Invasive alien species in Switzerland - Schweizer ...

Résumé 25
Changes in distribution of species are a natural phenomenon; ranges expand and retract
and species colonize new areas outside their natural range by long-distance dispersal,
for example reptiles on floating wood to new islands. However, these events are rare
and mostly restricted by natural barriers. The relatively recent globalization of trade
and travel has inadvertently led to the increased transport of organisms and introduction
of alien species, tearing down these natural barriers. Alien species are not bad per
se, in fact many species are used for human consumption, e.g. most crop species are
aliens in the majority of regions where they are grown. However, some of them may
subsequently become harmful and pose threats to the environment and human populations.
IAS are increasingly recognized as one of the major threats to biodiversity. These
negative effects are best documented in bird extinctions on islands where the majority
since 1800 have been caused by IAS (BirdLife International, 2000). This global problem
needs global and local responses, or, even better, proactive measures, and solutions.
The complexity of the IAS topic stems from the very different species involved, their
diverse origins, the variety of pathways used, their varied impacts on new environments,
their relationships with indigenous and other alien species, the ecosystem
changes caused, their dependence on other factors such as global warming, their human
dimensions including changes in political and ethical views, and their on-going evolution.
Invasive alien species are found in virtually every taxonomic group. The following
examples will attest this statement.
The West Nile virus causing encephalitis hitched a ride to the New World in an infected
bird, mosquito or human (Enserink, 1999).
The bacterium Vibrio cholerae (Pacini), the causal organism of the human disease
cholera, is a member of brackish water communities and is frequently found in ballast
water of ships (McCarthy and Khambaty, 1994), by which means some new highly
virulent strains have been redistributed leading to epidemic outbreaks of cholera.
Another bacterium, Erwinia amylovora (see Fact Sheet in chapter 9) is a serious threat
to the fruit industry in Switzerland.
Some fungal pathogens are amongst the IAS with the most disruptive impacts on
ecosystems. Some well-known examples include fungi attacking trees, e.g. chestnut
blight (Cryphonectria parasitica (Murrill) Barr) was introduced with alien chestnut
trees to North America, where it virtually eradicated the American chestnut (Castanea
dentata (Marsh.) Borkh.), which was a dominant tree in eastern forests, thereby changing
the entire ecosystem and composition of the forests (Hendrickson, 2002) and is
now, albeit with less severity, attacking trees in Switzerland.
Weeds are another predominant group of IAS known to cause economic problems as
well as deleterious effects on the environment. The giant reed (Arundo donax L.) is
used in many countries, for example as windbreaks, and is readily invading natural
areas; the small herb common ragweed (Ambrosia artemisiifolia L.) is swiftly expand-