Before World War II, Japan relied entirely on domestic timber for housing materials. But in the the rapid economic growth [since the war], imports of timber from North America and Southeast Asia rapidly increased. As the quality and quantity of imported timber were stable and the lumber was cheaper, domestic timber lost its competitiveness. Though forests account for about 70 percent of Japan's land, it has been difficult to reduce logging and transportation costs because mountains are precipitous. Sluggish sales of domestic timber are damaging forests.