Inventory Of Wood Used In Charcoal Production In Zambia
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Inventory Of Wood Used In Charcoal Production In Zambia |
Introduction and objectives Research methods
Wood biomass stocks and chemical composition Charcoal yield and chemical composition Charcoal consumption in Zambia Wood used in charcoal production Emmanuel N Chidumayo, Biology Department, University of Zambia, Box 32379, Lusaka, Zambia.
Fax: 260-1-253952, tel: 260-1-252514/292884, telex: UNZALU ZA 44370 (no email).
Total fuelwood (including charcoal) burnt in tropical Africa is estimated at 230 million tonnes (dry matter) per year and the amount of charcoal consumed is about 11 million tonnes (Delmas et al., 1991). Fuelwood burning generates greenhouse gases such as carbon dioxide. The national energy budget in Zambia is dominated by biomass which accounts for 70% of the total energy consumption of 4.33 million tonne oil equivalent (Department of Energy 1992). In rural areas the primary energy source is firewood while charcoal is predominantly an urban fuel. The high population growth and low rates of switching to non-carboniferous household energy sources in the developing world imply that the rate of carbon dioxide release from biomass burning is likely to increase in the foreseeable future. This will further accelerate the build-up of atmospheric carbon dioxide with consequential effects on global warming and climate change.
Zambia is a landlocked country in central southern Africa, lying between latitudes 8o and 18o south and longitudes 24o and 34o east, with an area of 75.26 million ha. With an average annual population growth rate of 3.2%, Zambia has one of the highest population growth rates in the world. The population increased from 3.5 million in 1963 to 5.88 million in 1980 and 7.82 million in 1990. In Zambia wood is carbonized to charcoal in traditional earth kilns (click here for pictures) but little is known about the national carbon budget in charcoal production and burning. It is necessary to know the amount and quality of wood used in charcoal production in order to construct the charcoal carbon budget. Two complementary projects were carried out in Zambia during 1993-1994 to generate this kind of data. One was on the Inventory of Wood Used in Charcoal Production and the other was on Emissions Produced in Charcoal Production.
The objectives of the project on inventory of wood used in charcoal production were to (i) classify the Zambian vegetation into biomass classes, (ii) estimate the existing wood biomass stocks, (iii) determine the physical and chemical characteristics of wood used in charcoal production, (iv) describe the charcoal production process and estimate charcoal yield and (v) estimate wood used in charcoal production on a dynamic basis. The study was carried out from June 1993 to August 1994 and was funded by the Biodiversity Support Program (Global Climate Change) a USAID funded consortium of World Wildlife Fund, The Nature Conservancy and The World Resources Institute in Washington, DC, USA. The project was implemented by Professor E.N. Chidumayo and the Biology Department of the University of Zambia at Lusaka. The project on emissions was implemented by Dr D. Ward of the USDA Forest Service and the Intermountain Research Station, Missoula, MT.
The product of area and average above ground (AG) wood biomass in each vegetation type was used to estimate wood biomass stocks. Stem enumeration and diameter measurements of 106 0.4 ha forest stands and biomass equations derived from 1,373 felled stems were used to estimate average AG wood standing stocks in different vegetation types. Charcoal yield was assessed in 65 earth kilns by comparing oven-dry wood mass and total charcoal produced. Carbon content in wood of 21 tree species and 103 charcoal samples was analyzed and the data used to construct the carbon budget in charcoal production and use in Zambia. Estimation of wood used in charcoal production was based on a back calculation from the amount of charcoal consumed and the yield rate in earth kilns. Charcoal consumption data were obtained from surveys conducted during 1978-1994.
Wood biomass stocks and chemical composition
For the purpose of this study, vegetation types in Zambia were placed in three wood biomass classes: forest, miombo woodland and savanna woodland and wood biomass stocks in the three biomass classes are given in Table 1. Miombo woodland contains two-thirds of the nearly 2,927 million tonnes (oven-dry, OD) of AG wood biomass; the forest and savanna woodland contain 21% and 13%, respectively (Fig.1).
The average chemical composition of wood of seventeen and four tree species in miombo and savanna woodlands, respectively, is given in Table 2. Miombo woodland species contain slightly more carbon (47%) than savanna woodland species (44%) but the latter contain almost twice as much ash and nitrogen. The estimated pool of carbon and nitrogen in the three biomass classes in Zambia was estimated at 1,373 million and 2 million tonnes, respectively, with the highest proportions of these elements being found in miombo woodland (Fig. 1). However, in spite of the greater AG wood biomass stock in the forest biomass class, savanna woodland contains 24% of the total nitrogen pool compared to 19% in the forest. This is because savanna woodland trees have a higher concentration of nitrogen than either miombo woodland or forest trees (Table 2).
Charcoal yield and chemical composition
Charcoal production is concentrated in miombo woodland. The production method involves tree felling, stem cross-cutting, kiln building by piling logs and covering with soil, wood carbonization and kiln breaking to recover the charcoal. Charcoal yield rate was calculated as follows:
Charcoal-yield rate = Charcoal-produced/Wood-carbonized
Average charcoal yield rate in earth kilns on an OD weight basis was 23.4% (SD = 7.2). This conversion rate gives a yield of 0.23 kg charcoal per 1.0 kg of carbonized wood while the output of recoverable charcoal was 0.22 kg per 1.0 kg of carbonized wood.
Figure 1. Distribution of Wood Biomass, Carbon and Nitrogen in Zambia
Table 1. Wood biomass classes and standing stock (oven-dry mass) in Zambia.
