Top Dieback of Cryptomeria japonica in Artificial Stands in the Chichibu Mountains

In recent years, actual conditions of the decline of mature Cryptomeria japonica (Sugi) in the Kanto plains have been often described. The cause of decline is not clear yet. Since top dieback of Sugi was obserbed in the 1980\u27s in the Chichibu Mountains of the Kanto district, the phenomena were examined with reference to the decline of Sugi. Detailed drawings of the top-dieback of Sugi were made and discoloration and decay of the wood was investigated. The electrical resistance of the heartwood decreased sharply below 180-200 kΩ, which is the critical reading for discoloration and decay, both of sound-looking and top-dieback Sugi. This phenomenon seems to be unique. However, any relations to cation consentrations such as K, Ca, and Mg were not found. As for micro flora in the wood of Sugi, several fungi and bacteria were isolated both from sound-looking and dieback Sugi. In mature Sugi, many kinds of fungi were isolated, however, some negative correlation was found in relation to electrical resistance in the living wood. For monitoring the water status of living Sugi, pressure-volume analysis was used. There were no differences in the water status between sound-looking and top-dieback Sugi. From the results of stem analysis and actual observation of top dieback, decreasing leaf mass seems to have occurred 4 or 5 years before. At the same time, diameter growth declined. Thereafter, the death of the tree top appeared. Therefore, decline of growth seems to have been caused by the decrease of leaf mass due to defoliation. At present, the cause of the defoliation is not clear. However, possible reasons for the decline of diameter growth of Sugi were discussed with reference to environmental stresses in the Chichibu Mountains