富山県における森林生態系多様性基礎調査データを用いたナラ枯れ被害材積統計値の検証

Abstract

Statistics regarding wood volume damaged by Japanese oak wilt (JOW) are presented annually in the governmentʼs annual report on forests and forestry. Although these statistics are used as basic information to consider countermeasures against damage due to JOW, they are unverified. Therefore, in this study, the statistics for private forests of Toyama Prefecture, where an epidemic of JOW occurred from 2004 to 2011, were verified. The statistics were based on the number of dead crowns counted visually from roads. The total statistics of damaged wood volume from 2002 to 2017, encompassing the period when mortality from JOW occurred, was 0.12 million m 3 . In contrast, the estimated damaged wood volume calculated from two successive measurements before and after the JOW epidemic in 101 plots of the National Forest Inventory, was 1.78 ± 0.81 million m 3 (point estimate ± 95％ confidence intervals). This suggests that the statistics are an underestimation; the main reason for this is probably the existence of parts that cannot be visually observed. The volume loss rates of Quercus crispula and Quercus serrata were estimated as 57 and 9％, respectively; thus, the impact of JOW on forest resources was clarified at a regional scale.