potential carbon sequestration in china’s forests

Environmental Science & Policy 6 (2003) 421–432

Potential carbon sequestration in China’s forests

Xiao-Quan Zhang∗, Deying XuInstitute of Forest Ecology and Environment, Chinese Academy of Forestry, Wan Shou Shan, Beijing 100091, China

Abstract

Forests are believed to be a major sink for atmospheric carbon dioxide. There are 158.94 million hectares (Mha) of forests in China,accounting for 16.5% of its land area. These extensive forests may play a vital role in the global carbon (C) cycle as well as making alarge contribution to the country’s economic and environmental well-being. Currently there is a trend towards increased development inthe forests. Hence, accounting for the role and potential of the forests in the global carbon budget is very important.

In this paper, we attempt to estimate the carbon emissions and sequestration by Chinese forests in 1990 and make projections for thefollowing 60 years based on three scenarios, i.e. “baseline”, “trend” and “planning”. A computer model F-CARBON 1.0, which takesinto account the different biomass density and growth rates for the forests in different age classes, the life time for biomass oxidation anddecomposition, and the change in soil carbon between harvesting and reforestation, was developed by the authors and used to make thecalculations and projections. Climate change is not modelled in this exercise.

We calculate that forests in China annually accumulate 118.1 Mt C in growth of trees and 18.4 Mt in forest soils, and release 38.9 Mt,resulting in a net sequestration of 97.6 Mt C, corresponding to 16.8% of the national CO2 emissions in 1990. From 1990 to 2050, soilcarbon accumulation was projected to increase slightly while carbon emissions increases by 73, 77 and 84%, and net carbon sequestrationincreases by−21, 52 and 90% for baseline, trend and planning scenarios, respectively. Carbon sequestration by China’s forests under theplanning scenario in 2000, 2010, 2030 and 2050 is approximately 20, 48, 111 and 142% higher than projected by the baseline scenario,and 8, 18, 34 and 26% higher than by the trend scenario, respectively. Over 9 Gt C is projected to accumulate in China’s forests from 1990to 2050 under the planning scenario, and this is 73 and 23% larger than projected for the baseline and trend scenarios, respectively. Duringthe period 2008–2012, Chinese forests are likely to have a net uptake of 667, 565 and 452 Mt C, respectively, for the planning, trend andbaseline scenarios. We conclude that China’s forests have a large potential for carbon sequestration through forest development. Sensitivityanalysis showed that the biggest uncertainty in the projection by the F-CARBON model came from the release coefficient of soil carbonbetween periods after harvesting and before reforestation.© 2003 Elsevier Ltd. All rights reserved.

Keywords: Chinese forests; Carbon uptake projections; F-CARBON model

1. Introduction

Global change has been widely acknowledged by gov-ernments at the Rio Summit in 1992 and at Kyoto in 1997.Deforestation, especially in the tropics was believed to bethe second largest source of rising atmospheric CO2 con-centration, behind fossil fuel burning. On the other hand,carbon (C) sequestration by growing forests has been shownto be a cost-effective option for mitigation of global climaticchange (e.g.Andrasko, 1990; Brown et al., 1996). The inter-governmental panel on climate change (IPCC) considered itpossible to sequester 60–87 Gt C by global afforestation andreforestation activities in the period 1995–2050, account-ing for 12–15% of projected fossil fuel C emissions over

∗ Corresponding author. Tel.:+86-10-628-89512;fax: +86-10-628-81937.

E-mail address: [email protected] (X.-Q. Zhang).

the same period (Brown et al., 1996). Individual countriesare claiming forest carbon sinks to offset some of their re-quirement to cut fossil fuel emissions (Cannell, 1999). It istherefore necessary to estimate clearly and to understand thepotential role of forests in the alleviation of global warm-ing. As the climate change debate advances, policy makersalso require more accurate information on the current andprojected carbon emissions and sequestration in forests.

A number of carbon sinks/sources for the forest sectorhave been estimated and projected at global, national and/orregional scales under several mitigation scenarios (e.g.Haoet al., 1990; Houghton, 1990; Kauppi and Tomppo, 1993;Cannell and Milne, 1995; Cannell et al., 1999; Rodriguez,1994; Schroeder and Winjum, 1995a, 1995b; Kokorin et al.,1996; Borjesson et al., 1997, Watson et al., 2000). Therehave always been uncertainties in all of the estimates as aresult of different definitions and methodologies and of thedifficulties associated with obtaining accurate data.

