Risk of Natural Spread of Hymenoscyphus fraxineus with Environmental Niche Modelling and Ensemble Forecasting Technique

Ash dieback, caused by the ascomycete Hymenoscyphus fraxineus, is rapidly expanding over large geographical areas in Europe. A myriad of factors influence pest invasions and long-term establishment, i.e., species’ life stage, the availability of suitable hosts and the suitability of the environment. This paper examines the principal environmental features that characterise naturally infected zones in order to forecast the potential distribution of the pathogen within the ranges of European ash species by means of Species Distribution Modelling and an ensemble forecasting technique. Furthermore, a network analysis permitted dispersal dynamics to be included in order to obtain realistic risk predictions for the natural spread. The multi-modelling procedure allowed the most endangered regions to be identified as the central and eastern Alps, Baltic States, southern Finland and the area encompassing Slovakia and southern Poland, whereas most marginal regions of the study area appeared less suitable for the natural establishment and spread of the disease. Statistical model predictions were highly correlated with abundant summer precipitation, high soil moisture and low air temperature. A novel approach to the ensemble forecasting technique in epidemiological modelling of plant pathogens is suggested as a tool to aid the survey of this infectious disease. Moreover, the final potential distribution maps may promote discussions about the control of the disease and the risks associated in the trade or movement of ash species.