Biomass
ClassExtent (million ha) Wood biomass (t/ha) Standing stock in
million tonnesTotal Dambo Grassland Crop Land Actual Extent Cord wood Twig wood Total Forest
Evergreen
Deciduous4.93 3.93
1.00
0.62 0.49
0.13
0.52 0.43
0.09
3.79 3.01
0.78
- 158
58
- 29
11
- 187
69
616.69 562.87
53.82
WetDryKalahari45.09 22.20
13.13
9.76
5.64 2.78
1.64
1.2
13.60 6.66
5.91
0.98
25.85 12.76
5.58
7.56
- 76
58
43
- 14
11
8
- 90
69
51
1919.00 1148.40
385.02
385.56
Savanna woodland
MungaMopane
Termitaria11.25 3.73
4.75
2.77
1.41 0.47
0.59
0.35
0.34 0.15
0.19
0.00
9.50 3.11
3.97
2.42
- 38
38
25
- 7
7
5
- 45
45
30
392.20 139.95
178.65
72.60
Grassland 13.01 0.00 1.43 11.58 0 0 0 0 Aquatic 0.98 0.00 0.00 0.98 0 0 0 0 Notes: Dambo grassland is calculated as 12.5% of total area (Chidumayo 1992); cropland is based on Schultz (1974); wood biomass in deciduous forest and mopane is calculated on the basis of dry miombo and munga woodland, respectively.
Table 2. Average chemical composition of oven-dry wood biomass in Zambian miombo and savanna woodlands. Standard deviations are given in brackets.
Biomass
ClassAverage Percent Composition Moisture Nitrogen Ash Carbon Other elements Miombo Woodland 4.37 (1.07) 0.06 (0.04) 2.69 (1.27) 47.41 (1.75) 45.47 (0.05) Savanna Woodland 4.81 (0.52) 0.12 (0.02) 5.81 (1.71) 43.79 (1.51) 45.48 (0.00) The average chemical composition of charcoal made from miombo woodland trees is compared with that of wood in Fig.2. The content of nitrogen, ash and carbon increased from 0.06%, 2.7% and 47%, respectively, in wood to 0.6%, 7.7% and 72% in charcoal.
Figure 2. Chemical composition of wood and charcoal of Miombo trees
Charcoal consumption in Zambia
In Zambia there is a positive correlation between household size and charcoal consumption (R-squared = 0.86) while correlation between per capita consumption and household size is negative (R-squared = 0.78). This means that although biomass energy consumption increases as household size increases, per capita consumption declines (Fig.3). Mean household size in Zambia increased from 4.7 in 1969 to 5.6 in 1990 and will probably continue to do so up to 2010 and beyond. By implication average charcoal consumption per household also increased while per capita consumption decreased. Fortunately, these changes were not large. For example, gross annual charcoal consumption per household averaged at 1043 kg in 1983 (Chidumayo & Chidumayo 1984), 984 kg in 1988 (World Bank/ESMAP 1990) and 1110 kg in 1994 (based on the 1994 survey data). Comparison between the 1988 and 1994 did not reveal significant differences (t < 1.50; P > 0.05). The average annual charcoal consumption in urban Zambia during 1983-1994 was therefore 1046 kg per household. From available data, average charcoal consumption per household in rural Zambia was estimated at 100 kg per year.
Figure 3. Correlation between household size and charcoal consumption
The household sector accounts for 96% of total charcoal consumption in the country (Department of Energy 1992). Total charcoal consumption was therefore estimated by dividing charcoal consumption in the household sector by 0.96. Table 3 shows trends in charcoal consumption based on growth in households and a constant average consumption per household calculated separately for rural and urban areas. Charcoal consumption increased from 0.32 million tonnes in 1969 to 0.47 million in 1980 and 0.66 million in 1990 and is projected to increase to 0.87 million and 1.16 million tonnes in 2000 and 2010, respectively. Except for 1969, these estimates are lower than those based on FAO data for the period 1978-1989 (Fig. 4).
Table 3. Charcoal consumption and wood used in charcoal production in Zambia.
Year Charcoal Consumption
(million tonnes)Charcoal Produced (million tonnes) Wood Used (million tonnes) 1696 0.330 0.340 1.479 1980 0.490 0.505 2.196 1990 0.685 0.706 3.070 2000 0.905 0.933 4.056 2010 1.211 1.248 5.428
Figure 4. Estimates of charcoal consumption in Zambia
Wood used in charcoal production
The wood used in charcoal production in Zambia was calculated as follows:
Wood-used = Charcoal-produced/Yield ratewhere charcoal produced equals charcoal consumed/0.97 and yield rate is 0.23. Table 3 shows wood used in charcoal production during 1969-1990 and projections for 2000 and 2010. The carbon balance in the charcoal industry in Zambia was calculated as follows:
C-in wood = C-rdp + C-rdb + C-ics
where C-rdp is carbon released during charcoal production, C-rdb is carbon released during charcoal burning and C-ics is carbon held in charcoal soil at kiln sites. Figure 5 shows trends in carbon release in the charcoal industry in Zambia. The quantity of carbon released increased from 0.67 million tonnes in 1969 to 0.99 million in 1980 and 1.38 million in 1990 and projected figures for 2000 and 2010 are 1.83 million and 2.45 million tonnes, respectively. All these figures are far in excess of the actual charcoal consumed because of the high loses of carbon during charcoal production.
Figure 5. Carbon release from charcoal production and burning in Zambia
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