Six indicators of material cycles for describing society's metabolism: application to wood resources in Japan

We estimated the material flows of wood resources during the period 1960-1999. By applying our six proposed indicators, we discussed the state of material cycling of wood resources. Through this analysis, we examined the utility and feasibility of the indicators: direct material input (DMI), use rate of recovered used products (URRUP), material use efficiency (MUE), material use time (MUT), recovery rate of used products (RRUP), and domestic processed output (DPO) for measuring the consumption of natural resources, recovery of used products (input side), recovery of by-products, reuse of used products, recovery of used products (output side), and the environmental load, respectively. We draw the following conclusions: (1) during 1960-1999, MUE (recovery of by-products) has been consistently high and both URRUP and RRUP (recovery of used products) have increased. However, DMI (the consumption of natural resources) and DPO (the environmental load) have not decreased. The recoveries of by-products and of used products have restrained the consumption of natural resources and the environmental load. However, they have not been able to reduce them; (2) MUE (recovery of by-products) is already relatively high. Therefore, the main goals in promoting material cycling in the future will be increase in MUT (reuse of used products), URRUP, and RRUP (recovery of used products). This is especially needed for used wood products. For wood products, MUT (reuse of used products) should be regarded as an important indicator as well as URRLT and RRUP (recovery of used products), because most wood products are durable. On the other hand, for paper products, URRUP and RRUP (recovery of used products) are more important than MUT (reuse of used products), because most paper products are used for short-term purposes; (3) the six indicators of material cycles are useful for analyzing the state of material cycles and discussing the future goals of material cycling. Among the practical problems in capturing material flows and calculating indicators, to capture the product stocks is most difficult to be solved. (C) 2003 Elsevier B.V. All rights reserved.