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422 X.-Q. Zhang, D. Xu / Environmental Science & Policy 6 (2003) 421–432

Few studies have estimated the carbon stocks and bud-get of China’s forests and major forest ecosystems (e.g.Liuet al., 2000; Xu et al., 2001; Zhou et al., 2000). Fang et al.(2001)used forest inventory data to estimate changes in for-est biomass carbon storage of China over the past 50 years.They demonstrated that China’s carbon storage in living for-est biomass has increased since the 1980s. This is an im-portant conclusion, although the methodology described isquestionable (Zhang and Xu, 2002). The disadvantages ofprevious studies are the followings: (1) certain tree cropsthat occupy a large area of China and have increased quickly,including orchards and bamboo stands, were mostly not in-cluded (e.g.Fang et al., 2001; Liu et al., 2000; Zhou et al.,2000). These wooded areas contain a substantial carbonstock and should not be ignored; (2) the soil carbon, a majorcomponent of carbon stock and flux in forest ecosystems,was not considered; (3) differences amongst carbon stocksand growth rate in different age classes were not identifiedand taken into account. AlthoughFang et al. (2001)men-tioned the carbon stocks of different age classes in theirmethodology, these were not taken into account in the cal-culations (Zhang and Xu, 2002); (4) the future forest carbonbudget in China was inadequately projected. AlthoughXu(1992, 1995, 1999)estimated the current and future carbonbudget of forests in China, the estimates were mainly basedon a relatively out-of-date forestry plan (CMOF, 1995a) andforest data (CMOF, 1983, 1989a, 1994a). The most recentforest data (CMOF, 2000a) show that there has been a largerthan expected increase in the area of forest in China in thepast 10 years. Moreover in the new forestry plan issued byCMOF (1999a), the future area of forest is expected to belarger than was anticipated in the older plan. It is thereforenecessary to re-estimate the current forest budget and thefuture potential carbon absorption of China’s forests, usingthe newest data, the most recent forestry plan and the cur-rent, improved methodology.

In this paper, we describe the historic and current forestresources and the most recent long-term forestry plan, andwe make estimates of the carbon uptake, emissions and bud-get for China’s forests in the base year 1990 and in subse-quent years up to 2050 under several scenarios. To realizethis objective, the F-CARBON 1.0 model was conceived anddeveloped by authors and used in the calculations.

2. Historic changes, current situation and future planfor forests in China

2.1. Forests in China

According to the latest forest inventory, made during1994–1998 (CMOF, 2000a), there are 263.29 Mha of landmanaged by forestry sectors, including 158.94 Mha offorested land (20.22 Mha of tree crops and orchards and4.36 Mha of bamboo stands were all included as forestedland); 7.22 Mha of open forest land; 35.32 Mha of shrub

woodland; 57.08 Mha of wasteland; 0.12 Mha of nurseryland; and 4.62 Mha of plantation in which the canopy hasnot yet closed. Although the land area under forest cover isone of the largest in the world, it accounts for only 16.55%of the land area of China. The forested area per capita isonly 0.13 h, which is much less than the global average of0.65 h per capita. The volume of the standing stock of treesis estimated to be 12,490 Mm3, of which 11,270 Mm3 isin forests. The average forest stock per capita in China isestimated at 9.03 m3, only about 14% of the world aver-age of 64.63 m3 (FAO, 2003). The forest stock per hectare(70.9 m3 ha−1) is also much less than the world average(100 m3 ha−1, FAO, 2003). Furthermore, China has about4.2% of the global forest area, but supports the require-ments of more than 20% of the world population, and hasthe responsibility for protecting the eco-environment of 7%of the world’s land. There are 46. 7 Mha of plantations witha standing volume of up to 1010 Mm3, which is the largestof any country in the world (CMOF, 2000a; FAO, 2003).

Both temperature and precipitation influence the distribu-tion of forests in China. Based on temperature, China ex-tends from the temperate zone through warm-temperate andsub-tropical zones to the tropical zone, and on the basis ofprecipitation passing from humid in the southeast throughsemi-humid and semi-arid to the arid zone in the northwest,where there are isohyets of 600 and 400 mm. Accordingly,the forests are mainly in the northeast, the south and thesouthwest parts of the country where the areas of forest makeup 21, 35 and 21%, respectively, of the national total landarea (CMOF, 1994a).

2.2. Historic changes of forests in China

Forest inventories were initially carried out in some re-gions 1950–1962 and the government then began to publishnational forest data. However, the data are thought to havelarge uncertainties as a result of incompleteness of the ar-eas investigated and the poor methodology (CMOF, 1983).Since 1973 there have been five periods of national forestinventory: 1973–1976, 1977–1981, 1984–1988, 1989–1993and 1994–1998. The forest inventory systems have grad-ually been improved. Permanent plots for periodic forestinventories numbered 140,000 in the period 1977–1981;255,000 in 1984–1988; 227,000 in 1989–1993 and 184,000in 1994–1998. There were also about 100,000 interpretationplots from aerial photographs and satellite images during theperiods 1989–1993 and 1994–1998 (CMOF, 1983, 1989a,1994a, 2000a). The statement inFang et al. (2001)that allinventories except that from 1949 were compiled from morethan 250,000 plots (160,000 permanent plots plus 90,000temporary sample plots) was somewhat inaccurate.

