Total Carbon Sink Research Articles

Carbon cycle in the epikarst systems and its ecological effects in South China

The carbon cycle in a global sense is the biogeochemical process by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the earth. For epikarst systems, it is the exchange of carbon among the atmosphere, water, and carbonate rocks. Southern China is located in the subtropical zone; its warm and humid weather creates favorable conditions for the dynamic physical, chemical, and ecological processes of the carbon cycle. This paper presents the mechanisms and characteristics of the carbon cycle in the epikarst systems in south China. The CO2 concentration in soils has clear seasonal variations, and its peak correlates well with the warm and rainy months. Stable carbon isotope analysis shows that a majority of the carbon in this cycle is from soils. The flow rate and flow velocity in an epikarst system and the composition of carbonate rocks control the carbon fluxes. It was estimated that the karst areas in south China contribute to about half of the total carbon sink by the carbonate system in China. By enhancing the movement of elements and dissolution of more chemical components, the active carbon cycle in the epikarst system helps to expand plant species. It also creates favorable environments for the calciphilic plants and biomass accumulation in the region. The findings from this study should help in better understanding of the carbon cycle in karst systems in south China, an essential component for the best management practices in combating rock desertification and in the ongoing study of the total carbon sink by the karst flow systems in China.

The spatial distribution of forest carbon sinks and sources in China

Forest ecosystems play an important role in the global carbon cycle. The implementation of the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol has made the study of forest ecosystem carbon cycling a hot topic of scientific research globally. This paper utilized Chinese national forest inventory data sets (for the periods 1984–1988 and 1999–2003), the vegetation map of China (1:1000000), and the spatially explicit net primary productivity (NPP) data sets derived with the remote sensing-based light use efficiency model (CASA model). We quantitatively estimated the spatial distribution of carbon sinks and sources of forest vegetation (with a resolution of 1 km) using the spatial downscaling technique. During the period 1984 to 2003 the forest vegetation in China represented a carbon sink. The total storage of carbon increased by 0.77 PgC, with a mean of 51.0 TgC a−1. The total carbon sink was 0.88 PgC and carbon source was 0.11 PgC during the study period. The carbon sink and carbon source of forest vegetation in China showed a clear spatial distribution pattern. Carbon sinks were mainly located in subtropical and temperate regions, with the highest values in Hainan Province, Hengduan mountain ranges, Changbai mountain ranges in Jilin, and south and northwest of the Da Hinggan Mountains; carbon sources were mainly distributed from the northeast to southwestern areas in China, with the highest values mainly concentrated in southern Yunnan Province, central Sichuan Basin, and northern Da Hinggan Mountains. Increase in NPP was strongly correlated with carbon sink strength. The regression model showed that more than 80% of the variation in the modeled carbon sinks in Northeast, Northern, Northwest and Southern China were explained by the variation in NPP increase. There was a strong relationship between carbon sink strength and forest stand age.

Changes in soil organic carbon, nitrogen, pH and bulk density with the development of larch (Larix gmelinii) plantations in China

Under the government of China's environmental program known as Returning Farmland To Forests (RFTF), about 28 million hectares of farmland have been converted to tree plantation. This has led to a large accumulation of biomass carbon, but less is known about underground carbon-related processes. One permanent plot (25 years of observation) and four chronosequence plot series comprising 159 plots of larch (Larix gmelinii) plantations in northeastern China were studied. Both methods found significant soil organic carbon (SOC) accumulation (96.4 g C m−2 yr−1) and bulk density decrease (5.7 mg cm−3 yr−1) in the surface soil layer (0–20 cm), but no consistent changes in deeper layers, indicating that larch planting under the RFTF program can increase SOC storage and improve the physical properties of surface soil. Nitrogen depletion (4.1–4.3 g m−2 yr−1), soil acidification (0.007–0.022 pH units yr−1) and carbon/nitrogen (C/N) ratio increase (0.16–0.46 per year) were observed in lessive soil, whereas no significant changes were found in typical dark-brown forest soil. This SOC accumulation rate (96.4 g m−2 yr−1) can take 39% of the total carbon sink capacity [net ecosystem exchange (NEE)] of larch forests in this region and the total soil carbon sequestration could be 87 Tg carbon within 20 years of plantation by approximating all larch plantations in northeastern China (4.5 Mha), showing the importance of soil carbon accumulation in the ecosystem carbon balance. By comparison with the rates of these processes in agricultural use, the RFTF program of reversing land use for agriculture will rehabilitate SOC, soil fertility and bulk density slowly (< 69% of the depletion rate in agricultural use), so that a much longer duration is needed to rehabilitate the underground function of soil via the RFTF program. Global forest plantations on abandoned farmland or function to protecting farmland are of steady growth and our findings may be important for understanding their underground carbon processes.

