Condition of the street trees (vitality)

Our street trees are exposed to diverse harmful factors, which occur in combination and partly worsen each other through interactions. For over 40 years, the Berlin Senate has commissioned a regular survey with assessment based on colour-infrared (CIR) aerial photography every 5 years in order to obtain knowledge about the condition of the trees in the Berlin inner-city. The results are summarised in the Berlin Inner City Street Tree Condition Report”. This report presents the condition of the city trees by surveyed inner-city areas as well as by the tree genera: lime, maple, horse chestnut and plane trees. Furthermore, the report contains a comparison with the results of the preceding evaluations. The evaluation of the surveying flights in the summer of 2020 is now available.

The comparison of the street tree condition reports of 2015 and 2020 disclosed a significant trend towards worsening with regard to crown vitality of the inner-city street trees.

Precise statements about the causes of the damage and about the traffic safety of trees cannot however be acquired with the colour-infrared aerial photography evaluation method.

In order to assess the vitality of the trees from an aerial photo, it is necessary to compare the foliage colour, leaf mass, crown shape and branches with so-called reference trees. The condition of the crown of these reference trees is examined on site from the ground at the time of the surveying flight and is described with regard to damage symptoms and particular features. This so-called interpretation key is used for the subsequent comparison of the appearance determined in-situ with the aerial photo. It is only with the help of this comparison that the vitality condition of the trees can be assessed using the CIR aerial photo.

For the CIR method, sample trees of the main tree genera: lime, maple, horse chestnut and plane trees, are assessed in sample areas and the results are then extrapolated statistically to the entire stock of all street trees planted in Berlin’s inner city up to 1990. The condition of the trees is assessed by classifying the them into crown vitality levels. Together, the main tree genera examined account for more than 3/4 of the total inner-city street tree stocks. Other genera could not be considered due to their small shares of the stocks. Here the Berlin inner-city is defined as the area within the urban railway (“S-Bahn”) ring, extended by the self-enclosed built areas of the old-districts of Steglitz, Weißensee, Pankow and the complete old Wedding district.