Vulnerability of ten major Nordic cities to potential tree losses caused by longhorned beetles

Abstract

Urban forest and urban trees are currently facing several challenges arising from a changing climate, complex inner-city environments and severe threats of pathogen and insect attacks. The latter have already had serious consequences for many cities, with outbreaks of diseases and pests causing large-scale tree losses that will take a long time to resolve. The pest species Asian longhorned beetle (Anoplophora glabripennis) and citrus longhorned beetle (A. chinensis) have large numbers of host species and genera and can hence be classified as one of the most serious future threats to the urban (and natural) tree landscape. The question is not whether these new threats will arrive in northern Europe, but rather when an infestation will occur and how well prepared are cities to deal with it. This study presents an up-to-date compilation of the urban tree population in 10 major Nordic cities, based on recent tree inventories, and investigates and discusses the effects of an outbreak of the two longhorned beetle species, based on information taken from a review of 35 papers presenting host-related data on these species. Evaluation of the data on host susceptibility to the two longhorned beetles revealed clear differences in tree losses between scenarios, with predicted tree losses of 15–98% in the different cities.