Bioenergy is expected to become one of the key energy resources in order to reduce the excessive global warming and the rate of exhaustion of fossil-fuel resources. Biomass is renewable and free from net CO₂ emissions as long as it is maintained sustainably. But the land area available for biomass production is limited and a certain amount of biomass must be reserved for material production (e.g. wood and food). Therefore bioenergy has not yet been competitive with exhaustible energy sources such as oil and coal, and there is no clear prospect for its supply in the future.

In the 21st century, biomass which is used for food, material, and energy will be more indispensable. Hence, it is required to know the biomass flow accurately for sustainable development.

In this study, we propose a “Biomass-Balance Table” which shows harvest, conversion, and consumption of biomass systematically. The scheme of the Biomass-Balance Table is similar to that of the energy-balance table.

Biomass resources (such as raw-wood materials, cereals, pasture harvested from the land, and seafood produced in the sea, rivers and lakes) are converted into biomass products (such as fuelwood, charcoal, paper, timber and food) by the biomass-processing industries (such as for paper and pulp, food and livestock industry). They are consumed by human beings. Some of them are recycled. In these processes, biomass residues are discharged and can be used for energy production.

This is divided into plantation bioenergy produced on the land and bioenergy residues discharged during the processes of harvesting, conversion and consumption for food, timber and paper.

A “Biomass-Balance Table” scheme is analogous to that of an energy-balance table: it shows the harvesting, conversion and consumption of biomass systematically.

In this study, we made tables for the world, a developed region, a developing region, 10 regions in the world (corresponding to New Earth 21 model) in 1990, expressed in Joules, but due to limitations of space, tables for only the world and Japan are shown.

Biomass processes as a result of (harvesting, conversion and consumption) are expressed in the columns, and biomass forms (primary, secondary and scrapped biomass) are expressed in the row. “Bioenergy consumption” in the column means the biomass used for energy production, i.e. the input to energy-conversion equipment. A positive value indicates harvesting, production or an import, whereas a negative value means an input, a consumption or an export; – indicates that there is no process.

For example, “industrial roundwood” in the row in Table 2A has an annual indigenous production of 0.39 EJ plus 0.5 EJ is imported and nothing exported. There is a supply of roundwood equivalent to 0.89 EJ in Japan. For woodpulp production, 0.39 EJ of roundwood is used and for timber production 0.50 EJ is used. Also 0.39 EJ of industrial roundwood used for woodpulp production becomes 0.17 EJ of woodpulp, 0.18 EJ of black liquor, and the rest, i.e. 0.04 EJ, is counted as a loss. For “Black liquor”, all the ultimate bioenergy potential of 0.18 EJ is used for energy production as shown in Table 2A.

Most data are derived from FAO (Food and Agriculture Organization) statistics.

1. Heating values: 15 GJ/t for general wood (of 20% moisture content), 28 GJ/t for charcoal, 12.5 GJ/t for black liquor are used.

2. Charcoal, fuelwood and other fiber: 1 J-charcoal is produced from 2.5 J-fuelwood. We assumed a conversion rate from other fiber crops (such as straw, bagasse, and bamboo) into other fiber pulp as 40%.

3. Industrial roundwood residue and fuelwood residue: It is assumed that 61% of forest biomass above ground is harvested and the rest is left in the forest. When 1 unit of industrial roundwood is produced, 0.64 ( ) units of industrial roundwood residues are discharged. On the other hand, when fuelwood is harvested, small branches are also harvested, so the discharge rate of fuelwood residues are set at 19.5%, i.e. half that of industrial roundwood residue. Therefore in producing 1 unit of fuelwood, 0.24 ( ) units of fuelwood residues are discharged.

4. Paper and pulp production: According to the data from the paper and pulp industries in Japan, process losses except that for producing black liquor are very little [a loss at the pulp production process is 1.4% (0.36 Mt) of input value, a loss at paper production process is 1.6% (0.46 Mt) of input value]. So we did not assume any loss for the pulp and paper production process.

5. Paper recycle and scrap: Some scrapped paper is recycled to make pulp. We assumed that the amount of the pulp made from scrapped paper recycling is set to cover the pulp shortage, which occurs when only woodpulp and other fiber pulp are used for paper production.

6. Timber recycling and scrap: Some small wood chips (6.57 Mt) and scrapped wood which are discharged during construction work (7.5 Mt) are recycled (the former being 3.09 Mt and the latter 2.3 Mt) in Japan in 1990. We assumed all of the above recycled timber is used as fuel. There is no global data available about this, so we did not put any figure into tables for regions other than Japan.

1. Heat value: Each heating value for food biomass is calculated on the basis of the data in “supply per capita (cal/cap)”*“population (cap)”/“food supply (ton)” which are shown in FAO Agrostat PC.

2. Energy crops: In Brazil 0.24 EJ of liquid fuel was produced from sugarcane in 1990.

3. Crop residue, sugarcane residue: 1.3 t (i.e. 15.6 GJ) crop residues are discharged from 1 t crop. From 1 t sugar cane, 0.15 t (0% moisture) (i.e. 2.30 GJ) of sugarcane residues are discharged.

4. Bagasse: 0.283 t (50% moisture) (i.e. 2.13 GJ) of bagasse is discharged from 1 t sugar cane. In Brazil, 0.48 EJ of bagasse was used for energy in 1990. In Okinawa, Japan, 0.25 Mt (2.6 PJ) bagasse was used in the same year.

5. Animal food production: Feed put into livestock is mainly converted into meat (such as dressed meat, milk, eggs and animal fat), dung and energy for respiration. For the conversion rate of the livestock digestion process, we used the livestock data for Japan in 1990.

6. Kitchen refuse: Food energy supply per capita was 2633 kcal/day, caloric intake was 2061 kcal/day, and the rate of loss was 21.8% in Japan in 1990. Therefore, we assume 21.8% of food supply is scrapped as kitchen refuse.

7. Human growth, respiration and human faeces: Using the characteristics of the digestion process of pigs, we assumed that 30% of caloric intake becomes human faeces. This is available for energy use. but at present it hardly leads to any net useful energy. So we did not assume any useful energy production here.