NOTE GREENHOUSE GAS EMISSIONS FROM FORESTRY, LAND-USE CHANGES, AND AGRICULTURE IN TANZANIA

R.S. MUYUNGI and C. OMUJUNI Centre for Energy, Environment, Science, and Technology, P.O. Box 5511, Dar es Salaam, Tanzania

Abstract. The purpose of the study was to identify and quantify anthropogenicsources and sinks of greenhouse gases from forestry, land-use changes and agriculture in Tanzania. The 1990 inventory revealed that, in the land-use sector, methane (CH4)and carbon dioxide (CO2) are the primarygases emitted. Enteric fermentation in livestockproduction systemsis the largest source of CH4. Although deforestationresults in greenhouse gas emissions, the managed forests of Tanzania are a major CO2 sink. I. Introduction Tanzania, the largest country in East Africa, covers a total area of 88.6 million ha. The topography and climate are complex, with an altitude ranging from sea level to the summit of Mt. Kilimanjaro, the highest mountain in Africa (5895 m). The coastal areas are dominated by plains of up to 1000-m elevation dissected by river systems. The interior is characterized by plateaus at 1000 to 1500 m. The natural vegetation types include forests, woodlands, grasslands, bushland, and the coastal woodland. Woodlands and forests, estimated at 44 million ha, comprise about one-half the land area in Tanzania. The economy of Tanzania is primarily agricultural. The agriculture sector employs about 84% of the working population and contributes about 61% of gross domestic product (GDP). Food-crop production dominates the agriculture sector, totaling 55% of agricultural GDE with livestock accounting for 30%. The agricultural sector is based in 8000 villages, with an average farm of less than 2 ha per family. Traditional cash crops include coffee, cotton, tobacco, tea, cashew nuts, and pyrethrum. Food crops include maize (Zea mays L.), rice (Oryza L.), wheat (Triticum L.), sorghum (Sorghum L.), millet (Panicum L.), cassava (Manihot), beans (Vicia), potatoes (Solanum), and bananas (Musa L.). There is a cattle herd of more than 13 million, 8 million goats, and 5 million sheep, all of which play an important role in the national economy. An estimated 90% of households keep livestock of some kind, primarily for subsistence. Cattle are particularly important for providing meat, milk, and manure. Within Africa, Tanzania ranks third in total livestock numbers after Sudan and Ethiopia. The analysis of greenhouse gas (GHG) sources and sinks in Tanzania was a followup to an initiative of the Intergovernmental Panel on Climate Change (IPCC), under the auspices of the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in response to growing concerns regarding global climate change (Houghton et aL 1992). To help the Government meet its obligations under

Environmental Monitoring and Assessment 38:313-316, 1995. © 1995 Kluwer Academic Publishers. Printed in the Netherlands.

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the United Nations Framework Convention on Climate Change (UNFCCC), the Tanzania Centre for Energy, Environment, Science and Technology (CEEST) was commissioned to characterize GHG sources and sinks in Tanzania. The main purpose of the study was to identify and quantify anthropogenic sources and sinks of GHGs in Tanzania.

2. M e t h o d s

Greenhouse gas emissions from land-use subsectors were analyzed using the UNEP/LPCC/ OECD/IEA (1995) methods. The following GHGs were evaluated: methane (CH4) emissions from rice cultivation; nitrous oxide (N20) emissions from the use of (N) nitrogen fertilizers; CH 4 emissions from enteric fermentation of domestic animals; C H 4 emissions from animal wastes; CH 4, carbon dioxide (CO2), nitrogen oxide (NOx), and N20 emissions from the burning of agricultural crop wastes; and CO 2sources and sinks of forest systems. A simple methodology was used to estimate CH 4 emitted from rice fields, under which a daily emission rate range is used to compute annual emissions (Bachelet and Neue, 1993). In Tanzania, rice is cultivated under three regimes: flooded/irrigated, rain-fed, and upland. The number of days in a rice growing season is 120 days and 95 days for the flooded and rain-fed regimes, respectively. The average annual area of rice is 340.75 xl03 ha (kha). Out of this, about 72 700 ha is upland rice area. The rice area under the irrigated regime is 41.9 x kha. The emissions of CH 4 from enteric fermentation were based on various feeding systems for animals (Lerner et al., 1988). Total C H 4 emissions depends on a number of factors, such as number and animal type, livestock management systems, size, and feeding and production characteristics. Simplified relationships for the estimation of CH 4 emissions were based on total animal feed intake and an estimate of the ratio of feed energy that is converted to CH 4. Methane is generated from animal wastes when organic material decomposes anaerobically. The amount of CH 4 produced will depend on the type of waste, in particular the amount of volatile solids present in the waste. The amount of C H 4 emitted was calculated using the IPCC guidelines for national GHG inventories (UNEP et al., 1995). The following assumptions were used in the calculations: • Most cattle are grazed under the pastoral system, with the methane conversion factor (MCF) assumed at 0.01, at the maximum. • In the case of poultry, the methane conversion factor of 0.01 was assumed. • Swine, horses, goats, and sheep graze pastorally and an MCF of 0.01 was assumed. Emissions of N are influenced by natural processes such as temperature, porosity, soil structure, precipitation, and farm management practices (for example, fertilizer type, crop type, and irrigation). Because interactions among the physical, chemical, and biological variables are complex, N20 fluxes are variable in both time and space. Emissions of N20 from fertilizer use were calculated using the IPCC Guidelines f o r National Greenhouse Gas Inventories (UNEP et al., 1995).

