Human Use of Land and Organic Materials: Modeling the Turnover of Biomass in the Global Food System

Sammanfattning: This thesis is directed towards the issue of the long-term demand and supply of biomass for food, energy and materials. In the coming decades, the global requirements for biomass for such services are likely to increase substantially. Therefore, improved knowledge of options for mitigating the long-term production requirements and the associated effects on the Earth system is essential.

The thesis gives a thorough survey of the current flows of biomass in the food system. This survey was carried out by means of a physical model which was developed as part of the work. For eight world regions, the model is used to calculate the necessary production of crops and other phytomass from a prescribed end-use of food, efficiency in food production and processing, as well as use of by-products and residues. The model includes all major categories of phytomass used in the food system, depicts all flows and processes on a mass and energy balance basis, and contains detailed descriptions of the production and use of all major by-products and residues generated within the system.

The global appropriation of terrestrial phytomass production induced by the food system was estimated to some 13 Pg dry matter per year in 1992-94. Of this phytomass, about 0.97 Pg, or 7.5 percent, ended up as food commodities eaten. Animal food systems accounted for roughly two-thirds of the total appropriation of phytomass, whereas their contribution to the human diet was about one-tenth. Use of by-products and residues as feed, and for other purposes within the food system, was estimated to about 1.8 Pg dry matter, or 14 percent of the total phytomass appropriation.

The results also show large differences in efficiency for animal food systems, between regions as well as between separate commodities. The feed conversion efficiencies of cattle meat systems were estimated to about 2 percent in industrial regions, and around 0.5 percent in most non-industrial regions (on gross energy basis). For pig and poultry systems, feed conversion efficiencies were roughly a factor of ten higher. The differences suggest that there is a substantial scope for mitigating the long-term production demand for crops and other phytomass by increases in efficiency and changes in dietary preferences.