Analysis of the windthrow of Sanbu-sugi cultivar of Cryptomeria japonica D. Don and Lithocarpus edulis (Makino) Nakai caused by the Reiwa 1 Boso Peninsula Typhoon

Abstract

The Reiwa 1 Boso Peninsula Typhoon caused many windthrows. Among them, we conducted tree census on the wind damage of the characteristic Sanbu-sugi cultivar forest and L. edulis forest. In the Sanbu-sugi cultivar forest established on the flat ground, all the stems with height / diameter ratio of 75 or more had stem breakage, and among the individuals with h/d ratio of 50 to 75, the stems with remarkable external symptoms of non-withered grooved wood decay disease increased stem breakage. The windthrow damage rate of the L. edulis forest established on land with a thick effective soil layer of 1 m or more was 66%, of which 85% was due to stem breakage. The windthrow damage rate of the L. edulis forest, which was established on a slope with a thin effective soil layer of 55 to 100 cm, was 75%, and 79% of L. edulis windthrown trees were due to uprooting.