Invasive alien species in Switzerland - Schweizer ...

An inventory of alien species and their threat to biodiversity and economy in Switzerland FOEN 2006 130
> Adventive plants: casual alien plants that have been accidentally introduced as a
result of human activity.
> Subspontaneous plants: casual alien plants escaped from cultures.
> Naturalized plants: Alien plants that reproduce consistently and sustain populations
over many life cycles without direct intervention by humans, (or in spite of human
intervention); they often recruit offspring freely, usually close to adult plants, and do
not necessarily invade their habitat.
> Invasive plants (plant invaders): Naturalized plants that produce reproductive
offspring, often in very large numbers, at considerable distances from parent plants,
and thus have the potential to spread over a considerable area. Invasive plants can
affect the invaded natural or semi-natural communities in various ways. Invasive
plants can also affect human-made habitats and have direct economic effects. The
term environmental weeds is sometimes used for those invasive plants having an
impact in natural areas and semi-natural areas; and the term alien weeds is sometimes
used for those alien plants that are weedy in managed habitats, such as agriculture.
> Weeds: native plants that grow in sites where they are not wanted and which have
detectable economic or environmental effects.
10.2 The native and alien flora of Switzerland
The list of alien species present in Switzerland (Table 10.6) includes both archaeophytes
and neophytes. However, in this list, the neophytes of Flora Helvetica (Lauber
and Wagner, 1998) are marked as such. A few species that have become naturalized
recently (e.g. Ludwigia grandiflora (Michaux) and Lysichiton americanus Hultén & St.
John) have been added to the alien species amongst the 3000 plant taxa listed in Flora
Helvetica. The plant status and life form for each species have been extracted from the
information provided by Lauber and Wagner (1998).
The Swiss flora of vascular plants includes some 162 families and over 3000 taxa
(species, subspecies and lower taxa). Of these, 20 plant families and 84 plant taxa
belong to the ferns and fern allies (Pteridophyta) while the other families and taxa
belong to the flowering plants (Spermatophyta).
The Swiss flora comprises 2505 native species belonging to 136 families (Table 10.1;
excluding subspecies and lower taxa). From the 470 taxa of alien origin recorded in
Switzerland, over 100 species are cultivated species that are not, or rarely, found in the
environment. The 362 remaining alien species have become subspontaneous, adventive
or naturalized. These alien species, which represent about 12.6 % of the flora of Switzerland,
are discussed below.
This percentage is similar to that observed in neighbouring countries, e.g. 9.1 % in
Austria, 10.2 % in France, but much less than in countries in North America, e.g. 28 %
in Canada, or on islands, e.g. 47 % in New Zealand (Heywood, 1989). The density of
alien species in Switzerland (i.e. the number of alien species per log country size in