The results of the five most recent forest inventories arepresented inTable 1 which shows that the area of forestdecreased in the 1970s but has tended to increase more andmore rapidly since the early 1980s. For example, there wasan average annual increase of 1.34 Mha over the period

X.-Q. Zhang, D. Xu / Environmental Science & Policy 6 (2003) 421–432 423

Table 1Historic changes of forests in China

Inventoryperiod

Area (Mha) Forestcoverage (%)

Stock volume (Mm3) Increment(Mm3 per year)

Consumption(Mm3 per year)

Data sources

Forests Plantations Growing stock Forest stock

1973–1976a 121.86 28.20 12.70 9530 8700 220 196 CMOF (1995d)1977–1981a 115.27 27.81 12.00 10261 9028 275 294 CMOF (1983)1984–1988a 124.65 31.01 12.98 11150 9595 329 344 CMOF (1989a)1989–1993a 133.70 33.79 13.92 11785 10137 419 320 CMOF (1994a)1989–1993b,c 145.19 36.42 15.121994–1998b 158.94 46.67 16.55 12490 11270 CMOF (2000a)

a The definition of forest is based on a canopy density with a threshold value of 0.3.b With a canopy threshold value of 0.2.c Announced by CMOF in 1999 (in Chinese).

between inventories in 1977–1981 and 1984–1988, of1.81 Mha over the period between 1984 and 1988 and 1989and 1993, and of 2.75 Mha over the period between 1989and 1993 and 1994 and 1998. The increases can mainly beattributed to large-scale afforestation and/or reforestationcampaigns especially in the last two decades of the 20thcentury. More than 46.7 Mha of plantations were establishedbetween 1949 and 1998. In the period from 1980 to 1988,the area of newly planted forests increased by 0.479 Mhaper year, and in the period from 1989 to 1993, it increasedat a rate of 2.2 Mha per year, more than four times the previ-ous rate (CMOF, 1994a). On average, the area of plantationincreased annually by 2.05 Mha over the period betweeninventories in 1989–1993 and 1994–1998, accounting for75% of the increase in the total area of forest (Table 1).

The consumption of forest resources was larger than thenet increment before 1989 and this has reversed since theend of the 1980s.

2.3. Forestry planning

Several mid- and/or long-term plans for forestry devel-opment have been put forward by the Chinese Ministryof Forestry (CMOF) in the recent years (CMOF, 1995a,b,1996a, 1999a; Li, 1996). Major goals and activities of theplans are listed inTable 2. The goals in earlier plans werelower than the latest one. In the National Planning of Eco-logical Re-establishment in China: Forestry Aspect, thereare three periodic goals (CMOF, 1999a):

(1) 1999–2010: 96.88 Mha of existing natural forest are tobe effectively protected and restored. Five megahectaresof farmlands are to be converted to forest. Areas offorests, nature reserves and forest parks are to increaseby 27.32, 18.88 and 11.8 Mha, respectively. Forest areasand nature reserve are to account for 19.4 and 8.33%,respectively, of the land area. The timber output is to bereduced by 16 Mm3. Farmland areas with forest wind-break belts are to increase by 13 Mha. Land subject tosoil erosion and to water loss is to decrease by 37 Mha.In addition, 22.7 Mha desertified land is to be broughtunder control.

(2) 2011–2030: Areas of forests, nature reserves and forestparks are intended to increase by 46, 35 and 9 Mha,respectively. The areas of forests and nature reserves areto increase to 24.2 and 12%. An additional 60 Mha ofland subject to soil erosion and water loss, and 27 Mhaof desertified land are to come under biological control.

(3) 2031–2050: Forest area should increase by 17.28 Mhabringing forest coverage up to about 26%. An additional22 Mha of land subject to soil erosion and water loss,and 11 Mha of desertified lands are to be controlled bybiological measures.

To realize these goals, 16 key projects will be imple-mented, including natural forest protection projects, wildlifeand plant conservation and forest park establishment, trop-ical forest conservation, conversion of farmland to forest,combating desertification, three-north (northeast, north andnorthwest of China) shelter-belt afforestation projects, etc.(CMOF, 1999a).

3. Methodology

3.1. F-CARBON model 1.0

A computer model, F-CARBON 1.0 developed by theauthors to calculate the carbon budget of China’s forests,has been described in detail byXu and Zhang (2002)andcan be summarized as follows.

