Bark beetles ravage Swiss forests

The bark beetle is killing thousands of Swiss spruce trees (wsl.ch) WSL

Switzerland’s forests are under attack from a foe that has thrived in the hot, dry conditions of summer's heatwave.

This summer’s record temperatures and lack of rain has meant tree defences are down, leaving the country’s spruces particularly vulnerable to the destructive bark beetle.

The ips typographus or bark beetle has a soft spot for spruce trees, which is bad news for cantons like Bern where spruces account for about 50 per cent of all forests.

“The situation is critical,” said Adrian Meier, who is currently spearheading efforts in canton Bern to minimise the spread of the insects.

Of some 170,000 hectares of forest in the canton, as much as ten per cent is categorised as being at risk.

“If we don’t win the fight, much is at stake – villages and roads could be at increased threat from avalanches and rockfalls,” Meier told swissinfo.

Christian von Grünigen, who is responsible for the canton’s forests in the Simmental, Saanenland and Frutigen, has been monitoring the rapid advance of the bark beetle.

“When the beetle arrives on the bark, the tree can normally defend itself with its resin. But when the tree is weak, it cannot,” he said.

“This year because of the lack of water and the trees flowering earlier in spring, the trees do not have enough resin.”

Rapid advance

Von Grünigen has 100 people currently working on his patch to stem the beetle tide – five times more than is usual during the summer months.

Their tasks include singling out trees that have been infected and then arranging for their disposal, with the aid of chainsaws, tractors and helicopters.

The teams have to work fast since it takes six weeks from an adult bark beetle arriving in a tree to the next generation of beetle flying off in search of new spruces.

A telltale sign that a spruce is under attack is the brown dust that is produced when the beetle begins to eat the bark. This tends to gather at the foot of the tree, on the leaves or on the bark itself.

Two to three weeks after infection, trees start to lose their needles. This means that von Grünigen’s team has a window of about three weeks to find the affected trees.

Tree clearing

In the shadow of the Niesen mountain, two of von Grünigen’s men are in the process of clearing 200 trees from one forest.

“We fell the sick trees and remove their bark using special machinery. It takes about an hour to process one cubic metre. The two of us deal with about 30 cubic metres a day,” explained Urs Imbaumgarten.

Not all of the felled trees are removed from the forest. Some are left, gradually decomposing into humus over two or three decades.

This kind of work costs about SFr75 ($53) per cubic metre, and by the end of July about SFr7 million had been spent on battling the beetle. The bill will be picked up by both the federal and cantonal governments.

The wood that is taken out of the forest is put on sale. The problem is that demand is slack both at home and in the countries that Switzerland normally exports to, like Italy, Austria and Germany.

“In Austria where we sold our trees last year, they had a storm last November and so there is not much need for our wood,” revealed von Grünigen.

In addition, the price for a cubic metre of damaged wood is low, at just SFr40.

Other factors

Von Grünigen stresses that it is not just the arid heat which is making matters worse.

After the battering the trees took during Hurricane Lothar in 1999, an explosion in the beetle population a few years later was to be expected. However, the scale of the infestation took the department by surprise.

And a large-scale extermination of the pests is not an option.

“We are not allowed to use chemicals in Swiss forests. We have some traps but they only help us to control the number of beetles mostly in spring. In summer, the tree is more interesting to the beetle than the traps,” said von Grünigen.

He suggests that forestry policy in Switzerland might also be to blame for the extent of the current infestation.

“Perhaps we did not cut enough wood during the last 50 years. We have quite a lot of old forests in Switzerland and many of them are now being attacked by the bark beetle,” he said.

Other cantons, including Lucerne, Basel and Fribourg, have also reported a substantial increase in bark beetle activity over the past last few weeks.

Technically this is a fight that could continue into early autumn, as there is no respite in beetle activity until the onset of winter.

swissinfo, Faryal Mirza in Spiez

Key facts

Male bark beetles identify a suitable spruce in which to breed.
As the larvae and young beetles develop, they eat their way through the bark.
Adult beetles can reach about 5mm in length and are dark brown in colour.