The Impact of Whaling on the Ocean Carbon Cycle: Why Bigger Was Better

BackgroundHumans have reduced the abundance of many large marine vertebrates, including whales, large fish, and sharks, to only a small percentage of their pre-exploitation levels. Industrial fishing and whaling also tended to preferentially harvest the largest species and largest individuals within a population. We consider the consequences of removing these animals on the ocean's ability to store carbon.Methodology/Principal FindingsBecause body size is critical to our arguments, our analysis focuses on populations of baleen whales. Using reconstructions of pre-whaling and modern abundances, we consider the impact of whaling on the amount of carbon stored in living whales and on the amount of carbon exported to the deep sea by sinking whale carcasses. Populations of large baleen whales now store 9.1×106 tons less carbon than before whaling. Some of the lost storage has been offset by increases in smaller competitors; however, due to the relative metabolic efficiency of larger organisms, a shift toward smaller animals could decrease the total community biomass by 30% or more. Because of their large size and few predators, whales and other large marine vertebrates can efficiently export carbon from the surface waters to the deep sea. We estimate that rebuilding whale populations would remove 1.6×105 tons of carbon each year through sinking whale carcasses.Conclusions/SignificanceEven though fish and whales are only a small portion of the ocean's overall biomass, fishing and whaling have altered the ocean's ability to store and sequester carbon. Although these changes are small relative to the total ocean carbon sink, rebuilding populations of fish and whales would be comparable to other carbon management schemes, including ocean iron fertilization.

A Bayesian calibration of a simple carbon cycle model: The role of observations in estimating and reducing uncertainty

The strengths of future carbon dioxide (CO2) sinks are highly uncertain. A sound methodology to characterize current and predictive uncertainties in carbon cycle models is crucial for the design of efficient carbon management strategies. We demonstrate such a methodology, Markov Chain Monte Carlo (MCMC), by performing a Bayesian calibration of a simple global‐scale carbon cycle model with historical carbon cycle observations to (1) estimate probability density functions (PDFs) of key carbon cycle parameters, (2) derive statistically sound probabilistic predictions of future CO2 sinks, and (3) assess the utility of hypothetical observation systems to reduce prediction uncertainties. We find that the PDFs of model parameter estimates are not normally distributed, and the residuals show statistically significant temporal autocorrelation. The assumption of normally distributed PDFs likely causes biased results, and the neglect of autocorrelation in the residual of the annual CO2 time series causes overconfidence in parameter estimates and predictions. Using interannually varying global temperature observations as forcing provides important information: terrestrial parameter PDFs are shifted and are more sharply constrained when compared to PDFs estimated when forcing the carbon cycle with a simple energy‐balance model. Although CO2 observations provide a strong constraint on the total carbon sink, adding independent observations of terrestrial and oceanic fluxes has the potential to reduce uncertainty in predictions of this total sink more rapidly. Assimilating hypothetical annual observations of terrestrial and oceanic CO2 fluxes with realistic uncertainties reduces predictive uncertainties about CO2 sinks in the year 2050 by as much as a factor of 2 compared to assimilating CO2 concentrations alone.

Variazione di superficie e fissazione di carbonio in foresta nel territorio montano della Regione Veneto in riferimento all’applicazione del Protocollo di Kyoto

The Parties that have signed the Kyoto Protocol must reduce global emissions of Greenhouse Gasses (GHG) during the First Commitment Period (2008 - 2012) by at least 5% with respect to 1990. This share is 6.5% for Italy. The Kyoto Protocol lays down some measures for reducing GHG emissions, which include actions in agriculture and forestry. it will thus be possible to take emissions and absorptions resulting from land use changes into account in the National Balances. Given the widespread forests in Italy, it is very important to have an assessment of the aptitude of this sector to act as a carbon sink. In this study we analysed the variation of forestland cover in a mountain area of the Veneto Region (NE Italy). The analysis was done by comparing aerial photos taken in 1991 with orthophotos reported to 2003, by photointerpretation of points with casual distribution on sample areas, according to a stratified sampling. We estimated a statistically relevant increment of about 0.095% of forest land only up to 1500 m compared to the estimated forest cover for 1990 (about 42 ha), underlining how this low increase is mainly due to forest management. The second step was to estimate the fixed carbon in the areas where forests increased. This was achieved by collecting biometrical data in the field, and then using allometric functions. The annual carbon sink was estimated as 0.69 Mg ha-1 year-1. Comparing these results with previous studies done in the pre-alpine region we estimate the annual increment of the forest area in the whole Veneto region to be about 409.94 ha and that the total carbon sink is about 282.86 Mg C year-1. A method for estimating carbon sink in afforestation/reforestation areas is proposed that could also be applied to other sites in Italy.