Forest types, areas, standing volume, biomass density,growth rate, wasteland areas suitable for forest growth andother bio-physical parameters in different regions of Chinavary greatly. In general forest biomass and productivity de-crease from south to north and from east to west across thecountry (Feng et al., 1999). The accuracy of estimation of theforest greenhouse gas (GHG) budget for entire China can beimproved when forests are analysed in smaller units, becausethis reduces heterogeneity of growth rates and other vari-ables. Thus, in the model, forests in China are divided intofive regions to minimise errors in the calculations, i.e. thenortheastern, southeastern, southwestern, northern & north-western China and Tibet, as shown inFig. 1.


Table 2Major activities and goals of the China forestry plan

Plans Activities and goals

National Planning of Ecological Re-establishment in China:Forestry Aspect (CMOF, 1999a)Newly-added forested area 27.32 Mha from 1999 to 2010, 46.00 Mha from 2011 to 2030 and

17.28 Mha from 2031 to 2050Forest coveragea Up to 19.4% in 2010, 24.2% in 2030 and 26.0% in 2050Newly-added area of nature reserve 18.88 Mha from 1999 to 2010 and 35.00 Mha from 2011 to 2030)Area of nature reserves Up to 80 Mha in 2010 and 115 Mha in 2030Newly-added area of forest parks 11.8 Mha from 1999 to 2010 and 9 Mha from 2011 to 2030Conversion farmland to forested land 1.2 Mha from 1999 to 2000, 23.714 Mha from 2001 to 2005 and

5 Mha from 1999 to 2010Reduction in timber output 12.361 Mm3 from 1998 to 2000 and 3.64 Mm3 from 2001 to 2003Area of natural forests under protection Up to 96.877 MhaNewly-added farmland with forest windbreak belts 13 Mha from 1999 to 2010

Forestry Action Plan for China’s Agenda 21 (CMOF, 1995a)Newly-added forested area 9.98 Mha from 1996 to 2000 and 1900 Mha from 2001 to 2010Forest coverageb Up to 15–16% in 2000 and 17% in 2010Area of nature reserves Up to 60.59, 70.68 and 80 Mha, respectively in 2000, 2010 and 2050Area of farmland with forest windbreak belts Up to 43.99 and 59.06 Mha, respectively in 2000 and 2030Area of forest parks Up to 9 and 19 Mha in 2000 and 2010, respectively

The 9th Five-Year-Plan and 2010 Goals for China Forestry(CMOF, 1995b)Forest coverageb Up to 15.5% in 2000 and 17.5% in 2010

Forestry Strategy toward 21st Century (Li, 1996)Forested areab Up to 160.5 Mha in 2010Forest coverageb Up to 16.1–17.4 in 2010

A Report on China Forest Resources (CMOF, 1996a)Forest coverageb 15–16% in 2000 and 17% in 2010

a The definition of forest is based on a canopy density with a threshold value of 0.3.b With a canopy threshold value of 0.2.

Forest-related bio-physical parameters also vary amongstdifferent age classes of the same forest type. TheF-CARBON 1.0 model incorporates five age classes ofstands, and the changes of parameters with ages, to account

Fig. 1. Zonation of China for calculation of carbon sequestration.

for the variation in biomass densities and growth rates ofthe different age classes. The five age classes are youngstand, mid-age stand, near-mature stand, mature stand andover-mature stand.


The model is composed of five sub-models, including for-est area, biomass accumulation, carbon emission, soil car-bon and carbon budget. The forest area submodel estimatedforest areas for each age class in subsequent years, in eachregion, based on the areas in base year (CMOF, 1994a),the annual age class conversion ratio, felling area and ac-tual/planned forest development. It was assumed that 5–12%of forests in one age class move automatically to a higherage class each year, depending on the average rotation peri-ods in the different regions. The felling area for each regionwas calculated using data for harvested volume and stand-ing volume of mature stands. These data are available foreach province from the forestry statistical year book (CMOF,1988, 1989b, 1990, 1991, 1992, 1993, 1994b, 1995c, 1996b,1997, 1998, 1999b, 2000b, 2001). Harvesting was assumedto have taken place mainly in over-mature stands, followedby mature stands, after all over-mature stands had been har-vested.

The biomass carbon accumulation submodel estimatedannual removal of carbon from the atmosphere by livingbiomass in the forests from volume growth rates, wooddensities, carbon densities, expansion factors relating stembiomass to above-ground biomass and total biomass andother biological parameters, for each age class, in each re-gion. Volume growth rate was derived from the nationalforestry inventory (CMOF, 1983, 1989a, 1994a, 2000a). Theimpacts of historic and future CO2 concentration and cli-mate change on growth rate was not addressed in the presentsimulations.

