The discussion about the introduction of exotics is almost as old as forestry on a scientific basis. It was launched already at the beginning of the last century. Mainly trees from North America were introduced in European Botanical Gardens already in the 16th century and animated foresters to start trials with some of the most promising species. In Switzerland small plantations with more than 60 exotic species were established in the last 200 years. In the last century Pinus strobus was the most important and most promising tree, but it got almost extincted in our country due to Cronartium ribicola. Actually only Douglas Fir (Pseudotsuga menziesii) and Red Oak (Quercus rubra) have a certain importance in Switzerland. But the whole amount of plantations with exotic tree species is less than 1% of the forested area in Switzerland. The criteria for plantations of exotic species in Switzerland could be summarized as follows: - the species shall be adapted to the site conditions and should not be endangered by pests and dieases (no chemical treatment in Swiss forests) - exotic species shall grow in mixed stands with indigenous species (no big scale pure plantations of one single species) - growth performance shall be better than for the indigenous species - the timber shall have qualities, which can not be met by indigenous species But the most important criteria is the silvicultural risk. Indigenous species showed since thousands of years, that they can live with the properties of the respective site. Since forests in Switzerland are not only producing timber, but have often an important protective function, minimizing the risks in forestry is a predominant task. And the risks with exotic species are higher than with indigenous species. Examples are C. ribicola at P. strobus and needle casts at Douglas Fir. A. Buergi WSL CH-8903 Birmensdorf
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