In recent decades numerous non-indigenous species of the evergreen broad-leaved (laurophyllous) type have started to colonise Swiss lowland forests. Nowadays, in southern Ticino, there are forest patches on southern slopes, especially along the Insubrian lakes, which are dominated by exotic laurophyllous species.
The present study provides an overview of the most important exotic species and their invasion history. Field experiments gave evidence on the crucial ecological factors for seedlings establishment of exotic species. Relevé plots from the seventies were resurveyed on both the northern and southern part of Switzerland.
On the northern side of the Alps, the first occurrence of the frost-hardier exotic laurophyllous species was recorded. The observed trends point generally to more mesic conditions; the species’ changes suggest habitat conditions which are moister, richer in nutrients and generally shadier. The change towards warmer conditions is reflected by both the decreasing number of montane species and the increasing number of thermophilous species, and in particular the aforementioned evergreen broad-leaved exotic species.
In southern Switzerland, especially in areas lower than 600 m a.s.l., the structure and composition of forests has completely changed due to the shift in the shrub layer from deciduous to evergreen broad-leaved species. The exotic laurophyllous species must be considered as naturalised and ecologically important components of the affected ecosystems. The particular character of these species and species groups, as well as the fact that their increase in abundance has occurred in the last thirty years, strongly implies changes in environmental factors within that period. The twofold set of climatic parameters, higher absolute minimum temperatures and lower frequency of frost, suggest an important influence of climate on the establishment of exotic evergreen broad-leaved species.

More information is available at:
http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13561