ESTONIAN ENVIRONMENTAL REVIEW 2009

Alien species
Most alien species are in their country of origin common
plants and animals and do not pose a danger to
the local ecosystem there as they are its natural part. A
majority of the alien species in a new environment do not
manage to survive in the new conditions and do not pose
a threat to Estonian nature. About one in ten adapts to the
new conditions and one-tenth of those in turn becomes
invasive – they can pose a risk to the ecosystem or parts
thereof; they may have a noteworthy negative effect on
the environment, agriculture and human health. Invasive
alien species are estimated to account for one in four or
even one in two (primarily on the islands) most important
factors H that reduce local biodiversity.
Alien species that have adapted to the new conditions
may invade niches in natural communities inhabited by
indigenous species. The newcomers do not have connections
to other species in the local ecosystem to the
extent that native species do; as a result the networks of
interconnections in the ecosystem become weaker and
biological diversity generally declines as well. The influx
of alien species can be accompanied by new diseases
and pests who find new food sources in their new land.
Often alien species intermingle with native relatives,
thus changing the species gene pool. The most dangerous
alien species are the ones that become domesticated,
i.e. become widespread and reproduce independently
in local natural communities. Unfortunately we are not
able to foresee invasiveness of alien species, and the shift
in timescale may be especially misleading. An explosive
spread may occur decades after the species is introduced.
The clearest sign of danger is the invasiveness of a species
in a region with similar natural conditions I .
A total of 942 alien species had been registered in Estonia
as of 2009. The invasive ones amount to 133, including
76 plants, 35 invertebrates, 14 fish, 4 mammals and 3
species of birds and 1 amphibian species (figure 8.10).
The invasive species with the biggest impact on Estonia
and the ones that have caused the greatest losses are the
American mink, raccoon dog, mosquito (Culex pipiens
molestus), pharaoh ant (Monomoria pharaonis), the webbing
clothes moth (Tineolea biselliella), the Sosnowski’s
hogweed (Heracleum sosnowskyi), the giant hogweed
(Heracleum mantegazzianum), Turkish rocket (Bunias
orientalis) and Garden Lupin (Lupinus polyphyllus).
Without immediate control measures, American crayfish
(Pacifastacus leniusculus) and Spanish slug (Arion lusitanicus)
may cause great damage in the near future.
Arion lusitanicus is a rapidly reproducing slug, data
on which began to be collected in Estonia in 2008. This
pest with a rapid reproductive capacity is mainly spread
through places that sell plants and nurseries.
In the near future, species from North America that
have reached Europe may spread to Estonia, such as
the Canadian beaver (Castor canadensis), Canada goose
(Branta canadensis) and eastern gray squirrel (Sciurus
carolinensis). Their influence on the European beaver,
Eurasian red squirrel and greylag goose may lead to their
extinction.
non-invasive or unknown
invasive or potentially invasive
100
80
1
10
135
60
40
20
%
0
4
3
mammals
birds
amphibians
fish
68
42
34
1
14
35
76
663
invertebrates
plants
Figure 8.10. Number of alien species in Estonia as of 2009. Data: Ministry of the Environment.
H
Maismaa võõrliikide käsiraamat. (Handbook of the world’s alien species.) (2008). / Ed. L. Eek, T. Kukk. Tallinn : Ministry of the Environment.
I
Invasiivsed võõrliigid Eestis. (Invasive species in Estonia.) (2005). / Compiled by. T. Kull, Ed. T. Kukk. Tallinn : Ministry of the Environment.
[WWW] http://www.envir.ee/orb.aw/class=file/action=preview/id=89801/Invasiivsed_voorliigid.pdf
131