Carbon Sequestration by Carbonization of Biomass and Forestation: Three Case Studies

We proposed the carbon sink project called “Carbon Sequestration by Forestation and Carbonization (CFC),” which involves biomass utilization and land conservation by incorporating the products of biomass carbonization into the agents for soil improvement, water purification, etc. Our purpose was to demonstrate the potential of the CFC scheme for carbon sequestration, particularly carbon storage in soil. Case studies were conducted in both developing and developed countries. 1. In southern Sumatra, Indonesia, 88,369 Mg-C year−1 of wood residue from a plantation forest and excess bark from a pulp mill would be converted into 15,571 Mg-C year−1 of the net carbon sink by biochar for soil improvement. The fixed carbon recovery of the system is 21.0%. 2. In a semiarid region in western Australia, the carbonization of wood residue was incorporated with multipurpose projects of a mallee eucalyptus plantation that involved the function of salinity prevention. During the project period of 35 years, the total carbon sink would reach 1,035,450 Mg-C with 14.0% by aboveground biomass, 33.1% by belowground biomass and 52.8% by biochar in soil. 3. In southern Kyushu, Japan, the study was focused on the effective use of surplus heat from a garbage incinerator for carbonizing woody materials. Sawdust of 936.0 Mg-C year−1 would be converted into the net carbon sink of 298.5 Mg-C year−1 by carbonization, with the fixed carbon recovery of the system being 31.9%. Consequently, the CFC project could encourage the creation of a carbon sink in soil. However, we recognize that the quality standard of biochar, the stability of biochar in soil, and the methods for monitoring biochar utilization must be clarified before incorporating biochar carbon into the carbon credit system.

Response of terrestrial carbon uptake to climate interannual variability in China

AbstractThe interest in national terrestrial ecosystem carbon budgets has been increasing because the Kyoto Protocol has included some terrestrial carbon sinks in a legally binding framework for controlling greenhouse gases emissions. Accurate quantification of the terrestrial carbon sink must account the interannual variations associated with climate variability and change. This study used a process‐based biogeochemical model and a remote sensing‐based production efficiency model to estimate the variations in net primary production (NPP), soil heterotrophic respiration (HR), and net ecosystem production (NEP) caused by climate variability and atmospheric CO2 increases in China during the period 1981–2000. The results show that China's terrestrial NPP varied between 2.86 and 3.37 Gt C yr−1 with a growth rate of 0.32% year−1 and HR varied between 2.89 and 3.21 Gt C yr−1 with a growth rate of 0.40% year−1 in the period 1981–1998. Whereas the increases in HR were related mainly to warming, the increases in NPP were attributed to increases in precipitation and atmospheric CO2. Net ecosystem production (NEP) varied between −0.32 and 0.25 Gt C yr−1 with a mean value of 0.07 Gt C yr−1, leading to carbon accumulation of 0.79 Gt in vegetation and 0.43 Gt in soils during the period. To the interannual variations in NEP changes in NPP contributed more than HR in arid northern China but less in moist southern China. NEP had no a statistically significant trend, but the mean annual NEP for the 1990s was lower than for the 1980s as the increases in NEP in southern China were offset by the decreases in northern China. These estimates indicate that China's terrestrial ecosystems were taking up carbon but the capacity was undermined by the ongoing climate change. The estimated NEP related to climate variation and atmospheric CO2 increases may account for from 40 to 80% to the total terrestrial carbon sink in China.

Increasing terrestrial carbon uptake from the 1980s to the 1990s with changes in climate and atmospheric CO2

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 CO2increases 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−1with a mean value of 0.62 Gt C yr−1, its decadal means increased from 0.23 Gt C yr−1in the 1980s to 1.10 Gt C yr−1in 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 (&gt;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 CO2increase, 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.

