The researchers estimated the changes in how much plants grow in Japan's forests from 1980 to 2005. They used data from forest surveys and direct measurements to calculate the amount of plant growth above the ground. They found that overall, the amount of plant growth increased by 1.9 Mg per hectare per year, mainly because of new plantations and fast growth in these planted forests. This increase in plant growth is important for understanding how forests in Japan are contributing to capturing carbon from the atmosphere.