Bye-bye spruce!

The Norway spruce die off.

A walk through the Sihlwald forest shows: The Norway spruce trees (picea abies) are dying. There are dry trunks everywhere; many trees have long been lying on the ground. There are many reasons for this development: the spruce - as the Norway spruce is also known - was artificially introduced to the Central Plateau. By nature, it grows at higher altitudes. However, this tree species does not tolerate heat and drought well, and global warming is causing it additional stress. The analysis of satellite images shows that over thirty percent of Norway spruce trees have died in the Sihlwald since 2018.

Deciduous trees replace Norway spruce

"This death brings light, water and nutrients for new growth. In forest areas with plenty of light, pioneers grow first: elder, hazel, willow and birch, for example. Later, depending on the altitude, tree species suited to the location such as sycamore and Norway maple, beech or silver fir become established," explains Isabelle Roth, Head of the Natural Forest Division at Wildnispark Zurich, "as experience over the last 25 years has shown."

A recent Bachelor's thesis from Bern University of Applied Sciences also confirms this forecast. Anne Wenk examined which young trees and seedlings can be found on dead spruce areas in the Sihlwald in 2025. It turns out that practically no Norway spruce trees are growing back at the moment.

The spruce comes, the spruce goes...

In the 19th century, Switzerland's forests were in a desolate state. The forested area was only half the size it is today, and where there were still forests, tree growth was sparse. In the Alps, entire mountain ridges were deforested in order to obtain firewood and timber. On the Central Plateau, farmers drove their sheep and goats into the forests to graze. It was not until the strict Forest Police Act of 1876 and the Forest Act of 1898 that the overexploitation came to an end.

On the Central Plateau in particular, forest owners began to plant Norway spruce on a large scale - a fast-growing tree species whose wood can be used in a variety of ways. In the Sihlwald, it provided timber for the city of Zurich.

Dying makes new life possible

Today, however, the Sihlwald is the largest natural forest reserve on the Central Plateau and a park of national importance. For 25 years, it has been allowed to develop freely and transform into a wilderness.

"It's also amazing to me how quickly the area has changed," explains Roth. In many places you can still see that the Sihlwald was heavily used, but today you can already observe primeval forest-like structures: Like a mosaic, dark sections of forest alternate with light areas with few trees. Fallen trees lie on the ground like an oversized game of Mikado, with the occasional rootstock turning into mounds of earth. Forest recycling has begun. Fresh, nutrient-rich soil is available for young trees. Roth: "The dynamic development of the Sihlwald forest ecosystem is a benefit for biodiversity!"

Nature lovers have the opportunity to witness an impressive transformation. "I cordially invite everyone to make a note in their diary of at least two dates for hiking excursions in the Sihlwald. One in the next few weeks and the second in the forest of the future, for example in the year 2040," says Roth with a smile. "It will be exciting to see whether Norway spruce trees are still standing and which bushes and trees have taken their place."

 

Photo: Dominique Meienberg / Zürcher Wanderwege, Via Natura