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Forest under pressure: Diseases, pests and disturbances

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Forests are exposed to a wide range of disturbances, including damage caused by insects, pathogenic agents and storms. Non-native organisms also alter various ecosystems. We investigate how illnesses affect trees and forests, how they can withstand such disturbances and how well they recover afterwards.


Fungi and – in rarer cases – bacteria, nematodes, phytoplasms or viruses along with a huge variety of insects infest and cause harm to trees. Disease can cause symptoms in all parts of the tree, such as the roots (e.g. phytophthora), the bark (as is the case for bark beetles) or in the crown (ash dieback).

Trees weakened as a result of dryness, frost, poor light or nutrients are more susceptible to pests and diseases. Climate change is expected to increase infestation by harmful organisms. A warmer climate will also favour the survival of non-native pests, which trees are less well-equipped to combat than native pests.