The general assessment of tree health has always relied on a careful study of symptoms. Since symptoms are often the only evidence available for diagnosis, their recognition and interpretation are the key elements of this guide. It may not always be possible to make a definitive diagnosis or to confirm the precise cause of a problem, but informed observations can provide invaluable information and help in decision-making in the field. This is a major advantage for people who cannot obtain technical assistance or advisory support every time trees become unhealthy. Recognizing a previously unknown type of symptom helps to identify a new problem at an early stage.
A symptom-based approach considers all possible factors that affect tree health. The interpretation of symptoms is discussed in Chapter 6. Guidelines are provided on how to make a preliminary diagnosis, which acts as the basis for further action. The next step may be to do nothing, to seek further help, to remove the tree or to replant with a different tree species. Replanting with a new tree species should always be the last option because of cost and the risk of further damage if the cause of the original problem is still unresolved.