Mixed forests can reduce the risk of forest damage in warm climates

Forests with few tree species are at much greater risk of damage, and introduced lodgepole pines are particularly vulnerable. This is the result of a new study published in Ecosphere by researchers from Umeå University and the Swedish University of Agricultural Sciences (Uppsala). The results will help prevent forest damage and economic losses related to forestry.

Fungi, insects, fire, and deer such as moose are examples of natural factors behind tree damage in Swedish forests. In some cases, damage can be so extensive that it affects the functioning of forest ecosystems, particularly the ability of forests to provide timber and other tree products.

“Forest damage is expected to become more common and severe as the climate warms, extreme weather events and new pests increase, and forestry becomes more active. Therefore, what causes forest damage and how can it be prevented? “It is important to understand whether this is the case,” says Mikael Jonsson, a researcher at Umeå University who led the study.

The Swedish National Forest Inventory collects extensive data from Sweden’s forests. Data on forest damage has also been collected since 2003.

For the new study, the researchers analyzed 15 years of data from across Sweden to find out what types of damage are most common and what factors determine the risk of tree damage. This study is more extensive both temporally and geographically than previous studies.

Wind and snow cause the most damage

The results show that the most common cause of tree damage is wind and snow, followed by forestry and fungi. Damage caused by deer (mainly elk) ranks fifth. Overall, 94% of all trees had some damage. Coniferous and young stands were shown to have the highest risk of damage, and in warmer regions of Sweden, stands with fewer tree species were shown to have a significantly higher risk of damage than stands with a higher number of tree species.

“Our results show that changes in forest management can potentially reduce the risk of forest damage. In particular, higher proportions of broadleaf trees in conifer-dominated production forests result in less damage. For example, we find that “lodgepole pine introduced by forestry is at the highest risk of damage, and therefore its introduction impedes profitable forestry,” Johnson says. .

Weaknesses of data materials

The results also show that a higher number of tree species in a stand acts as insurance against widespread forest damage in warmer climates.

“We must adapt Swedish forests and forest management methods to a future warmer climate. Including more tree species in production forests seems to be a successful adaptation measure,” said co-author says Jan Bengtsson of the Swedish University of Agricultural Sciences.

However, this study also shows that the data material has some weaknesses. For example, it was not possible to determine the cause behind most of the damage.

“The National Forest Inventory collects important data to understand our forests, but when it comes to damage inventories, the quality of the data needs to be improved so that it can be fully used in the forestry field.” Author John Moen says: