Ozone Load
 

The ozone load is clearly higher than the critical level of 5 ppm h > 40 ppb for the forest. Consequences for the trees are visible injuries, an reduced growth and an impaired carbon allocation to the roots.

   
The ozone concentrations in Schönenbuch have decreased during the nineties but have increased again since. The figure presents the exceedance of the Swiss air quality limit (120 mg/m3 during one hour, blue bars) and of the UN/ECE critical level for the forest (5ppm h >40 ppb, red line). 
 
Ozone impairs the translocation of carbohydrates from leaves and needles to the roots. Thus, less reserve substances are stored in the roots in autumn. The formation of fine roots and the vitality of mycorrhizal fungi may therefore be impaired. 
 

Bronze type discoloration of beech as a consequence of ozone.
 
 
The higher the ozone dose was at the site where young Norway spruce were exposed, the less starch was directed to the roots, and the more starch remained in the needles. 
 
The effect of nonfiltered air on young beech and Norway spruce is compaired with the effect of filtered air in a chamberless fumigation system.
Parasites, especially sucking insects, are able to profit from the changes in the trees caused by ozone. In spruce as well as in beech the infestation with aphids living on leaves, on shoots and forming galls was increased.