Plants are covering the peak of Mount Oyama on Miyakejima island south of Tokyo for the first time since the volcano erupted in July 2000.
"The amount of volcanic gases has significantly declined since last year, likely allowing plants to grow rapidly around the summit," said Hiroyoshi Higuchi, a professor emeritus of the University of Tokyo, who has been studying the ecosystem of the island each year since the eruption.
The eruption forced the evacuation of all islanders.
The peak of Mount Oyama is still off-limits, so Higuchi observed the top from a distance in July.
In 2002, weeds were found at an altitude up to 400 meters on the 775-meter mountain, indicating the ecosystem there would soon recover.
However, volcanic gases killed trees that had survived the eruption and continued to spew out from around the summit, making life impossible there.
Around 1,000 tons of gas were released daily even 10 years after the eruption, according to the Japan Meteorological Agency. The volume started dropping sharply in the latter half of last year, and now dozens of tons of gas are released daily.
Higuchi’s observation found "hachijo susuki" and "hachijo itadori" plants growing, as well as a shrub called Alnus sieboldiana around the mountain summit.
With the plants covering a wider area, birds such as the Japanese white-eye and bush warbler were found even at relatively high altitudes, he said.