Urban Trees in Munich City
Is Munich getting greener? An attempt to find missing trees retrospectively
TL;DR: here are 👉 some quick facts and an interactive map about missing trees in Munich.
🇩🇪 auch auf [Deutsch]
In response to our climate crisis there are several ambitious tree-planting projects and initiatives planned or taking place in Munich. On the other hand there is also a massive amount of lost trees reported constantly every year despite of tree protection by the city government.
From my own experience of daily living in Munich in the last few years I do see unfortunately only more and more grown trees disappearing everywhere than new trees planted. It makes me ask: Is Munich really getting greener as many people might believe? 🤔
Without starting with a long-term ecological study and debating on the importance between “protecting old trees” and “planting new trees” , I would try to answer my question simply with numbers and pictures for the last few years retrospectively.
Thanks to more and more transparency in politics, many data or information about the city is available to everyone! According to the available statistics² Munich is indeed getting greener if we look at only public area. Namely, from 2010 to 2022 many trees are planted in public and it results in net total 9,535 trees increased in public area. 🥳
However if we count both public and private areas from the year 2010 to 2022, there are unfortunately documented net total 24,751 trees disappearing from the whole city within about ten years! With another interpretation the city has lost at least total 104,814 mature and old trees which are essential to urban microclimate. 😲
It should be common sense that old trees can store more carbon than younger trees and on the other hand newly planted trees will only have more difficulty to survive from worsen climate condition such as drought, heat and extreme wind.
Now the next question would be: Where are those missing trees?
Unfortunately there is no public tree register in Munich yet as in other cities and there is certainly no tree register for every tree in private areas due to cost and private sphere concerns. To be honest, why should we ever give every tree an ID if all trees could grow healthily and we never hear about climate change?
A simple solution for finding missing trees is simply counting them in pictures. More precisely: we can count trees in aerial images like Google Map and compare them between different time points. Thankfully the advanced technology and openness of data we have today make it possible for everyone to find out the answer.
There are many urban aerial images freely available to everyone as Open Data. Some cities such as Berlin even provides high resolution images with infrared imaging from almost every past year. There are few sources of aerial images covering Munich area and two useful sources available are:
- Aerial image with 60cm resolution (i.e. one pixel in an image corresponds to 60cm in the actual World) provided by Munich Open Data. The images are taken in the summer 2017.
- Aerial image with 80cm resolution provided by Bayerische Vermessungsverwaltung. The images are taken in late April 2020. (Note: in the springtime some trees may not get their leaves yet which can make it difficult to identify a tree in an aerial image.)
To detect and count trees in aerial images I use object detection techniques with computers. It is nothing different than your favourite App on your mobile phone which can detect cat faces in your photos.😼
The following two pictures give an example showing how well the trees can be detected automatically by computer. It is not perfect and requiring further improvement¹, however it suits the need if we just want to find missing trees in a large extent in the first place.
Now if we put images of detected trees from two different time points (in this case: year 2017 and 2020) one above the other (of course with different colours), then we can visually inspect the difference (i.e. missing trees) pretty easily.
Here is an example with a map where the trees from 2017 in red-ish colour are at the bottom layer and those from 2020 in blue-ish colour are at the top layer. Taking the inaccuracy due to imperfection of object detection and mediocre image quality from different seasons of the year into consideration we should roughly only see blue-ish colour in the map unless a tree is disappeared between 2017 and 2020.
Let’s take a walk virtually around Munich.🚶
After this quick tour we can easily have an idea how the urban trees in Munich have changed in the last few years. Trees are disappearing everywhere, even the whole city map may still look green enough today. We should see it as a warning sign and take action before the environmental degradation of the city takes place at an exponential speed. It would be great if such map could make more people aware of trees closely around us.
A sustainable urban environment does not depend merely on the number of trees and people need place for living, education and developing culture. Urban planning itself can be a highly complex science to find a balance (or compromise) among different aspects from safety, health, human rights, social fairness, environment protection to many others. We all hope that we are on the right course.
Are you also interested in how many trees are around you and if any tree is missing in your neighbourhood in Munich? Here is the interactive map which you can try it out by yourself.
The map data is far from perfect at the moment and is not precise enough to serve as a reliable tree register. Nevertheless the map can be useful as a visual assist to find missing tress in the past. I will try to keep improving and updating it regularly. Any feedback or suggestions is welcome.
Footnotes:
[1] I document this experiment in an Open Source project. The work-in-progress project uses machine learning techniques to determine urban tree automatically from publicly available aerial imagery. It is based on open source projects such as DeepForest, DetecTree and many others.
[2] The statistics about urban trees in Munich is published regularly in Rathaus Umschau by Die Untere Naturschutzbehörde, Referat für Stadtplanung und Bauordnung München. Older statistics can be found on the information platform from the Munich city government. Everyone can also inquiry such information directly from the city government via FragDenStaat platform. Special thanks also go to Angela Burkhardt-Keller from BUND Naturschutz Kreisgruppe München for her kindly shared data.
