Carbon cycle of terrestrial ecosystems of the former Soviet Union

Environmental Science and Policy 1 (1998) 115±128

Carbon cycle of terrestrial ecosystems of the former Soviet Union Tatyana P. Kolchugina *, Ted S. Vinson Department of Civil±Environmental Engineering, Apperson Hall 107, Oregon State University, Corvallis, OR 97331, USA

Abstract Two to three percent of the organic matter accumulating annually in the terrestrial ecosystems of the FSU (8.2 Pg C/yr) was sequestered in relatively long-term storage pools. The total C store of the FSU, estimated at 601.1 Pg C (with 84% allocated in SOM, 10% in phytomass and approximately 3% each in CWD and litter), was increasing by 0.03%/yr. The remaining C was returned to the atmosphere through natural processes (over 90%) and disturbances (5%). Terrestrial ecosystems of the FSU represented a sink for 0.181 Pg C/yr. This C sink was provided by forest ecosystems (0.375 Pg C/yr), while agro±ecosystems and peatlands represented a net source of C to the atmosphere (0.194 Pg C/yr). Implementation of a number of forest management practices to a full extent would result in an increase in the forest C pools by 0.5%/yr. Management options in the agricultural sector may increase the total SOM C pool by 0.1%/yr. With climate warming, FSU terrestrial ecosystems within the permafrost area may make a transition to become a source of 0.2±0.5 Pg C/yr, which may concurrently be balanced by forest migration to the north and an increase in plant productivity. In the future, FSU terrestrial ecosystems may still represent a sink for atmospheric C if there would be a substantial amount of young to maturing forest ecosystems and forest logging would not increase dramatically. # 1998 Published by Elsevier Science Ltd. All rights reserved. Keywords: Carbon cycle; Terrestrial ecosystems; Russia; Former Soviet Union; Carbon pools; Carbon ¯uxes; Management options; Forests; Peatlands; Arable land

1. Introduction It is recognized that the accumulation of greenhouse gases (CO2, CH4, etc.) in the atmosphere may lead to global warming and could result in negative changes in the functioning of terrestrial ecosystems. Recently, the international community began developing management strategies for terrestrial ecosystems aimed at the mitigation of and the adaptation to potential climate change (IPCC, 1990, 1996). The territory of the FSU plays an important role in the global carbon (C) cycle. Before its dissolution, the former Soviet Union (FSU) occupied one-sixth of the land surface of the Earth. The total land area of the FSU was 2,240  106 ha (Mha). In 1983, the population of the FSU was 271.4 million. The former republics of the Soviet Union included Russia, Belorus, Ukraine, Moldova, Baltic states (i.e., Lithuania, Latvia, and Estonia), Armenia, Georgia, Azerbaijan, Tajikistan, Turkmenistan, Uzbekistan, * Corresponding author.

Kazakhstan, and Kyrgyzstan. The consumption of energy by the FSU was 18% of the total global energy consumption. Industrial C emissions in the FSU were between 0.998 Pg C/yr (1988) (Subak et al., 1993) to 1.02 Pg C/yr (1990) (Makarov and Bashmakov, 1990). The territory of the FSU is represented by a variety of climate conditions. The major part of the territory is in the boreal and temperate biogeographic zones. The climate of the FSU changes from arctic and subarctic in the north to warm temperate and desert in the south. From west to east the climate makes a transition from maritime to continental to monsoon. The vegetation of the FSU includes forest, woodland, grassland, tundra, desert, peatlands, and cultivated land (Kolchugina and Vinson, 1993a). Arctic deserts and tundra formations are found in the northern regions of the FSU; deserts and semi-deserts occur in the southern regions. A vast area is occupied by forests. The FSU has the greatest expanse of peatlands in the world (Tyuremnov, 1976). A signi®cant area of the FSU is underlain by continuous permafrost (estimated at 824.2 Mha, Kolchugina and Vinson, 1993b,c).

1462-9011/98/$19.00 # 1998 Published by Elsevier Science Ltd. All rights reserved. PII: S 1 4 6 2 - 9 0 1 1 ( 9 8 ) 0 0 0 1 1 - 2

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About 95% of the forested area in the FSU is in Russia. The deforestation of Russian forests began in the 17th century and continued through the mid 20th century (Kobak and Kondrasheva, 1985; Kobak, 1988). After World War II, reforestation e€orts were initiated throughout the FSU. Forest inventory data from 1966 to 1988 (Alimov et al., 1989; Vorobyov, 1985) indicate that the area of forested land under State forest management in the FSU has remained at a stable level. At present, FSU forests are intensively exploited. The annual area of principal logging in 1988 was approximately 2.0 Mha but dropped in 1993. An understanding of the C stores of terrestrial ecosystems of the FSU is crucial to the development of international management strategies aimed at mitigation of global climate change. Also, knowledge of the present-day C pools and ¯uxes of the FSU may facilitate an assessment of future changes in terrestrial C stores under di€erent climatic regimes and management practices. Several studies related to the assessment of the C pools and ¯uxes of a number of terrestrial ecosystems of the FSU were conducted (e.g., Isayev et al., 1993; Gaston et al., 1993; Kolchugina and Vinson, 1993a,b,c,d,e,f, 1995a; Alexeyev and Birdsey, 1994; Botch et al., 1995; etc.). The C pools and ¯uxes for all major types of terrestrial ecosystems of the FSU, however, were not previously presented and discussed together. 2. Objectives The objective of this paper is to present methods and a summary of the results of research work to assess the C pools and ¯uxes of the major types of terrestrial ecosystems of the FSU. The scope of work includes the assessment of the C pools and ¯uxes associated with living vegetation and plant debris and soils. Management options aimed at an increase in the terrestrial C pools and a decrease in the C emissions from the terrestrial ecosystems of the FSU to the atmosphere are also discussed. 3. Methods The C cycle consists of a combination of pools and ¯uxes. The pools are C stored in soil and vegetation, including living vegetation (i.e., phytomass) and coarse woody debris (CWD), above-ground and belowground, soil organic matter (SOM), and litter (i.e., the upper soil layer consisting of ®ne woody debris and leaves that are not completely decomposed) (Kolchugina and Vinson, 1993a; Vinson and Kolchugina, 1993). The processes associated with the formation of new organic matter in vegetation and soil

