Bark beetle invasion was found to slow tree growth early

A recent study from the University of Eastern Finland, published in Trees, Forests and People, bark has already begun to dry out before visible signs appear.

A team of researchers led by Dr. Samuli Juntila, an associate professor of forest health and earth observation, conducted dendritic measurements of bark permeated 26 bark and 31 healthy trees between 2020 and 2022.

A dendrometer is an instrument used to measure the diameter of a tree stem. In this study, a dendrometer was used to measure stem diameter with micrometer level accuracy every 15 minutes.

Researchers wanted to compare variations in stem diameter between healthy trees and those infected with bark beetles. Stem diameters vary naturally during the day. During the day, the trees evaporate more water and are thin. At night, it becomes thicker to hold more water.

“We wanted to capture this change during the day because this change is important to the tree. Tree growth occurs primarily at night when more water is available,” Junttila notes.

Researchers found that when bark enters a tree, that is, it stops growing, and when the tree dies, it slows the growth of the tree. The infected tree had a sudden drop in diameter as it began to dry out.

European spruce bark (IPS Typographus) is a bark beetle that primarily damages spruce trees. European bark beetles are an important part of the ecosystem and contribute to biodiversity, but can cause major damage to monocultural spruce forests. Due to the recent hot and dry summers, this is particularly visible in Central Europe and Sweden. In Finland, warm temperatures have expanded European bark habitat and accelerated reproduction, resulting in increased forest damage caused by bark.

With the abundance of commercial spruce plantations in Central and Northern Europe, it is important to study, monitor and understand the behaviour of spruce bark in Europe as climate change progresses.

“However, there was plenty of variation between the individual trees, which could be influenced by the number of bark that lives in the tree and the amount of other stresses that the tree has experience with,” Junttila concludes.

It is led by Associate Professor Junttila, Global Ecosystem Health Observatory located at GEHO, University of Eastern Finland. According to Junttila, the study shows that remote sensing methods alone are not sufficient to detect the effects of bark beetles early enough for preemptive action.

“In-site monitoring is also needed, and is supported by research investigating which areas are susceptible to bark beetles,” says Junttila.