This is not another book about the effects of air pollution on trees. Instead, it attempts to cover the subject of forest decline. Forest decline is frequently assumed to be inextricably linked with air pollution, but this is not so. There are some situations where air pollution has caused the decline and even death of forests, but it is also quite clear that forests can decline in the absence of air pollution. There has been a huge amount of experimental research on the effects of air pollutants on trees under artificial conditions. This has yielded valuable information on the mechanisms of the biological effects of pollutants and the concentrations of specific pollutants that are likely to cause injury. However, applying these results to trees grown in the uncontrolled conditions represented by the natural environment is extremely difficult. Consequently, very few studies (if any) have succeeded in bridging the gap between experimental environments and the real world. Because of this, experimental research on the effects of air pollution on trees has not been reviewed. Where appropriate, reference is made to some more relevant experiments, particularly if the experimental design and analysis of the experiments are known to have been valid. Regrettably, many studies had to be excluded either on the grounds of irrelevance or of poor scientific practice.
