Invasive alien species in Switzerland - Schweizer ...

10 > Plants – Planta 135
In total, 28.2 % of all alien species have become naturalized. No naturalization at all is
observed in 31 families (comprising 55 alien species). The highest rate of failure is in
the Amaranthaceae with nine alien but no naturalized species. In contrast, 100 %
naturalization is observed in 17 families accounting for 20 alien species. The number
of naturalized species is correlated to the number of species introduced (Fig. 10.4).
10.6 Life form
The 11 life forms that are defined in Flora Helvetica (see also Table 10.6) have been
pooled into eight different ones. The categories ‘trees’ and ‘shrubs’ include both
deciduous and evergreen plants. The category ‘small shrubs’ includes both woody and
herbaceous chamaephytic plants. Chamaephytic plants are perennial species with
persistent stems and buds overwintering above ground level. Geophytic plants are
perennial herbs with tubers, bulbs or rhizomes.
In all, 46.4 % of the alien flora of Switzerland consists of annual and biennial species
(n=168) but only 21.6 % of the naturalized flora is in these groups (n=22) (Table 10.4).
In contrast, perennial species form 53.6 % of the alien flora but 78.4 % of the naturalized
flora. Thus, of the alien species present in Switzerland, relatively more aquatic
plants (78 %), small shrubs (55 %) and trees (47 %), and indeed perennial plants as a
whole (41 %) have become naturalised, compared to biennial plants (13 %) and annual
herbs (13 %).
Tab. 10.4 > The life form of vascular plants in Switzerland: number of species (% of total).
Life forms Alien species Naturalized species Invasive species Native species
Perennials Trees 30 (8.3) 14 (13.7) 5 (25.0) 68 (2.7)
Shrubs 25 (6.9) 8 (7.8) 2 (10.0) 103 (4.1)
Small shrubs 22 (6.1) 12 (11.8) 0 238 (9.6)
Geophytic plants 48 (13.3) 18 (17.6) 7 (35.0) 383 (15.4)
Herbs 60 (16.6) 21 (20.6) 1 (5.0) 1120 (44.9)
Aquatic plants 9 (2.5) 7 (6.9) 2 (10.0) 62 (2.5)
Perennials (total) 194 (53.6) 80 (78.4) 17 (85) 1974 (79.1)
Biennial herbs 54 (14.9) 7 (6.9) 1 (5.0) 239 (9.6)
Annual herbs 114 (31.5) 15 (14.7) 2 (10.0) 279 (11.2)
Total 362 102 20 2492
Woody and geophytic plants account for 70 % of invasive species in Switzerland
(Table 10.4). Perhaps surprisingly, no chamaephytic and only one herbaceous perennial
have become invasive. The proportions of shrubs and aquatic plants in the invasive
flora are similar, as are the proportions of these two life forms in the naturalized flora,
i.e. 7–10 %. Thus, there are again a disproportionate number of large woody perennials