Leaf damage is the most striking damage of the tree but can have many causes. Leaf damage can be caused by the influence of stress factors such as air pollution, acid rain and radiation.
A dried-out soil, sunburn, insects, shortage of oxygen in the soil or to much water in the soil can cause leaf reduction. These are all acknowledged common for this problem. But as we found out this is not the cause in many cases.
Many trees with brown withered leaves are found in the urban surroundings without finding one of the postulated circumstances. Also the shedding of leaves seems to be affected. Many trees still have their leaves in November or even December. They should shed months ago! The opposite is also the case. Trees shed their leaves already in the summer. This is of course much too early in this season.
The photoperiodic response seems to be affected by a new influence in our environment. Also this reactions must be investigated because leaf damage lead to decrease of the vitality of the tree.