Environmental Engineering Reference
In-Depth Information
(Cook
et al
. 1996). A small stand of mimosa trees were found in Kakadu National
Park (KNP) in 1983. h e staff at KNP immediately sent out a team to fi nd any
mimosa trees in the park and intervene. h ere are now occasional reports of a tree
found in the park that is quickly eliminated, but no large stands. h e programme
costs the park about $2 per hectare per year. In a nearby fl oodplain called Oenpelli
a stand of about 200ha was found at about the same time. h e response was not
as swift and by the year 1990 the infestation covered about 8200 hectares of the
fl oodplain. A control eff ort was fi nally undertaken and a very large aerial spray
operation was carried out. h e spray programme cost $220 per hectare per year for
5 years to get the tree under control. Now they, like KNP, spend about $2 per hec-
tare per year for maintenance. h is is a clear example of the costs associated with
neglecting rapid response.
h ere are two distinct types of invasion that should be recognized when discuss-
ing early detection (Fig. 3.1). h e fi rst type of invasion is one in which a native
species moves within its own native country, state, or habitat. If it moves to an area
where it did not previously exist it can be considered as invading that area. For
example, many game fi sh species in the western USA are non-native transplants.
h ese fi sh disturb the native ecology of the western lakes, yet they have remained
in their country of origin.
h e second type of invasion crosses international borders and oceans, often mov-
ing between similar ecological zones. Tamarisk (
Tamarix
spp.), which comes from
very arid regions of the Middle East and Asia, exemplifi es this. It has invaded the
southwestern USA in a climate similar to its native range. It is possible for invasions
such as this one to be intercepted at the borders of the country (Lodge
et al.
2006).
Land managers could benefi t from accurate maps showing current distributions
and local and sub-regional models of potential habitats of invaders to address both
of these types of invasion. Knowing current species distribution would help land
managers concentrate on the frontier of invasion and control small invasions in
new areas separate from larger invasions. Identifying these small, isolated areas
would be benefi cial because the most eff ective time for control is when an invasion
is small (Rejmanek and Pitcairn 2002). Determining the potential distribution of
invasions would help managers focus on the areas at a high risk of being invaded,
aiding in early detection/rapid assessments of new areas being invaded (Stohlgren
and Schnase 2006).
Basic components of an early detection and rapid assessment (EDRA) programme
include:
1)
Access to current and reliable scientifi c and management information.
2)
Ability to identify species quickly.
3)
A functional risk assessment plan.
4)
Mechanisms in place to coordinate a control effort.
