Invasive alien species in Switzerland - Schweizer ...

10 > Plants – Planta 133
10.4
These two sets of data each give a similar picture for the Central European flora. The
total numbers of neophytes in Austria and the Czech Republic are around 1,000 species
and the numbers of problematic species in Germany and Switzerland are 25 and 27,
respectively. It should be noted that the figure of 1,000 neophytes given by Essl and
Rabitsch (2002) for Austria is much higher than the 300 introduced species given by
Heywood (1989) for the same country.
The percentage of deliberate introductions that have become problematic is between
75 % and 84 %, while it is lower for all neophytes, i.e. between 55 % and 59 %. The
comparison indicates that species selected for introduction are more likely to become
problematic species than those arriving accidentally. These differences may be attributed
to human dimensions in the success of invasions, in particular propagule pressure.
Tab. 10.3 > Pathways of introductions into four European countries.
The numbers for Switzerland and Germany are based on problematic plants (authors’ data and
Kowarik, 2003), while the numbers for Austria (Essl and Rabitsch, 2002) and Czech Republic
(Pysek et al., 2002) are neophytes.
Switzerland
Germany Austria Czech Republic
Total number 20 25 1110 924
Deliberate 15 21 652 504
Accidental 4 4 372 420
Unknown 1 - 86 -
Deliberate/Accidental as percentage of total 75 / 25 84 / 16 59 / 33 55 / 45
Status of the alien species of Switzerland
Of the 362 alien species recorded in Switzerland, 102 species (28.2 %) have become
naturalized and 20 species have become invasive (5.5 %) (Fig. 10.3), which also means
that a quarter of all naturalized species have become invasive. The remaining species
are either adventive or subspontaneous, or of unknown status. Thus, 3.6 % of the Swiss
flora consists of naturalized species.
The 362 alien species belong to 80 plant families, i.e. about half of all plant families
present in Switzerland (Table 10.1). The percentage of alien species per family ranges
from 2.8 % (Juncaceae) to 100 % for 20 plant families which are represented by alien
species only, usually by one or two species (Table 10.7). The percentage of alien
species in the large families (>30 species) ranges from 2.8 (Juncaceae) to 25.6 %
(Polygonaceae). The largest family, Asteraceae, comprises 340 species of which some
12.4 % are alien species. Thirty percent of all alien species belong to the Asteraceae,
Brassicaceae and Poaceae.
Some 50 plant families in Switzerland include no alien species. Most of these are small
or very small families. Exceptions are the Orchidaceae (62 species), Gentianaceae (34
species), Potamogetonaceae (21 species) and Orobanchaceae (20 species).