Yahoo News Western Australia’s eucalypt forests fade to brown as century-old giant jarrahs die in heat and drought
A couple of weeks ago, Joe Fontaine stood in the middle of one of Western Australia’s eucalypt forests on another hot and dry day that was stripped of the usually raucous backing-track of bird calls.
“I could hear this scratching-crunching noise coming from the trees,” says Fontaine, a forest ecologist at Perth’s Murdoch University.
Peeling back the bark, a handful of beetle larvae “about the size of your pinky” were eating away at the dead and dying wood. “When the trees are stressed, the beetles get the upper hand,” he says.
Above Fontaine, the forest canopy was turning brown. Trees more than a century old are barely alive. Some of these giant jarrahs might survive, but some won’t.
It’s a scene that’s being replicated in forests and coastal shrublands spanning more than 1,000km (620 miles) across the state’s south-west after drought and baking heat.
Many of these ecosystems are dominated by eucalypt trees such as jarrah and marri, and coastal shrublands spread with banksias, the likes of which are found nowhere else on Earth.
Pictures of dead and dying shrubs and trees have been flooding Fontaine’s inbox. One of the earliest signs came in February when Perth’s street trees started dying after a record run of days above 40C. The city had its driest six months – from October to March – since records began.
There were similar scenes in the state’s south-west eucalypt forests in 2010 and 2011 – a die-back event that prompted more than a dozen studies. Drought-hit forests were hit by fire years later, releasing carbon dioxide, and raising concerns the forests could switch to become a source, rather than a store, of carbon.
Dr Katinka Ruthrof, a senior research scientist in the state government’s Department of Biodiversity, Conservation and Attractions, says the current die-off has similar characteristics to the 2011 event. The department is assessing the damage using imagery from satellites, fixed wing aircraft and drones, along with field checking.
“Some plants may be able to survive and resprout when conditions improve, but many may die,” she says. “This depends on how much longer the dry season lasts.”
Ruthrof says changes to the structure and composition of the habitats would have flow-on effects for some species, including the provision of habitat and food resources for wildlife.
Dr Mark Harvey, curator of spiders, millipedes and centipedes at the Western Australian Museum, says the south-west has hundreds of invertebrate species found nowhere else.
“The south-west corner of Western Australia has been isolated from other parts of the continent for the last three million years. That’s allowed species to develop in isolation.”
Those species have been used to moist conditions for many thousands of years, he says.
“We’re quite concerned about this drying event. If the animals don’t have a coping mechanism like burrowing to escape the heat, they literally die.
“They become locally extinct. They have nowhere to go. It will take thousands of years to recolonise, even if the habitat came good again. The prognosis is not good.”
Fontaine says seeing the death of shrublands and forests is “distressing” and he’s worried about the wildlife.
“I’m going hell for leather now to get people to go ‘oh shit, we need to document this’,” he says.
Clear climate signal
Fontaine’s Murdoch University colleague, atmospheric scientist Dr Kerryn Hawke, says the region’s trees and plants are used to a Mediterranean-style climate with cold fronts from the ocean to the south bringing good rainfall in the winter.
But studies have shown these fronts have been shifting further south, away from the coast.
She says: “These fronts no longer reach as far north, and that means we’re seeing less frontal rains and, when they do reach us, it’s not as intense. And we’re seeing more and more very hot days because of climate change. The vegetation just isn’t used to such low rainfall.”
Over the past 12 months, much of the state’s west has seen rainfall well below average and in some places the lowest on record, while temperatures have been among the highest on record.
“It’s a perfect storm of temperature and rainfall. But the stand out was the heat we had very early on,” she says, pointing to heatwaves in September and November.
The conditions in recent months are part of a distinct drying that scientists have seen in the region since the 1970s.
Compared with the period from 1901 to 1960, cool season rainfall in the last two decades has dropped by 20%. Very wet years have almost completely disappeared.
About half of this change has been blamed on rising greenhouse gas emissions, which could be an underestimate, according to one study led by Bureau of Meteorology scientists.
Even with rapid reductions in greenhouse gas emissions, the study suggested, the drying trend would probably continue for the rest of this century.
Dr Michael Grose, a climate scientist at the Australian government’s Commonwealth Scientific and Industrial Research Organisation, says as early as the 1970s scientists were seeing a drying trend.
“It is one of the clearest and strongest signals in mean rainfall anywhere in the world,” he says.
Fire and fear
There appears little relief on the horizon, with forecasts for the next three months suggesting more hot and dry weather to come.
Fontaine says with so much dead vegetation around, the risk of bushfires is rising.
Fire authorities will need to be cautious, he says, as they carry out prescribed burning to try to reduce the risk of larger out of control fires.
About 430km south-east of Perth is Walpole, where David Edmonds has a beef and orchid farm while volunteering with the Walpole-Nornalup National Parks Association.
He grew up in Walpole and this year has watched parts of the wilderness region – including giant 90-metre karri trees – turning brown.
“The rain just stopped really early. The die-off is becoming really obvious on the granite outcrops,” he says.
“It’s saddening. You worry if this is a one-off or something that’s going to be more common. We can’t start watering the trees.”
