Invasive alien species in Switzerland - Schweizer ...

10 > Plants – Planta 131
10.3
square kilometres) is 78.4 and slightly higher than in several other European countries.
This may be due to the topography and diversity of climates encountered in Switzerland
which allow plant species as different as Agave americana L. and Reynoutria
japonica Houttuyn to become naturalized (see also Weber, 1999a, b). France, which
offers an even wider range of habitats and climates, has a density of alien species of
87.1 (Heywood, 1989), whereas in Austria, the density of alien species is 60.9.
According to Lauber and Wagner (1998), the group containing ferns and its allies does
not include any alien species (Table 10.1). There is a high proportion of alien gymnosperm
species (28.6 %), i.e. four alien gymnosperm species out of 14 recorded. The
frequency of alien species in the dicotyledons and monocotyledons is quite similar, i.e.
13.5 % and 11.0 %, respectively.
Tab. 10.1 > Synopsis of the native and alien flora of Switzerland: number of species (% of total).
Pteridophyta Spermatophyta Total
Gymnosperms Dicotyledons Monocotyledons
Native species*
84 (3.4)
10 (0.4)
1879 (75.0)
532 (21.2)
2505 (100)
Families
20 (14.7)
4 (2.9)
93 (68.4)
19 (14.0)
136 (100)
Alien species**
0
4 (1.1)
292 (80.7)
66 (18.2)
362 (100)
Families which include alien spp.
0
2 (2.5)
64 (80.0)
14 (17.5)
80 (100)
TOTAL no. species 84 (2.9) 14 (0.5) 2171 (75.7) 598 (20.9) 2867 (100)
% alien species / total no. species 0 28.6 13.5 11.0 12.6
* Excluding subspecies and varieties
** Excluding cultivated species which are not, or only rarely, found in the environment
The geographic origin of alien and naturalized species
About one-fifth of all alien plant species in Switzerland have been introduced from
each of the following areas: North America, Asia and the Mediterranean (Fig. 10.1;
Table 10.2). Some 15 % have been introduced from the rest of Europe and Eurasia/the
Caucasus. The distribution of the so-called Eurasian species usually extends from
eastern and south-eastern Europe to Asia Minor. Approximately one-fifth of the species
of Asian origin were restricted to western Asia and the other four-fifths to Central
Asia, China and east Asia. Only three species originate from Africa, three from Central
America and 14 from South America (Table 10.6). One species is native to Australia.
Seven per cent of all alien species in Switzerland are of unknown origin.
One hundred and two alien species have become naturalized. Although 71 alien plant
species in Switzerland have been introduced from North America and 76 from the
Mediterranean region, only 18.4 % from the Mediterranean region have become naturalized
whereas 43.7 % of those of North American origin have done so. Also, 31.1 %
of the alien species of European origin have become naturalized but only 25.8 % of
those of Asian/Eurasian origin. It should be noted that three out of five species introduced
from the Caucasus have become naturalized and two of them are considered to
be invasive (Heracleum mantegazzianum and Rubus armeniacus Focke).