Entire hillsides of trees turned brown this summer. Is it the start of ecosystem collapse?



Rachael Nolan, CC BY-NC

Rachael Helene Nolan, Western Sydney University; Belinda Medlyn, Western Sydney University; Brendan Choat, Western Sydney University, and Rhiannon Smith, University of New England

The drought in eastern Australia was a significant driver of this season’s unprecedented bushfires. But it also caused another, less well known environmental calamity this summer: entire hillsides of trees turned from green to brown.

We’ve observed extensive canopy dieback from southeast Queensland down to Canberra. Reports of more dead and dying trees from other regions across Australia are flowing in through the citizen science project, the Dead Tree Detective.




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A few dead trees are not an unusual sight during a drought. But in some places, it is the first time in living memory so much canopy has died off.

Ecologists are now pondering the implications. There are warnings that some Australian tree species could disappear from large parts of their ranges as the climate changes. Could we be witnessing the start of ecosystem collapse?

Extensive canopy dieback in Kains Flat, NSW, January 2020.
Matt Herbert

Why are canopies dying now?

Much of eastern Australia has been in drought since the start of 2017. While this drought is not yet as long as the Millennium Drought, it appears to be more intense. Many areas have received the lowest rainfall on record, including long periods of time with no rainfall. This has been coupled with above-average temperatures and extreme heatwaves.

The higher the temperature, the greater the moisture loss from leaves. This is usually good for a tree because it cools the canopy. But if there is not enough water in the soil, the increased water loss can push trees over a threshold, causing extensive leaf “scorching”, or browning. The extensive canopy dieback we have observed this summer suggests that the soil had finally become too dry for many trees.

Widespread rainfall deciciencies and higher temperatures across many parts of Australia.
Bureau of Meteorology

Are the trees dead?

Brown or bare trees are not necessarily dead. Many eucalypts can lose all their leaves but resprout after rain.

Many parts of eastern Australia are now flushed with green after rain. In these areas, it will be important to assess the extent of tree recovery. If trees are not showing signs of recovery after significant rainfall, they’re unlikely to survive. In some cases carbohydrate reserves – which trees need to resprout new leaves – may be too depleted for trees to recover.

Snowgums in the New England area resprouting in March 2020, following heavy rain. The trees lost most of their canopy during drought in 2019.
Trevor Stace, University of New England

The drought may also hinder post-fire recovery. Most eucalypt forests eventually recover from bushfires by resprouting new leaves. Some forests also recover when fire triggers seedlings to germinate.

But it’s likely that some forests now recovering from fire were already struggling with canopy dieback. So these two disturbances will test how resilient our forests are to back-to-back drought and bushfire.

Trees recovering from drought and/or fire may also enter the “dieback spiral”. The new flush of leaves following rain can make a particularly tasty meal for insects. Trees will then attempt to grow more foliage in response, but their ability to keep producing new leaves gradually declines as they deplete their carbohydrate reserves, and they can die.

Dieback spiral has led to extensive tree loss in the past, including in the New England area of NSW.

Should we be worried?

The capacity of eucalypts to resprout makes them naturally resilient to extended drought. There are some records of canopy dieback from severe droughts in the past, such as the Federation Drought. We assume (although we don’t know for sure) the forests recovered after these events. So they may bounce back after the current drought.

However, it’s hard not to be concerned. Climate change will bring increased drought, heatwaves and fires that could, over time, see extensive losses of trees across the landscape – as happened on the Monaro High Plain after the Millennium Drought.




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Australian research in 2016 warned that due to climate change, the habitat of 90% of eucalypt species could decline and 16 species were expected to lose their home environments within 60 years.

Such a change would have huge consequences for how ecosystems function – reducing the capacity for ecosystem services such as carbon storage, altering catchment water resources and reducing habitat for native animals.

Some trees resprouted new leaves after losing their canopy. But in some cases these leaves are now dying, like on these scribbly gums in the NSW Pilliga in August 2019.
Rachael Nolan

Where to from here?

Records of dead and dying trees on the Dead Tree Detective map.
Dead Tree Detective

Landholders can help bush on their property recover after drought, by protecting germinating seedlings from livestock and collecting local seed for later revegetation. Trees that appear dead should not be cut down as they may recover, and even if dead can provide valuable animal habitat.

Most importantly, however, we need to monitor trees carefully to see where they’ve died, and where they are recovering. A citizen science project, the Dead Tree Detective, is helping map the extent of tree die-off across Australia.

People send in photos of dead and dying trees – to date, over 267 records have been uploaded. These records can be used to target where to monitor forests during drought, including on-ground assessments of tree health and quantifying the physiological responses of trees to drought stress.

There is no ongoing forest health monitoring program in Australia, so this dataset is invaluable in helping us determine exactly how vulnerable Australia’s forests are to the double whammy of severe drought and bushfires.The Conversation

Rachael Helene Nolan, Postdoctoral research fellow, Western Sydney University; Belinda Medlyn, Professor, Western Sydney University; Brendan Choat, Associate Professor, Western Sydney University, and Rhiannon Smith, Research Fellow, University of New England

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Sure, save furry animals after the bushfires – but our river creatures are suffering too


Jamie Pittock, Australian National University

The hellish summer of bushfires in southeast Australia triggered global concern for our iconic mammals. Donations flooded in from at home and around the world to help protect furry species.

