The basic prerequisite for the development of a vital tree that can cope with climate change is professional tree planting. The planting itself is carried out by external companies. They also look after the young tree for two years and water it for a further two years. The tree then becomes the responsibility of the city. Along roads, the tree beds have to be extensively renovated before new trees can be planted. Most existing tree beds are too small by today's planting standards. The staff at the Office for the Environment and Urban Greenery are therefore examining whether they can be enlarged. Under certain circumstances, this could lead to a reduction in parking space. Various demands on the use of urban and street space must be weighed up here.

Once a suitable tree plot is available, the planting pit is dug first. This should be at least twelve cubic meters in size: 1.5 meters deep, two meters wide and four meters long. These are the minimum requirements so that the trees have a chance to develop well. Larger planting pits would be even better, but this space is rarely available, especially in the old, narrower districts. This is optimized as far as possible. The planting pits are then filled with a special tree substrate, which provides the young tree with optimum starting conditions. Root protection is installed to protect both the roots of the tree and the pipes in the ground from damage.

Anchoring: As the tree does not yet have the necessary stability shortly after planting, it is stabilized with a tripod. This also promotes the straight growth of the young tree.

Trunk coating: A white protective coating is applied to the trunk. This is breathable and does not impair the thickness growth of the tree trunk. The special trunk coating protects the bark of the young tree from heat damage. Especially in heavily sealed areas, heat radiation from asphalt and paving slabs can cause enormous heat stress.

The watering ring: A watering ring is installed with the planting. This can hold around 100 liters of water. This ensures that the tree is supplied with sufficient water and that it flows directly to the root ball of the young tree.

Underplanting: Finally, the bed is planted with various ground cover plants or insect-friendly perennial mixtures. This increases ecological diversity and beautifies the tree bed.

Protecting the tree grate: Bollards, boulders or tree protection brackets are used to secure the tree grate, especially in parking areas. This prevents the tree trunk from being damaged and the tree disc from being compacted by careless parking.

If an urban tree has to be felled in the street, it is always checked whether a replacement planting is possible at the corresponding location. In this case, too, planting in the street poses a particular challenge: Each individual tree slice must be checked.

A felled tree that was still protected at the time does not guarantee replanting in the same location. In rare cases, empty tree grates cannot be replanted with a tree. For example, because supply lines run in the area of the planting pit to be enlarged, trees from private properties have grown into the public traffic area or property entrances and street lamps are in the way. In this case, the employees check whether the tree slice can be relocated.

Only in exceptional cases is no replacement planting possible. It can sometimes take two to three years between the removal of the tree and the implementation of the replacement planting.

In addition to professional planting, the choice of tree species is also crucial to whether the tree will grow successfully and develop in the long term. We check which tree species is suitable for each location. Many years of experience and the latest research findings are equally important here. This is because various factors must be taken into account when selecting the right tree species:

• Complementing the cityscape: Tree planting should generally complement the existing trees at the location. For example, if a single tree in an avenue of lime trees needs to be replaced, then another lime tree is planted. In other locations, however, new species and varieties are deliberately planted to increase biodiversity.
• Resistance to tough conditions in the city: The street is a tough place for trees. They must be resistant to typical urban stress factors. These include soil compaction, road salt and tight spaces. Some species or varieties can cope with this better than others. This resilience is an important factor when selecting the right tree species.
• Future trees for sustainable urban greenery: The effects of climate change are additional stress factors. Increasing drought and heat are making things difficult for some tree species, even if they have coped well in the city in the past. Other species, on the other hand, are well adapted to the new conditions and will continue to provide the city with shade in the future.
• Strengthen ecological biodiversity: Trees that are ecologically valuable are also preferred. For example, they provide food for pollinating insects or nesting sites for native bird species. In this way, tree planting strengthens urban biodiversity.

Many demands are placed on urban trees. The staff at the Office for the Environment and Urban Greenery select the right tree for each location. They can draw on their many years of experience when making their selection. However, new findings on future and climate trees from various research institutions are also taken into account.

A list of such climate-resistant future trees has been compiled, for example, by the German Garden Managers' Conference (GALK e.V.). Bonn is participating in another GALK test series. Future trees are being tested specifically for locations in cities and along roads. After all, the planting of today should also enrich our city in the future.

With the tree concept, the city aims to further develop the tree population in Bonn in a targeted manner. New locations are to be created, particularly in neighborhoods where there are currently only a few trees.