Environmental Engineering Reference
In-Depth Information
to that unit of land even though the same level of eff ort may be more cost-eff ective
and strategic if it was directed elsewhere. Decisions will be infl uenced by the mea-
sured and perceived impacts, the costs and benefi ts of control actions, and how
those costs and benefi ts are distributed amongst stakeholders. A number of action
scenarios are possible under the infl uence of these potentially confl icting forces:
Effort is directed toward places where the invasive species is most abundant.
Such a decision could be based on (a) a realization or perception by managers
of such locations that the invasive species is having major impacts there; (b)
information or perception that by directing effort at areas of high population
density, the risk to adjacent areas may be reduced or that population growth
by the invasive species will be more severely impaired.
Effort is directed toward places where the invasive species is least abundant.
The decision to take this course of action could be based on a perception or
information indicating that the costs of control are relatively low in such cir-
cumstances and impacts that would result from a higher density of the inva-
sive species can be avoided or delayed.
Effort is focused on areas of particularly high value irrespective of the costs.
Such a strategy could be taken, for instance, where a particular species, com-
munity, ecosystem, or human enterprise is especially susceptible to the inva-
sive species.
5.3.5 Coordinate management of multiple, functionally
similar invasive species
Many ecosystems are subject to invasion by multiple alien species that have similar
impacts. One example of this is discussed in section 5.4.3 where a number of intro-
duced predators combine to affect the survival and breeding success of endemic
New Zealand birds. Often, many species of invasive plants combine to affect the
composition and structure of native vegetation (e.g. Lawes et al . 2006). Attempts
to address problems caused by a single invasive species in an environment in which
there are multiple, functionally similar invasive species is likely to be an ineffective
use of resources.
5.3.6 Take action early in the invasion process
In the case of containment, the benefi ts of early intervention will take the form
of potential range not occupied. Early containment action has two advantages:
one is that the boundary to the species' distribution along which effort has to be
expended is shorter, so the effort required is lower; the other is that the ratio of
occupied range to unoccupied potential range is lower so that, assuming the con-
tainment programme is effective, a greater area will be saved from invasion.
In the case of control, early intervention will generally involve dealing with a
lower overall density of the invasive species which may be less expensive. Where
it is necessary to kill or capture each individual, the costs per individual will often
 
 
 
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