But there’s a risk the government and public responses will not see the fish for the koalas.

Of the 113 priority fauna species identified by the federal government as worst impacted by bushfires, 61 (54%) are freshwater species that live in or around our inland rivers, such as fish, frogs, turtles and the iconic platypus.

These animals and ecosystems were already struggling due to prolonged drought and mismanagement of the Murray Darling Basin. Saving koalas and other mammals is of course important, but freshwater species should also be a priority for post-fire environmental programs.

A picture of devastation

The government’s priority species list includes three turtle species, 17 frogs, 22 crayfish, 17 fish and the platypus. Rounding out the list is an alpine stonefly, although many other invertebrates are also likely to be affected (as well as other species that depend on moist, streamside forest habitats).

Excluding tropical savannah, the recent bushfires burnt more than 7.7 million hectares in Victoria, South Australia, New South Wales, Queensland and Western Australia. Rainforests and riparian (riverside) forests were extensively damaged along the Australian east coast and alps. These are normally moist environments, which are not adapted to fire.

Plant and animal species at the edge of waterways, in peat wetlands and in riverside forests are likely to have been burnt or killed by heat, such as crustaceans , lizards, and corroboree and mountain frogs in the alps and east coast rainforests.




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Burnt riverside forests no longer shade the water, making water temperatures hotter and leading to increased evaporation that may stress surviving wildlife. The loss of vegetation cover also leaves prey exposed to predators.

Following recent rain, water flowing into rivers has washed ash into streams. This clogs fish gills and brings nutrients that drive algal blooms. Sediment washed into waterways fills in the gaps between rocks and holes in river beds – places where many species shelter and breed. For instance, the River Murray catchment’s last population of Macquarie perch was impacted as rain washed ash and sediment into Mannus Creek in southern NSW.

Fires tend to burn forests in patches, sometimes leaving refuges for land-based animals. However fire damage to waterways flows downstream, systematically degrading the habitat of aquatic animals by leaving little clean water to hide in.

Bushfire silt clogging the usually pristine Tambo river in the Victorian high country in January.
David Crosling/AAP

Long-term damage

The devastating impact of the fires in river environments may be long-lived.

When aquatic animals species are wiped out in particular rivers, they may not be able to recolonise from surviving populations in other unconnected rivers.

Some species will invariably now be closer to extinction. For example many key peat swamp habitats of the critically endangered northern corroboree frog have been burnt in the Bogong Peaks and Brindabella mountains of NSW and the ACT.




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And after fires, fast-growing young eucalyptus forests transpire much more water than older burnt trees. This may reduce inflows into streams for a century.

The recent bushfires followed several years of extreme drought across much of Australia. In the Murray-Darling Basin, these challenges were compounded by poor water management that contributed to dried-up rivers and mass fish deaths.

Water-sharing rules in the basin determine how much water is allocated to agriculture and the environment. Current water-sharing plans do not explicitly include allocations to manage losses due to climate change, and as the plans will only be updated once a decade, it is questionable whether they will be adjusted to sustain flows needed to conserve threatened species.

Much corroboree frog habitat was destroyed during the fires.
Melbourne Zoo

Here’s what to do

After the fires, government officials and scientists rescued a number of “insurance” populations of threatened aquatic animals such as turtle and fish species, and took them to captive breeding facilities, such as the stocky galaxias fish in the alps. We must ensure healthy habitat is available for these animals to re-establish viable populations when released.

In the short term, we must protect surviving and regenerating habitat. Government programs are off to a good start in promising to cull feral predators such as cats and foxes, as well as grazing animals such as pigs, deer and goats. The NSW and Victorian governments must also remove feral horses in the Australian Alps that are damaging the swamp habitats and streams.

Now so many infested riverside forests are accessible, it is a key time to control weed regrowth.




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In the medium term, we should expand programs to fence livestock out of waterways, install other watering points for these animals and revegetate stream banks.

Deep holes in rivers and streams with cool water are important refuges for aquatic animals, and ways to restore them should be investigated.

Impediments to fish migration, such as weirs, should be removed or fish “ladders” installed to aid fish movement. Aquatic species often won’t breed unless the water is the right temperature in the right season; to prevent the release of overly cold water from the bottom of dams, better water release structures should be installed.

Years of drought meant rivers and aquatic life were already vulnerable before the fires.
Dean Lewins/AAP

An opportunity for change

Successive governments have been asleep at the tiller when it comes to threatened aquatic animals. Official recovery plans for many fire-affected species have not been adequately funded or implemented.

In the Murray-Darling Basin for example, a native fish strategy was shelved in 2013 after the NSW government reportedly pulled funding.

The impending release of a new fish strategy, and other post-fire recovery actions, are an opportunity for governments to right past wrongs and ensure our precious freshwater species thrive into the future.The Conversation

Jamie Pittock, Professor, Fenner School of Environment & Society, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.