Environmental Engineering Reference
In-Depth Information
stage of low abundance may be relatively low, though detection costs per individ-
ual will be relatively high. On the other hand, in the early stages of an invasion,
there may be little motivation to take action simply because impacts are low. h e
perception may be that the species in question does not warrant attention. h is
highlights the need for a capacity to predict the impacts of an invasive species on
the basis of observations and data collected during the early stages of the invasion
or from other parts of its introduced range. Such information, therefore, provides
some basis for making decisions to control (or eradicate or contain) at a stage of
invasion when those options can be pursued cost-eff ectively.
Priorities for programmes to eradicate, contain, or control invasive species should
be based on an evaluation of their impacts. There are few, if any, quantitative data
for most invaders but action should not be delayed while waiting for comprehen-
sive measures of their impacts. World-wide there is a reasonable body of knowledge
of the processes and impacts whereby invasive species affect ecosystems (Mooney
2005). Extrapolation from data gathered elsewhere, combined with local observa-
tions and informed opinion, often enables some evaluation of a species' impact
in systems for which there are no or few quantitative data (Grice
et al
.
2004).
Convincing evidence of specifi c impacts is especially useful in the case of conten-
tious invasive species where it may be necessary to use fi rm evidence to help resolve
confl icting interests.
and responses to management
Containment and control of an invasive species must be based on knowledge of
its biology and ecology, including the specifi cs of how the species functions in its
invaded range (e.g. Grice 1998; Campbell and Grice 2000). Knowledge of the
species' life cycle, basic habitat requirements, means of dispersal, and reproductive
capacity are useful. For plants, the time taken to fi rst reproduction is important
because it determines the minimum time before propagules newly arrived at a
site can produce plants that are themselves sources of seeds. Seed longevity and
germination requirements are important in determining how long a site must be
monitored after established individuals have been removed. It is also useful to
know about a plant's capacity for vegetative reproduction and spread.
Measures to counter incursions of invasive species will always be based on
imperfect knowledge of their biology and ecology. Especially in cases of new
incursions of high-risk species, countermeasures should not be delayed more than
absolutely necessary because an early response can be critical (see section 5.3.6).
Additional knowledge can be acquired as containment and control programmes
