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.