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Mesquite burns in Hughenden, north
Queensland
Photo: Catherine Setter
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A two-year study has found that fire is an
effective weapon in the fight against the invasive woody weed
Algaroba mesquite.
A team from Queensland Department of Natural Resources conducted
studies at sites near Hughenden, north Queensland, where the
density of mesquite before burning was about 1760 plants per
hectare. Three months after burning only 7 per cent of these were
still alive; and these were either in areas that had not been
burnt, or had received only minimal damage.
The trial was undertaken on Prosopis pallida, commonly referred
to as Algaroba mesquite, one of four species currently invading the
rangelands of north Queensland. The other three species are P.
velutina, P. juliflora and a hybrid. Studies on how effective fire
is on these species have not been done, and the findings apply only
to P. pallida.
As well as killing adult plants burning also reduced the amount
of seedlings that came up in the year after burning, said Dr Shane
Campbell, one of the DNR researchers who undertook the study.
“In some species, many of the acacias for instance, fire
will actually help seeds to germinate and can result in increased
density of plants,” said Dr Campbell. “So it is
important to test for this when undertaking burning trials.
Fortunately this was not the case with mesquite.”
Pre- and post-fire grazing management is particularly important,
said Dr Campbell. Grazing has to be managed to allow sufficient
fuel to build up in order to carry a fire. He warned that if
animals introduced after burning come from an area containing
mesquite trees with pods, mesquite would be spread in to the clean
paddocks once again.
Though fire reduces the amount of seedlings that germinate,
those that do come up grow better in burnt areas, Dr Campbell
explained. “It is important to keep an eye on them and treat
them before they grow too large,” he said. “This might
involve using chemicals or a follow-up burn a couple of years after
the first burn.
“However, establishing good grass cover is the best way to
control seedling regrowth and will keep them under control,”
he added. “To achieve this may require reducing the grazing
pressure or reseeding in areas where there is little
grass.”
