Invasive alien species in Switzerland - Schweizer ...

An inventory of alien species and their threat to biodiversity and economy in Switzerland FOEN 2006 140
Alien plants are a threat to the areas of ecological compensation, the restoration of
riverbanks and mires, abandoned grassland and forests, and all previously or currently
disturbed natural areas in Switzerland. For example, the rehabilitation of riverbanks
can be seriously handicapped by alien species. Many invasive species increase erosion
(e.g. Reynoutria japonica, Buddleja davidii), which in turn accelerates the establishment
of invasive species, thus preventing the restoration of native plant communities.
The problems caused by alien species in cultivated land are still relatively minor but
may increase in the future because of newly naturalized species and because changes in
land use may favour establishment of alien species in extensive agro-ecosystems.
Weber (1999a) recorded 38 alien plants that are known to occur in arable land. For
example, Conyza canadensis (L.) and Epilobium ciliatum Rafinesque are of increasing
importance in arable land, gardens, orchards and tree nurseries. Galinsoga parviflora
Cavanilles is known to be a serious problem in vegetable crops in other countries and
Cyperus esculentus is considered to be one of the world’s worst weeds. Ambrosia
artemisiifolia is most abundant in sunflower crops owing to the botanical similarity
between the weed and the crop itself, and therefore only a limited number of herbicides
are available that are effective against A. artemisiifolia alone. Senecio inaequidens is a
potential problem in pastures and meadows. Unlike those in a natural environment,
most alien plants in arable land are ruderal species and the majority of them are short
lived.
Alien species can also become a public health problem. Ambrosia artemisiifolia is a
strongly allergenic plant. Exposure to the sap of Heracleum manteggazianum sensitizes
the skin to sunlight and causes severe irritation and painful blisters. Contact with the
sap of Ailanthus altissima (Miller) may also cause skin eruptions.
Most of the 20 declared invasive plants in Switzerland are also invasive in neighbouring
countries. An analysis of the invasive flora of several European countries shows
that over 130 alien plants are of concern in Europe. The status of alien plants in Europe
should be one aspect considered in developing a dynamic ‘Watch List’ of alien plants
in Switzerland. In addition to the known invasive species of Switzerland, over 30 alien
plants should be monitored over time to predict their invasive potential.
In conclusion, a careful review of invasive and potentially invasive plants in Europe
combined with some key biological and ecological traits associated with naturalized
species rather than alien plants, as well as field observations, should contribute to
assessing the invasiveness of alien plant species in Switzerland. More research is
needed to understand the naturalization and invasion process and to evaluate the impact
of invasive species on the environment and the agro-ecosystem. More research is also
needed to establish long-term and environmentally friendly management tools for
invasive plants in Switzerland.