Invasive alien species in Switzerland - Schweizer ...

An inventory of alien species and their threat to biodiversity and economy in Switzerland FOEN 2006 128
10 > Plants – Planta
Prepared by André Gassmann and Ewald Weber
10.1 Introduction and terminology
The expansion of alien plants within Central Europe began with the introduction of
agriculture about 7,000 years ago and the subsequent spread of weeds. In Europe, as in
most regions of the world, the number of alien plant species has increased considerably
in the past 200 years as a result of increasing trade, tourism and disturbance. The
increasing number of naturalized alien plant species with negative impacts on plant
communities is viewed as a major component of global change. Successful invaders
can affect the invaded communities in various ways, e.g. reducing the local diversity,
driving rare native species to extinction (e.g. by competition or hybridization), changing
habitat structures and ecosystem functioning, or increasing erosion. Plants are
particularly notorious invaders, since they are capable of changing the food web at the
base, which can ripple through the entire ecosystem. In Switzerland, with the exception
of the Alps, wildlife and areas of conservation value are usually restricted to small
areas, surrounded by heavily disturbed habitats or urban areas. In such small areas,
invasive plant species pose additional threats to the native plant and animal diversity.
Moreover, new plant invaders in Switzerland and in Europe can also affect human
health (e.g. Ambrosia artemisiifolia L. and Heracleum mantegazzianum Sommier et
Levier) or are a potential threat to the agro-economy (e.g. Senecio inaequidens DC.).
This report gives an overview of alien and invasive plant species with regard to the
Swiss flora. Some of the ecological and biological characteristics of alien plants in
Switzerland are discussed and a list of plant invaders or potential invaders is provided.
In this context, it is important to note that different original sources may cite different
numbers of alien plant species. For example, Moser et al. (2002) list 350 neophytes. A
number of these species are given a different status in Lauber and Wagner (1998). In
addition, the species lists are not identical. For example, Moser et al. (2002) list two
ferns as neophytes (Cyrtomium falcatum K. Presl, C. fortunei J. Sm.) which are not
included in Lauber and Wagner (1998). The same holds for Crataegus lindmanii
Hrabetova and C. rhipidophylla Gand. In contrast, species like Cotoneaster bullata
Bois, C. dammeri Schneider, Helianthus rigidus (Cassini) and Paspalum dilatatum
Poiret are not included in Moser et al. (2002). Excluding cultivated species that occur
rarely as subspontaneous species (‘C’ plants in Moser et al. (2002)), we found in total
over 70 alien species which are included in either one of the two lists but not in the
other. Most of the variation originates from whether cultivated species are considered
to be subspontaneous or not. In addition, another 60 species of European origin are
controversial with regard to their alien status in Switzerland. Thus, different authors