The carbon emission sub-model includes on-site burningof slash, oxidation resulting from timber utilization and de-composition of forest litter and slash left after burning. Insubtropical and tropical regions, slash and burn is a commonpractice for site preparation prior to reforestation. In tem-perate regions, the incidence of on-site burning is relativelysmall. Carbon emission from on-site burning was estimatedon the basis of harvested area, standing volume of harvestedstands (over-mature and/or mature), wood density, carbondensity, burnt slash biomass left on-site and other biologicalparameters, for each region.

Depending on the end use, harvested wood has differentlifetimes that influence periodicity of oxidation and the car-bon emission.Xue and Zhu (1990)classified 36 main typesof product from wood harvested in China. In this model,they were grouped into the following eight categories de-pending on the lifetime of the products: (1) wood usedin underground mines: 200 years; (2) veneer, building: 80years; (3) farm houses and furniture: 50 years; (4) machin-ery, ship and transportation tools: 20 years; (5) sleepers,poles, farm tools, coffins: 10 years; (6) packing: 5 years; (7)mushroom production: 3 years; (8) pulp, fuelwood: 2 years.The total carbon emission from commercial timber use wasestimated from harvested biomass, and the proportion andlifetime of each product category. It was assumed that 70%of the standing volume is used as commercial timber andthat timber is oxidized linearly over its lifetime. The carbon

emission resulting from decomposition of forest litter andslash left after burning was estimated assuming that theydecompose exponentially (Row and Phelps, 1996). Theparameter in the exponential decomposition equation wasestimated on the basis of more than 50 published detritusdecomposition studies in China.

In the soil carbon sub-model, the net change of soil carbonis the difference between soil carbon release and input. Soilcarbon release each year from felled areas is assumed to be aproportion of the original soil carbon stock. Soil carbon inputis calculated from below-ground biomass left on-site andannual above-ground litterfall. The latter is a proportion ofabove-ground biomass estimated from the biomass databaseand the annual litterfall database.

Finally, the carbon budget for the forests of China wasestimated as the sum of all carbon accumulation minus thetotal carbon emissions.

The base year recorded is 1990. However, in order tocalculate the emissions in 1990 and to eliminate errors overthe first few years, the model was initialised in 1984 and runsubsequently in 1 year steps.

3.2. Parameterization

Estimates of parameters and data value used in the cal-culations were mainly based on forest inventories for theperiods 1973–1976 (CMOF, 1995d), 1977–1981 (CMOF,1983), 1984–1988 (CMOF, 1989a), 1989–1993 (CMOF,1994a) and 1994–1998 (CMOF, 2000a). Other parameterswere taken from the forestry statistical year books (CMOF,1988, 1989b, 1990, 1991, 1992, 1993, 1994b, 1995c, 1996b,1997, 1998, 1999b, 2000b, 2001), the long-term forestryplan (CMOF, 1999a) and established databases based onChinese ecological research reports in China. A summaryof the parameters used in the model is given inTable 3.

3.3. Scenarios

Three forest scenarios were evaluated:

(1) Baseline: In this scenario it is assumed that the forestedarea remains unchanged, i.e. there is no afforestation ofwasteland, and the harvested area remains at the levelof the base year, but felled areas are reforested within 3years after harvest.

(2) Trend: In this scenario the forested area after thebase year 1990 is estimated from historic changes ofthe forest area, specifically from the inventory period1973–1977 to 1989–1993. The increase in area is as-sumed to result from afforestation of wasteland. Theharvested area remains at the level of the base year, butfelled areas are reforested within the years after harvest.

(3) Planning: This scenario was based on the long-termforestry plan issued by the Chinese Ministry of Forestry(CMOF, 1999a).

The goals of the three scenarios are listed inTable 4.


Table 3Parameters for the calculation of carbon budget in relation to forests in China

Parameters Regions

Northeast Southwest Southeast North &Northwest

Tibet

Forest area at base year (Mha)a 28.28 24.83 47.03 31.92 7.23Waste land available for forest development (Mha)a 9.31 35.52 27.81 48.91 4.44Harvested area at base year (Mha)a 0.51 0.32 1.35 0.45 0.0004Carbon density(t C t−1)b 0.45 0.45 0.45 0.45 0.45Wood density (t m−3) 0.44 0.48 0.38 0.40 0.51Ratio of above-ground biomass to stem biomassc 1.75 1.67 1.58 1.69 1.71Total to above-ground biomass ratioc 1.34 1.29 1.23 1.36 1.35Forest soil carbon (t ha−1)d 163.80 167.10 73.20 159.90 205.40Annual growth (m3 ha−1 per year)a 2.91 3.34 2.81 2.91 2.48Relative growth factors for five age classes 0.70 (young) 1.15 (mid-aged) 1.20 (near-mature) 1.15 (mature) 0.8 (over-mature)

