The Effect of Improvement of Light Condition on Flowering of Wild Rhododendron in Secondary Forest Floor

Abstract

Such wild Rhododendron as R. reticulatum, R. kaempferi and R. macrosepalum are frequently seen in abandoned secondary woodlands in which fuel material is no longer gathered. Since the forest canopy and floor shrubs intercept the sunlight, the Rhododendron produce few blooms due to the light shortage. The purpose of this paper is to ascertain the reasonable light condition or stand composition in which flowering will occur when we utilize the forest for recreational use. For the previously listed three species, experimental work and field surveys were conducted in Quercus woods or Pinus woods in Miki in Hyogo prefecture and in Musashi Hill in Saitama prefecture. The results are as follows: The data suggest that at least 30% relative light intensity is necessary for satisfactory flowering of R. reticulatum, 20% in the case of R. kaempferi, and even 40% is not adequate light for R. macrosepalum. The flower color becomes more pale under the darker condition, and the number of blooms decreases significantly with only 5-10% reduction in the specified light levels. An anatomical survey revealed that the beginning of flower formation occurs about 1st-8th in July. Therefore, it is necessary that at least by the beginning of June we must provide the appropriate tree stand density in order to open the canopy and remove floor shrubs except the Rhododendron.