Legumes do very well in these tropical environments and many
have become significant weeds. Leucaena, or coffee bush, is a
legume originating from Central America and known in some circles
as the "miracle bush" because of the amount of weight that cattle
gain when feeding on it. For this reason, there are now more than
50,000 ha of Queensland planted with this bush and graziers are
being encouraged to grow more and more. Another half a million
hectares are suggested for planting. In the absence of grazing,
this plant can form dense thickets that exclude native plants,
especially along watercourses.
Prickly acacia covers more than 7 million
hectares of north Queensland Photo: Joel Brown
From a potential problem now to a recognised disaster: prickly
acacia (Acacia nilotica). This spiny tree originates from
Africa and was introduced to Australia as an ornamental and shade
tree and as fodder for cattle. The plants escaped into the bush and
this weed now covers a staggering 7 million ha of the dry regions
in Queensland, mostly in the Mitchell Grasslands.
There are also coastal infestations around Home Hill and Bowen.
Not only does this plant suppress native vegetation, but it also
severely restricts the movement of wildlife and cattle. There are
attempts to find biological controls for this weed. In the
meantime, it is a declared weed which is generally controlled using
chemical and mechanical techniques.
Another prickly Acacia species found in north east Queensland is
the mimosa bush (Acacia farnesiana)—not to be confused
with Mimosa pigra in the NT. Although some believe this is a
native plant, it was originally introduced for the perfume industry
because of its beautifully scented flowers and is also favoured as
stock feed by graziers.
Mesquite (Prosopis spp.) is another invasive woody plant
and though not as widespread as prickly acacia, is estimated to
have the potential to spread over more than 60 per cent of
Queensland's grazing lands.
They were introduced to Australia as ornamentals in station
homesteads or town gardens and used in mine dumps and other soil
Unfortunately mesquite has a tendency to form dense thickets
which out-compete other vegetation, interfere with mustering and
block access to water. The sharp thorns can also injure animals and
Prosopis spp. are native to North and South America and
have caused severe economic losses in these countries. There are
three species of mesquite in Queensland: P. pallida, P.
velutina and P. glandulosa and a hybrid, with P.
pallida being by far the most widespread. A number of control
techniques have been developed including mechanical, chemical and
biological control options and the use of fire. Fire is
particularly effective for mesquite. See link to Savanna
Links article below, and see Mesquite page in this section on
using fire to manage mesquite.
Jerusalem thorn, or Parkinsonia, can form
thickets along bores and dams, preventing water access to stock and
wildlife Photo: Greg Calvert
The final plant in this group of weedy tree legumes is the
Jerusalem thorn, also known by its scientific name Parkinsonia
This prickly weed was introduced in the 1800s as a shade tree
and is now a declared weed.
Small thickets occur on the coastal areas of north east
Queensland, but inland it forms impenetrable thickets along bore
drains and around dams, preventing water access to stock and
Study adds fire to arsenal against mesquite
A two-year study has found that fire is an effective weapon in the fight against the invasive woody weed Algaroba mesquite. From Savanna Links, Issue 11, Sept - Oct 1999 [read more...