Area weighting factors for five age classesa

Young stand 0.3391 0.3360 0.5067 0.3577 0.0453Mid-aged 0.3893 0.2621 0.3456 0.3264 0.0721Near-mature 0.0953 0.1195 0.0891 0.1330 0.0793Mature 0.1309 0.1536 0.0434 0.1200 0.3815Over-mature 0.0456 0.1288 0.0152 0.0630 0.4218

Volume weighting factors for five age classesa

Young stand 0.1312 0.0938 0.2010 0.1112 0.0058Mid-aged 0.3950 0.1822 0.4783 0.3202 0.0315Near-mature 0.1463 0.1275 0.1691 0.1776 0.0499Mature 0.2378 0.2669 0.1119 0.2283 0.3601Over-mature 0.0896 0.3296 0.0396 0.1626 0.5527

Litter decomposition parametere 0.10 0.30 0.30 0.20 0.10Burnt proportion in slash and burn practice (%) 10 30 70 10 10Proportion of litterfall in above-ground biomass (%)f 2.5 1.4 1.3 3.3 1.0Rotation (year) 80 40 30 60 100Proportion of area of lower age class to

higher age class (%)6 10 12 8 5

a Calculated based on forestry inventory during 1984–1988 and 1989–1993 (CMOF, 1989a, 1994a).b Levine et al. (1995), Olson et al. (1983).c Estimated based on biomass database with about 600 biomass measurements in China.d Average organic carbon in forest soils, with 65 samples for northern China and 77 for north and northwestern China.e Estimated based on database of debris decomposition in Chinaf Estimated based on database of annual litterfall and biomass in China.

Table 4Goals for three scenariosa

Scenarios Items 1990b 2000 2010 2030 2050

Baseline Newly-added forested areac

Forested areac 139.29 139.29 139.29 139.29 139.29Forest coverage (%) 14.51 14.51 14.51 14.51 14.51

Historic trend scenario Newly-added forested areac 8.40 12.00 24.00 24.00Forested areac 139.29 153.59 165.59 189.59 213.59Forest coverage (%) 14.51 15.99 17.24 19.74 22.24

Governmental plan scenario Newly-added forested areac 24.19 23.00 46.00 17.28Forested areac 139.29 163.48 186.48 232.48 249.76Forest coverage (%) 14.51 17.02 19.42 24.21 26.01Reduction in timber outputd 4.12 Mm3 from 1998 to 2000 and 121 Mm3 from 2001 to 2003

a Based on 0.2 threshold of canopy density.b Calculated based on forestry inventory during 1984–1988 and 1989–1993 (CMOF, 1989a, 1994a).c In million hectare (Mha).d In million cubic meter (Mm3).


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Fig. 2. Forest carbon budget for the planning scenario.

4. Results

4.1. Sequestration in the base year 1990

With an area of 139.29 Mha, China’s forests in 1990 hada carbon stock of 21,434 Mt C, with an average carbon den-sity of 153.86 t C ha−1. The net carbon uptake in 1990 was97.61 Mt C per year. This was the net result of 118.10 Mt Cper year of tree growth and 18.41 Mt C per year of soil carbonaccumulation, less 38.9 Mt C per year of emissions result-ing from biomass burning and decomposition. In 1990, totalemissions from the industrial and energy sectors amountedto 581.5 Mt C (RTCCCCS, 1999), and thus forest carbon se-questration accounted for 16.8% of the national emissions.

4.2. Sequestration projections from 1990 to 2050

The projected carbon emissions, biomass carbon accumu-lation, soil carbon changes, carbon emissions and net budgetof China’s forests, for the three scenarios, for the period from1990 to 2050, calculated by the F-CARBON model 1.0, areillustrated in Figs. 2–4. There were significant differences

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Fig. 3. Forest carbon budget for the trend scenario.

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Fig. 4. Forest carbon budget for the baseline scenario.

in the carbon sequestration among the three scenarios. Car-bon uptake through biomass growth increases rapidly in theplanning scenario, particularly before 2030 (Fig. 2). In thetrend scenario, it increased linearly but the rate of increaserate was less than for the planning scenario before 2030, andhigher than for the planning scenario after 2030 (Fig. 3).For the baseline scenario, the carbon uptake in forest growthincreased slightly before 2010 and decreased afterwards,because the proportion of mature and over-mature forestsincreased and growth rate decreased over the time (Fig. 4).Soil carbon accumulation is predited to increase slightlywhile carbon emissions increase significantly by 73–84%for the baseline, trend and planning scenarios, respectively,and the difference among scenarios was not significant.