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The burning of crop wastes leads to the emission of CO 2, CH 4, CO, N20, and NO X. Three crops have been considered in this analysis: cotton, sugarcane, and rice. Greenhouse gas emissions from the burning of these residues are estimated on the basis of the amount of C and N burned and the emission ratios of the gases (Ilukor and Oluka, 1995). Land-use change results in a net exchange of GHGs. Because biomass is about 45% C by weight, clearing by burning leads to instantaneous release of CO 2, and also CH 4, CO, N20, and NO x. When forests are converted to cultivated land, not all cleared aboveground biomass is burned in Tanzania. About 75% of the cleared biomass is collected as woodfuel, while approximately 20% is burned in the field, 10% of which remains on the ground as charcoal. The remaining 5% of aboveground biomass, such as foliage and twigs, decays in the fields over an average period of 10 years, releasing 1/10thof its C content annually. Based on the quantity of CO 2 released from burning of aboveground biomass, GHGs are released instantaneously (Crutzen and Andreae, 1990). Greenhouse gas emissions as a result of land-use change, especially deforestation, were estimated using methods and assumptions described by Dixon et al. (1993). Sequestration and storage of CO 2by forest systems in Tanzania were estimated using the mean carbon (C) storage method. Carbon accretion and storage were calculated by summing the C standing crop for every year in the rotation and dividing by rotation length (Winjum et aL, 1992). 3. Results

The land-use sector of Tanzania produces significant GHG emissions (Table I). Within the agricultural subsector, enteric fermentation is the leading source of CH4, followed by the burning of agricultural residues. Manure management, rice cultivation, and savanna burning are also significant sources of CH 4. The application of N fertilizer releases 0.57 Gg of N20. Combustion of savanna and agricultural residues produces insignificant amounts of N20, NO x, and CO. Forest systems are a significant CO 2 sink in Tanzania sequestering over 38 000 Gg annually. Vegetation regrowth on abandoned lands also sequesters CO 2. In contrast, conversion of forests and grasslands to agriculture releases small amounts of CO 2, CH 4, N20, NO x, and CO. In balance, natural forest and agroecosystem of Tanzania sequester more CO 2than released. 4. Discussion and conclusions

In 1990, the land-use sector of Tanzania was a net sink for CO 2, but a small source of CH 4, N20, NO x, and CO from agricultural practices. Energy sector emissions in Tanzania are not significant given the agrarian socioeconomic conditions. Thus, Tanzania is not a major GHG producer in Africa (Houghton et al., 1992).

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TABLE I Summary of greenhouse gas sources and sinks in the agriculture and land-use sectors in Tanzania in 1990 (Gg)

Source and sink

CO:

CH4

N20

NOx

CO

Agriculture Enteric fermentation

845

Manure management

26 /

Rice cultivation

~8

Agricultural soils (fertilizers)

0.57

Savanna burning Burning of agricultural residues

56

0.70

16

2 457

327

0.57

13

1 053

10

0.1

2

144

1.94

31

3 654

Land-use changes Forestation and forest growth

-38156

Forest and grassland conversion

3 506

Reclamation of abandoned lands

- 2 599

Totals

-37 249

1 326

The IPCC Guidelines for National Greenhouse Gas Inventories (UNEP et al., 1995) yield meaningful estimates of GHG sources and sinks in Tanzania. A systematic examination of transparent and common methodologies is needed within the land-use sector to narrow the variability of GHG emissions. A comparison of Tanzania GHG emissions to other countries reveals preliminary estimates are credible (Siddiqi, 1995). References Bachelet, D. and Neue, H.:1993, Methane emissions from wetland rice areas of Asia, Chemosphere 26, 219237. Crutzen, P.J. and Andreae, M.O.: 1990, Biomass burning in the tropics: Impact on atmospheric chemistry and biogeochemical cycles, Science 250, 1669-1678. Dixon, R.K., Winjum, J.K., and Sehroeder, P.E.: 1993, Conservation and sequestration of carbon: the potential of forest and agroforest management practices, Global Environmental Change 2, 159-173. Houghton, J.T., Callander, B.A., and Varney, S.K.: 1992, Climate Change 1992, The supplementary report to the IPCC Scientific Assessment, Cambridge, U.K.: Cambridge University Press. Ilukor, J.O. and Oluka, S.O.: 1995, Carbon-to-nitrogen ratios in agricultural residues, Environmental Monitoring and Assessment, in press. Lerner, J., Mathews, E., and Fung, I.: 1988, Methane emission from animals: a global high-resolution data base, Global Biogeochemical Cycles 2, 139-156. Siddiqi, T: 1995, Asiawide emissions of greenhouse gases, Annual Review of Energy and Environment 20, in press. Winjum, J.K., Dixon, R.K., and Schroeder, P.E.: 1992, Estimating the global potential of forest and agroforest management practices to conserve and sequester carbon, Water,Air, and Soil Pollution 64, 213-227. UNEP, OECD, IEA, IPCC (United Nations Environment Programme, Organisation for Economic Cooperation and Development, International Energy Agency, Intergovernmental Panel on Climate Change): 1995, IPCC Guidelines for National Greenhouse Gas Inventories, IPCC, Bracknell, 3 Volumes. 210

Greenhouse gas emissions from forestry, land-use changes, and agriculture in Tanzania.

The purpose of the study was to identify and quantify anthropogenic sources and sinks of greenhouse gases from forestry, land-use changes and agricult...
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