Ailanthus and paulownia: "The New Wild" in Swiss forests?
"The New Wild" resulting from biological invasions is a controversial concept focussing on the integration of exotic species into indigenous ecosystems. Following this rationale, the great vitality of the new species could be exploited to populate ecosystems heavily altered or largely destroyed by man. Here we discuss this integration approach using the example of Ailanthus altissima and Paulownia tomentosa. Both species have begun to spread spontaneously into some forests in Switzerland. New studies indicate that the two pioneer tree species will not prevail on a large scale and that they do not necessarily reduce the required forest services. For example, Ailanthus trees growing in forests protecting from natural hazards appear to be similarly resistant to rockfall as the local tree species and less affected by heart rot decay than originally feared. For Switzerland, a spatially differentiated strategy with control and integration measures is required.