The dynamics of net carbon uptake by China’s forests fol-low carbon uptake through biomass growth, and the differ-ences among the three scenarios were mainly the result ofthe different amount of biomass growth. From 1990 to 2050,the net carbon sequestration by China’s forests increased by90.4 and 51.5% in the planning and trend scenarios, respec-tively, while it decreased by 21.4% in the baseline scenario(Figs. 3 and 4). The net carbon sequestration relative to thetotal CO2 emissions (“Business As Usual” scenario) by theindustrial and energy sectors decreased in all the three sce-narios, although the decrease was most in the baseline andleast in the planning scenario (Fig. 5).

Comparison of net carbon sequestration for the three sce-narios is shown in Fig. 6. Forest carbon sequestration for theplanning scenario in 2000, 2010, 2030 and 2050 are calcu-lated as 120, 48, 111 and 142% larger than for the baselinescenario, and 8, 18, 34 and 26% larger than for the trendscenario, respectively.

Fig. 7 shows accumulated carbon sequestration for thethree scenarios and the additional accumulation by theplanning and trend scenarios over and above the baselinescenario. 9106.6 Mt C is predicted to accumulate in theforests from 1990 to 2050 in the planning scenario. This is72.6 and 22.6% larger than the figures for the baseline andtrend scenario, respectively. As a result, are estimated to be26.7–30.5 Gt C depending on the model (but without taking


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Fig. 5. Percentages of net carbon uptakes by Chinese forests relative tocarbon emission from the industrial and energy sectors.

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Fig. 7. Accumulated net carbon uptakes by China’s forests from 1990 to 2050.

climate change into account). During the first Kyoto Com-mitment Period 2008–2012, the corresponding estimates ofnet uptake are 667, 565 and 452 Mt C, respectively, for theplanning, trend and baseline scenarios.

5. Discussion

5.1. Sequestration in the base year 1990

The forested area in China in 1990 accounted for 3.34% ofthe world forest area (4170 Mha, Watson et al., 2000), but itscarbon stock (21,434 Mt C) amounted to only 1.87% of thatin the global forests (1,146,000 Mt C, Watson et al., 2000).The carbon density of China’s forests is much less than theglobal forests average (274.8 t C ha−1, Watson et al., 2000).Our estimate of carbon stock was less than the 28,116 Mt Cestimated by Zhou et al. (2000), probably because of muchhigher soil carbon density used in their calculation, but ourfigure was in agreement with the estimation by Xu (1992).

The estimated sequestration by China’s forests in 1990was 86.27 Mt C per year in the China Climate ChangeCountry Study (RTCCCCS, 1999), and 74.4 Mt C per year(net emission from forests) in the Asian Least-cost Green-house Gas Abatement Strategy (ALGAS), derived by theIPCC standard method (Xu, 1999). In ALGAS, the estimatedemission (47.3 Mt C per year) was higher, and tree growth(110.8 Mt C per year) and soil carbon accumulation (8.6 MtC per year) were lower than in the present study, resulting ina smaller net sequestration. The percentage forest sequestra-tion relative to the total CO2 emission from China’s indus-trial and energy sectors (16.8% in 1990) was higher than inthe USA (9%), Japan (7%), Germany (3%), and most other


Annex I countries, other than those with sparse industry,such as New Zealand (81%), or very extensive forests, suchas Sweden (62%) and Finland (56%) (UNFCCC, 1997).

5.2. Sequestration projections

Fang et al. (2001) estimated that the carbon accumula-tion rates during the periods 1989–1993 and 1994–1998 are35 and 26 Mt C per year, figures that are much lower thanour estimations. There are likely to be at least three rea-sons for this: (1) Fang et al. (2001) did not include thecarbon accumulation in soils, which accounted for about20% of the net sequestration in this study; (2) we find thatthere are 145.19 and 158.94 Mha forests during the peri-ods 1989–1993 and 1994–1998, respectively, but Fang et al.(2001) used figures of only 108.63 and 105.82 Mha, respec-tively, so that about one-third of forests were ignored. Theignored forests are bamboo stands, and economic tree cropsand forests in Taiwan and part of Tibet; (3) the calculationsby Fang et al. (2001) were based only on stand volume ofthe forests whereas we have used growth rate of stand vol-ume, as well as emissions resulting from decomposition anddecay of wood and litter and from site burning.

The sequestration by China’s forests from 1990 to 2030was also projected in the China Climate Change CountryStudy (RTCCCCS, 1999) and the ALGAS project under sev-eral scenarios (Xu, 1999). Projected forest areas and carbonsequestration for different studies are shown and comparedin Figs. 8 and 9. The forest area in the China Climate ChangeCountry Study is similar to that in the trend scenario of thisstudy before 2010, and lies between the trend and planningscenarios from 2010 to 2030. However, the calculated netcarbon sequestration on that area is significantly higher thanin all other studies or scenarios. Forest areas in the base-line and scenario 1 variants of the ALGAS project are closeto the trend and planning scenarios of this study, but the

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Fig. 8. Projected forest area for different studies.

projected carbon sequestration in ALGAS is 13–36% lowerthan in this study (Figs. 8 and 9). Such discrepancies be-tween the different studies may also result from the differentestimation methods and/or bio-physical parameters used.

