Australia’s forests are being reshaped by climate change as droughts, heat waves, rising temperatures and bushfires drive ecosystems towards collapse, ecologists said.
Trees are dying, canopies are getting thinner and the rate that plants produce seeds is falling.
Ecologists have long predicted that climate change would have major consequences for Australia’s forests. Now they believe that those effects are unfolding.
Illustration: Yusha
“The whole thing is unraveling,” said David Bowman, a professor of environmental change biology at the University of Tasmania who studies the effects of climate change and fire on trees. “Most people have no idea that it’s even happening. The system is trying to tell you that if you don’t pay attention, then the whole thing will implode. We have to get a grip on climate change.”
According to last year’s State of the Climate 2018 report published by the Commonwealth Scientific and Industrial Research Organisation and the Australian Bureau of Meteorology, large parts of the country have experienced increases in weather patterns favorable to fires.
Rainfall has dropped in the southeast and southwest of the country, temperatures have warmed by an average of 1°C, and a “shift to a warmer climate in Australia is accompanied by more extreme daily heat events,” the report said.
Forests across Australia are changing, Murdoch University ecologist Joe Fontaine said.
“Impacts are direct — trees dying from heat and drought — as well as indirect — more fire, fewer seeds and a raft of associated feedbacks,” Fontaine said.
Leaves are the “machinery that makes the plant work” and how those leaves cope with heat depends on moisture reserves, he said.
“The question then is, how much do you have in reserve?” he said. “A lot of us are really concerned about that.”
Fontaine has studied one large shrub species — the southwestern native Hooker’s banksia — and found that seed production has “halved in the last 30 years,” which was “definitely a climate-driven problem with increased drought,” he said.
Last spring, Fontaine and colleagues inspected an area 300km north of Perth where the banksias had been hit by fire several years earlier. He wanted to know if they could cope with fire on top of the area’s long-term reduction in rainfall.
“At this stage, years after fire, those plants should be recovering and really going for it,” he said. “Except instead these banksias were dead and falling over left and right. The young plants were dying too — this area was losing all their young vigorous plants. With more bushfire, this species is at real risk of being wiped off the map.”
INTERVAL SQUEEZE
A study of the effects of a heat wave in 2010 and 2011 in southwest Australia that followed long-term drops in rainfall found that the large jarrah eucalypts and the area’s giant banksias were severely affected.
A knock-on effect was that the area became even more prone to fires, another study said.
Bowman said that the consequences of the changing climate are “absolutely” happening.
He said that he and his colleagues have found that big eucalypts grow slower as temperatures rise and alpine ash forests are at risk of being wiped out because fires are coming along too often.
That is part of a phenomenon known as the “interval squeeze,” where species that are adapted to cope with drought or fire struggle when the time between impacts gets shorter.
The idea that Australia’s forests are well-adapted to the country’s variable climate and can withstand fire and drought was incorrect, Bowman said.
“A big misapprehension is that these things are climatologically flexible, but they’re just not,” he said.
Australia’s dominant eucalypts have “fine-tuned their life history around assumptions of fire frequency,” he said, but “climate change is just blowing that up.”
“All this is non-linear,” Bowman said. “What will happen is the system will crash faster than we realize. Yes, it will reassemble and there will be forests, but they won’t look anything like what we have now. We are going to see this transformation before our eyes.”
PREDICTIONS
The climate change effects are not only restricted to old-growth forests — the changing climate is also causing problems for groups trying to reforest areas that have been previously cleared.
Usually, revegetation projects will gather seeds from the local area to sow or propagate in a practice known as provenance planting.
However, two major groups are using climate projection tools to second-guess the changes in rainfall and heat expected in the areas where they are planting.
Landcare Australia and Bush Heritage Australia have started to source seeds from places that better match the expected climate conditions in coming decades.
Matt Appleby, a senior ecologist at Bush Heritage Australia, said that in about 2014, the group began to see dead patches in a replanting project at Nardoo Hills in Victoria State and the problem worsened each year.
“We had a heat wave back in 2014, with about a week of temperatures well over 40°C and that was combined with already low soil moisture,” he said. “We think that combination meant the trees were under so much stress they reach a critical point and were dying.”
Now the group has started a climate-ready revegetation project for the reserve. Even among the same species of tree, there can be subtle genetic variations that give the same species different tolerances depending on where they are growing.
The group has used climate tools to find areas in the country known as “climate analogues” that match the hotter and drier conditions expected at Nardoo.
“We are collecting seeds from those locations and bringing them to Nardoo Hills to propagate and plant out,” Appleby said. “What happens then is that in 20 years the seeds of those plants will be better adapted to the area — they should have that little bit more resilience.”
He said he is concerned that the job of gathering seeds for rarer species could get more difficult.
“Trying to get seed this past year has been incredibly difficult,” he said. “What happens if in five years’ time we get a run of 49°C days?”
“How are we going to get seed then, if everything is under pressure?” he asked. “People need to start thinking about seed banks and seed production areas so there’s enough seed down the track to sustain this.”
Landcare Australia chief executive Shane Norrish said that like for many organizations carrying out major revegetation works, climate change is presenting a challenge.
For one major revegetation project at Dakalanta on the Eyre Peninsula, Landcare Australia has also used a “climate-ready” approach when sourcing some of their seeds, Norrish said.
“What you will never be able to deal with is the run of extreme hot days that we’ve experienced in southern Australia — that level of extreme variability challenges everyone,” she said.
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