Increasing carbon stocks in the forest soils of western Europe

The soils of western European forests may be accumulating carbon, because tree biomass has been expanding in these forests already for decades, and the more numerous and larger trees can produce more litter. We calculated the carbon budget of soils and trees in the forests of 14 EU countries plus Norway and Switzerland from 1950 to 2040 by integrating forest resource information (inventory data from 1950 to 1990 and a forest resource forecast from 2000 to 2040), biomass allocation and turnover information, and a dynamic soil carbon model. The carbon stock of the soils increased throughout the studied period. In 1990, the soil carbon sink was 26 Tg per year. This is 32 or 48% compared with our two estimates of the tree carbon sink for that year. Until 2040, the soil carbon sink was estimated to increase to 43 Tg per year. This would already be 61 or 69% compared with the tree carbon sink that year. In 1990, the soils contributed most to the total forest carbon sink in central Europe, where the soil carbon sink was almost as large as the tree carbon sink. The soils were least important in southern Europe, where the soil carbon sink was less than 25% compared with the tree carbon sink. In the future, the contribution of the soils to the total forest carbon sink was estimated to increase everywhere except in southern Europe. The soil carbon stocks increased mainly because litter fall from living trees increased while the other sources of soil carbon, i.e. the residues of harvests and natural disturbances, varied less. This litter fall was also the largest source of soil carbon accounting for 70–80% of the total. The soil carbon stocks in these forests could thus be most effectively controlled by forest management actions, such as the choices of harvest regimes or tree species, which especially affect the litter production of living trees. According to an uncertainty analysis, we may have overestimated the soil carbon sink by 35% or underestimated it by 50% throughout the studied period. The largest uncertainties were related to calculating the litter production of living trees and decomposition in soil.

Estimating carbon accumulation rates of undrained mires in Finland–application to boreal and subarctic regions

Equations based on empirical relationships of peat physical properties were used to estimate the average long-term apparent rate of carbon accumulation (LORCA) in Finnish mire vegetation regions. The results were generalized to the boreal and subarctic regions. Analyses of 1302 dated peat cores were used to infer carbon accumulation for each mire vegetation region of Finland. The area-weighted LORCA for Finnish undrained mire areas was 18.5 g m 2 yr 1 and the total carbon sink 0.79 Tg yr 1 (1 Tg = 1012g). The total carbon pool of Finnish undrained mires was estimated as 2257 Tg. The aapa-mire region included 80% of the total net accumulation rate of carbon and 85% of the total carbon reservoirs of Finnish undrained mires. LORCA was signi” cantly higher in the raised-bog region, 26.1 g m 2 yr 1, compared with the aapa-mire region, 17.3 g m 2 yr 1, and bogs generally had a higher LORCA 20.8 g m 2 yr 1, than fens 16.9 g m 2 yr 1. The total C sink for boreal and subarctic mires was estimated at 66 Tg yr 1 which is about 31% lower than the previous estimates. The total C pool of all boreal and subarctic mires was estimated at 270–370 Pg (1 Pg = 1015g).

The climatic-induced net carbon sink by terrestrial biosphere over 1901–1995

The spatial and temporal variability of land carbon flux over the past one hundred years was investigated based on an empirical model directly calculating soil respiration rate. Our model shows that during 1901–1995, about 44-89 PgC (equals to 0.5, 0.9 PgC/yr respectively) were absorbed by terrestrial biosphere. The simulated net ecosystem productivity (NEP) after the 1930s was close to the estimated value of “ missing C sink” from deconvolution analysis. Most of the total carbon sink happened during 1951–1985 with the estimated value of 33–50 PgC. Three major sinks were located in the tropics (10°S–10°N), Northern mid-latitudes (30°–60°N) and Southern subtropics (10°–40°S). During 1940s-mid-1970s, carbon sinks by terrestrial ecosystem increased with time, and decreased after the mid-1970s. These may be due to the changing of climate condition, as during the 1940s–1970s, temperature decreased and precipitation increased, while after the mid-1970s, an opposite climate situation occurred with evident increasing in temperature and decreasing in precipitation. Usually, warmer and dryer climate condition is not favor for carbon absorption by biosphere and even induces net carbon release from soil, while cooler and wetter condition may induce more carbon sink. Our model results show that the net carbon flux is particularly dependent on moisture / precipitation effect despite of temperature effect. The changing of climate in the past century may be a possible factor inducing increases in carbon sink in addition to CO2 and N fertilizer.