5.3. Sensitivity analysis

Most parameters used in the F-CARBON model werederived from the forest inventories, such as forest area,harvested area, available wasteland area, growth rate andstand volume for different regions and age classes. Otherparameters, including carbon density, wood density, forestsoil carbon density, rotation periods, etc. were commonlyused values or calculated from bio-physiological observa-tions. By comparison, the most uncertain parameters in theF-CARBON model are those affecting soil carbon turnoverand emissions, including decomposition rate, proportion ofbiomass in litterfall, humification coefficient, soil carbonchanges between harvesting and reforestation.

Sensitivity analysis on the F-CARBON model showedthat the largest uncertainty in the projections came fromthe soil carbon release coefficient during the period afterharvesting and before reforestation. Under the planningscenario, ±5% changes of the coefficient could result in±75.7% variation in the calculated soil carbon flux leadingto ±12.7% variation in the net carbon sequestration. How-ever, ±50% changes of the decomposition rate, proportionof biomass in litterfall and humidification coefficient ledto only ±2 to 3% variation in the calculated net carbonsequestration (Table 5).

Another shortcoming is that our current version ofF-CARBON model does not consider the impact of climatechange on growth rate, decomposition rate and humidifi-cation coefficient. Liu et al. (1998) predicted that the NPPof our forests would increase 1–10% by 2030 under theclimate scenarios projected from seven General Circulation


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Fig. 9. Projected carbon sequestration for different studies.

Table 5Sensitivity analysis for the F-CARBON model

Parameters Variation (%) Errors (%)

Emissions Soil carbon Budget

Humification coefficient ±50 ±0.3 ±18.8 ±3.2

Soil carbon releasing coefficient between harvesting and reforestation ±5 – ±75.7 ±12.7±15 – ±212.1 ±35.6

Decomposition rate factor ±50 ±9.1 – ±2.9Proportion of litterfall in biomass ±50 ±2.7 ±18.8 ±2.2

Models (GCMs). Fang (2000) estimated that the NPP of ourforests would increase by 17–35% as a result of a doublingof the atmospheric CO2 concentration. On the other hand,decomposition rate is very sensitive to changes in temper-ature and moisture so that the associated parameters foremissions may need to be different, as a result of changesin temperature and precipitation, especially for soil carbonrelease coefficient to which our model is very sensitive.Nonetheless, the effects of changes in environmental con-ditions on forest growth dynamics during past periods havealready been accounted for in the inventory data, and sowere partially represented in the F-CARBON model. Ourfuture version of the model will try to take the impacts ofclimate changes into account.

Acknowledgements

We thank Paul G. Jarvis of the University of Edinburgh,United Kingdom, and Willy Makundi, International EnergyStudies of Lawrence Berkeley National Laboratory, fortheir valuable comments, and Margaret Jarvis for improv-ing the English of our manuscript. We would also like to

give our appreciation to the China Ministry of Science andTechnology for its financial support under the project No.2002CB412508 and 2001-BA611B-04.

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Xiao-Quan Zhang is a associate research professor in the ChineseAcademy of Forestry. He graduated from the China Southwest ForestryCollege in 1986 and gained his PhD in the Chinese Academy of Forestryin 1999. He received training on fine-root ecology for 6 months in 1999in the University of Goettingen, Germany. In the past decade, his interestshave involved climate change and forest issues, soil carbon in relation toland-use change, and eco-physiology of trees. He is currently one of theleading invited authors of IPCC-LULUCF Good Practice Guidance andone of the 25 experts on the IPCC Emission Factors Database EditorialBoard.

Deying Xu, research professor, is a forest meteorologist and forest ecol-ogist in the Chinese Academy of Forestry. He is a member of China’snational technical committee for environmental monitoring, deputy leaderof the China forest ecosystem research network. Prof. Xu was en-gaged in forest meteorology and climate before 1980s. He worked inAustralia in 1989 as a visiting scholar. Since the end of 1980s, hehas been involved in impacts of climate change on forests, forest car-bon budgets, GHGs emission/sequestration in the land-use change andforestry sectors, global change and forestry strategy, etc. and has or-ganized many relevant projects. Since 1989, he has been a member ofIPCC Working Group II (domestic and international). Between 1993and 1995, he was the Lead Author of the Second Assessment Reportof IPCC, and in 1999–2000 he was the leading author of the SpecialReport on land use, land-use change and forestry for IPCC. He is cur-rently an invited leading author of the IPCC-LULUCF Good PracticeGuidance.

potential carbon sequestration in china’s forests

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