Distribution of Different Carbon Pools

The two main carbon pools are biomass and soil carbon. Biomass is defined as the total quantity of live and inert or dead organic matter, above and below the ground, expressed in tonnes of dry matter per unit area, such as a hectare. Soil carbon is carbon held in soil as organic matter, humified material and in stable structures such as charcoal. Biomass is converted to carbon by multiplying it with a carbon fraction of dry matter. The exact value of the fraction varies within a small range for different species and components of plants, and is usually about 0.5 (IPCC 2006).

Total carbon = biomass carbon + soil carbon

Biomass carbon = above-ground biomass carbon + below-ground biomass carbon + dead organic matter carbon

An illustrative distribution of different carbon pools in forests of different regions is given in Table 4.1. In Africa, for example, carbon in living biomass is predominant, accounting for about 60%, followed by soil carbon (approximately 34%), whereas in Europe, soil carbon is the predominant fraction (64%), and living biomass accounts for only 25% of the carbon. Thus, the proportions of living biomass and soil carbon vary with the region but together account for more than 90% of the total biomass. The share of deadwood and litter together is less than 11% in all regions. Carbon in the litter pool is less than 5% in all regions (Table 4.1), and soil carbon is the dominant pool in grassland and cropland systems (Table 2.2).

A study of different forest types in southern India estimated the stocks of different carbon pools (Table 4.2). Above-ground biomass accounted for 25-46% of the total carbon stocks. Below-ground biomass accounted for less than 12% of the total carbon stocks in all the forest types. Soil carbon dominated the scrub forest (68%), southern thorn forest (56%) and evergreen forest (54%). Dead organic matter carbon pool was not reported in this study. When dead organic matter was excluded, the share of above-ground biomass and soil carbon together was as much as 88-95% of the total carbon pools. In absolute terms, the total biomass and soil

Table 4.1 Distribution (%) of carbon among different pools in forests and other wooded lands (FAO 2006)_

Carbon in

Region/subregion

Living biomass

Deadwood

Litter

Soil

Total

East and South Africa

63.5

7.5

2.1

-

73.1

North Africa

26.0

3.3

2.1

33.5

64.9

West and Central Africa

155.0

9.8

2.1

56.0

222.9

Total Africa

95.8

7.6

2.1

55.3

160.8

(59.5)

(4.6)

(1.6)

(34.3)

(100.0)

E. Asia

37.0

5.0

-

-

41.9

South and South-east Asia

77.0

9.0

2.7

68.4

157.1

West and Central Asia

39.0

3.6

11.4

41.0

95.8

Total Asia

57.0

6.9

2.9

66.1

132.9

Total Europe

43.9

14.0

6.1

112.9

176.9

(24.8)

(7.9)

(3.4)

(63.9)

(100.0)

Caribbean

99.7

8.8

2.2

70.5

181.2

Central America

119.4

14.4

2.1

43.3

179.2

North America

57.8

8.8

15.4

35.8

117.8

Total North and Central

60.1

9.0

14.8

36.6

120.6

America

Total Oceania

55.0

7.4

9.5

101.2

173.1

Total South America

110.0

9.2

4.2

71.1

194.6

World average

71.5

9.7

6.3

73.5

161.0

(44.4)

(6.1)

(3.9)

(45.6)

(100.0)

Figures in parentheses are

percentages of the row

totals

Table 4.2 Carbon stocks (tC/ha) in different pools in different forest types of Namakkal district of Tamilnadu (Ramachandran et al. 2007) and Varanasi (Misra 1972), India

Varanasi

Tamilnadu

Deciduous

Evergreen

Deciduous

Secondary

Southern

Euphorbia

Carbon pools

deciduous

thorn

scrub

AGB

102.7

122

100

96

52

22

(40.5)

(36.2)

(41.6)

(46.8)

(38.5)

(24.9)

BGB

17.1

31

25

24

6

5

(6.7)

(9.3)

(10.7)

(12.1)

(5.0)

(6.4)

Deadwood

3.8

-

-

-

-

-

(1.5)

SOC

129.5

184

114

84

76

63

(0-90 cm)

(51.3)

(54.5)

(47.7)

(41.1)

(56.5)

(68.7)

Total

253.2

337

240

205

136

91

(100.0)

(100.0)

(100.0)

(100.0)

(100.0)

(100.0)

AGB; above-ground biomass; BGB; below-ground biomass; SOC; soil organic carbon. Figures in parenthesis indicate percentages

AGB; above-ground biomass; BGB; below-ground biomass; SOC; soil organic carbon. Figures in parenthesis indicate percentages carbon stocks varied from 91 tC/ha in scrub forest to 337 tC/ha in evergreen forests (Table 4.2). Data from a deciduous forest in Varanasi, northern India, showed that dead organic matter pool is insignificant and above-ground biomass and soil carbon together account for 92% of the total carbon stocks.

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