(e.g., net primary productivity (NPP) and humus formation) represent C in¯uxes. E‚uxes are associated with C emissions resulting from plant respiration and decomposition of organic matter and disturbances (natural and anthropogenic, e.g., forest ®res, agricultural activities, peat mining and burning, etc.). The estimates of the C pools, NPP and the net C ¯ux relate to the time period associated with collecting the data which are incorporated in the assessment. The assessment presented herein relied on data related to the period from the 1970s to the early 1990s and, therefore, re¯ects this period. 3.1. C pools The C pools of terrestrial ecosystems may be estimated using di€erent approaches. For example, a number of ecoregions (i.e. relatively homogeneous regions with respect to densities per ha of phytomass, CWD, litter and SOM) may be isolated with thematic maps. When C values of phytomass, CWD, litter, and SOM are assigned to these ecoregions and the ecoregional estimates are aggregated, a calculation of the C budget components may be performed at the regional or national scale (Kolchugina and Vinson, 1993a,e; Vinson and Kolchugina, 1993). As another example, countries with signi®cant timber resources typically have extensive forest statistical databases. Forest statistical data can be used to estimate forest phytomass and CWD (Kolchugina and Vinson, 1993d,f). These approaches have their advantages and disadvantages. The approach based upon thematic maps has the advantage of describing ecosystem types and geographical location of the ecosystem. Data on C in soil and vegetation combined with the areal extent of speci®c ecosystems identi®ed with the help of thematic maps may serve as a basis for C pool and ¯ux estimates. The main disadvantage is that most of these data do not speci®cally describe C accumulation that is dependent upon ecosystem age. Also, only a limited number of site measurements is provided; hence, it is dicult to assess the spatial variation of C accumulation parameters. An approach using forest statistical data has the advantage of containing an accurate assessment of commercial timber volume based on a large number of measurements, but no information is given with respect to ecosystem components (i.e., branches, roots, understory, shrubs) other than stem volume. Use of all available data in a combination approach would undoubtedly result in the most comprehensive, and possibly reliable, estimate of the C budget. This approach was undertaken herein. About 95% of the territory of the FSU, including Russia, Ukraine, Belorus, Moldova, Kazakhstan, and the Baltic states, was categorized with the help of a

T.P. Kolchugina, T.S. Vinson / Environmental Science and Policy 1 (1998) 115±128

map showing soil±vegetation associations, i.e., ecosystems (Ryabchikov, 1988). The remaining 5% of the territory is represented by mostly mountainous or desert/semidesert ecosystems which do not hold signi®cant quantities of C compared to the area analyzed. Forest ecosystems of all FSU republics were included in the assessment. The main ecosystem types identi®ed with the help of this map were the polar desert, tundra, forest±tundra/sparse taiga, taiga, mixed-deciduous forest, forest±steppe, and warm temperate woodlands, steppe, and desert±semidesert. Forest inventory data on percent forest cover (Vorobyov, 1985; USSR State Forestry Committee, 1990) were used to estimate the areal extent of non-forest ecosystems within the forest biomass (Kolchugina and Vinson, 1993d). The estimate of the forested area (forests with the level of stocking 0.3 and higher) was based on the information provided by the USSR State Forestry Committee which is the best available source of information related to FSU forests. The estimate of the areal extent of peatlands was based on the recent assessment by Botch et al. (1995) which considered the peatland types, distribution, and FSU peat statistical information. The area of agricultural land (cropland, pasturelands, and haylands) was obtained from the World Resource Institute report (WRI, 1992; Kolchugina and Vinson, 1994a). The C pools for major ecosystem types were estimated using site speci®c data on C accumulation parameters for terrestrial ecosystems of the FSU (Bazilevich, 1986; Kobak, 1988) and geographic information systems analyses (Kolchugina and Vinson, 1993a,e; Vinson and Kolchugina, 1993). Phytomass of FSU arable land was estimated from data on economic yields of major FSU crops applying harvest indexes (Gaston and Kolchugina, 1995). The overall loss of the initial C content was estimated for current conditions of the arable land of the FSU using dependencies developed by Mann (1986) to predict current carbon content of cultivated soil as a function of the initial C content to major soil types in the FSU (Gaston et al., 1993). The estimate of phytomass and CWD of coniferous and deciduous forests was based on forest statistical data (data on the total growing stock (GS)) (Alimov et al., 1989; USSR State Forestry Committee, 1990; Kolchugina and Vinson, 1995a) applying conversion factors developed by Isayev et al. (1993) speci®cally for FSU forests depending upon tree genera and forest 1 Bazilevich collected and summarized NPP data for approximately 1,500 vegetation associations in the FSU. 2 The terms `hard and soft deciduous forests' are widely used in FSU forest statistical data; these terms indicate deciduous forest with di€erent wood density: hard deciduous Ð stony birch, oak, etc.; soft deciduous Ð birch, aspen, linden, etc.

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age. The density of phytomass was obtained by dividing the total phytomass of the coniferous and deciduous forests by their area. The density of CWD was estimated based on the ratio of stem volume to aboveground CWD derived from FSU yield tables as described in Kolchugina and Vinson (1993f). The distribution of phytomass and CWD by above and below-ground parts was made according to Bazilevich (1986) and Yermolenko and Yermolenko (1982). 3.2. C ¯uxes 3.2.1. NPP NPP may be used as a measure of the annual rate of the C turnover in an ecosystem. The NPP densities of meadows, grasslands, and peatlands were calculated as area weighted averages by dividing the total NPP of a speci®c ecosystem by its areal extent. The total NPPs for a speci®c ecosystem were obtained using an ecoregional approach and incorporating Bazilevich (1986) data1 (Table 1). The NPP of croplands was assumed to be equal to their phytomass (Gaston and Kolchugina, 1995). The NPP density of coniferous, hard deciduous, and soft deciduous2 forests was estimated using an ecoregional approach and Bazilevich data adjusted for the presence of young forest ecosystems (i.e., using data on the age±class distribution reported in FSU forest statistical data (Kolchugina and Vinson, 1993d)). 3.2.2. Net C ¯ux The net ecosystem productivity (NEP) represents net accumulation of organic matter in an ecosystem after C is expended for autotrophic and heterotrophic respiration (Odum, 1953). The C ¯ux between forest ecosystems and the atmosphere is the di€erence between C sequestered during growth and C released through natural and anthropogenic disturbances. 3.2.2.1. Non-forest ecosystems. In the undisturbed state, non-forest ecosystems may be considered to be in equilibrium with respect to atmospheric C (i.e., net accumulation of phytomass (NAPh), net accumulation of CWD (NACWD), and net accumulation of soil organic matter (NASOM) are zero). The accumulation of phytomass, CWD, and labile SOM is balanced by decomposition processes. The rate of accumulation of stable SOM is slow and the formation of the soil organic pro®le requires hundreds of years. Herein, it was assumed that only the net accumulation of stable SOM (NASOM) and peat were associated with the C sink of undisturbed non-forest ecosystems. Density (per ha) of NASOM was derived from data reported by Kobak (1988). For each vegetation type shown in Table 1, a representative soil type was de®ned based on the Ryabchikov (1988) soil±vegetation map. The

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Table 1 Areas and densities of phytomass, CWD, litter, and SOM of major ecosystems and land-use types of the FSU Ecosystem/land-use type

