Will Australia’s forests bounce back after devastating fires?

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Some of the world’s most ancient rainforests lie in the north of the
Australian state of New South Wales. Continually wet since the time of the
dinosaurs, these forests once covered the supercontinent Gondwana. Today,
vestiges harbor many endemic and evolutionarily unique plants and animals.

“Normally vibrant, green and lustrous,” these forests “feed your soul,” says
Mark Graham, an ecologist with the Nature Conservation Council of New South
Wales, who is based in the region. “You step into them and breathe deeply, and
you are at peace.”

Typically moist, these environments don’t burn. But unprecedented fires
have now ravaged more than 11 million hectares in eastern Australia,
penetrating these strongholds that rarely, if ever, faced fires before.

Last year was Australia’s hottest and driest year in 120 years. Made
vulnerable by a record drought and heat wave, more than 50 percent of the vast area
that makes up the Gondwana Rainforests World Heritage Area has gone up in
flames, Graham says. “There’s now concern about the long-term viability of
these globally significant forests.”

Drier types of Australian forest, which have some fire tolerance, could
be taking a beating too in the wake of blazes that, as
researchers report January 8 in Global
Change Biology
, are becoming more
intense and frequent with climate change
. “Most of our eucalyptus forests and
woodlands have had a long history of fire,” says John Woinarski, a conservation
biologist at Charles Darwin University in Darwin. But, like their wetter
counterparts, “they’re burning, in many cases, not long after the last major
fire in these environments.”

Overall, more than 50 percent of the entire
ranges of about 115 threatened plant and animal species
have gone up in
smoke, many in eucalypt forests in the continent’s southeast, Australian
officials reported January 20. The question now is: Can these areas, especially
the forests that are the foundation of so many Australian ecosystems, recover,
or are they forever changed?

Waiting for answers

“We are in uncharted territory,” says Richard Hobbs, an ecologist at the
University of Western Australia in Perth. “We haven’t had fires so early in the
season and covering such large areas before. We’ve had ecosystems that haven’t
burned in living memory going up, so how they are going to respond is anybody’s
guess.”

Environments likely to be hardest hit are those with an infrequent history
of fire and little tolerance to it. Take the tall, wet forests in the
southeastern state of Victoria. They have now experienced their fourth fire in
20 years, Woinarski
says, and that’s slowly removing their dominant mountain and alpine ash trees. One 2013
study
in Global Change Biology warned that increasing fire frequency
could lead to the loss of these types of forest: There isn’t enough time for
the trees to reach maturity and produce viable seeds for the next generation
before another fire comes through.

Botanist
Robert Kooyman has seen firsthand what the fires have done to another forest, this
one in Nightcap National Park, part of the Gondwana Rainforests. In the 1980s,
Kooyman, who is based at Macquarie University in Sydney, found and described the Nightcap
oak (Eidothea hardeniana), a critically endangered endemic tree. He was one of the first scientists
to return to Nightcap in January after the 2019–20 fires swept through.

Now, the rainforest floor is blackened, he told Science News from the field. Scorch marks higher in the trees reveal
the fires’ appetite. The blazes burned through the thin bark of many rainforest
trees, which are “still green and clinging to life, but doomed,” he says.   

Seeing
this kind of damage in environments where he’s worked for 40 years was
“emotionally tough,” Kooyman says. “Sadness, like the smell of burned ground
and the last residues of smoke, hung heavy on the air.”

Nightcap National Park
Nightcap National Park (shown before fires burned through during the 2019–20 season) in New South Wales is part of the Gondwana Rainforests World Heritage Area, where some of the world’s most ancient rainforests are found.John Spencer/DPIE

His initial surveys suggest that 10 percent of the rare Nightcap oaks, which
numbered just 250 before the fires, are dead, but more may succumb with time.

That’s just the tale of one species. In Nightcap National Park alone — one
of 30 parks and reserves that make up the Gondwana Rainforests — 16 threatened
plants and 27 threatened animals have been affected by fire, including the
peach myrtle (Uromyrtus australis) and Albert’s lyrebird (Menura
alberti
), a pheasant-sized, ground dweller that mimics other birds.

Mature trees of some species here can be 500 to 1,000 years old, which
means full recovery won’t happen until well after our life spans, Kooyman says.
Regeneration will come from resprouting on some trees and the emergence of new
seedlings. But the loss of large trees, which form the canopy and are major
producers of fruit for animals to eat, will damage how this entire ecosystem and
food web functions, he says.  

Limits of tolerance

Australia’s more arid habitats, its savannas, spinifex grasslands and dry
eucalypt forests, evolved in the presence of fire. Within weeks or even days of
fire passing through, burned species of eucalypt trees in these environments
are famously able to throw out new buds and shoots from their trunks and the
base of the trees.

The drought has not broken. But as some rains have started to return,
regrowth is already being seen on gum trees like eucalyptus in more fire-tolerant
habitats along Australia’s east coast. These places will burst back into
greenery as heavy rains return in coming months, experts expect, but bigger
problems may be brewing.

“Yes, some
species are adapted to fire, but that doesn’t mean they are resilient to more
severe, large and frequently occurring fire, which is what we are experiencing
in some parts of Australia, because of the drought and climate change,” says Euan Ritchie, an ecologist
at Deakin University in Melbourne. “If we see more and more of these really hot, large fires, even
species that are somewhat fire-tolerant might become increasingly threatened.”

