AUSTRALIA – More than 100 plant species had their entire populations burned in the Black Summer bushfires, according to the most detailed study yet of the impact on Australia’s plants.
An estimated 816 species had at least half the areas they grow burned, according to estimates in the study, and some ecosystems are now at risk of “regeneration failure”.
While many of the species studied are adapted to recover from fire – either by reshooting or growing from seeds waiting dormant in nearby soils – there are fears that the loss of mature plants has left some species and entire ecosystems vulnerable.
CSIRO researcher and lead author of the study Dr Bob Godfree and 14 other researchers published their analysis, which used satellite data to map the fires, in the journal Nature Communications.
The fires, which burned at least 7.5m hectares of eucalyptus forests in the south-east of the continent, had left rainforest species particularly exposed.
“To have so much burn in such a short period of time was quite staggering,” Godfree said.
He said plants underpinned the function of entire ecosystems, providing food and shelter for wildlife and stabilising soils, as well as storing carbon.
“Changes in vegetation is natural over very long time frames, but if that change occurs very rapidly it can be disruptive,” he said.
Researchers analysed data from four satellites alongside more than 1.4m records of plants in south-east Australia across forests, woodlands, healthlands, grasslands, shrublands and in and around rainforests.
The research said: “All known populations of an estimated 116 species (14% of the total) burnt, which is more than double the number of plant species endemic to the British Isles.”
Fears that rare and ancient plants in Australia’s network of Gondwana rainforest reserves were now further threatened were confirmed, the study said.
Godfree said one group of rainforest plants particularly vulnerable were known as epiphytic orchids, which grow on trees rather than on the ground.
“They’re killed by fires, especially crown fires, and they don’t have much of a seed bank,” he said.
Some 251 plant species in the study were highly adapted to fire and had traits to recover, such as the ability to sprout from burnt trunks or underground tubers, store seeds in nearby soils or have seeds that germinated after exposure to smoke or heat.
But another 122 species that in theory could persist after fire were considered vulnerable because of invasive disease like myrtle rust, grazing from invasive species like deer, and more intense droughts.
Godfree said: “The impacts of these fires was certainly unprecedented in their scale. They impacted more plant species in a single fire season since anything that’s happened since European settlement, possibly longer.”
Importantly, Godfree said, the fires burned across wide areas and across species that were already being affected by changes to climate.
The study warns there is emerging evidence globally that catastrophic fire events have the ability to trigger tipping points, where forests are replaced with other vegetation.
Much of the vegetation affected by the fires was already under stress from extreme drought and record high temperatures which, the study said, could alone drive major changes.
More research was needed to find out if some forests were undergoing “regenerative failure”, the study concluded.
Plant ecologist Dr Rod Fensham, of the University of Queensland, who was not an author of the research, said the study was “impressive” but said the reported impacts on rainforest species needed further study.
He said: “We ecologists are on edge and nervous about what the meteorologists are telling us about these events and how they’re going to get more frequent.”