Area Mha

Phytomass Mg C/ha aboveground

Polar desert Tundra Coniferous (needleleaf) forest Hard deciduous forest Soft deciduous forest Cold meadows (partially tundra) Boreal and temperate meadows Dry temperate grasslands Desert/semidesert Peatlandsa Arable landb

8.1 226.0 610.7 35.1 168.5 112.1 297.9 113.0 169.0 164.8 227.0

Subtotal ± nonforest ecosystems Subtotal ± forest ecosystems Total

1317.9 814.3 2132.2

0.2 2.9 48.2 50.9 38.8 2.1 1.3 1.1 1.2 20.0 0.5

CWD Mg C/ha belowground 0.1 5.8 16.1 12.7 9.7 9.1 5.4 4.9 3.9 NA 2.3

aboveground 0.3 4.1 11.1 11.7 9.0 2.9 0.4 1.2 1.2 NA 0

Litter Mg C/ha

SOM Mg C/ha

NASOM Mg C/ha/yr

belowground 0.1 8.3 3.7 2.9 2.2 12.6 5.8 5.0 3.6 NA 0

0.2 4.7 15.3 7.2 7.2 0.6 0.7 1.3 0.5 16.9 0

50.0 200.0 120.0 160.0 120.0 150.0 185.0 292.0 45.0 1299.0 153.5

0.001 0.002 0.034 0.042 0.034 0.005 0.011 0.007 0.001 0.320 ÿ0.415

a

No comprehensive data exist on the below-ground phytomass and CWD for peatlands; these data entries were omitted. Also, CWD and litter was assumed to be negligible for arable land. b CWD and litter was assumed to be negligible for arable land.

rate of peat accumulation in FSU peatlands was based on estimates made by Botch et al. (1995). The research considered the rate of peat accumulation and the areal extent of every peatland zone of the FSU. To estimate the methane emissions from natural wetlands in the FSU, data on the distribution of peatlands by climatic zone (Botch et al., 1995) were combined with data on the rate of methane emissions from wetlands reported for the world (Matthews and Fung, 1987; Kolchugina and Vinson, 1994a,b). The main types of disturbances of non-forest ecosystems which result in C emissions to the atmosphere are agricultural activities and peat mining3. Agricultural activities are associated with water and wind erosion of soils and SOM mineralization. Some regions of the FSU are subjected to catastrophic soil erosion which removes large quantities of C with rich soil particles (e.g., Kretinin, 1992). However, these areas are limited. The C losses resulting from soil erosion of cultivated lands of the FSU were estimated as described in Kolchugina et al. (1995). The current loss of SOM due to mineralization within the arable land of the FSU was estimated based on the distribution of the main crops within the cultivated area and data on the rates of humus mineraliz3 Disturbances such as anthropogenic impact on tundra ecosystems were not considered herein; their e€ect might be substantial and requires special consideration. Fires of non-forest ecosystems (i.e., grasslands) were also ignored since it was assumed that the major C ¯ux from ®res is associated with forests. Peat ®res were considered under the forest ®re category.

ation±accumulation under di€erent crops (i.e., grain, industrial crops, potatoes, vegetables, fodder crops, perennial grasses, legume and cereal grasses, and clean fallow; the variation of SOM loss±gain is ÿ0.7 Mg C/ ha/yr to 1.0 Mg C/ha/yr) (data on ®le with the Dockuchaev Soil Institute, Moscow, provided by Rozhkov, 1992, personal communication; Kolchugina and Vinson, 1996). In the agricultural sector, three sources of methane emissions to the atmosphere were included, namely, methane emissions from (1) rice wetlands, (2) other waterlogged agricultural areas, and (3) livestock. The methane emissions from rice wetlands (0.67 Mha) and other waterlogged areas (4 Mha) were estimated using methodology similar to the methodology for natural wetlands as described above (Kolchugina and Vinson, 1996). The assessment of the methane emissions from livestock was based on data reported by the World Resource Institute (WRI, 1992). The anthropogenic impact on peatlands (e.g., peatland drainage for agricultural needs, peat mining, and usage of peat for horticulture and as a fuel) is substantial (Botch et al., 1995). In the 1970s and 1980s, peat production in the FSU was 200±230 Tg/yr (Tyuremnov, 1976; CIA, 1985; Pjavchenko, 1985). The C in peat extracted in the FSU corresponds to 112± 131 Tg C/yr (or 122 Tg C/yr on average) considering 56±57% C content (Botch et al., 1995). Masing et al. (1990) indicate that drainage of 10% of the world's peatlands may result in an additional ¯ux of 11 Pg C to the atmosphere. Many of peatland regions in the FSU are inaccessible. It is dicult to imagine that sig-

T.P. Kolchugina, T.S. Vinson / Environmental Science and Policy 1 (1998) 115±128

ni®cant peatland areas will be drained despite the fact that only 1% of FSU peatlands is protected (Botch, 1993). 3.2.2.2. Forest ecosystems. The rate at which C is sequestered or NEP depends on the successional stage of a forest ecosystem (forest age±structure) (Odum, 1953; Vorobyov, 1985) and upon previous and current land use. The NEP is maximum at some intermediate age, depending on forest type, e.g., 20 to 80 years for Russian forests (Vorobyov, 1986; Kolchugina and Vinson, 1993d). The NEP is the sum of NAPh, NACWD, and NASOM. Forest age±structure is closely connected with the history of past disturbances. Disturbance of Russian forests was especially intensive at the end of the 19th century and continued through the mid-20th century. This fact suggests that Russian forests could have a signi®cant area of young ecosystems and, therefore, substantial sequestration potential (Kolchugina and Vinson, 1995a). A complete record for forest age±class distribution and the average age is provided for 654 Mha of FSU forests (1988 Forest Inventory (Alimov et al., 1989)). The total forested areas of Russia and the FSU are 771 Mha and 814 Mha, or 15% and 20% greater, respectively, than the area for which the complete inventory is given (USSR State Forestry Committee, 1990). Young to maturing forests (which are most actively accumulating C) occupy approximately one-half of the total forested area. The mature/overmature category of forests includes all forests which are older than the age at which forests are eligible for main cuttings (i.e., industrial cuttings other than thinnings and sanitary cuttings) (Vorobyov, 1986). The mature/overmature forests include a variety of forest stands: (1) the relatively even-age forests which are approximately 80±100 years and older (for the soft deciduous forests the age of main cutting may be designated at a much earlier age, e.g., 60 years and younger), and (2) the unevenage very old primary forest ecosystems (Kolchugina and Vinson, 1995a) (`old' is a relative term and refers to the fact that these forests have reached the successional stage when they can be described as `climax' forests (Odum, 1953)). Russian forests may continue to sequester C beyond the age of technical maturity (Kozlovski and Pavlov, 1967; Kolchugina and Vinson, 1993d). The NEP of FSU forests was estimated as described in Kolchugina and Vinson (1995a) for Russian forests. The NEP of young to maturing forests was estimated from the net annual increment of stem wood (NIW) using conversion factors developed speci®cally for Russian forests (Isayev et al., 1993) to convert m3 of stem wood to Mg of total tree phytomass. The NIW of the young to maturing forests was estimated as the