Carbon accumulation in West Siberian Mires, Russia Sphagnum peatland distribution in North America and Eurasia during the past 21,000 years

The rates of carbon (C) accumulation and the role of fires in the C dynamics of the major types of boreal West Siberian mires were investigated. Detailed analysis of dry bulk density, C, and N concentration and age of the peat layers were used to determine C accumulation rates throughout the Holocene. The average long‐term apparent rate of carbon accumulation (LORCA) at 11 studied sites was 17.2±1.0 (SE) g m−2 yr−1, ranging from 12.1 to 23.7 g m−2 yr−1, and the total apparent carbon sink 11.8 Tg yr−1 (1 Tg = 1012 g) for Russian raised string bogs (68.5 million hectares). These estimates of C accumulation in West Siberian mires are roughly a half of the earlier estimates for these boreal mires. Differences in LORCA for three major mire types in the study area, the ridge‐hollow pine bogs, Sphagnum fuscum pine bogs, and dwarf‐shrub pine bogs, were not significant. The age versus depth (measured as cumulative carbon from the surface downward) curve was slightly convex, indicating a general declining trend in LORCA with decreasing age. About 55% of the present carbon store was already accumulated about 6000 cal. BP. The most intensive expansion phase of the study area occurred between 7000 and 8000 cal. BP. The subsequent lateral expansion has been very slow in the later Holocene. The charcoal data indicated that these mires have burned only 2–3 times during the past 7000–8000 cal. BP, and only a strip of a few meters along the mire margins has burned relatively frequently. No evidence of significant carbon losses due to fires could be found. The charcoal layers at the mire margins suggest a declining trend in burning rates during the later Holocene.

Anthropogenic CO2 invasion into the northeast Pacific based on concurrent δ13CDIC and nutrient profiles from the California Current

The stable isotopic signature of dissolved inorganic carbon (δ13CDIC) in the northeast Pacific Ocean is lower in near‐surface waters by ≈1.1‰ relative to values predicted from global oceanic trends of δ13CDIC versus nutrients. A combination of anthropogenic carbon uptake from the atmosphere and thermodynamic, air‐sea gas exchange processes in different water mass source areas account for the isotopic depletion. Here we evaluate the efficacy of using a concurrent nutrient‐δ13C strategy to separate these two effects, with the goal of improving estimates of anthropogenic carbon uptake over the course of the Industrial Revolution. In depth profiles from the sea surface to 2500 m at four stations across the California Current (42°N), nitrate, rather than phosphate, is best correlated to δ13CDIC providing the best choice for this experiment. On the basis of an assumption of no anthropogenic carbon in North Pacific Deep Waters between 1000–2500 m depth (potential densities, σθ ∼ 27.3–27.7), the “anthropogenic— preanthropogenic” carbon isotope shift (Δδ13Ca−p) in near‐surface waters of the northeast Pacific is inferred to be −0.62 ± 0.17‰, while the thermodynamic air‐sea gas exchange signature is estimated at −0.48 ± 0.17‰. Values of Δδ13Ca−p (similar to the regional patterns of Δ14C and Tritium penetration) approach zero for σθ &gt; 26.8, indicating little penetration of anthropogenic carbon into the North Pacific Intermediate Water or the upper North Pacific Deep Water. Our results suggest an upper North Pacific sink of anthropogenic carbon over the past ∼200 years that is ∼40% greater than that estimated for the interval between ∼1970 and ∼1990 by Quay et al., [1992]. Our estimate of the North Pacific inventory of anthropogenic carbon, added to published estimates from the North Atlantic and Indian Ocean, is smaller than model predictions of the total carbon sink, suggesting that a significant portion of anthropogenic carbon enters the deep sea via the Southern Ocean.

Responses in NPP and carbon stores of the northern biomes to a CO2-induced climatic change, as evaluated by the Frankfurt biosphere model (FBM)

