Weed booster
From the February 2008 edition of Agriculture Today.
Regional weeds co-ordinator at Dubbo, Peter Gray, runs his finger over thorns sharp enough to penetrate vehicle tyres.
A major consequence of climate change will be the boost it will give to Australia's already daunting $4 billion weed problem.
Increasing temperatures attributable to climate change will effect the distribution of weeds and generally shift the range of all species southward in NSW, according to NSW Department of Primary Industries (DPI) weed ecologist, Dr Stephen Johnson.
Late last year, CEO of the Co-operative Research Centre for Australian Weed Management (Weeds CRC), Dr Rachel McFadyen, warned climate change would provide opportunities for weeds to do what they do best - invade.
Weed scientists say the problem is one widely overlooked by commentators.
New weed invasions will be aided by the sort of extreme events anticipated by climate change scenarios, such as more and bigger fires, floods and storms.
Dr Johnson, DPI’s acting team leader of invasive species strategy and planning, said "since many weeds spreading southward are already widespread in NSW, current management practices will need to continue".
"Frost-intolerant species such as prickly acacia and Siam weed will expand their range further south."
Similarly, increased water temperatures and different flow regimes may increase the spread of marine weeds like caulerpa.
"Weeds currently restricted to lower altitudes by cool temperatures are more likely to move into higher altitude areas, for example fireweed," Dr Johnson said.
"Conversely, higher altitude environments may become less suitable for weed species that require cool-temperate conditions.
"This may result in a decrease in these weeds, for example of gorse and scotch broom."
Native cool-temperate and alpine habitats are at increased threat of weed invasion and require ongoing monitoring and weed management.
Dr Johnson said in these geographic locations, NSW DPI would work with NSW Department of Environment and Climate Change to help achieve better natural resource management.
Weed species that are not yet a problem in NSW, for example the hawkweed species, or others that have not yet been found, for example the witchweed species, could become difficult in future.
"Continued monitoring and management of these weeds is needed, so is risk assessment of potential new species," he said.
Changes in rainfall will effect the distribution of weeds and weeds favoured by high rainfall, such as lantana, may be reduced.
In contrast, weeds favoured by lower rainfall and reductions in frost, for example the cacti species, could spread further.
Lower rainfall could weaken existing vegetation - planted crops and pastures, or native plants - making these areas more prone to invasion.
Increased levels of atmospheric carbon dioxide are expected to favour the invasiveness of some plants, for example parthenium, which may become even more competitive as a result.
Climate change may also result in some weeds such as common ragweed becoming more allergenic.
"Increased exposure to this weed could result if it is allowed to spread further south to higher populated coastal areas," Dr Johnson warned.
Contact Stephen Johnson, Orange (02) 6391 3146, stephen.johnson@dpi.nsw.gov.au
