Urban forestry, or arboriculture, deals with the protection of the sustainable development of woody plants and green spaces in the residential areas of cities. In North America, this specialized branch of forestry has developed into a field that is concerned with waterways, biotope management, recreation areas, general tree care services and the production of wood as a resource in the inner cities. In Germany, the urban green spaces are also gaining meaning and purpose this appreciation increases from one year to the next.
Fig. 1: On the 180 ha large park of the Nymphenburg palace in Munich there are 158 ha of tree stands. It is an important area for urban forestry and is worthy of a visit for trained forestry professionals (Picture: A. Gerngross, FOTAG.de).
The effect on the urban climate is noteworthy
Cities heat up more profoundly than the surrounding areas. This is due to the densely built up areas, the limited air circulation and the predominantly high proportion of sealed surfaces. On top of these heat effects the urban trees, in particularly trees next to streets, have to be able to cope with a number of stress factors (e.g. emissions, road salt, soil compaction, gas, drought, dog urine and mechanical damage).
The urban tree stands are primarily composed of by native tree species such as sycamore and Norway maple, littleleaf linden, English oak and silver birch. Non-native tree species include the horse-chestnut (e.g. in beer gardens), black locust and silver maple to name a few. Many conifers such as the Serbian spruce, European yew and Austrian pine also play a role.
Exotic tree species have already been planted in city parks since the 18th century. Examples include the tree of heaven, honey locust, London plane tree, Pagoda tree, silver linden, red oak, Turkish hazel and the manna ash. Since the urban climate is one to two degrees Celsius warmer than the climate in the surrounding areas, we can cautiously make some inferences about the possibility to cultivate these trees in the forest with a warming climate. It is to be expected that urban trees will be subject to an increase in the frequencies of drought and water stress as a result of climate change. At the same time, the importance of urban green spaces as an oasis for a warming urban climate will also grow.
The significance of trees in the city
Urban forests and trees fulfill important ecological and social functions. Beside aesthetical aspects, urban green spaces help to guarantee the quality of life in the cities. Trees can reduce emissions, absorb noise and help to cool on hot days. It is known, that cities with numerous stands of trees are more aesthetically pleasing.
Trees and woody plants in urban areas enhance the biodiversity, reduce air pollution and help to mitigate the heat island effect. The production of shade and evaporation provide relief from the heat on hot summer days in the city. The general public has found this to be a pleasant aspect. Besides noise, wind and privacy protection, city trees are a refuge for various plant and animal species.
For human senses the appearance of the tree species plays a significant role. The green spaces in the city are inconceivable without the decorative flowering of the horse chestnut in spring, the yellow-green flowers of the Norway maple before bud break, the silvery undersides of the leaves from the silver linden or the spectacular autumn colors from various maples.
Foresters know trees and their needs
Fig. 2: A 176-year-old pine in the park of the Nymphenburg palace whose entire crown has successfully expanded after being released through the harvest of neighboring trees (Picture: R. Mößmer).
The city trees and green spaces can be a chance and challenge for conventional forestry and forest science. Forestry personnel have a high level of professional expertise when it comes to site requirements of tree species, their appropriateness on extreme sites in cities and endangerments that also include forest pests. Generally, the same pests infest both urban trees and those in the forest, however, their appraisal is different (e.g. due to inconveniences and hygienic questions). Forestry personnel can judge growth dynamics and behavior with competition particularly well due to their training and competence. Many universities and universities of applied science currently offer an emphasis or even a bachelor’s degree in aboriculture on top of the required classes related to urban forestry.
Through urban forestry and aboriculture a wide spectrum of the general public can be won over and be made aware of the principles of forestry such as the sustainable usage of trees and forests. The knowledge of sustainable and organized forest management from forestry professionals provides an excellent base for the further development of urban forestry programs. Additionally, aboriculture offers an outstanding scope of duties in order to collaborate with specialists from other fields such as horticulture, landscape architecture, city planning and ecology.