A portrait of every tree

On two consecutively clear days in February this year, a helicopter circled about 400 meters above Merano to use a special laser technique (LiDAR) to measure the city's most beautiful feature: its historic tree population. More than 200 species grow in the city, including many exotics - a legacy of Merano’s spa history that attracted aristocracy and bourgeoisie from all over Europe in the late 18th century - when plants were shipped in from all over the world. Many of these trees are over a hundred years old, the oldest over 150. Depending on their location, their exposure to urban impositions such as soil compaction, exhaust fumes, road salt, dog urine, varies. One thing does unite the trees of Merano: all of them are having to endure the greater heat and longer periods of drought that climate change is bringing. These trees need a lot of attention and care, and the 8000 or so that grow on city-owned land have received both in recent years. “We know every public tree very well,” says forester Anni Schwarz, the former director of the city’s horticulture department who was long responsible for looking after the city’s trees. Now Schwarz has taken over the management of the JUSTNature project as a technical officer. The project, funded by the EU's Horizon Program, delves deeper, seeking to know the city’s privately owned trees more precisely to better protect them. The laser scan from a helicopter was the first step.

In the EU JUSTNature project, pilot cities throughout Europe are working to create better living conditions for everyone through “nature-based” solutions. The fact that Merano is also focusing on private trees in the process is “interesting and important,” says Eurac Research biologist and spatial planning expert Sonja Gantioler, who is coordinating the entire project. “Usually, nature-based solutions are discussed mainly in relation to public spaces. In some cities, however, most green space is privately owned.” In the case of Merano's green space, it’s a good two-thirds. But how many trees are there in private parks and gardens? What type and size are they? And who are their owners? Answers to all these questions will be available once the huge amount of LiDAR data has been evaluated – the data covers a point cloud as large as the entire area of Merano. Ideally, the aim would be to create a similarly complete inventory of the private trees as the one the city already has of the public trees in its tree cadastre. This catalogue contains the “identity cards” of the city’s public trees and will be very helpful in identifying its private ones too.

One to two hundred particularly valuable trees will then be filtered out of the huge number of private trees in order to have their health expertly assessed with project funds. Once this has been undertaken, experts will decide if any measures are necessary – whether dead wood needs to be removed or a branches need to be secured, for example. Thanks to the LiDAR data, each tree in the city will have a “digital twin”: a digital 3D representation that shows the tree’s its position and characteristics.

At some point, these twins might even serve as a kind of “laboratory” on which changing conditions can be simulated and the effects observed, Gantioler explains. The images will be of immediate use to the Landscape Commission, for example, in order to get a true picture of the situation when it has to assess construction projects: Are there really only three small trees, as the project manager claims, or are they magnificent specimens? Although details on private green space may be fuzzy, one thing has been clear for a long time: the pressure to build up is enormous. “The city is very attractive; it is growing, but it should not grow beyond its limits because if it does, the spaces for living will get more crowded and green spaces will get lost.” explains Schwarz.

Not, however, from another risk of climate change: the increasing extreme events in which trees themselves can become a hazard. In 2019, strong gusts of wind damaged or uprooted several trees in Merano, injuring a mother and her child. “That was traumatic for the whole city,” says Schwarz, whose management of the city’s gardening department not only provided insight into gardens with magnificent old trees, but also into the owners’ states of mind: “The dominant feeling there is fear of responsibility.” She understands that fear well; after all, she was responsible for thousands of trees. “When you have an old cedar standing in front of your house and you see how it leans back and forth during storms, it can be enough to make you lose sleep.”

That’s why, she says, the central goal of the project is to help tree owners - and in a much broader sense than through the free appraisals which in any event are limited by the budget only being available for the next three years. “Above all, it's also about showing more appreciation for the owners of the trees themselves who are doing enormously important things for the community by taking care of these trees - a service that involves costs, work and, indeed, responsibility.”

But instead of receiving recognition, tree owners are often even subjected to “hostility,” according to a press release from the city of Merano. This could be because of the leaves in the fall, or because the shade that is welcome in the summer is less welcome in the other seasons. Added to this is the conflict with photovoltaics, says Schwarz.

Faced with these challenges, Merano wants to create a new awareness, instead of dark forebodings and evil glances from neighbours, people should be proud of the trees in their gardens and the contribution they make to the urban quality of life, says Marco Masin, the new service manager of the city’s horticulture department. There are already ideas about how to strengthen this feeling, for example through organized tours of particularly valuable private trees or through tree sponsorships.

Another possibility is to publish the digital twins on a platform for the co-governance of green space, as is currently being developed within the framework of JUSTNature, explains Gantioler: “Anyone who wants to, should be able to take responsibility for a piece of green space and help shape it. People could also get involved in this way for specific trees.” That would be a further step: an innovative implementation of the beautiful idea that trees, no matter where they are,concern everyone.