Validation of treatments for conservation of native rhododendrons, the symbol of Satoyama, in the dry granite region of Japan

概要

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To develop an appropriate method of conservation for the native Rhododendron sections Brachycalyx and Tsutsusi, the symbol of Satoyama, field experiments were performed in the dry granite region in Japan. When carpet-type landscape of native rhododendrons was desired, all plants were cut at 20 cm above the ground level of all trees and shrubs, and the herbs and ferns were weeded (once and three times, respectively). When the shrubby-type landscape of native rhododendrons was desired, all plants, excluding native rhododendrons, were cut at 20 cm above the ground level of all trees and shrubs, the herbs and ferns were weeded, and the litter was swept. After three years of monitoring the percentage and depth of crowns with flower buds, the following major results were obtained. Cutting all plants excluding native rhododendrons was effective to keep the depth of crowns with flower buds. However, weeding and sweeping of litter on the ground caused desiccation of surface soil, which induced a transitory decrease in the percentage of crowns with flower buds. One weeding was effective in keeping the depth of crowns with flower buds; however, the second and third weeding had no distinct effect. In a dry granite region, considerable attention to desiccation of surface soil is critical, in opposition to limiting attention to maintenance of sunlight, which is the common practice.