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Condition of the street trees (vitality)

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Eiche mit schweren Kronenschäden

Image: SenUVK

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.

CIR aerial photo Berlin 2005 (CIR - Colour-Infrared)

CIR aerial photo Berlin 2005 (CIR - Colour-Infrared)

Image: SenUVK

CIR method

The method, of recording and assessing the condition of street trees using colour-infrared aerial photos, is based on the fact that the images map the respective vitality condition of the tree crowns due to reflection differences. The different reflections are caused, for example, by foliage damage and losses.

Maple with moderate crown damage

Maple with moderate crown damage

Image: SenUVK

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.

Linde ohne nennenswerte Kronenschäden

Image: SenUVK

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.

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Street tree condition report 2020

The results of the recording of the condition by the surveying flight of 2020 show that the condition of the street trees in almost all Berlin’s districts have worsened significantly compare to 2015. Thus, it is unfortunately determined that the negative trend indicated by the street tree condition report of 2015 has continued.

While in 2015, around 52 % in total of the examined trees were classified as not damaged, in 2020 it is only around 44 %.

Percentage of damaged trees of the four main Berlin tree genera: lime, maple, plane and horse chestnut (data as of 2020)

Overall result of the sample assessment

Image: SenUVK

Overall result of the sample assessment

In detail, the lime trees, with around 56 % undamaged trees, have the best crown vitality (2015: around 60 %). The plane follows with a share of 30 % undamaged trees (2015: around 50 %). The horse chestnut has an undamaged sample of trees of around 11 % (2015: 47 %) and the maple around 29 % (2015: around 38 %). Thus, compared to 2015, the horse chestnut in particular has a very significant trend towards worsening.

Tree genera and planting year classes 2020

Tree genera and planting year classes 2020

Image: SenUVK

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Causes of street tree damage

The respective causes of the street tree damage cannot be determined from the aerial photo. Furthermore, different damaging factors interact, so that it is not possible to determine a clear cause without prior precise analysis. However, the worsening of the crown condition of Berlin’s inner city street trees does at least show that the sum of the damaging influences has increased. These are probably a mixture of the main factors
  • City climate with increased heat, dryness and radiation, amplified by the effects of climate change,
  • mechanical damage due to construction work in the root area and general construction activity,
  • damage due to de-icing salt
  • impairments caused by soil sealing and compaction,
  • damage due to traffic accidents and
  • chemical burns due to dog urine.

The weather extremes of recent years, particularly the dry-hot weather with increasing radiation, have caused severe stress for the trees and have amplified the other negative influences.

De-icing salt is also a significant harmful factor for the street trees in the Berlin inner-city. Although pre-wetted salt is only spread on certain roads in specific weather conditions, it accumulates in the soil. Private persons also spread de-icing salt on footpaths, although this is prohibited. As a consequence, in recent years – and particularly in the summers since 2010 – increased de-icing salt leaf damage symptoms have been observed, including in younger street trees. De-icing salt unfolds its negative effect on the street trees particularly during periods of high water shortage (water stress) in the summer, which is in turn amplified by the effects of climate change.

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Street tree condition reports 2020, 2015, 2010 (in German)

  • Straßenbaum-Zustandsbericht "Berliner Innenstadt 2020"

    PDF-Document (8.4 MB)

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  • Straßenbaum-Zustandsbericht "Berliner Innenstadt 2015"

    PDF-Document (2.3 MB)

    Download
  • Straßenbaum-Zustandsbericht "Berliner Innenstadt 2010"

    PDF-Document (749.7 kB)

    Download

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