These fire-savvy
species might only tolerate relatively infrequent or low-intensity fires, agrees
Camille Stevens-Rumann, an ecologist at Colorado State University in Fort
Collins. “When we see an increase in frequency, sometimes species are able to
recover from the first fire. But if suddenly you have another one much sooner
than it would have been historically, [a species] doesn’t have time to reach
maturity and may not be able to reproduce,” she says.

In a report published in December by the U.S. Joint Fire Science Program, she and her
colleagues found that trees in the Rocky Mountains — such as ponderosa pines,
whose thick, jigsaw puzzle bark can often withstand fire — are similarly struggling
to regenerate
under hotter and drier conditions and increasingly
frequent fires.

In
dry eucalypt forests, severe fires can promote denser, shrubby style gum trees that are more flammable,
exacerbating the problem, a 2018 study in Ecosphere found. And as more
and more old-growth eucalypt trees fall to fire, the consequences will
reverberate through the ecosystem. The trees’ large hollows, which animals from
possums to cockatoos rely on to survive, take 50 to 100 years to form. While
some hollows will remain in such forests, there will be increased competition
for them. “It’ll be a fight for a diminishing resource,” Woinarski says.

Cockatoo in tree hollow
Large hollows in trees, which many different types of animals from possums to cockatoos rely on to survive, can take up to a century to form. Recent Australian fires likely destroyed many hollows, which could negatively affect those animals, scientists say.Anne Harrison/iStock/Getty Images Plus

Seed survival

Some plant species don’t just tolerate fire. They depend on it.  Their seeds lie dormant in the soil waiting
for the flames: They require the heat and smoke of bushfires to germinate and
sprout.

The
seedlings replace adult plants. “But if fires have been really frequent, that fire-stimulated
seed bank might be depleted, so there might not be any seeds left to recover
the ecosystem,” says Lucy Commander, who studies seed ecology at the University
of Western Australia in Perth.  A 2014
study
in the Journal of Ecology showed that some plants in
southwestern Australia that resprout from seed following fires were more likely
to go locally extinct when faced with a combination of drought and shortened
intervals between fires.

The problem of too-frequent fires depleting soil seed banks is not
unique to Australia. A study published
in 2004
looked at the impact of fires passing through the chaparral ecosystems
of California’s Santa Monica Mountains more than every six years. Some species
that usually resprouted following fires began to diminish, leading to a
thinning of the shrubby ecosystem and the invasion of nonnative grasses.

Islands of greenery

The severity of Australia’s ongoing fires may cause
other problems, too. 

Normally when fires sweep through, they leave some patches unburnt by
fluke or because of the topography of the landscape. “Those unburnt patches are
really important for recolonizing of plant and animal species, back to the
burnt landscape, as it is regrowing,” Woinarski says.

Those unburnt refuges are where animals can shelter from flames and eventually
start repopulating surrounding burnt regions
, preventing local
extinctions, Ritchie and his colleagues reported in 2013 in the Journal of Applied Ecology. Surviving
patches are also an important source of plants and seeds for revegetation.

But the intensity of fires this summer may mean “there will be far fewer
refuge areas within burnt areas than is typical, or they may be too small to support
viable populations of species,” Woinarski says.

Protecting — or even creating — refuges like these from fires will be increasingly
important as the climate continues to change
, according to a
study in Global Change Biology in January 2019.  That’s just what emergency workers did in
December. As flames advanced on a hidden canyon in the Greater Blue Mountains,
Australian firefighters raced to protect its rare occupant: the critically
endangered dinosaur-era tree, the Wollemi pine. They doused the trees with
water and fire retardant and then hoped. When the smoke cleared, some trees
were charred, but the forest
was still standing
, government officials reported January 15.

firefighter in Wollemi pine forest
In January, firefighters went to great lengths, including hosing down the forest floor, to protect the world’s last remaining wild Wollemi pines from bushfires in New South Wales, Australia. These trees, one of the world’s oldest and rarest plants, have lived on Earth since the time of the dinosaurs.AP

Road to recovery

“There is a huge commitment across Australian society to try to recover
from this tragedy,” Woinarski says. “We can’t give up yet on any of the
species, environments, or vegetation types that have been so charred and
degraded.”

One of the best things to do to help forests bounce back is to leave
them to regenerate
naturally
and not disturb them further, Commander says. Clearing burnt vegetation
and disturbing soils full of seeds ready to resprout can slow recovery.

In places where there are small patches of habitat left unburnt, “making
sure that those continue to be protected, and can form nuclei for onward
regeneration, is going to be an important thing,” Hobbs says.

But if the past is prologue, change is inevitable. As the continent drifted north,
starting about 45 million years ago, the climate changed. “We know from the fossil record that these wet forests were lost in other
parts of Australia, and aridity and fire is the likely explanation,” says David Bowman, a pyrogeographer at
the University of Tasmania in Hobart.

Over time, some fire-tolerant dry forests could
eventually turn into grasslands, and wet forests and rainforests could slowly
shift into dry forests, or less dense savanna-woodland type habitats, experts
say. In the wake of the 2019–20 fire season, some of those changes may be already
under way. “The margins and
parts of the [rainforest] core have been compromised, which means future fire
events can penetrate deeper into what were previously permanently wet refuges,”
Graham says.

Only time will tell what recovery looks like — and how far Australian
forests can be pushed by fire before they pass tipping points that see them
devolve into other types of ecosystem entirely. “We don’t really know the answer to that
because these rainforests haven’t experienced fires recently. We haven’t really
studied it,” Hobbs says.

Adds
Bowman: “It’s a pyrogeographic experiment at a continental scale.”

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