Monitoring of Tree Crown Condition for Detecting Decline and Damage of Japanese Forests in the 1990s

Abstract

Japan was covered with a grid having a 20 km ~ 20 km mesh size, and an appropriate monitoring site was selected for each mesh (total 1000 sites). Thirty percent of the monitored stands had trees with some symptoms of decline or damage in the tree crown, primarily due to high tree density of the stand. Damage caused by severe climate conditions such as typhoons and heavy snow was the second leading cause. Insect damage and fungal deceases were found in 3% of all the stands. Unknown causes, which suggest forest decline from air pollution and acid rain, were responsible for less than 10% of the damage in all stands. The monitoring confirmed the absence of damage due to anthropogenic pollutants in Japanese forest areas.