The upper reach of the Tama River in Japan, is located between valleys, and chasmophytic vegetation is formed on the rock along the river. The vegetation consists of shrubs including Spiraea thunbergii and herbs. In common with other riparian vegetation, chasmophytic vegetation is easily influenced by flooding. According to water level-observational data in Chofubashi gauging station (Ome-city, Tokyo), flooding in September 2011 was the second-largest after September 2007 in the last decade, and water level rose by nearly 2-2.5m. We have observed several sites (mainly Oyanagi area and Sawai area) in the upper reach of the river since 2007.

We observed the sites after flooding in September 2011 to examine effects of this flooding on chasmophytic vegetation. Degree of destruction of vegetation by this flooding was observed less than flooding in September 2007 in Sawai area. Many leaves of individuals of S. thunbergii growing between rocks were come off of the branches there.

In winter, we set up 6 quadrats (five were 10cm×10cm and one is 30cm×35cm) at moss cover on rocks in November 2011 and then monitored number of seedlings of vascular plants regularly to examine the effects of moss cover on seedlings of vascular plants. We have observed growth stage of S. thunbergii since November 2011 and confirmed that a portion of S. thunbergii has bloomed out of season.