advantages and disadvantages of different methods of carbon sequestration. He advises against sequestration in environmentally active carbon pools such as the oceans, because it may merely trade one environmental problem for another. Better sequestration options include underground injection and (possibly underground) neutralization. Taking into account carbon capture, transport, and storage, the author concludes that in the short and medium term, sequestration would almost certainly be cheaper than a full transition to nuclear, wind, or solar energy.

G. B. Bonan (2008). Forests and climate change: forcings, feedbacks, and the climate benefits of forests. Science 320 (5882): 1444-1449

ABSTRACT: The world's forests influence climate through physical, chemical, and biological processes that affect planetary energetics, the hydrologic cycle, and atmospheric composition. These complex and nonlinear forest-atmosphere interactions can dampen or amplify anthropogenic climate change. Tropical, temperate, and boreal reforestation and afforestation attenuate global warming through carbon sequestration. Biogeophysical feedbacks can enhance or diminish this negative climate forcing. Tropical forests mitigate warming through evaporative cooling, but the low albedo of boreal forests is a positive climate forcing. The evaporative effect of temperate forests is unclear. The net climate forcing from these and other processes is not known. Forests are under tremendous pressure from global change. Interdisciplinary science that integrates knowledge of the many interacting climate services of forests with the impacts of global change is necessary to identify and understand as yet unexplored feedbacks in the Earth system and the potential of forests to mitigate climate change.

Rhemtullaa, J. M., Mladenoff, D. J., Clayton, M. K. (2009). Historical forest baselines reveal potential for continued carbon sequestration. Proceedings of the National Academy of Sciences 106 (15): 6082-6087

ABSTRACT: One-third of net CO2 emissions to the atmosphere since 1850 are the result of land-use change, primarily from the clearing of forests for timber and agriculture, but quantifying these changes is complicated by the lack of historical data on both former ecosystem conditions and the extent and spatial configuration of subsequent land use. Using fine-resolution historical survey records, we reconstruct pre-EuroAmerican settlement (1850s) forest carbon in the state of Wisconsin, examine changes in carbon after logging and agricultural conversion, and assess the potential for future sequestration through forest recovery. Results suggest that total above-ground live forest carbon (AGC) fell from 434 TgC before settlement to 120 TgC at the peak of agricultural clearing in the 1930s and has since recovered to approximately 276 TgC. The spatial distribution of AGC, however, has shifted significantly. Former savanna ecosystems in the south now store more AGC because of fire suppression and forest ingrowth, despite the fact that most of the region remains in agriculture, whereas northern forests still store much less carbon than before settlement. Across the state, continued sequestration in existing forests has the potential to contribute an additional 69 TgC. Reforestation of agricultural lands, in particular, the formerly high C-density forests in the north-central region that are now agricultural lands less optimal than those in the south, could contribute 150 TgC. Restoring historical carbon stocks across the landscape will therefore require reassessing overall land-use choices, but a range of options can be ranked and considered under changing needs for ecosystem services.

Keith, H., Mackey, B. G., Lindenmayer, D. B. (2009). Re-evaluation of forest biomass carbon stocks and lessons from the world's most carbon-dense forests. Proceedings of the National Academy of Sciences 106 (28): 11635-11640

ABSTRACT: From analysis of published global site biomass data (n = 136) from primary forests, we discovered (i) the world's highest known total biomass carbon density (living plus dead) of 1,867 tonnes carbon per ha (average value from 13 sites) occurs in Australian temperate moistEucalyptus regnans forests, and (ii) average values of the global site biomass data were higher for sampled temperate moist forests (n = 44) than for sampled tropical (n = 36) and boreal (n = 52) forests (n is number of sites per forest biome). Spatially averaged Intergovernmental Panel on Climate Change biome default values are lower than our average site values for temperate moist forests, because the temperate biome contains a diversity of forest ecosystem types that support a range of mature carbon stocks or have a long land-use history with reduced carbon stocks. We describe a framework for identifying forests important for carbon storage based on the factors that account for high biomass carbon densities, including (i) relatively cool temperatures and moderately high precipitation producing rates of fast growth but slow decomposition, and (ii) older forests that are often multiaged and multilayered and have experienced minimal human disturbance. Our results are relevant to negotiations under the United Nations Framework Convention on Climate Change regarding forest conservation, management, and restoration. Conserving forests with large stocks of biomass from deforestation and degradation avoids significant carbon emissions to the atmosphere, irrespective of the source country, and should be among allowable mitigation activities. Similarly, management that allows restoration of a forest's carbon sequestration potential also should be recognized.

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