119

di€erence of the growing stock (GS) densities of a given and preceding age±class, divided by the di€erence in age, and multiplied by the area of a given age± class. It was not possible to apply the methodology presented for young to maturing forests to estimate NAPh of mature/overmature forests. At the present time, precise data on the age±structure and the GS of mature/overmature forests are not available. Two di€erent approaches were used to estimate NAPh and NACWD of the mature/overmature forests (Kolchugina and Vinson, 1995a) Under approach I, the average age of the mature/overmature forests was estimated from data on the areal extent of forest age± classes, the average age of every age±class, and the average age of FSU forests (Alimov et al., 1989; USSR State Forestry Committee, 1990). Approach II was based on the estimation of the di€erence in the GS of the mature/overmature forests between 1983 and 1988 (Alimov et al., 1989) which re¯ects the dynamics of timber growth, main cuttings, and other disturbances which took place during the period considered. This approach assumes inventory procedures are consistent with time and that equivalent forest areas are inventoried. (Both approaches are described in detail in Kolchugina and Vinson, 1995a). The area and C ¯ux associated with forest ®res (direct and post®re C emissions) was based on (1) the area of forest ®res reported for the area of active ®re monitoring (which is 64% of the total forest area under State forest management), (2) the ratio of the areas of surface, intense crown, and ground ®res (Prilepo, 1988, Korovin, 1993), and (3) on a set of assumptions on the speci®c type of ®re frequency in di€erent forest stands (Kolchugina and Vinson, 1995a). The FSU timber production is equivalent to that for Russia, since most FSU forests are in Russia. The C emissions associated with logging were estimated from data on timber production in the FSU during the 1960s to 1980s (Vorobyov, 1986; Alimov et al., 1989), disposition of timber within timber product categories (WRI, 1992), and data on timber products decomposition presented by Melillo et al. (1988) (Kolchugina and Vinson, 1995a). Industrial pollution in the FSU is localized; in 1989, 0.070 Mha of FSU forests were killed. Approximately 0.039 Mha/yr of forests were killed by pests, diseases, and wild animals. The total area severely a€ected by pollutants, pests, and diseases is 3.0 Mha; an additional 0.14 Mha of forests were cleared for purposes other than commercial timber production (USSR Committee for the Protection of Nature, 1989; Izrael and Rovinskyi, 1990). The decrease in productivity of a€ected forest ecosystems was ignored herein, because this area is only 0.4% of Russian forests. Besides, for-

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ests a€ected by pollutants, pests, and diseases would be the primary target for ®res. Therefore, the productivity loss in forests a€ected by pollution, pests, and diseases may be accounted for in forest ®re emissions. Also, forests severely a€ected by insects, pollutants and diseases may be accounted for in the forest statistical data.

4. Results and discussion 4.1. Areas of major ecosystem types The areas of the major ecosystem types of the FSU are presented in Table 1. Forest ecosystems occupied over one-third of the total area studied. Kolchugina and Vinson (1993d), using the Ryabchikov (1988) map and data on percent forest cover, arrived at approximately the same result. The area of forest ecosystems considered herein (forests with an average level of stocking 0.3 and greater4) was slightly lower than estimates made by Gaston and Kolchugina (1995) (875 Mha) based on global vegetation index (GVI) images. The di€erence between Gaston and Kolchugina (1995) and the forested area presented herein corresponds to the area of understocked forest ecosystems (stocking lower than 0.3) (USSR State Forestry Committee, 1990) of the FSU which were not included in the present assessment (i.e., area of forest ecosystems and the C pools related to vegetation)5. The area of peatlands reported herein (Table 1) was twice the area estimated by Kolchugina and Vinson (1993a) who based their assessment on the Isachenko (1988) map which underrepresents peatlands of the tundra zone and the Far East. 4.2. C pools The variation in the densities (i.e., C pools per ha) of phytomass (0.3 to 63.6 Mg C/ha) between di€erent ecosystem were more signi®cant than variations in the densities of CWD (0.4±14.8 Mg C/ha), litter (0.2±16.9 Mg C/ha), and SOM of all ecosystems, except peatlands (50±292 Mg C/ha) (peat density is 1,299 Mg C/ ha, on average) (Table 1). Below-ground parts (i.e., live and dead roots and buried stems) are important components of all ecosystems, especially in herbaceous 4 The level of stocking used in FSU forest inventory is a relative value determined from the full stocking of a forest stand (stocking 1.0). Full stocking is characteristic to the local environmental conditions and is estimated based on the basal area (Vorobyov, 1986). 5 The C pool of SOM includes understocked forest ecosystems because the SOM C pool was estimated from the area of forest ecosystems determined using the Ryabchikov (1988) map and the average density of C characteristic to these ecosystems.

formations (i.e., grasslands, meadows, and tundra). In forest ecosystems, below-ground phytomass or CWD was 20±30% of the above-ground parts, whereas in meadows, grasslands, southern deserts, and arable land, below-ground phytomass was three to ®ve times greater than above-ground components. The CWD and below-ground ecosystem components should be considered in the accounting of the C pools of terrestrial ecosystems. (No comprehensive data exist on the below-ground phytomass and CWD for peatlands; in Table 1, these data entries were omitted. Also, CWD and litter was assumed to be negligible for arable land.) In the assessment of the C budget of a region with a number of di€erent ecosystems, it is important to correctly identify a vegetation type and assign proper values for the above- and below-ground phytomass and CWD components. While the soil types may di€er under the same vegetation types, the variations in their C content are less than the variations in the phytomass and CWD densities of di€erent vegetation types. The SOM represented the major C pool in all ecosystems, especially in polar deserts (98%), tundra (89%), meadows, grasslands, southern deserts/semideserts, peatlands, and arable land (81±98% of the total C pools) (Table 1). In forest ecosystems, the SOM C pool was 56±65% of the total ecosystem C stores. The phytomass C pool was 26±30% of the total forest ecosystems' C stores while in non-forest ecosystems, phytomass was 1.5±9% of the total non-forest ecosystems' C stores. The total phytomass C pool of FSU terrestrial ecosystems was estimated at approximately 60.4 Pg C with 41.2 Pg C and 19.2 Pg C above- and belowground, respectively (Table 2). The total CWD C pool of the FSU was estimated at 19.3 Pg C (10.4 and 8.9 Pg C above- and below-ground) or 30% of the total phytomass C pool. The total litter pool was estimated at 15.2 Pg C. The SOM C pool was estimated at 506 Pg C. A major contribution was provided by peatlands (214.1 Pg C). The total C store of the FSU was estimated at 601.1 Pg C with 84% allocated in SOM, 10% in phytomass and approximately 3% each in CWD and litter. Non-forest ecosystems contained 72% of the total C store of FSU terrestrial ecosystems allocated mainly in the SOM (95%). Forest ecosystems contained 28% of the total terrestrial C store of the FSU; their phytomass had 82% of the total phytomass C pool of the FSU. Ninety ®ve percent of FSU forests are in Russia. This study presents an assessment of C pools of terrestrial ecosystems for the territory of the FSU, including Russia. To the best of the authors' knowledge this is the only assessment related to the FSU. Several assessments were made of the Russian territory. For example, the phytomass of Russian forest ecosystems

