The Crown Prince attended a greenery protection meeting Sunday in the town of Motobu, Okinawa Prefecture.
About 1,000 people from across the country attended the meeting, at which 109 groups involved in local greenery promotion activities were honored.
Among those honored was a group from Nagasaki Prefecture, which has been attempting to revive forested areas around Mount Unzen on the Shimabara Peninsula in the prefecture since a volcanic eruption there in 1990.
"I believe it is our duty to protect and grow greenery as an important property to pass on to the future," the Crown Prince said at the gathering.
The Crown Princess had been scheduled to accompany her husband on the three-day Okinawa visit, but following the announcement Monday that the princess is showing signs of pregnancy, the prince made the trip alone.