This paper analyzed the relation between such environmental condition as the amount of insolation' temperature and the flowering amount of wild Rhododendrons in the secondary forest floor of the northwest Kumamoto, Kyushu. As a result of the correlative analysis, there was positive correlation between the amount of insolation in the first ten days in June on the flowering initiation and flowering amount of the two species of Rhododendron in the next year. The flowering amount of Rhododendron kaempheri increases at the convex site or the slope site and the flowering amount of Rhododendron reticulatum tends to increase at the East slope site. Also, as a result of the multi regression analysis, the following became in the clarifying. The flowering amount of R. kaempheri tends to increase under the cool environment with low temperature through the all day. The flowering amount of R. reticulatum tends to increase in the site where becomes cool in night and becomes a high temperature sufficiently in the daytime. On the other hand, since the investigated forest was dominantly composed by broad leaves evergreen trees and shrubs, in the natural succession, wild Rhododendron's flower was hardly seen. Thus it is considered that is a possibility of making the Rhododendron to produce more flowering amount, even including in the dark stands, by the thinning and removing broad-leaved evergreen trees and shrubs at a suitable rate.
