Urban tree concept

Cities profit from trees

Cities profit from trees in various ways. Important functions include enhancing the cityscape (aesthetics), improving the microclimate (air hygiene), providing shade and evaporative cooling as a contribution to well-being (climate comfort). However, urban and especially street trees are sometimes exposed to extreme conditions that are hardly comparable to those in forests or the open countryside. In the city, they are often confronted with drought stress, air pollution, road salt, compacted soils and many other stress factors, which is why they are usually barely able to reach half of their potential age span.

Problems due to the changed conditions caused by climate change

The effects of climate change (e.g. increasing heat stress and increasing drought) are making these already unfavorable site conditions even worse. Some proven tree species are already showing clear signs of problems due to the changing conditions caused by climate change. Therefore, precautions must be taken to ensure that they can continue to fulfill their many important functions (ecosystem services) in the future.

Abb.: Die Bedeutung von Stadtbäumen als kühlende und beschattende Elemente, Klimakomfort im Stadtpark Jena-Paradies

© Stadt Jena

Planning and decision-making aid

Between 2014 and 2016, an urban and street tree concept was developed as part of the JenKAS urbanization process, which serves as a planning and decision-making aid to show how the urban tree population can be kept vital and therefore functional - despite the direct and indirect effects of climate change.

Climate-suitable tree species selection

The influence of climate change has been integrated into the concept as a central element in order to be able to work towards adapting the tree population in the urban area of Jena under future conditions. This concept is helpful in selecting tree species that are suitable for the respective location and suitable for the climate, thus saving costs for irrigation, maintenance and also through replacement planting and making a contribution to climate protection due to the increased CO2 binding capacity of vital, long-lived urban trees.

The concept was implemented on behalf of the Department of Urban Development and Environment with the support of the Thuringian Institute for Sustainability and Climate Protection (ThINK GmbH, Jena) and in close cooperation with Prof. Dr. Andreas Roloff as head of the Chair of Forest Botany at the TU Dresden.

At the same time, the UFZ - Helmholtz Center for Environmental Research Leipzig enriched the entire development process with scientific knowledge. The freelance garden and landscape architect Ulrich Boock (Jena) provided support with questions on design and spatial aspects.

Numerous committed representatives of the city administration (urban development and green planning, environmental and nature conservation, monument protection), the municipal service (tree care) and the municipal utilities also took part in the regular working meetings during the one-and-a-half-year processing period.

Location parameters

The basic methodological idea of the present concept was to collect and present all relevant site parameters for urban and street trees throughout the city, to intersect them with a geographical information system (GIS) and to use a cluster analysis to identify different sub-areas (site types) with similar site and living conditions within the Jena city area.

Climatic parameters

The effects of climate change are given weight by regionalizing the climatic parameters (temperature, climatic water balance and wind) that are included in the analysis on the basis of climate projections for a future period (climate period 2071 to 2100).

In addition to the location parameters, spatial planning and design criteria based on the design manual of the city of Jena were also taken into account.

Spatial type map

A spatial type map is used to differentiate spatial types for the selection of tree species according to climatic, location and design aspects. In this way, a total of ten spatial types could be derived in the Jena urban area, which place very different demands on urban greenery. In some spatial types, for example, a significant deterioration in the water supply (climatic water balance) for plants (e.g. Jena-North), in others increased heat stress (e.g. Jena-Altstadt) is to be expected.

Selection of climate-suitable tree species

The selection of climate-suitable tree species was carried out with regard to drought stress tolerance and winter hardiness of individual tree species. In addition, comprehensive research was carried out on important site characteristics and influencing factors (e.g. immissions, soil contamination, sealing) as well as components of aesthetic effect (e.g. growth forms or leaf colors), on which a prioritization of the individual tree species with regard to their suitability for the different types of space could be based.

Furthermore, the tree biology expertise of Prof. Dr. Roloff on the topic of "Use of non-native tree species as street trees" enriches the concept. In this context, the contribution on dealing with tree species with invasive potential should also be seen as an important part of the conceptual work.

The result is a range of practical products that can be used to help make decisions when planting new urban and street trees.

Tree species recommendation list

The tree species recommendation list is a central result of the concept. It lists around 160 recommended tree species suitable for Jena. For the sake of clarity, some details on habitus, ecology, ornamental value and special features are illustrated by symbols, which are explained in a separate overview table in the concept.

35 model street profiles

In addition, 35 model street profiles were drawn up for selected street areas in the city of Jena, in which tree species are proposed that take into account the future climatic, site-specific and design criteria and requirements in each specific street area.

30 tree species portraits

As part of 30 tree species portraits , a selection of tree species suitable for future climatic conditions was also made from around 160 tree species recommendations. The tree species are presented and illustrated in more detail in the portraits

Project report

The summarizing project report "Urban and street trees in a changing climate - urban tree concept for the sustainable protection and development of the tree population in Jena" rounds off the results. This has been published as a brochure as part of the "Schriften zur Stadtentwicklung" series and is thus made available to a broad public.

Resolution of the Jena City Council

The concept "Urban and street trees in climate change" was confirmed as a municipal guideline and basis for action for specialist planning by resolution of the Jena City Council on 27.04.2016.

Thuringian Environmental Award 2015

In November 2015, the concept was awarded the "Thuringian Environmental Prize 2015" by the Ministry for the Environment, Energy and Nature Conservation for the concept idea and methodical approach of the contractor ThINK (Thuringian Institute for Sustainability and Climate Protection) and became known throughout Thuringia.

"Climate-active municipality 2016" competition

This recognition was enhanced by the award presented to the city of Jena on November 28, 2016 in the "Climate Active Municipality 2016" competition for the coordination and implementation of the urban tree concept in the "Climate adaptation in municipalities" category. The award in the competition organized by the Federal Ministry for the Environment and the German Institute of Urban Affairs gives the urban tree concept special recognition and appreciation.