森林資源の利活用に関わる建築分野での環境負荷削減策に関する研究

MFA・LCAを用いた全国及び広島県の環境動態分析

抄録

 This study was aimed to clarify the environmental dynamics in the life cycle of woody resource and its utilization through material flow analysis and lifecycle assessment, which were focused on the areas of Japan nationwide and Hiroshima Prefecture. In addition, from the viewpoint of the party involved in building industry, discussion was made about effective measures for environmental impact reduction. The results were as follows:

 

 1) Material flow analysis

 A set of material flows was developed as of the year 2016 to represent the whole life cycle of woody resource, which actually included processes in building industry, forestry and lumbering, and pulping and paper making. Also, as for processes with large outputs, they were subdivided into as many segments as practically possible.

 The results showed that, in comparison to the Japan (nationwide, 2010) and Hiroshima Prefecture (2012) respectively in the amount of lumber consumption, the outputs of our study (2016) showed only slight increase; and also that, in each area of Japan and Hiroshima, the ratio between domestically produced to imports was nearly 1 to 1. However, as for consumption of domestic lumber, nearly 80% of it was used for buildings in Japan and only a little more than 40% in Hiroshima. This clear-cut difference suggested that most careful consideration should be given to way of resource utilization in building industry. In addition, the material flows developed in this study helped reveal the dominant factor in each process quantitatively.

 

 2) Lifecycle assessment

 Based on the developed material flows, the environmental loads were calculated by using LCA, and thus way to reduce the loads in the building industry was discussed. In the outputs from Integration, which is a single index, the loads caused by woody resource used for buildings were a little over 40% in Japan, and more than 20% in Hiroshima Pref. In both cases, the dominant factor was log manufacturing or the process segment of growing cedar and cypress trees which includes foresting and harvesting. The results of damage assessment, which is composed of the four safeguard subjects (human health, social asset, biodiversity and primary productivity), showed that in the primary productivity the same segment was most responsible for the damages and that it affected integration significantly. And the dominant factors of primary productivity were consumption of woody resources of cedar and cypress. In view of other subjects, almost all impacts were caused by paper and pulping industry.

 Based on the results of the impact assessment, sensitivity analysis on the log manufacturing process was examined. As a result, it showed that the influence of the reforestation rate was extremely large. In this case study, it was set at 35% in Japan Nationwide and 23.7% in Hiroshima Pref. Therefore, these improvements resulted in being indispensable. If the issue of reforestation rates could be solved, the next biggest impact would be the fossil fuel consumption in each process. This suggest that reduction in fossil-fuel consumption in the lumbering process should also be very important.