What’s happening to Norway spruce trees in Trentino?

There’s an outbreak of European spruce bark beetles in our woods

In the woods of Trentino, there’s a widespread outbreak of European spruce bark beetles. The insects mainly attack Norway spruces and the clearest sign of their presence is a rusty red colour in the leaves of trees during the summer, which is totally different from the hues traditionally seen in autumn foliage.

But what are European spruce bark beetles? Why are they spreading so widely? What can be done to deal with them? Read the article to find out.


What are European spruce bark beetles?

The European spruce bark beetle (Ips typographus) is a species of beetle that is 4-5 mm long, cylindrical and brown. It is native to the woods of Trentino and mainly attacks Norway spruce trees, burrowing under the bark to form complex, highly distinctive networks of tunnels that look like writing, hence the word “typographus” (which means “printer”) in the scientific name of the species.

Unfortunately, these tunnels block the flow of sap, quickly leading to the death of the host trees.


Why are they becoming a problem?

Populations of European spruce bark beetles are naturally found in the woods of Trentino. In normal circumstances, the insects play an important ecological role by attacking trees that are weak or have come to the end of their life cycles. However, they are reaching epidemic levels due to Storm Adrian and climate change.

The former was the biggest contributing factor. Storm Adrian in October 2018 damaged huge numbers of trees and made them vulnerable to infestation by the insects. Toppled trees provided significant amounts of food for European spruce bark beetles, thus enabling them to reproduce on an extraordinary scale and increasing their population density.

Their spread was also favoured by a long period of hot, dry weather in spring and summer.

The trees that survived the storm were extremely vulnerable to attacks by European spruce bark beetles, partly because they were weakened and partly because the insects put them under huge amounts of pressure.


What impact do the beetles have on trees?

Both the larvae and the adult beetles burrow under the bark of trees. Their tunnels block the flow of sap, leading to the death of the host trees.

Infected trees can be spotted because their foliage changes colour. The shades of the affected leaves can range from amber yellow to rusty red. In general, this means that the insects have already moved on.

In the final stage, the trees turn grey and lose all of their needles. By this point, the beetles will be long gone and the trees will soon be dead.


What can be done to contain the epidemic?

The plant health and forestry authorities in the affected areas are actively monitoring and taking measures to contain European spruce bark beetle populations.

The most effective way to contain their numbers is to identify infected trees early and fell them immediately, then strip their bark or remove them from the woods. This obviously has to be done very carefully and without exposing the area to hydrogeological hazards.

If the leaves have already turned red or grey, it is best to actually leave the trees in the woods to protect the ones that are still healthy. As well as shading other plants from sunlight, these trees can help to contain bark beetle populations because they still contain natural enemies of the insects.


Nature takes its course

The circumstances of the current outbreak are exceptional but it is nonetheless a natural phenomenon. All of the practical difficulties associated with such a widespread attack must be taken into account during the management of the situation. The population is expected to increase in the coming years and eventually reach numbers that will lead to a sharp decline, due to competition for food and mates, natural enemies of the beetles and resistance from trees that manage to adapt to the new environmental conditions, thanks in part to forest management measures.

A new development phase will then begin in the woods. New species of trees will arrive and – over the course of a period spanning at least a hundred years – this will lead to diversification in the composition of the woods, leaving the entire ecosystem more capable of withstanding any future disasters.


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Published on 23/11/2022