The climate crisis is causing city centers to heat up more and more in summer. The city of Bonn has been working intensively on the issue of climate change prevention for several years. In  research projects (opens in a new tab), the urban climate has been comprehensively examined, heat hotspots defined and strategies developed to effectively counteract heat development in the city. The integrated climate protection and adaptation concept has created the basis for measures to adapt to climate change. However, it is important that concrete measures now emerge from research and investigations.

Increasing the volume of green space in all its forms is a central component of this. In addition to unsealing surfaces, significantly more trees are needed above all. They provide shade, cool through evaporation and bind dust via their leaf surfaces. The older a tree is, the greater its ecological and climatic benefits. That is why it is important to start planting new trees now for the climate-adapted and liveable city of tomorrow.

Trees in green spaces are also important, but street trees are much more valuable for climate adaptation. In otherwise sealed areas such as streets, the temperature-reducing effect of trees is particularly noticeable during periods of summer heat.

At the same time, the small-scale unsealing also promotes water storage and every tree bed provides a habitat for many animal species. Last but not least, street trees shape our cityscape and contribute to a better quality of life in the neighborhood.

With the adoption of the tree concept in June 2023, the council instructed the city administration to plant new trees in the districts that the survey showed to be in the greatest need. This requires detailed planning in each case, which is submitted to the district councils for a decision. The tree concept makes it possible to prioritize the districts, which will be worked through one by one. Based on the evaluation of all criteria, the Neu-Duisdorf district forms the starting point.

In the winter half-year 2024/2025, new tree locations are to be created in another district. The district council will also decide on this first. Residents will be involved at an early stage.

Public space is very limited and has to meet numerous requirements. The search for new tree locations is a challenge that raises questions such as:

• Is there enough space for pedestrians, cyclists and cars?
• Where are the entrances to properties?
• Are there underground cables that make tree planting impossible?

High parking pressure in the neighborhood is also taken into account in the tree concept. Nevertheless, today sealed parking areas are often the only opportunity to create new tree locations in a street. The city tries to take a moderate approach and ensures that sufficient parking spaces are retained in the neighborhood.

In future, the city will involve local residents in future planting projects at an early stage in order to inform them about the specific plans and the importance of street trees for climate adaptation.

Yes, they are. A minimum lane width of 3.5 meters is maintained next to each bed to ensure passage for ambulances and the fire department, for example.

If the roots have sufficient space for their growth, pipes are of no interest to the roots if they have been made tight and secure.

Nevertheless, the underground pipes are protected with the help of a film that is installed on three outer sides of the bed to a depth of 1.5 meters. This so-called root guide or root protection film consists of a multi-layered root protection membrane that does not allow roots to penetrate.

Root growth beyond 1.5 meters is not to be expected with the selected tree species.

In preparation for the planting, the areas must first be unsealed and the tree beds created.

Particular attention is paid to quality so that the young trees can develop well and remain vital for as many decades as possible: According to the currently recognized rules of technology, the tree beds should be at least two by four meters wide and one and a half meters deep. This 12 m³ is a minimum size, which should be exceeded if possible. A mature tree (approx. 50 years old) requires around 75 m³ of root space.

Irrigation technology also plays an important role: according to the sponge city principle, the tree grates are laid out in such a way that as much rainwater as possible can be absorbed and benefit the trees. A larger tree pit is of course also a larger water reservoir.

For the new plantings, the Office for the Environment and Urban Greenery selects "future trees" that are particularly resistant to heat, drought and dust. The trees should also be able to cope with temporary overwatering of the root area, for example during heavy rainfall.

Depending on the surrounding buildings (proximity to the façade), the trees must be selected according to their species-specific growth habit and be as narrow as possible and not too overhanging in the crown. If there is sufficient space, trees that develop a larger crown are of course also selected.

Another criterion is a wide range of food for insects and birds in order to promote the biotope network. In the Neu-Duisdorf district, for example, purple alder, red maple and swamp oak are planted. The tree beds will also receive a flowering and insect-friendly undersowing of native herbs.

The city provides continuous information on the current status of the implementation of the tree concept. Information on planned planting work is available online, in press releases or via the City of Bonn's social media channels.

The city also attaches great importance to involving residents in the neighborhoods more closely in the future. This is because there is generally broad support in society for climate adaptation measures and the demand for more tree planting. The city would also like to encourage this support in the concrete implementation of projects when conflicts between individual interests and the common good become apparent.

Decisions on tree planting projects in the city districts are made by the district councils. In future, the city will invite residents to an information event at an early stage and be available to answer questions before the specific work is awarded.