Biology Reference
In-Depth Information
high inflammability exacerbates its ability to alter communities. Removing C. odo-
rata from arable fields is so difficult that it has rendered agricultural fields function-
ally worthless (R.N. Mack, pers. observ.). Consequently, its discovery in northern
Queensland in 1994 (Waterhouse 1994) sparked a justified outcry for its eradica-
tion: its potential new range in Australia includes much of the eastern country's
coast (McFadyen and Skarratt 1996) and possibly much more (Queensland
Department of Primary Industries and Fisheries 2007a).
The National (Australian) Siam Weed Eradication Program is attempting to
eliminate C. odorata from Queensland. Elimination of Siam weed in several
hundred small infestations was once thought to be a difficult but attainable goal;
it has unfortunately proved much more complicated. As is so often the case with
a rapidly spreading invader, the shrub has appeared in multiple and widely sepa-
rated locales in Queensland - aided in part by its dispersal via severe tropical
storms, such as Cyclone Larry in 2006. Invasion so far consists mainly of popula-
tions occupying < 50 ha, although the largest infestation covers 1,400 ha in or
near Townsville and Thuringowa. Siam weed is being destroyed at many of the
known sites, even as detection continues for any newly established or previously
undetected populations (Queensland Department of Primary Industries and
Fisheries 2007a).
The conditions and circumstances encountered in eradicating C. odorata seem
extraordinarily challenging. Much of the survey must be conducted on foot, as
effective aerial reconnaissance is limited to a two-week flowering period when
the shrub's white inflorescences can be detected. Eradication is conducted com-
monly in remote tropical forests on steep terrain that have few roads or trails.
Furthermore, the use of vehicles can be counter-productive to eradication, as
C. odorata seeds readily attach to vehicles. Consequently, herbicide sprayers
must be hand-carried to infestations or the plants must be hand-pulled. Finally,
crocodiles, cassowaries, feral pigs, and lethally poisonous snakes can be encoun-
tered during fieldwork, and there is the added risk to workers of contracting
Leptospirosis or Scrub Typhus (Queensland Department of Primary Industries
and Fisheries 2007a)!
As indicated above, this eradication program may hold the dubious distinction
of being conducted under the worse possible conditions. Yet the stakes are enor-
mously high for Australia. The potential damage for much of coastal Australia is
readily apparent in the horrific damage this South American shrub has already
inflicted in India and West Africa (Day and McFadyen 2004). If not eradicated,
Siam weed has the potential to alter much coastal forest in Australia, and the nation
would be hard pressed to wage a long-term campaign of control, given so many
other pressing biological invasions (Humphries et al. 1991).
To its credit, the Queensland Government is simultaneously conducting eradica-
tion campaigns against six other invasive species Clidemia hirta , Limnocharis
flava , Mikania micrantha , M. calvescens , Miconia racemosa , and Miconia nervosa .
None is as widespread as Siam weed, but each presents environmental problems
that rival the reputation of C. odorata , especially Clidemia hirta , Mikania micran-
tha , and the aforementioned M. calvescens . Left unchecked each has the potential
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