Invasions of forest pathogens generally occur at a large scale affecting tree species with a widespread distribution in Europe. This project will focus on selected tree species currently threatened by different invasive pathogens; elm (Ulmus minor/ U. glabra) and Ophiostoma novo-ulmi (causing Dutch Elm Disease), ash (Fraxinus excelsior) and Chalara fraxinea (causing ash dieback), alder (Alnus glutinosa) threatened by Phytophthora alni and oak (Quercus spp) being affected by both Erysiphe alphitoides and P. cinnamomi. The selected tree species are not only an integral part of their ecosystems but are also economically important and supply crucial environmental services to European society, such as biodiversity, watershed protection, climate regulation, stabilisation of river banks, as well as recreational and cultural values. Thus, a multidisciplinary approach is required to evaluate the impact ofinvaders in economic terms.
Due to different mortality patterns, the array of host-pathogen combinations enables the study of differential effects on the host population in terms of demographics and evolution. Although widespread, the different invasive pathogens to be studied here have not yet affected the entire tree population in Europe. The participating countries in the proposal cover a range of sub- populations of the selected tree species which have experienced the invasive pathogens for different periods of time or not yet affected. Working at a European scale will allow us to study invasions at different stages and along gradients far exceeding those obtained at a national scale.
The economic team in the project will calculate the effects of pathogens on the value of European forests as carbon sinks in the EU 2050 climate policy. The value is then calculated as the reduction in costs for reaching climate targets when forest carbon is included compared to when it is not included. Several studies have shown that this value of forest carbon sink can be considerable. When pathogen hampers forest growth, this value will be reduced. In this project, a dynamic optimization model which accounts for forest growth is developed for calculating the effects of pathogens on the value of forest carbon sink.