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Pergamon Energy Convers. Mgmt Vol. 38, Suppl., pp. $569-$573, 1997 © 1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain PII: S0196-8904(96)00329-9 0196-8904/97 $17.00 + 0.00 POTENTIAL LAND AREA FOR REFORESTATION AND CARBON DIOXIDE MITIGATION EFFECT THROUGH BIOMASS ENERGY CONVERSION SHIN-YA YOKOYAMA National Institute for Resources and Environment 16-3, Onogawa, Tsukuba, lbaraki 305, Japan ABSTRACT Reforestation has a great potential to fix carbon dioxide (CO2) in the atmosphere through photosynthesis of biomass and biomass energy conversion. The magnitude of CO2 fixation depends on the potential land area. We have proposed a potential area of about 350 Mha for reforestation in tropical and semi-tropical areas. If such land is used for energy plantation aimed at substitutive energy production by power generation, the CO2 mitigation effect can be evaluated on the assumption of short rotation energy plantation(6-year rotation), plantation area (1Mha), biomass productivity (10.5 dry ton/ha/y), energy efficiency of power generation(0.27), etc. Assuming these factors, the net carbon dioxide mitigation effect is 1.4 billion t-C on 340 Mha. © 1997 Elsevier Science Ltd KEYWORDS Biomass, plantation, reforestation, power generation carbon dioxide fixation, energy conversion, POTENTIAL LAND AREA FOR REFORESTATION A total amount of the CO 2 fixation by planted trees highly depends on the practical planting areas, and it is no exaggeration to say that the evaluation of the biological CO2 fixation is controlled by the estimation of this value of area. Most past assessment of practically planted areas were roughly estimated by an approximation of already cut forest areas in the past, but recent estimates of the area of lands available for planting have become much more practical. There are two ways for the estimations of practical planting areas. One is the so-called "top-down method" that depends on the multiplication of factors based on the Food and Agriculture Organization (FAO) data, and another is the so-called "bottom-up method" that integrates practical planted areas published by federal and local governments. It is needless to say that the bottom-up method is superior, but in fact it is impossible to darify the potential practical planting areas in the world by this method. Examples $569

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Page 1: Potential land area for reforestation and carbon dioxide mitigation effect through biomass energy conversion

Pergamon Energy Convers. Mgmt Vol. 38, Suppl., pp. $569-$573, 1997

© 1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain

P I I : S0196-8904(96)00329-9 0196-8904/97 $17.00 + 0.00

POTENTIAL LAND AREA FOR REFORESTATION AND CARBON DIOXIDE MITIGATION EFFECT THROUGH BIOMASS ENERGY CONVERSION

SHIN-YA YOKOYAMA

National Institute for Resources and Environment 16-3, Onogawa, Tsukuba, lbaraki 305, Japan

ABSTRACT

Reforestation has a great potential to fix carbon dioxide (CO2) in the atmosphere through photosynthesis of biomass and biomass energy conversion. The magnitude of CO2 fixation depends on the potential land area. We have proposed a potential area of about 350 Mha for reforestation in tropical and semi-tropical areas. If such land is used for energy plantation aimed at substitutive energy production by power generation, the CO2 mitigation effect can be evaluated on the assumption of short rotation energy plantation(6-year rotation), plantation area (1Mha), biomass productivity (10.5 dry ton/ha/y), energy efficiency of power generation(0.27), etc. Assuming these factors, the net carbon dioxide mitigation effect is 1.4 billion t-C on 340 Mha. © 1997 Elsevier Science Ltd

KEYWORDS Biomass, plantation, reforestation, power generation

carbon dioxide fixation, energy conversion,

POTENTIAL LAND AREA FOR REFORESTATION

A total amount of the CO 2 fixation by planted trees highly depends on the practical planting areas, and it is no exaggeration to say that the evaluation of the biological CO 2 fixation is controlled by the estimation of this value of area. Most past assessment of practically planted areas were roughly estimated by an approximation of already cut forest areas in the past, but recent estimates of the area of lands available for planting have become much more practical. There are two ways for the estimations of practical planting areas. One is the so-called "top-down method" that depends on the multiplication of factors based on the Food and Agriculture Organization (FAO) data, and another is the so-called "bottom-up method" that integrates practical planted areas published by federal and local governments. It is needless to say that the bottom-up method is superior, but in fact it is impossible to darify the potential practical planting areas in the world by this method. Examples

$569

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$570 YOKOYAMA: REFORESTATION AND CO.~ MITIGATION

of est imated practical plant ing areas to date are s h o w n in Table 1.

