Forest health under climate change: impact of insect pests

The impact of climate change on forests is difficult to predict, as it depends on multiple factors and the final effect may vary in different parts of our planet. However, these effects can be sorted in “direct”, when they act directly on plants, and “indirect”, when they act through other agents. Among the indirect ones, there are those mediated by biotic factors, particularly insect pests. The impact of climate change on insect pests varies depending on the insect species and the type of forest. Some plant-feeding insects may be disfavoured by climate change, with a consequent reduction in population density and thus in damage to forests. However, many outbreaks of forest insects have been recently recorded as related to climate change. In fact, some insect pests, in certain regions of the world, may benefit from higher temperatures, as it has been demonstrated for some devastating defoliators. In addition, more frequent drought and extreme events may favour other pests, particularly bark beetles and wood-boring insects. Bark beetles are the most dangerous ones because their aggressiveness changes with population density. They can attack only stressed trees at low population densities, while, once the populations have reached high density, they are even able to attack healthy trees in widespread areas.