Abstract :
Within the European forest health monitoring system, assessments are currently made of defoliation and discoloration of individual trees, based on a systematic grid of sample plots. In addition, damage is ascribed to one of 8 classes: game and grazing, insects, fungi, abiotic agents, direct action of man, fire, known local or regional pollutants and other causes. The results indicate that the majority of countries undertaking inventories do not attribute ant damage to pollution injury. This may be because the injury is not observed (for example, it may occur on the upper sides of leaves in the upper crown), because it has been confused with other symptoms or because it is absent. Considerable care needs to be taken with the interpretation of the results and the absence of a record should not be taken as meaning that a particular cause of injury was not present. Recent results from Switzerland suggest that ozone injury may be much more widespread than previously recognised, suggesting that the failure to observe the symptoms may be an important reason for their scarcity.
