Almost no wind, a few clouds, around 20 degrees: As if out of nowhere, a more than 20 meter high beech tree in Würzburg's Ringpark tips over and buries a woman under the heavy branches. The 59-year-old, who was riding a bicycle, died a few hours later in a clinic.
In addition to the shocked relatives, what remains are perplexed city representatives. Comparable cases in Germany are rare - some people may still remember the death of a small child in Augsburg who died in a playground two years ago from a fallen tree.
Five to ten deaths every year
"The risk of dying from a tree in Germany is extremely low. We are approximately one in ten million," says Steffen Rust, an expert in tree diagnosis at the Hildesheim/Holzminden/Göttingen University of Applied Science and Arts.
He points to five to ten deaths every year, often due to bad weather. "That's about the same as the probability of being struck by lightning." For comparison: According to the Federal Statistical Office, 2,788 people died on German roads last year.
According to environmental officer Martin Heilig, the tree in Würzburg, which is around 100 years old, was routinely checked in December and then looked at again and again. The inspectors knew that the beech was not healthy - like most of the trees in the park that surrounds the old town. However, there were no indications that the huge tree could tip over. “This is a tragedy,” says Heilig. The police and public prosecutor's office now want to investigate possible omissions.
Too hot, too dry, too many exhaust fumes - the municipal gardening authorities will soon no longer know what to plant in times of climate change. According to scientists from the Bavarian State Institute for Viticulture and Horticulture (LWG), especially in cities, trees such as linden, chestnut and maple are coping increasingly poorly with drought and radiant heat.
Inconspicuous fungal infection, hidden crack in the bark
The dry and hot years since 2017 have accelerated the death of trees in the communities. In Würzburg, for example, an average of 160 city trees used to die per year. “In 2019 there were 1,470 street, park and cemetery trees,” says Susanne Böll from the LWG urban green work area. "And it wasn't much different in other cities. This is the new normal, and it can get worse."
Sometimes it is an inconspicuous fungal infection that indicates a tree disease, sometimes a hidden crack in the bark that reveals rot. A critical examination of the root base can show how stable the trunk is.
Every one to three years, Germany's city trees are inspected on average, most of them by visual inspection, as tree care expert Rust explains. If there are signs of a lack of stability, this can be checked with a tensile test.
“A rope is attached at a height of 10 to 15 meters,” explains Rust. "The tree is equipped with measuring devices. We pull the tree with a hand winch and thus simulate a wind load." From the movement of the tree you can then estimate what load it can withstand before it tips over.
Inspectors look for signs of reduced stability
According to his knowledge, tree inspectors examine around 100 trees every day. “This costs between three and nine euros per tree,” says Rust, and only takes a few minutes. A detailed investigation is only carried out if the inspector sees signs of reduced stability or breakage.
For example, an acoustic tomography would be possible for 300 to 800 euros, which would show the cross-section of the trunk and say something about its resistance to breakage. Tensile tests usually cost significantly more than 1000 euros. “You only do this with really valuable trees because municipalities generally don’t have that much money for such investigations,” explains Rust.
About a year ago, a large beech tree suddenly collapsed in Freiburg's city garden - fungus-related wood rot had affected the tree. There were no injuries. In the case in Augsburg, a fungus had also weakened the tree. The accident involving the girl who was killed in July 2021 will be heard in the district court on Monday (September 25th). The public prosecutor's office accuses a tree inspector of negligent homicide and negligent bodily harm.
Based on an expert report, the prosecution assumes that the city employee should have noticed the fungal infestation when checking the maple tree in May 2020 and taken further measures. The defense attorney, however, explained that there was a counter-report according to which the employee had taken sufficient measures. His client was unable to recognize the impending tree fall.
Experts consider control intervals to be sufficient
In Würzburg, which is far too dry, there have recently been more staff for tree care and inspection due to the stressed city trees, equipped with probing rods, binoculars, tape measures and folding rules. Almost one million euros would also be spent annually on external experts and care measures for the more than 44,000 city trees.
“Conspicuous trees will be checked,” assures city spokesman Christian Weiß. "Defects inside the trunk and in the underground root area cannot be easily recognized."
Tree expert Rust believes the control intervals are sufficient. "We are very meticulous in Germany." In other countries the intervals are significantly longer, "and no more people die."