More and more the outside characteristics of the trunk seem to change. Bark degeneration develops rapidly in trees in urban regions. The likely cause of death of cells in the protective outer cell layers of the bark, and the resulting shedding of the periderm. The degeneration of the protective periderm enables lichens, algae and pathogenic bacteria, viruses and fungi to invade the tree trunk. Although no statistics regarding bark degeneration are available at this time, this problem is increasing at a rapid rate. The number of broadleaf trees in the municipality’s urban regions is affected by this phenomenon is estimated to be at least 5% .
The influence of environmental changes in the urban regions can have a relation with these ever increasing new tree diseases. More scientific research is necessary.