To assess the role of the boreal and temperate forests and the tundra ecosystems in a future CO 2 -induced climate change, the Frankfurt biosphere model (FBM) was applied to the 3 × CO 2 climate as calculated by the GCM of the MPI fur Meteorologie in Hamburg. The FBM predicts on a 1° × 1° spatial grid the seasonal and perannual course of leaf biomass and feeder roots, woody biomass, soil carbon and soil water in response to the seasonal course of light, precipitation and temperature. The phenology is controlled by the flux balance of carbon gains and losses, thus being dependent on the driving climate and the state of vegetation. Two equilibrium runs based on the 3 × CO 2 climate were performed: (1) Considering the pure climate effect (with no direct CO 2 fertilization) we obtained a 22% decrease of the net primary production (NPP) due to enhanced autotrophic respiration and increased water limitation. Together with the effect on the soils this results in a 170 Gt carbon source. (2) Considering a CO 2 -induced enhancement of the maximum photosynthesis the pure climate effect is more than compensated and we predict a NPP increase of 9% and a total carbon sink of 50 Gt C. This effect may even be an underestimate if one takes into consideration a shift in the optimum temperature for photosynthesis under enhanced levels of atmospheric CO 2 as proposed by Long and Drake. DOI: 10.1034/j.1600-0889.47.issue1.16.x

Responses in NPP and carbon stores of the northern biomes to a CO&lt;sub&gt;2&lt;/sub&gt;-induced climatic change, as evaluated by the Frankfurt biosphere model (FBM)

To assess the role of the boreal and temperate forests and the tundra ecosystems in a future CO 2 -induced climate change, the Frankfurt biosphere model (FBM) was applied to the 3 × CO 2 climate as calculated by the GCM of the MPI fur Meteorologie in Hamburg. The FBM predicts on a 1° × 1° spatial grid the seasonal and perannual course of leaf biomass and feeder roots, woody biomass, soil carbon and soil water in response to the seasonal course of light, precipitation and temperature. The phenology is controlled by the flux balance of carbon gains and losses, thus being dependent on the driving climate and the state of vegetation. Two equilibrium runs based on the 3 × CO 2 climate were performed: (1) Considering the pure climate effect (with no direct CO 2 fertilization) we obtained a 22% decrease of the net primary production (NPP) due to enhanced autotrophic respiration and increased water limitation. Together with the effect on the soils this results in a 170 Gt carbon source. (2) Considering a CO 2 -induced enhancement of the maximum photosynthesis the pure climate effect is more than compensated and we predict a NPP increase of 9% and a total carbon sink of 50 Gt C. This effect may even be an underestimate if one takes into consideration a shift in the optimum temperature for photosynthesis under enhanced levels of atmospheric CO 2 as proposed by Long and Drake. DOI: 10.1034/j.1600-0889.47.issue1.16.x

Carbon sources and sinks in forest biomes of the former Soviet Union

The carbon budget of the forest biomes of the former Soviet Union (FSU) and their sequestration potential were assessed by considering (1) net ecosystem productivity (NEP) of different age forest stands and actual forest coverage, (2) carbon flux related to forest fires, (3) the rate of peat accumulation, and (4) anthropogenic influences. The area of forest biomes in the FSU was estimated at 1426.1 million hectares (Mha); forest ecosystems comprised 799.9 Mha, nonforest ecosystems and arable land comprised 506.3 and 119.9 Mha, respectively. The vegetation pool (phytomass and coarse woody debris) was 68.7 Gt C (carbon). The litter and soil carbon pools were 12.2 and 319.1 Gt C, respectively. The net primary productivity (NPP) of forest biomes ecosystems was 5.6 Gt C/yr, the rate of foliage formation was 2.3 Gt C/yr, the rate of humus formation was 161 Mt C/yr with 73 Mt C/yr in the stable form. The NEP of the forest biomes was assessed from the data on NEP of young, middle‐age, and premature forest stands. The NEP of the forest biomes was 825 Mt C/yr. Peat was accumulating at an average rate of 23 Mt C/yr. Carbon effluxes from mortmass, litter, and soil organic matter decomposition were calculated from the NPP, NEP, foliage, and humus formation rates. The efflux from mortmass decomposition was 2.6 Gt C/yr, from litter decomposition 2.1 Gt C/yr, and from soil organic matter decomposition 61 Mt C/yr. Peat combustion represented a carbon efflux of 30 Mt C/yr. The carbon efflux from forest fires and agricultural activities was 199 and 10 Mt C/yr, respectively. Carbon efflux from wood harvesting (carbon sequestration in regrowing vegetation was excluded) was 152 Mt C/yr. Considering all components of the natural carbon cycle and the anthropogenic influences, FSU forest biomes were a net sink of 485 Mt C/yr of atmospheric carbon. The Siberian and Far East forests represent approximately 82% of the net sink. The total carbon sink in FSU forests was equivalent to one half of the annual CO2 fossil fuel emissions in the FSU or one half the carbon released from deforestation in subtropical regions.