Returning to Japan in 1960, he applied the methods of mapping potential natural vegetation (PNV). He found relics of ancient forests still present in the vicinity of temples and shrines (surrounding Chinju-no-mori sacred groves). Inventorying over 10,000 sites throughout Japan, he was able to identify this potential flora affected by different types of human activity, including in mountainous areas, river banks, rural villages and urban areas.