Australia — Lantana’s quick-growing woody nature increases the frequency and intensity of fires in dry rainforests in Australia’s north, a study has found.
Scientists have long suspected the invasive plant, listed as one of Australia’s worst weeds, changes the fire cycles of forests.
But how Lantana camara did this, especially in forests not usually susceptible to fire, was unknown.
The study, by a team of researchers at the School for Field Studies Center for Rainforest Studies in North Queensland, has established that the weed increases the fuel load in the understorey of dry rainforests.
Understanding this mechanism will lead to better conservation of these types of forests around the world, says study co-author Dr Tim Curran, now based at Lincoln University in New Zealand.
The team’s findings are published in the journal Weed Research.
Introduced into Australia in the 19th century for its pretty flowers, lantana is a voracious pest, rapidly invading ecosystems disturbed by clearing or fire. It quickly forms into dense clumps, outcompetes other plants, and makes forests more susceptible to fires.
“Invading [lantana] promotes further fires or changes to the fire regime – either hotter or more frequent fires. That then favours the lantana to the detriment of native species. Then you get more lantana and the cycle repeats itself,” explains Curran.
As part of their study the researchers wanted to assess exactly how lantana changed the ecology of dry rainforests pockets of which can be found across northern Australia, Queensland and as far south as Gunnedah in northern New South Wales.
“The reason they’re called rainforests is because fire has very rarely occurred there, if ever. So introducing this quite large biomass of flammable material into them creates quite a threat to these ecosystems,” says Curran.
“The forests we worked in the Forty Mile Scrub National Park has had a really bad recent fire history over the last 30 years of lantana invasion and this demonstrates how that occurred just by changing the fuel load.”
The team measured fuel bed loads and conducted twig and leaf burning trials.
They found that lantana wasn’t more flammable than the other native species they tested.
“In fact, in most cases it was the least flammable species. So it was less likely to ignite and less likely at a stem level to promote fire, but it did change fuel loads quite substantially,” says Curran.
He says it acts as a ‘ladder fuel’ sending fire into the canopy causing more intense and destructive fires.
Curran says the study indicates that the best way to manage lantana infestations is to either remove the weed from the boundaries between dry rainforest and more fire-prone savannah land, or to remove it from around high-conservation areas within the forest.
While he is unsure about whether the same mechanism applies to other types of Australian forests and rainforests infested with lantana, he says the research could be applied to similar ecosystems around the world.
“This type of rainforest is usually called dry forest elsewhere, is found in South Africa, South East Asia and into Thailand.”
Originally a native of Central and South America, lantana is considered an invasive pest in more than 60 countries and is on the International Union for Conservation of Nature’s list of top 100 invasive species in the world.