Survival and Mortality Rates for 17 Years in a Quercus serrata Secondary Forest Damaged by Mass Mortality Due to Japanese Oak Wilt

Abstract

In 2009, mass mortality caused by Japanese oak wilt was confirmed in a Quercus serrata secondary forest at Shimane University. In a 1 ha study area within the forest, we investigated Q. serrata stem diameter, mortality, and survivorship from 2001 to 2018, and the distribution of dead oak trees from 2012 to 2014. Although the total basal area of stems had been increasing before the occurrence of Japanese oak wilt, the area decreased continuously until 2018 after the infection occurred. Many small oak trees had died before the outbreak, while the disease killed various sized trees in 2012 and 2013 and killed small ones in 2014 when it spread. Moreover, the trees killed by the disease were in the valley. The numbers of dead trees found in 2013 and 2014 were similar to those found during the 5 years prior to disease occurrence. During the 17-year study period, the mortality rate due to Japanese oak wilt was 18.1％, whereas that due to other factors was 32.2％. We predict that this mass mortality event will alter the structure of this secondary forest, due to the rapid death of various sized trees, including large ones.