T.P. Kolchugina, T.S. Vinson / Environmental Science and Policy 1 (1998) 115±128

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Table 2 Summary: Carbon pools, ¯uxes, net sequestration, and emissions Carbon Pools Phytomass Coarse woody debris (CWD) Litter Soil organic matter (SOM) Subtotal

Pg C

Sink Pg C/yr

Source (ÿPg C/yr)

60.4 19.3 15.2 506.0 601.1a

Fluxes Net primary productivity, including CH4 emissions from peatlands and agricultural sector Net Accumulation Non-forest ecosystems Peat Soil Subtotal Forest ecosystems Approach Phytomass CWD SOM (labile, stable) Subtotal Total

8.2

(0.033)

0.053 0.005 0.058 I 0.519 0.118 0.039 0.676 0.734

II 0.240 0.298 0.577b 0.635

Emissions Nonforest ecosystems Arable land (soil) Peat utilization Subtotal Forest ecosystems/disturbances Fires Logging Subtotal Industrial CO2 CH4 Subtotal Total Approach Net ¯ux (FSU) (including industrial emissions) Net ¯ux in terrestrial ecosystems Net ¯ux in forest ecosystems Net ¯ux in non-forest ecosystems

(0.097) (0.122) (0.219) (0.137) (0.115) (0.252) (1.020) (0.026) (1.046) (1.514) I 0.230 0.424

II 0.131 0.325b

I II (0.780±0.879) (0.194)

a

The discrepancy between the total pool and the sum of the constitutes is due to rounding. NEP of Russian forests is 0.662 Pg C/yr; net ¯ux of Russian forests is 0.410 Pg C/yr; Russian forests o€set 47 to 65% of national industrial emissions (0.7±0.8 Pg C/yr (Karaban et al., 1993)). b

was estimated by Isayev et al. (1993) (40 Pg C for 771 Mha of Russian forests) and Alexeyev and Birdsey (1994) (28 Pg C for 771 Mha of Russian forests). These estimates may be compared to the 44 Pg C in Russian forest phytomass incorporated in the present assessment (Kolchugina et al., 1992). The disagreement is possibly due to di€erent conversion factors used to estimate the C stock of forest ecosystems from the same source of data on the GS of commercial timber (USSR State Forestry Committee, 1990). There are no published data related to the assessment of the C stores of CWD and litter and below-

ground ecosystem components of the FSU and Russia. Shvidenko et al. (1995) consider the fact that forest ecosystems dieback may comprise 20±35% of the GS depending upon the age of forest ecosystems. The SOM C pool of the FSU estimated herein (506 Pg C for 2,132.2 Mha) agrees well with the assessment made by Rozhkov et al. (1996) for Russia (342 Pg C for 1,660.6 Mha) and was greater than the assessment for Russia made by Orlov and Biryukova (1995) (296 Pg C for 1,714.0 Mha). Because the area of the FSU includes such republics as the Ukraine with a vast extent of chernozem soils containing high quantities of

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C, the estimates of the C pools of the FSU should be greater than those made for Russia. Studies related to Russian peatlands by Orlov and Biryukova (1995) (113 Pg C in Russian peatlands), Vompersky et al. (1994) (139 Pg C in Russian peatlands), and Alexeyev and Birdsey (1994) (118 Pg C in commercial peatlands of Russia) obtained lower estimates for the peatland C pool than presented herein (i.e., 214 Pg C in FSU peatlands corresponding to approximately 210 Pg C in Russian peatlands). The assessment presented herein was based on Botch et al. (1995) who considered commercial and non-commercial peatlands of all natural zones of the FSU (164.8 Mha), including vast peatland areas in the tundra zone and the Russian Far-East often omitted on thematic maps and not included in the statistical data on commercial peat resources. The C pool of SOM of FSU arable lands (210 Mha) included in the present assessment was 32.4 Pg C with 19.0 Pg C in the arable land of Russia (Gaston et al., 1993; Kolchugina and Vinson, 1996). Orlov and Biryukova (1995) estimated the C pool of SOM in the arable land of Russia to be 27 Pg C, which is 30% higher than the present assessment. The disagreement with Orlov and Biryukova (1995) may be related to the fact that the assessment presented herein considered the current loss of approximately 24% from the precultivated level of C in the arable land due to mineralization of SOM (Gaston et al., 1993). 4.3. C ¯uxes 4.3.1. NPP The variation in NPP values per ha between di€erent ecosystem and land-use types did not exceed a factor of three (Table 1). The NPP is closely connected with the production of the green-assimilating parts of plants and was related to the normalized di€erence of vegetation index (NDVI), hence, a remote sensing technique was used to estimate the NPP of terrestrial ecosystems (e.g., Kimes et al., 1981; Tucker et al., 1981; Goward et al., 1987). When applying remote sensing techniques (e.g., NDVI data) it is important to consider that a signi®cant fraction of NPP may be allocated below-ground and that in vegetation formations containing woody plants, NPP is not equivalent to green assimilating parts and the growth of stems, branches and roots should be accounted for (Vinson and Kolchugina, 1993; Gaston and Kolchugina, 1995). NPP was only 4±9% of phytomass in forest ecosystems which indicates the presence of relatively longterm pools of plant mass (i.e. woody parts, above- and below-ground). In polar desert, tundra, and peatlands, and in cold meadow, NPP was approximately 20±40% (cold meadows) of the phytomass. In boreal and tem-

