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1st April 2019
'Whole thing is unraveling': climate change reshaping Australia's forests

Wed 6 Mar 2019 / The Guardian

Droughts, heatwaves, bushfires and rising temperatures are driving ecosystems towards collapse

Australia’s forests are being reshaped by climate change as droughts, heatwaves, rising temperatures and bushfires drive ecosystems towards collapse, ecologists have told Guardian Australia. 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 those impacts are unfolding.

“The whole thing is unravelling,” says Prof David Bowman, who studies the impacts of climate change and fire on trees at the University of Tasmania. “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 the 2018 State of the Climate Report, produced by CSIRO and the Bureau of Meteorology, large parts of the country are experiencing increases in weather patterns favourable to fires. The report found that rainfall has dropped in the south-east and south-west of the country, temperatures have warmed by an average of 1C, and a “shift to a warmer climate in Australia is accompanied by more extreme daily heat events”.

Dr Joe Fontaine, an ecologist at Murdoch University, says forests across Australia are changing. “Impacts are direct – trees dying from heat and drought – as well as indirect – more fire, fewer seeds and a raft of associated feedbacks.”

Fontaine says leaves are the “machinery that makes the plant work” and how those leaves cope with heat depends on moisture reserves. “The question then is, how much do you have in reserve? A lot of us are really concerned about that.”

Fontaine has studied one large shrub species – the south-western native Hooker’s banksia – and found seed production has “halved in the last 30 years”, which was “definitely a climate-driven problem with increased drought”.

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 says. “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.”

The interval squeeze

A study of the impacts of a heatwave in 2010 and 2011 in the south-west that followed long-term drops in rainfall found that the the large jarrah eucalypts and the area’s giant banksias were severely affected. A knock-on effect, another study found, was that the area became even more prone to fires.

Bowman says the impacts of the changing climate are “absolutely” happening. Bowman and 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.

This 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.

Bowman says the idea that Australia’s forests are well adapted to the country’s variable climate and can withstand fire and drought, ia incorrect. “A big misapprehension is that these things are climatologically flexible, but they’re just not,” he says, explaining that Australia’s dominant eucalypts have “fine-tuned their life history around assumptions of fire frequency”, but “climate change is just blowing that up”.

“All this is non-linear,” he says. “What will happen is the system will crash faster than we realise. 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.”

Predicting the future?

The climate change impacts 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.

But 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 climate conditions in coming decades.

Dr Matt Appleby, a senior ecologist at Bush Heritage Australia, says that in about 2014, the group began to see dead patches in a replanting project at Nardoo Hills in Victoria, and the problem worsened each year.

“We had a heatwave back in 2014 with about a week of temperatures well over 40C and that was combined with already low soil moisture,” he says. “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 says. 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.”

Appleby is concerned the job of gathering seeds for rarer species could get more difficult. “Trying to get seed this past year has been incredibly difficult. What happens if in five years’ time we get a run of 49C days?” he says.

“How are we going to get seed then if everything is under pressure? People need to start thinking about seed banks and seed production areas so there’s enough seed down the track to sustain this.”

Dr Shane Norrish, the chief executive of Landcare Australia, says like many other organisations carrying out major revegetation works, climate change was presenting a challenge. For one major revegetation project at Dakalanta on the Eyre peninsula, Landcare Australia has also used this “climate-ready” approach when sourcing some of their seeds.

“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.”

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