The impact of rubber vine in riparian areas is
devastating, but landholders in northern Queensland can now add
fire to their repertoire in the fight against the
weed—particularly for large-scale infestations.
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Rubbervine—the tall dark shrubs covering
the trees—invades the banks of the Burdekin River in
Queensland
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CSIRO Sustainable Ecosystems researcher, Dr Tony Grice, and his
team of researchers, along with a Seventy Mile Range Landcare group
and the Mount Cooper Bushfire Brigade have developed a practical
means of managing large-scale infestations of riparian rubber vine
using fire. The researchers have also shown that fire is effective
against smaller-scale infestations of the weed.
"The real advantage of fire (as opposed to chemicals or
mechanical treatment) is that is can be used on a large scale and
that individual plants don’t have to be located and treated,"
Tony explained. "Small parts of the landscape can also be targeted
with fire."
However, because controlling rubber vine is a long-term process,
landholders will still have to use a combination of mechanical,
chemical and biological means such as rust to successfully manage
the weed.
Effect on other vegetation
The team examined the short- to medium-term responses of rubber
vine to fire and how these fires affected native plant species.
"These fires did not cause significant changes in the densities
of most species of native trees and shrubs," Tony said. The fires
stimulated germination of Acacia spp., notably Acacia
holosericea . After burning, the exotic stoloniferous grass
Indian couch and native perennial tussock grasses still dominated
the herbaceous layer, although there was an increase in native
legumes.
Fire results
The results demonstrated that the overall impact of the fire
regime on rubber vine was considerable. For example, a single
wet-season fire reduced the density of rubber vine from 2147 to
1165 plants per hectare.
The project recommends a regime comprising fires in the first
and third year of a 10-year cycle. This regime would allow for two
fires of adequate intensity and sufficiently close in time to be
very effective. The approach is particularly relevant to
Queensland’s Burdekin Catchment where the vegetation is very
similar to that of the study sites. Several landholders in the
vicinity have now begun to use fire specifically to control rubber
vine.
Rubber vine is currently only present in Queensland but is a
threat to Northern Territory and northern Western Australia. One
infestation has been found in the Kimberley, but was dealt
with.
A closely related but less weedy species, Cryptostegia
madagascariensis , is found in both the Northern Territory and
Western Australia. It was declared noxious in WA.
Management issues
Tony emphasised that for rubber vine management on pastoral
properties, it was essential to link a fire management program with
a grazing management plan. Graziers must consider whether, to what
extent and when they might have to adjust stocking rates in order
to be able to burn or in order to allow the grasses on burnt
country to recover.
Secondly, most savanna systems are under threat from more than
one weed species. Management that targets one species may open
opportunities for invasion by others. Thus, attention must be given
to understanding and managing ‘weed complexes’. For
example, removing rubber vine may well allow other weeds to
increase.
"This is a very real threat," Tony explained, "though there is
little or no documentation of the effect."
Continuing research in riparian weeds as well as new weed
research in rangelands may give some insight into weed complexes in
the long term. In the meantime, though, careful observation and
management is required.
Weed strategy
Not only will the project’s results be beneficial for
landholders in northern Queensland, but also they will contribute
to the National Rubber vine Strategy that is part of the National
Weed Strategy. The research is a joint Tropical Savannas CRC, CSIRO
and Queensland Department of Natural Resources and Mines
project.
"It would not have been possible without the collaboration of
members of the Seventy Mile Range Landcare Group and the Mount
Cooper Bushfire Brigade," said Tony. "Linkages with these groups
facilitated effective communication of the work’s results to
landholders who are confronted by the practical challenges of weed
management in the region."
