Forest Decline in Switzerland: A Review

Berlin

1993

S. 3-17

43 Lit. Ang.

Bandaufführung

13151

75880

Close analysis shows that inexplicable forest damage Switzerland has not escalated, as was feared in the early 1980s. Nevertheless, the increasing trend towards crown defoliation since 1984, especially in the protecting forests of mountainous areas, is to be taken seriously. The significance of this trend in defoliation, together with other parameters affecting forest vitality, is difficult to interpret at present. Even the question as to whether the level of defoliation in the 1980s lies beyond the range of natural variability remains unanswered, and cannot be addressed by present-day forest damage inventories, as we have no comparable data from earlier times. Consequently, the question is whether the spatial extension of crown defoliation is really a new phenomenon. Today, however, the proportion of trees with visible crown defoliation cannot be ignored. In Switzerland, it is difficult to distinguish between different types of crown damage. Damage takes mainly the form of non-specific crown defoliation and, so far, no plausible hypothesis as to its extent and course of development in various regions or arious species has been advanced. The latest findings, especially those of the National Research Programme 14+, have not provided any evidence of a general air pollution effect on the crown condition of trees. At the same time, various studies indicate potential pollution threats to the forest ecosystem. A more short-term risk factor is ozone, the dominant pollutant in rural areas; in the long run, risks could be incurred from atmospheric deposition and from the potential climate change due to the emission of greenhouse gases. Although, or perhaps because, these potential risks to our modern civilization are difficult to assess, it is more than reasonable to pursue our efforts in reducing air pollution. In this regard, the arguments on environmental policy must keep pace with the latest research findings. The realization of the objectives concerning air pollution depends last, but not least, on valid arguments in which ideological opinions are distinguished from scientific facts and the certainty and range of valid research results are taken into consideration. In view of the risks threatening the forest, it is essential not only to continue observations but also to intensify them. Well-coordinated, interdisciplinary monotoring systems must be developed to allow a comprehensive characterization of changes in the vitality of forest ecosystems and of the factors that influence them. In causal research, not only the effect of air pollution, but also other potentially influencing factors such as weather patterns, pathogens or human activities must be given serious consideration. Improved knowledge of the normal states in various forest ecosystems and the range of their natural reactions is a prerequisite for better estimating the risks of ....