perate meadows and grasslands, NPP was equivalent to the phytomass. These ecosystems may not be associated with a long-term phytomass storage. The overall rate of C turnover in terrestrial ecosystems of the FSU (i.e., NPP) was 8.2 Pg C which is 1.4% of their combined C pool (Table 2). Of this amount, methane emissions accounted for 0.033 Pg C/ yr. 4.3.2. Net accumulation of C 4.3.2.1. Non-forest ecosystems. The NASOM of nonforest ecosystems (excluding arable land) varied by approximately an order of magnitude (Table 1) and was greatest in boreal and temperate meadows. Non-forest ecosystems (including peatlands) accounted for 58.1 Tg C/yr of NASOM. Arable land represented a source of 94.2 Tg C/yr (Kolchugina and Vinson, 1996) (or 0.42 Mg C/ha/yr, on average, Table 1). The total methane emissions (C± CH4) in the agricultural sector were estimated at 2.74 Tg C/yr (0.09 Tg C/yr, 0.45 Tg C/yr, and 2.2 Tg C/yr, for rice wetlands, other waterlogged areas, and livestock, respectively). Peat burning was a source of approximately 122 Tg C/yr. Considering disturbances, non-forest ecosystems were a source of 219 Tg C/yr to the atmosphere (with 96.9 Tg C/yr in agricultural sector) (Table 2). 4.3.2.2. Forest ecosystems. The estimates of NAPh and NACWD are based on the data reported for 654.3 Mha of FSU forests (Kolchugina and Vinson, 1995a). (Theses estimates were extrapolated to the entire FSU forested area (i.e., 814 Mha).) The NAPh, NACWD, and NASOM of young to maturing forests were estimated at 369.2 Tg C/yr, 91.0 Tg C/yr, and 48.5 Tg C/ yr, respectively. Using approach I, the NAPh and NACWD of mature to overmature FSU forests were estimated at 150.0 Tg C/yr and 27.1 Tg C/yr, respectively. Using approach II, the NAPh was estimated at ÿ128.2 Tg C/yr (loss) which was accompanied by formation of a CWD C pool of 206.9 Tg C/yr (i.e., NACWD (based on the estimate of Kolchugina and Vinson (1995a) for Russian forests). Approach I incorporated an assessment of the average age of this forest category which is dicult to estimate precisely. Approach I may overestimate the current rate of NEP. Approach II relied on a correct assessment of the GS of mature/overmature forests in 1983 and 1988. This procedure may result in an underestimate of NEP (Kolchugina and Vinson, 1995a). If the estimate of the NACWD of the mature/overmature forests is correct, the C pool of newly formed CWD will continue to decompose during the next half century. The inherited C emissions should be accounted for in future C budgets. The accumulation of SOM within the mature/

T.P. Kolchugina, T.S. Vinson / Environmental Science and Policy 1 (1998) 115±128

overmature forests was assumed to be balanced by decompositional processes. The total NAPh, of Russian forests estimated using approach I (492 Tg C/yr) and approach II (228 Tg C/ yr) (Kolchugina and Vinson, 1995a) was higher than the estimate of 184 Tg C/yr obtained by Isaev et al. (1995) (the same conversion factors were applied). Although the Isaev et al. approach was similar to approach I presented herein, Isaev et al. assumed the mature/overmature category of forests to be in equilibrium. Also, 49.7 Mha of maturing coniferous forests were estimated to lose C (NAPh was (ÿ)14.06 Tg C yrÿ1), whereas in the present study, the NAPh for this age category and an equivalent area was estimated at 33.5 Tg C yrÿ1 (Kolchugina and Vinson, 1995a). Maturing forests, by de®nition, are actively accumulating timber. Industrial cuttings are not allowed within this age category. At the present time it is not possible to refute either approach I or II. Consequently, the total NEP of FSU forests was estimated at 6262 50 Tg C/yr. This estimate relied on the results of the 1988 forest inventory. The inventory is conducted every decade for the forest area under State management (allows 210 to 15% error in the GS estimates (Kobak, 1993; personal communication)); over 51% of the forest zone area is subjected to a complete ground inventory and the remaining area is studied through aerial photography and limited ground measurements (Vorobyov, 1986). Another source of uncertainty related to the assessment of C pools and ¯uxes of forest ecosystems is introduced during conversion of forest inventory data (GS) to the total ecosystem plant mass. The present estimate re¯ects the quality and stocking of Russian forests and C losses due to the in¯uence of pests, diseases, and pollutants and possibly due to intermediate and crown ®res. Losses of phytomass and CWD burned during light ®res, CWD burned during intermediate and intense ®res, burned soils, and post®re emissions are not included in forest statistical accounting. An earlier estimate of NEP for FSU forests was 0.83 Pg C/yr (Kolchugina and Vinson, 1993d) based on the limited number of site speci®c and age-dependent NEP data extrapolated for the entire FSU forested area. Also, the NEP of FSU forests was estimated at 0.93 Pg C/yr from data on the mean annual increment and using a greater conversion factor of 0.53 for all forest types (Kolchugina and Vinson, 1993f). These overestimate NEP by 24 and 37%, respectively. Direct emissions from forest ®res in Russia (excluding ground ®res) were estimated at 78 Tg C/yr. The C e‚ux related to ground ®res was estimated at 15 Tg C/yr assuming that ground ®res are predominant in peatlands and that one-half of the peat layer is burned.

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Post®re C emissions (i.e., decomposition of killed trees) were estimated at 42 Tg C/yr. Post®re emissions associated with the soil surface were estimated at 2.4 Tg C/yr. However, waterlogging or a decrease in soil moisture as a result of the exposure to sun may slow the rate of organic matter decomposition. The total C emissions associated with forest ®res were estimated at 137 Tg C/yr (Kolchugina and Vinson, 1995a) which agrees very well with the assessment made by Shvidenko et al. (1995) (i.e., 150 Tg C/yr). Light surface ®res were 77% of the ®re area, but contributed only 16% to the total C emissions associated with forest ®res. Intermediate surface ®res represented 17% of the ®re area, but contributed 30% to the C emissions. Intense crown ®res were ®ve percent of the total ®re area, but contributed 42% to C emissions. Peatland ®res accounted for 0.2% of the ®re area, but contributed 11% to C emissions. The net C emissions from forest logging were estimated at 115 Tg C/yr. The decrease in productivity of a€ected forest ecosystems was ignored herein, because this area is only 0.4% of Russian forests. Besides, forests a€ected by pollutants, pests, and diseases would be the primary target for ®res. Therefore, the productivity loss in forests a€ected by pollution, pests, and diseases may be accounted for in forest ®re emissions. FSU forests represented a sink for 375 2 50 Tg C/yr (Table 2). Therefore, C store of forest ecosystems of Russia (161 Pg C: 44 Pg C of above- and belowground phytomass, 12 Pg C of above- and belowground CWD, and 105 Pg C of SOM and forest ¯oor (Kolchugina and Vinson, 1993f; Kolchugina et al., 1992)) was increasing by approximately 0.2%/yr. The estimate presented herein is close to Sedjo's estimate (Sedjo, 1992), and consistent with the assessment made by Bonan (1993) who predicted the existence of a substantial high-latitude C sink. The present estimate was much greater than estimates made by Melillo et al. (1988), Krankina and Dixon (1993), and Lelyakin et al. (1996) who did not consider the age±structure of Russian forests. The net sink for Russian forests exceeded the net sink estimated for Canadian forests (Apps et al., 1993; Kurz and Apps, 1993). 4.3.3. C ¯ux of forest ecosystems in the future In 1993, logging of Russian forest (and, by analogy, FSU forests) was at least 40% less than in 1988 (Russian Federal Forest Service, 1994) corresponding to 69 Tg C/yr. The percentage of the area of middleage forests increased in 1993 compared to 1988 (Table 3). The GS density of all age±classes in 1988 and 1993 was similar (less than 5% di€erence) and the total forested area did not change (Korovin, 1995, personal communication). Therefore, it is appropriate to assume that in 1993, the NEP of Russian forests was