Table 1. Reported Potential Land Area for Reforestation

Potential Land Area

(Mha)

G rainger(1988) 758

Myers(1989) 300

Houghton(1990) 865

Winjum et a1.(1992) 600-1200

Alpert et al.(1992) 952

Bekkering(1992) 385-553

Nakicenovic et al.(1993) 265

Because the practical plant ing areas are highly related to the cost of reforestation, it is possible to plant trees at desert areas w h e n no l imi ta t ion on the cost is allowable. Then, if plantat ions are established at sites where no large scale irrigation or soil i m p r o v e m e n t are necessary, wi th ranges of $1,000 - 2,000/ha for plant ing in the developing countries, grasslands and a part of shrub lands where irrigation is necessary become infeasible.

Table 2 Estimated Potential Land Area for Reforestation

Central Africa Madagascar Mexico Argentine Bolivia Brazil Chile Colombia Peru Uruguay Venezuela

Potential Land Area(Mha)

16.2 7.2

80.4 16.5 8.6

105.9 8.6 9.0

16.8 0.1

23.5

Sub total 292.8

Turkey Vietnam Thailand Myanmer

11.3 13.7 1.7

20.7

Sub total 47.4

Total 340.2

Bekkering (1992) presented an idea that surplus lands should be used for reforestation in the tropical zone, wi th sufficient rainfall and wi th ~ood condit ions

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for the food supply. On the basis of this idea, the land becomes about 300 Mha for sites proposed for reforestation, as shown in Table 2. Eleven countries with fairly good stable conditions in food supplies are candidates in South America and Central Africa, though several of them are listed as the food importing countries. If four countries of fairly good food supplies in the Southeast Asian region are added, the total area becomes 340 Mha.

THE GENERATION OF ELECTRICITY BY BIOMASS COMBUSTION

The mitigation of CO2 is estimated here when electricity is generated by combustion of biomass such as fast growing trees, for example, Eucalyptus , it is important to note that the net accumulation of CO 2 in the atmosphere can be maintained if the amount of biomass which is used for energy combustion is balanced with that of biomass planted. If forests are managed and utilized for energy in a sustainable manner, CO2 emission from combustion of fossil fuels can be avoided. Two cases are discussed for the electricity generation from biomass combustion.

Case I : Eucalyptus plantation of 20 km in diameter, with a 6- year rotation and 5230 ha/y harvested

Parameters: net production of Eucalyptus harvested area calorific value of Eucalyptus efficiency of power generation efficiency of power generation carbon emission from coal combustion

10.5 dry ton/ha 5230 ha 20 GJ/dry ton 0.22 (biomass combustion) 0.33 (coal combustion) 0.027 t-C/GJ

The net production of Eucalyptus (10.5 dry ton/ha/y) seems reasonable because that of Eucalyptus has been reported to be more than 40 wet ton/ha/y in Brazil. In this case, the carbon content in wood is about 45 - 50%. The calorific value of Eucalyptus is 20GJ/dry weight (about 4800 kcal) and the efficiency of direct combustion is 22%, because a small scale power generation plant is adopted in this case. At this time, no consideration is given to energy consumption for the construction of the power plant.

The mitigation of CO2 is calculated as follows: 10.5(dry ton/ha / y) x 31400 (ha) x 20 (GJ / dry ton) x 0.22 / 0.33 x 0.0247 (t-C / GJ) = 108.6 kt-C/y

As for the energy used in cultivation of Eucalyptus, energy is necessary for the preparation of land, planting, fertilization, management and thinning. Furthermore, the energy needed for cutting and transportation must be considered when harvesting. These are assumed to be:

ECM 38/SUPI T

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energy needed for tree growth energy needed for tree harvesting carbon emission from gasoline

11.94 GJ/ha/y 4.1 GJ/ha/y 0.0208 t-C/GJ

Taking into consideration the energy needed for the growth and harvest of trees, it is calculated to be 3.5kt-C/y. The above-mentioned value is based on the data reported by Larson (1995). The energy input of fossil fuel for tree growth and harvest is converted to the energy of gasoline. Thus, the true CO 2 mitigation effect becomes 108.6 - 3.5 = 105.1 kt-C/y. In other words, 105,100 t of carbon can be reduced on this area each year.

