Biology Reference
In-Depth Information
of containing the plant is also considered, since herbicide treatments may easily
contain a plant even if it has established.
16.5.2.6
Potential Economic Consequences (Including Environmental Impacts)
In the case of introduced plants, establishment and spread do not necessarily imply
that there is a negative impact. Introduced species may even increase biological
diversity (the Mediterranean flora contains about 20% of exotic species). So it is
necessary to evaluate further whether there are potential negative economic impacts
(including environmental and social impacts). Any such effects are documented and
evaluated for the current area of distribution of the plant, and estimated for the PRA
area. This may be done in monetary terms, especially for control costs. For example,
in the EPPO PRA for
Crassula helmsii
: “one recent estimate puts the cost of control
of
C. helmsii
at between 1.45 and 3 million euros based on the treatment of 500 sites
over a period of 2-3 years in the British Isles” (Leach and Dawson 1999).
For invasive alien plants, it is particularly important to evaluate environmental
impacts such as reduction of keystone species; reduction of species that are major
components of ecosystems, and of endangered species; significant reduction, dis-
placement or elimination of other species; indirect effects on plant communities
(species richness, biodiversity); significant change in ecological processes, and the
structure, stability of an ecosystem (including further effects on plant species), etc.
are evaluated. For example, in the assessment of the environmental impact of
Crassula helmsii
, part of the information provided in the PRA is: “[…]. The rare
starfruit
Damasonium alisma
, one of the rarest plants in UK, is thought to be threat-
ened by
C. helmsii
(Watson 2001). Moreover, Leach and Dawson (1999) state that
in an artificially managed lake (Priors Down Lake, Stalbridge, Dorset), evidence
suggests changes in floral dominance,
C. helmsii
excluding
Ludwigia palustris
and
Galium debile
(Dawson and Warman 1987) […].”
Invasive alien plants may also have social impacts, which can be taken into
account as they would be for any other kind of pest. For example, these social impacts
could include damaging the livelihood of a proportion of the human population and
affecting human activities (e.g. water quality, recreational uses, tourism, animal graz-
ing, hunting and fishing). Some of these effects, such as those on human or animal
health, the water table or tourism, might have also to be considered, as appropriate,
by other agencies/authorities. Information provided for
Crassula helmsii
was: “The
mats formed by the plant choke ponds and drainage ditches. Strongly invaded waters
lose their attractiveness for recreation and flooding may be caused. The mats can be
dangerous to pets, livestock and children who mistake them for dry land”.
Whether for entry, establishment or economic effects, the areas and degree of
uncertainty should be noted. They ensure transparency of the process (according to
the SPS Agreement principle of transparency) and may orientate additional research
to complete the PRA or give it more accuracy.
The overall conclusion of the pest risk assessment is to decide whether the pest
qualifies as a quarantine pest, on the basis of the answers given. If so, PRA continues