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Table 3 Comparison of age±class distribution of Russian forests in 1988 and 1993 Year of inventory Percent of forested area Young Middle-age Maturing Mature/overmature Growing stock density (m3/ha) Young Middle-age Maturing Mature/overmature a b

1988a

1993b

18 23 10 49

18 26 10 46

26.4 111.6 147.8 139.0

29.0 106.3 148.9 139.4

Based on Alimov et al., 1989. Based on Russian Federal Forest Service, 1994.

the same as in 1988. No catastrophic ®res was reported in Russia in 1988±1993 period and, thus, C emissions associated with forest ®res in 1993 may be assumed at mid-late 1980s rate. In 1993, Russian forests represented a net sink for 0.42 Pg C/yr, i.e., the sink increased by 12% compared to 1988 estimate. 4.3.4. C ¯ux of FSU terrestrial ecosystems Terrestrial ecosystems of the FSU represented a sink for 181 250 Tg C/yr (non-forest ecosystems were a net source of 194 Pg C/yr, whereas forest ecosystems represented a sink for 3752 50 Pg C/yr). Only two to three percent of the organic matter accumulating annually in the terrestrial ecosystems of the FSU was sequestered in relatively long-term storage pools (i.e., phytomass, CWD, and SOM). The remaining C was returned to the atmosphere through natural decompositional processes (over 90%) and disturbances (5%). The total C storage of terrestrial ecosystems of the FSU was increasing by 0.03%/yr. FSU forests were o€setting 37±40% of FSU industrial emissions, whereas Russian forests were o€setting 47±65% of the national emissions (Table 2)6. Accumulation of forest phytomass represented the largest constituent of the total C sequestration in FSU terrestrial ecosystems, followed by the accumulation of CWD, peat, forest SOM, and SOM of non-forest ecosystems. The largest source of C was associated with forest ®res, followed by peat mining, logging, and agricultural activities. Overall, the C emissions from dis6 Industrial emissions were estimated at 1.020 Pg C/yr (Makarov and Bashmakov, 1990). Methane emissions from industrial processes (Kolchugina and Vinson, 1994a,b) amount to 0.026 Pg C/yr. Emissions of chloro¯uorocarbons are insigni®cant (WRI, 1992; Subak et al., 1993). Current industrial emissions in Russia are 0.7± 0.8 Pg C/yr (Karaban et al., 1993). Russian forests were o€setting at least one-half of the national industrial emissions.

turbances of non-forest ecosystems (i.e., agricultural activities and peat mining) was equivalent to the C emissions from disturbances of forest ecosystems (forest ®res and logging). The estimates of the imbalance between the C accumulation in the atmosphere, C industrial emissions, and the C uptake by the oceans vary from 0.3 Pg C/yr (Sarmiento et al., 1992; Orr, 1993) Ð 3.2 Pg C/yr (Tans et al., 1990; Orr, 1993). Depending upon which estimate is considered, FSU terrestrial ecosystems (which occupied approximately one-sixth of the land area of the Earth) were balancing the global C cycle or accounted for 8% of the high estimate. Under constant climate conditions and 1980s disturbance regimes, Russian forests (771 Mha) would still act as a net sink for approximately 0.4±0.5 Pg C/ yr of atmospheric C through the ®rst half of the 21st century (Kolchugina and Vinson, 1995a). However, ®res, low-quality planting (Shvidenko and Nilsson, 1994), low temperatures, and permafrost, and result in low survival rates of regenerating forests which means a reduced area of young to maturing forests in the future and a reduction of the sequestration potential of Russian forests. Consequently, the present assessment of the potential role of Russian and, hence, FSU forests in the future C cycle may be optimistic taking also into account a potential reduction in the area of young to maturing forests (Kolchugina and Vinson, 1995a). Peat mining may be substantially decreased in the future with the consumption of accessible peat resources. Therefore, the C ¯ux associated with peat mining may also decrease in the future. Agricultural activities most likely will not be subjected to any signi®cant change. If abandonment of cultivated lands occurs, the mineralization of SOM and, hence, C emissions would decrease. There is no indication that new lands will be involved in the agricultural production. Under changing climatic conditions, the area of FSU forests may remain at the same level. Coniferous forest may be replaced by mix-deciduous forests in the southern parts which would result in the increase in C sequestration and the decrease in the frequencies of forest ®res, hence the C sink associated with the FSU (Russian) forests may increase (Kolchugina and Vinson, 1993g). An assessment made by Lelyakin et al. (1996) predicts that the net sink associated with the Russian forests may double with climate warming especially in the Siberian middle and northern taiga and the Far-East. In northern areas, under a warming climate, 0.46± 0.72 Pg C/yr may be gradually released to the atmosphere, mainly due to the increase in CWD and litter decomposition (Kolchugina and Vinson, 1993b). The increased C e‚ux may be concurrently balanced by the C uptake by vegetation as a results of enhanced

T.P. Kolchugina, T.S. Vinson / Environmental Science and Policy 1 (1998) 115±128

productivity and forest migration to the north. However, the possibility exists that a lag between increased C e‚ux and uptake by vegetation may occur. The equilibrium of the C cycle may be reestablished, but at a higher rate of C turnover. Though climate warming may result in the degradation of permafrost, there is a possibility that it will not have a substantial in¯uence on future C emissions7. The dynamics of the net C ¯ux associated with the terrestrial ecosystems of the FSU may be presented as follows. In the late 1980s and through the middle of the 21st century, FSU forests will provide a sink for atmospheric C while non-forest ecosystems will be a smaller C source. The resulting C sink of terrestrial ecosystems is 0.25±0.3 Pg C/yr. With climate warming, FSU terrestrial ecosystems may make a transition to become a source of 0.2±0.5 Pg C/yr, which will be concurrently balanced by forest migration to the north and the increase in plant productivity. In the future, FSU terrestrial ecosystems may still represent a sink for atmospheric C if there would be a substantial amount of young to maturing forest ecosystems and forest logging would not increase dramatically.

