In this forest area in North Rhine-Westphalia, the bark beetle destroyed large areas of spruce.
Photo: Jochen Tack / imago images
The increasing drought weakens the forests, pests such as the bark beetle spread as a result.
The amount of damaged wood is increasing accordingly: in 2020 to 60.1 million cubic meters.
Five years earlier this figure was 12.9 million.
The amount of damaged wood has increased almost fivefold.
These figures come from a report by the Federal Statistical Office.
The increase in insect infestation is particularly alarming: pests - and above all the bark beetles - are mostly the main cause of the development of damaged wood. Almost three quarters of the amount from last year can be attributed to this - a record value.
In 2015, insects caused only a quarter of the wood damaged.
In comparison, the amount of wood that has been destroyed by insects is almost 13 times as large in 2020.
In contrast, the influence of wind and storms, which was still the most important cause in 2015, has decreased.
There are also causes for the increased occurrence of the bark beetle.
Probably the most important is the increasing and persistent drought.
Bark beetles are a species-rich group of brown or black beetles that partly feed on wood.
A well-known representative is the book printer.
This species causes the most damage in Germany.
The printer mainly attacks conifers.
This can also be seen in the damaged wood statistics: A proportion of 99 percent of the wood destroyed by insect infestation was accounted for by conifers such as spruce, fir or pine.
Weakened trees can hardly defend themselves against pests
Trees that get too little water are weakened.
A healthy tree is more likely to defend itself against a bark beetle attack - for example, by allowing resin to escape at the point where the beetle digs into the bark.
In the case of a weakened tree, this protective mechanism often no longer works.
If the bark beetle finds enough dead or diseased trees, it will reproduce in large numbers.
Soon whole colonies of beetles attack the surrounding trees.
Even a healthy tree can hardly compete with too many beetles at once.
According to the Federal Statistical Office, the share of damaged wood in the total amount of wood felled in 2020 was around three quarters.
In 2015 this value was 23 percent.
A look into the canopy of a forest can also provide information about its condition.
If the crowns form a dense blanket of needles or leaves, this is a good sign: the forest shields the ground from the sun and the trees clearly have enough strength.
In the meantime, however, a “clear crown defoliation” can be determined in 37 percent of the trees.
This information can be found in the federal government's forest status survey for 2020. The value has never been so high since the collection of this data began in 1984.
The crown is only unimpaired in 2020 in one fifth of the trees.