Differential phase of Platypus quercivorus attacks in urban green space: A case study on 2 urban parks in Tokyo

Abstract

The ambrosia beetle Platypus quercivorus (Maruyama) transmits the pathogenic fungus Raffaelea quercivora Kubono et Shin. Ito, causing Japanese oak wilt and subsequent tree dieback. In recent years, there has been a marked increase in mortality of secondary forests due to Japanese oak wilt, especially in suburban and urban parks, as P. quercivorus finds suitable host trees and environments. To prevent extensive mortality from P. quercivorus attacks, it is crucial to establish effective management strategies for secondary forests. In this study, we aimed to investigate the occurrence patterns of P. quercivorus attacks and identify effective management strategies in urban parks that have experienced recent outbreaks of Japanese oak wilt to find any hints for establishing effective management strategies. Over a two-year period, we surveyed the occurrence of P. quercivorus attacks on Quercus serrata Murray trees along walking trails and assessed surrounding conditions. Through data analysis, we identified significant factors influencing attacks. The results revealed distinct differences in host tree condition and attack severity between parks. Although the proportion of attacked trees in one park markedly increased over the two-year period, the other park remained stable, suggesting different attack phases between parks. In the former park, the occurrence of attacks was positively correlated with tree size, severity of nearby attacks, and nearby tree dieback but negatively correlated with surrounding tree density and occurrences of last year attack. Conversely, in the latter park, only occurrences of last year attack showed a significant negative correlation with attack occurrence. This discrepancy may be attributed to variations in the attack phase of P. quercivorus in each park. From a management perspective, park managers should establish flexible forest management strategies in suburban and urban parks to adapt to different attack phases.