The relationship between the number of boring by Platypus quercivorus and the wood of water content in the mass mortality of oak trees

Abstract

We investigated the decline of oak trees in Tottori Prefecture from 1994 to 1996. In 1994, the mass mortalities occurred in four towns and villages of the eastern part of Tottori Prefecture, and in 1996 also in Koge town, the south side of the area of decline in 1994. The dead trees were mass-attacked invariabley by Platypus quercivorus. In one of our experimental plot, the mortality rate of Quercus mongolica was higher than that of Q. serrata, and the enlargement growth was larger in dead trees rather than live trees in Q. mongolica. There was large variation in water content among Quercus trees. This variation persisted for experimental period. The water content of a dead tree had been always within the range of those of 10 live trees. So, it was suggested that water content would not be an indicater of the wilting.