The predicted increase in temperature, dry summers, and extreme meteorological events will affect many harmful species both by directly accelerating their propagation rates as well as by weakening their host plants. There might also be shifts in the interrelations in species communities that can hardly be predicted. Some fungal species, that had previously been inconspicuous, caused notable damages in the drought periods of the last two decades. Higher winter temperatures often increase the survival rates of many fungal and insect species. Because hot and dry summers are likely to become more frequent and heavy storms tend to occur more often, an increase in massive outbreaks of bark beetles with corresponding damage is to be expected. As a result of global trade, more invasive alien fungi and insects are introduced into Europe where the climatic conditions become more favorable for them to establish themselves on native or introduced host trees.
Insects and diseases can have a profound impact on forest dynamics. Therefore, these disturbances must be included in the discussion of future tree species composition and of forest development scenarios.