Case 2 : Eucalyptus plantation of 1 Mha, with a 6-year rotation and 0.167 Mha/y harvested

Parameters: net production of Eucalyptus harvested area calorific value of Eucalyptus efficiency of power generation efficiency of power generation carbon emission from coal combustion

10.5 dry ton/ha 0.167 Mha 20 GJ / dry ton 0.27 (biomass combustion) 0.33 (coal combustion) 0.027 t-C/GJ

In this case, the efficiency of power generation with biomass is raised to 0.27 from 0.22 due to the scale effect of power plant.

The mitigation of C O 2 is calculated as follows: 10.5(dry ton/ha/y) x 1.0 (Mha) x 20 (GJ/dry ton) x 0.27/0.33 x 0.0247 (t-C/GJ) = 4.24 Mt-C/y

Energy needed for cultivation and harvest is as follows: energy needed for tree growth 4.1 GJ/ha/y energy needed for tree harvesting 13.76 GJ/ha/y carbon emission from gasoline 0.0208 t-C/GJ

In this case, the energy for harvesting is larger than for Case I due to the longer distance for tree transportation. The true CO 2 mitigation effect for 1 Mha becomes 4.24-0.12=4.12 Mt-C/y. Therefore, the net CO2 mitigation effect is 1.4 billion t-C on

340 Mha.

SUMMARY

Biomass energy is understood as a key technology against global warming. According to the Intergovernmental Panel on Climate Change (IPCC), the land for biomass plantation is evaluated about 600 Mha or more. However, it is considered that the available land area is smaller than expected in the scenario if looking at the real situation of the developing countries in the tropical region where forest has

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YOKOYAMA: REFORESTATION AND CO2 MITIGATION $573

been cut down due to urbanization, industrialization, and conversion to farming. In this article, the available land is estimated to be about 340 Mha taking into account the necessity of irrigation and soil improvement in addition to the situation of food supply of each country.

As for the individual species of wood and energy conversion technology of biomass, fast growing Eucalyptus is chosen and the generation of electricity by direct combustion of biomass is considered. In this analysis, about 4 mil l ion tons of carbon can be reduced on 1Mha(100km x 100kin) land. Thus, 1.4 billion tons of carbon can be reduced on 340 Mha if sustainable management of biomass energy plantation is carried out for power generation from biomass.

REFERENCES

Alpert, S. B., D. F. Spencer,. and G. Hidy (1992). Biospheric options for mitigating atmospheric carbon dioxide levels. Energy Conserv. Mgmt., 33, 729-736.

Bekkering, T. D. (1992). Using tropical forests to fix atmospheric carbon: The potential in theory and practice. Ambio, 21,414-419

Graigner, A. (1988). Estimating areas of degraded tropical lands requiring replace- ment of forest cover. The International Tree Crops |ournal, 5, 31-61.

Houghton, R. A. (1990). The future role of tropical forests in affecting the carbon dioxide concentration of the atmosphere. Ambio, 19, 204-209.

Larson, E. D., C. I. Marrison and R. H. Williams (1995). CO2 mitigation potential of biomass energy plantations in developing regions. Private communications.

Myers, N. (1989). The greenhouse effect: A tropical forestry response. Biomass, 18, 73-75.

Nakicenovic, N., A. Grubler, A. Inaba, S. Messner, S. Nilsson, L. Y. Nishimura, H- H. Rogner, A. Schafer, L. Schrattenholzer, M. Strubegger, J. Swisher, D. Victor, and D. Wilson (1993). Long-term strategies for mitigating global warming, Energy, 18, 401-609.

Winjum, J. K., R. K. Dixon and P. E. Schroeder (1992). Estimating the global poten- tial of forest and agroforest management practices to sequester carbon.Water, Air and Soil Pollution, 64, 312-227.