Carbon sequestration is suggested as a low-cost option for climate change mitigation, the functioning of which can be threatened by pathogen infestation. This study calculates the effects of infectious pathogens on the cost of achieving the EU's 2050 climate targets by combining the so-called production function method with the replacement cost method. Pathogens are then assumed to affect carbon sink enhancement through the impact on productivity of forest land, and carbon sequestration is valued as the replacement for costly reductions in emissions from fossil fuels for reaching the EU's 2050 climate targets. To this end, we have constructed a numerical dynamic optimization model with a logistic forest growth function, a simple allometr+ic representation of the spread of pathogens in forests, and reductions in emissions from fossil fuels. The results show that the annual value of forest carbon sequestration ranges between approximately 6.4 and 14.9 billion Euros, depending on the impact and dispersal of pathogens. Relatively large values are obtained for countries with large emissions from fossil fuels, e.g., Germany, France, Spain and Italy, which also face costs of pathogen together with countries with large forest area, such as Romania. © 2018 by the authors.