An international team of researchers has assessed the potential economic impact of the invasive pathogen Phytophthora ramorum, which causes forest decline and tree mortality in Europe. The study, co-authored by Dr Thomas Jung from the Faculty of Forestry and Wood Technology at MENDELU, estimates that annual losses could exceed €247 million under worst-case scenarios. The findings have been published in Forest Ecology and Management and provide important information for forest health management and policy development across Europe.
Phytophthora ramorum is an invasive, airborne plant pathogen that was introduced to Europe and North America in the 1990s. It is responsible for two lethal bark canker epidemics of major forest trees, Sudden Oak Death in the western United States and Sudden Larch Death in several European countries. The pathogen affects more than 170 plant species and can cause extensive forest decline and tree mortality.
“The pathogen has been present in Europe for more than three decades, but until now no quantitative assessment existed of its potential economic impact on European forestry,” explained co-author Dr Thomas Jung from the Department of Forest Protection and Wildlife Management, MENDELU.
To address this knowledge gap, researchers from Wageningen University, MENDELU, and collaborating Australian institutions combined climate modelling, forest distribution data, and economic analysis. Using the CLIMEX climate niche model with updated parameter values refined according to pathogen ecology and lifestyle and Phytophthora ramorum occurrence records from symptomatic forest trees, they identified areas where environmental conditions are favourable not only for the survival of the pathogen but also for disease development in forest trees, symptom expression, and tree mortality.
The results show that approximately 10% of Europe’s land area provides optimal climatic conditions for disease expression. Within these regions, around 4,223 km² of larch (Larix decidua) forests and 2,577 km² of beech (Fagus sylvatica) forests are considered particularly vulnerable. The highest risks were identified in countries such as the United Kingdom, Italy, Austria, Germany, Ireland, and Switzerland.
“Our analysis focused on larch and beech, two economically and ecologically important tree species in Europe. We found that climatic suitability for Phytophthora ramorum inoculum production, spread and infection, and host distribution strongly influence where serious damage may occur,” said Thomas Jung.
The researchers then modelled various disease-spread and tree-mortality scenarios. Under the most severe assumptions, annual direct damage costs could exceed €117 million for larch forests and €130 million for beech forests. Even under moderate scenarios, losses could reach tens of millions of euros per year.
According to the authors, the study highlights the importance of continued monitoring and management efforts. While current regulations focus on limiting the spread of P. ramorum, the results demonstrate the potentially significant economic consequences if the pathogen becomes more widespread in susceptible forest ecosystems.
“The study provides updated information on the current post-invasion situation in Europe and offers valuable support for decision-makers developing forest protection strategies under changing environmental conditions,” concluded Thomas Jung.
The study was published in 2026 in the journal Forest Ecology and Management (volume 601, article 123367) under the title Modelling disease expression of Phytophthora ramorum to estimate potential economic impacts in European forests
Photo: Coastal forest in California with high mortality of tanoaks caused by Phytophthora ramorum.
Contacts for more information: Dr. Thomas Jung, Phytophthora Research Centre, Department of Forest Protection and Wildlife Management, Faculty of Forestry and Wood Technology, MENDELU, Brno; thomas.jung@mendelu.cz
Stelios Kartakis, Wageningen University, Agricultural Economics and Rural Policy Group, Wageningen, the Netherlands; stelios.kartakis@wur.nl
This publication received funding from the European Union’s Horizon Europe project Plant Pest Prevention through Technology-Guided Monitoring and Site-Specific Control (Grant Agreement No. 101060634).
Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or European Research Executive Agency (REA). Neither the European Union nor the granting authority can be held responsible for them.
