Environmental Engineering Reference
In-Depth Information
considered and confi ning assessments to priority habitats, thereby reducing the
costs of managing invasive species.
Signifi cant hurdles remain in assessing risks for multiple species and multiple
habitats and regions. Holt
et al
. (2006) provide a quantitative approach to aver-
aging scores based on establishment potential, host range, dispersal potential,
economic impact, environmental impact, and pathway potential (and trading
partners), where categorical scores from one to three are subjectively deter-
mined for each factor. h en, the upper limits and lower limits are considered
along with average rankings across species. Obviously, such determinations are
greatly aff ected by the completeness and accuracy of the information about each
species.
A tremendous challenge remains in documenting, mapping, and predicting the
establishment and spread of biological organisms in space and time (Chong
et al
.
2001; Schnase
et al
. 2002b). Imagine the often di
cult case of predicting gener-
ally large chemical spills, collecting basic information on where a spill occurred,
the toxicity and amount of the chemical, knowledge of physical dispersion pro-
cesses involved in the rate and direction of spread, and the potential impacts and
costs to the environment, economy, and human health relative to containment
costs. Now, imagine the di
culties in detecting the initial establishment of tiny,
often cryptic organisms that can have long lag times from introduction and estab-
lishment to successful invasion; that can reproduce and spread rapidly by phys-
ical and biological processes; and that may have leap-frog like re-introductions by
human transportation and trade. Many species that arrive in a country are inten-
tionally introduced (via seed trade, horticulture, released unwanted pets, etc.). For
example, 50% of the alien plant species in China were intentionally introduced as
pasture, food or forage, ornamental plants, textile, or medicinal plants, while 25%
of alien invasive animals were intentionally introduced (Xu
et al
. 2006a). In add-
ition, many species are introduced unintentionally as 'hitchhikers' (i.e., pathogens,
ballast water species).
Because there is a continuing threat of intentional and unintentional introduc-
tions of harmful species, a formal approach to risk assessment is needed to:
Guide prevention and screening eff orts;
•
•
Plan an early detection and rapid response programme;
•
Help select priority species and priority areas from control and restoration;
and
Iteratively improve and integrate all these aspects of invasive species manage-
•
ment to reduce the costs and eff ects of current and future invasions.
We outline the general components of risk assessment for invasive species, along
with examples from the fi eld and laboratory.
