Insect disturbances

Defoliating insects

Insect attacks can be dynamic events by defoliating insects where trees usually survive the attack and sometimes refoliate later in the growing season. An example is the sub-arctic birch forest in northern Sweden that are attacked by defoliating birch moth larvae with cycles of 9-10 years.

Beetle outbreaks following disturbance

The spruce bark beetle Ips typographus is an economically important forest pest in Europe. Spruce bark beetle outbreaks are common in Norway spruce forests following windstorm damage. The bark beetle population may increase rapidly after a storm event, as newly wind thrown trees are suitable for breeding. At high population densities, I. typographus can overcome the defense system of living spruce trees, and millions of trees have been killed by during large outbreaks.

Climate change may increase yearly beetle generations

The spruce bark beetle may become a more severe problem in the future, as a warmer climate will increase the likelihood of an additional generation per year. Ecosystem modelling is a useful tool for analyzing the interaction between factors, and we have developed a model to simulate the impact of climate change on forest predisposition to storm damage and subsequent bark beetle attacks in relation to a range of forest management options. 

Further readings

Remote sensing - monitoring ecosystem disturbances