Technical highlights - Department of Primary Industries ...

17. Weed eradication and containment: feasibility and program evaluation
Project dates
July 2003 – June 2013
Project leader
Dr Dane Panetta
Ecosciences Precinct
Tel: (07) 3255 4472
Email: dane.panetta@deedi.qld.gov.au
Other staff in 2010–11
Simon Brooks and Shane Campbell
Objectives
• Provide a scientifically based
rationale for decisions about the
eradication and containment of weed
incursions.
• Refine eradication methods by using
ecological information.
• Monitor selected eradication programs
and document associated costs.
• Develop criteria for assessing the
progress of eradication.
• Develop procedures for assessing the
feasibility of containment.
Rationale
Early intervention is the most costeffective
means of preventing weed
incursions from rapidly expanding.
Strategies to achieve this aim range
from eradication (where the objective
is to drive the incursion to extinction)
to containment (which may vary from
absolute to degrees of slowing its spread).
In previous research we have developed
measures for evaluating eradication
progress with regard to the delimitation
(determining the extent of the incursion)
and extirpation (local extinction)
criteria. We also have developed
dynamic models that provide estimates
of eradication program duration (and
total program costs when economic data
is available).
Research conducted worldwide over
the past decade has shown that the
circumstances under which weed
eradication can be achieved are highly
constrained, suggesting that eradication
may not be widely applicable as a
weed-invasion management strategy.
However, if a weed is sufficiently serious
to consider eradication there may often
be a strong justification for attempting
to slow its spread (partial containment)
should eradication prove impossible.
As some weeds may be more readily
contained than others, it is important
to better define the scope for partial
containment.
Ongoing eradication and containment
feasibility work should contribute to
management decisions. Case-study data
is needed to determine to what degree
management objectives have been
achieved and to assess progress towards
eradication or containment.
Methods
We collate data on eradication resources
and progress for each infestation of
clidemia (Clidemia hirta), limnocharis
(Limnocharis flava), miconia
(Miconia calvescens, M. nervosa and
M. racemosa), mikania vine (Mikania
micrantha)—under the National Four
Tropical Weeds Eradication Program—
and Siam weed (Chromolaena odorata)
in Queensland. Data includes method of
detection, discovery over time, trends in
infested areas, population decline and
time since last detection.
Research on assessing the feasibility
of containment has adopted both
qualitative and quantitative approaches.
Progress in 2010–11
‘Four tropical weeds’ database
We are currently converting the
eradication progress reporting units
from a buffered infestation area
to fixed management areas of 1 ha
(100 m × 100 m). This transition has
been accompanied by more intense
recording of plant presence and absence
and will enable more consistent and
accurate reporting from year to year
over fixed areas. The transition will
also enable portions of infestations
to progress to a monitoring stage and
improve the progression factors for large
infestations, including the melastome
species known only at single locations.
A finer scale of recording and reporting
can also increase the discovery rate of
management areas in the short term
and increase the rate of reversion
(from monitoring to control status).
Eventually, this new spatial regime will
enable field crews to target searching
to areas potentially containing plants
resulting from abiotic dispersal, such as
wind and water, rather than relying on
large generic dispersal buffers.
Assessing feasibility of
containment
The reduction of seed production in
weed infestations is likely to play
an important part in containment.
However, this is the case for virtually
all weeds and hence not a particularly
discriminating feature for assessing the
feasibility of containment. Therefore,
our research has focused on the fates
of seeds that are produced. That is,
while management interventions can
reduce propagule production (fecundity
control) in source populations, weed
spread can also be reduced through
actions that interfere with dispersal
and establishment, and/or lead to
the detection and control of new
infestations. Undetected new infestations
may reproduce and give rise to further
dispersal (shown as the dotted line in
Figure 17.1).
Three case studies have been used in
initial qualitative assessments of the
feasibility of containment (Figure 17.2).
The distance of dispersal affects feasibility
of containment, but the ability to
predict where seeds are deposited is also
important, since this influences both the
potential for detection of new infestations
and the effort required to do so. Branched
broomrape (Orobanche ramosa, a parasitic
annual weed targeted for eradication
in South Australia) is considered most
containable, since its dispersal is mainly
human-mediated and can be traced.
Parthenium is similar, but its seeds can
be dispersed widely by floodwaters, so
new infestations could be more difficult
to find. The feasibility of containment of
miconia is considered lowest, since it is
dispersed primarily by birds in relatively
unpredictable directions.
Quantitative assessment of the feasibility
of containment is based on a model that
includes the area that must be searched,
the effort required to detect a weed
within this area and the potential for
colonisation and establishment in sites
where foci of infestation are unlikely to
be detected.
Part 2 Landscape protection and restoration 37