Switzerland has been undertaking assessments of forest condition since 1984, although the inventory methods have only been consistent since 1985. Observations are made on a systematic grid, using fixed-area (on a horizontal plane) plots. The grid for the observations was changed in 1993, from a 4 km x 4 km net to an 8 km x 8 km net. This was the maximum reduction that could be undertaken without unduly affecting the results for the country as a whole. The reduction in sample size means that regional breakdowns are no longer possible, but breakdowns by the main species (Norway spruce, silver fir and beech) are still possible. Observations have primarily been related to the assessment of individual tree crowns, with unexplained defoliation being the most frequently utilised assessment. This indicator suggests that the crown condition of trees in Switzerland has deteriorated over the period 1985-1993 (INNES et al. 1994). Other assessments have been made, but have not been so widely reported.
In 1993, the programme was extended to include assessments of the soils and ground vegetation at the sites and a modelling exercise is being undertaken to determine the past climate and pollution conditions for each plot. The modelling is difficult because of the complex terrain of Switzerland and the widespread occurrence of phenomena such as temperature inversions and anabatic-katabatic wind systems. However, reasonable estimates of the climate and pollution conditions at particular sites should be possible.
A major concern has been data quality assurance and considerable efforts are made to maximise the consistency of the subjective assessments made during the inventories. In addition, the chemical laboratory undertaking the soil analyses has been involved in a number of international quality assurance projects. The results for the laboratory are encouraging, but a number of major problems exist with the field assessments. These are currently being a reviewed with a view to simplifying and/or quantifying some of the assessments, providing more detailed training and developing better documentation for some of the indicators.