Forest health assessment and monitoring: issues for consideration

Assessment and monitoring of forest health represents a key point for environmental policy and for the management of environmental resources. With the renewed interest in assessment and monitoring of forest health generated by the suspected occurrence of a widespread forest decline in Europe and North America, many activities have been undertaken: however, some questions should be considered and clarified when attempting to estimate forest health. Particularly, the objective(s) of the assessment and monitoring program should be carefully identified. Identification of a program's task has a number of implications and consequences: it implies a definition of what concept of forest health (forest ecosystem health, forest health or forest trees health?) is assumed, what will be the target entity to be monitored, and therefore the identification of the relevant assessment questions and assessment endpoints. Consequences concern the definition of the spatial scale (from international to landscape and plot scale monitoring) and ecological coverage (from single species population to population of ecosystems) of the program, which can have a considerable influence on the choice of the proper sampling strategy and tactic, as well as on the most suitable methods, indicators and indices to be used. Although much of the work in the field of forest health and air pollution has concentrated on surveys on crown transparency and discoloration, there is an entire range of methods, indicators and indices developed to assess the health status of forests. The decision as to which ones should be used will depend on the aim of the program and on economic and practical considerations. A further consideration concerns the time span of the program, but any decision in this field is subject to many limitations due to difficulties in predicting future monitoring needs. All these points should be carefully considered and implemented according to a rigorous Quality Assurance procedure since any decision will influence future work for many years.