抄録
Objective. Domestic woods are generally recognized as eco-friendly material compared with imported ones because of its short distance for transport. However, there are not so many studies looking at GHG emissions between domestic and imported woods based on life cycle thinking. In this study, we estimate GHG emissions from log production and manufacturing to the point of consumption in Japan of domestic and imported wooden building materials, using life cycle inventory analysis. The products were classified as follows from view point of its origin in order to get more reliable results in this study. 1) The term “domestic products” means products are manufactured in Japan from raw material to product. 2) The term “quasi-domestic products” means products are manufactured in Japan except raw materials, i.e., raw materials for quasi-domestic products are manufactured abroad. 3) The term “imported products” means products are manufactured abroad from raw material to product.
Results and Discussion. In a comparison of GHG emissions under the same energy conditions of the boiler, the emissions of “domestic products” were lower than that of “quasi-domestic products”, but were not always lower than that of “imported products”. These are two major reasons. One is that the structure of electricity causes a significant decrease in the emissions from the production process in foreign country. The other is that the emissions from product transportation are not so great because density of the products are lower than that of logs, and energy consumption of a ship for a unit product is smaller than that of a truck.
Conclusions. The results showed that environmental superiority of the wooden building materials should not judged only by the transportation miles. In carrying out a life cycle inventory analysis of the imported wooden building materials, it is necessary to set up the evaluation condition such as the electrical power consumption rate, the energy source of the boiler, the pathway and means of its transportation. While it is important for “domestic products” to use factory waste wood for the boiler, there is limitation to reduce the emissions from the production process because of constraint of the electrical power consumption rate. To supply more eco-friendly wooden products, we have to consider how to reduce the transportation distance of logs.