5. Management options to increase C pools by policymakers The results presented herein may be used by policymakers to identify management strategies to increase terrestrial C stores and decrease C sources to the atmosphere. An analyses of Table 1 suggests that management of forest ecosystems would be the ®rst choice among options aimed at an increase in terrestrial C stores. For example, an increase of forest ecosystem phytomass by 10% would result in the additional accumulation of 6 Pg C in forest living vegetation and CWD. A number of management options which target the increase in the C pools of forest ecosystems was identi®ed in Russia (Kolchugina and Vinson, 1995b; Vinson et al., 1996). These options include reforestation and a€orestation of lands with suitable environmental conditions, enhancement of forest stand productivity, preservation of understory vegetation during harvest, an increase in stand age of the industrial harvest, an 7 The present depth of the active layer (i.e., layer of seasonal freezing and thawing) in mineral soils exceeds the depth of the organic horizons. In peatlands, thawing of the permafrost with an increase in the active layer could cause an additional mass of organic matter to become available for decomposition. However, thawing of the permafrost in peatlands may not be this extensive because of the low thermal conductivity and high latent heat capacity of peat (Kolchugina and Vinson, 1993b).

125

increase in the eciency of wood utilization, and enhanced ®re, pest and disease controls. Implementation of all these management practices to a full extent (which, in reality, may not be possible to achieve due to technical, economic, and political constraints in Russia and other republics of the FSU) would result in the increase in the forest phytomass, CWD, and litter C pools by 0.5%/yr (i.e., 0.39 Tg C/yr) (overall, approximately 374 Mha may be a€ected). Non-forest ecosystems (e.g., peatlands, agro±ecosystems, grasslands, etc.) should primarily be managed for maintenance of and an increase in the SOM C pools. However, the accumulation of SOM (speci®cally stable or protected SOM) is a slow process; the formation of the soil pro®le may require hundreds of years. Preservation of peatlands would avoid a C source to the atmosphere and result in the increase in peat stores by 1,300 Mg C/ha. The e€orts to manage non-forest ecosystems other than peatlands should be placed on the preservation of the SOM, i.e. avoidance of SOM loss through mineralization during agricultural activities and soil erosion. Management options in the agricultural sector, such as no-till management of cultivated lands, shelterbelt protection of the arable land and pastures, and alteration of conventional crop rotation practices, may increase the total SOM C pool by 0.1%/ yr (0.54 Pg C/yr; approximately 510 Mha of agricultural land should be a€ected (Kolchugina and Vinson, 1995b)). The agricultural management practices are also limited by technical, economic and political constraints and by the time period when the accumulation/conservation of SOM may occur (i.e., 10 to 60 yrs) (Gaston et al., 1993; Kolchugina and Vinson, 1995b).

6. Application of results to other studies The results of the assessment presented herein may be used in the assessments of the C pools of other regions of the world. Thus, the relationships between phytomass, CWD, litter, and SOM of boreal and temperate ecosystems of the FSU may be used in cases where some of the ecosystem components are known and some values are missing (i.e., the ratios between ecosystem components presented herein may be applied). Also, it is possible to assess if C pools of boreal and temperate regions which consider only selected components of the ecosystems (e.g., above-ground phytomass) are underestimated. Furthermore, the data presented may also be applied in studies using remote sensing data to properly assess the distribution of the below-ground and SOM C pools which may be easily

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omitted because they are not the part of the remotely sensed signals from the land surface. 7. Conclusion The total C store of the FSU was estimated at 601.1 Pg C with 84% allocated in SOM, 10% in phytomass and approximately 3% each in CWD and litter. While the soil types may di€er under the same vegetation types, soil C contents exhibit lower variability than C contents of ecosystem phytomass and CWD. Belowground phytomass and CWD (i.e., live and dead roots and buried stems) are important components of all ecosystems, especially in herbaceous formations (e.g., grasslands, meadows, and tundra). A major contribution to the SOM C pool was provided by peatlands (214.1 Pg C). Forest ecosystems contained 28% of the total terrestrial C store of the FSU; their phytomass had 82% of the total phytomass C pool of the FSU. Ninety ®ve percent of FSU forests is in Russia. The rate of C turnover in terrestrial ecosystems of the FSU (i.e., NPP) was 8.2 Pg C which is 1.4% of their combined C pool. Of this amount, methane emissions accounted for 0.033 Pg C/yr. Terrestrial ecosystems of the FSU represented a sink for 0.215 2 0.049 Pg C/yr (non-forest ecosystems were a net source of 0.194 Pg C/yr, whereas forest ecosystems represented a sink for 0.375 2 0.050 Pg C/yr). Only two to three percent of the organic matter accumulating annually in terrestrial ecosystems of the FSU was sequestered in relatively long-term storage pools (i.e., phytomass, CWD, and SOM). The remaining C was returned to the atmosphere through natural decompositional processes (over 90%) and disturbances (5%). The total C storage of terrestrial ecosystems of the FSU was increasing by 0.03%/yr. FSU forests were o€setting 37±40% of FSU industrial emissions, whereas Russian forests were o€setting 42±65% of the national emissions. Accumulation of forest phytomass represented the largest constituent of the total C sequestration in FSU terrestrial ecosystems, followed by the accumulation of CWD, peat, forest SOM, and SOM of non-forest ecosystems. The largest source of C was associated with forest ®res, followed by peat mining, logging, and agricultural activities. Overall, the C emissions from disturbances of non-forest ecosystems (i.e., agricultural activities and peat mining) was equivalent to the C emissions from disturbances of forest ecosystems (forest ®res and logging). FSU terrestrial ecosystems (which occupied approximately one-sixth of the land area of the Earth) were balancing the global C cycle or accounted for 8% of the high estimate. Management of forest ecosystems would be the ®rst choice among options aimed at the increase in the ter-

restrial C stores and minimization of C emissions associated with natural and anthropogenic disturbances. Implementation of a number of forest management practices to a full extent would result in an increase in the combined forest C pool by 0.5%/yr. Non-forest ecosystems should primarily be managed for maintenance of and an increase in the SOM C pools. Management options in the agricultural sector may increase the total SOM C pool by 0.1%/yr. Agricultural activities most likely will not be subjected to any signi®cant change. There is no indication that the C ¯ux associated with agricultural lands would change substantially. Preservation of peatlands would avoid a signi®cant C source to the atmosphere. The C ¯ux associated with peat mining may decrease in the future. Russian forests have a potential to serve as a net sink for atmospheric C through the ®rst half of the 21st century. However, natural disturbances, the presence of permafrost, and poor forest management practices may constrain forest regeneration leading to a decrease in the area of young to maturing forests; hence, the C sink potential of Russian forests may not be realized. With climate warming, FSU terrestrial ecosystems within the permafrost area may make a transition to become a source of 0.2±0.5 Pg C/yr, which may concurrently be balanced by forest migration to the north and an increase in plant productivity. In the future, FSU terrestrial ecosystems may still represent a sink for atmospheric C if there would be a substantial amount of young to maturing forest ecosystems and forest logging would not increase dramatically.

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