For decades, chainsaws have ripped through the native forests of south-east Australia.
Across Australia, Victoria's forests have been logged more than any other mainland state over the past two decades.
Now the state is shutting its native logging industry in a matter of weeks, and the forests that were once given to Victoria's state-run logging agency, VicForests, are being returned to the public.
By law, the logging agency is required to regenerate the areas it has logged and hand them back to the public in a healthy state. But until now, how much that has actually happened has largely been a mystery.
An AI-based analysis of 20 years of VicForests' logging, researchers say, shows the scale of failed regeneration in Victoria's state forests.
The data, which has been shared exclusively with the ABC, suggests that 20 per cent of Victoria's state forests have not regenerated after logging.
This 69 hectare section of native forest, about 300 kilometres north east of Melbourne, was logged over a three-month period from March 3, 2021.
By law, VicForests is required to regrow this logging area — also known as a coupe — before it is returned to public ownership. In this case that means replacing the towering alpine ash gums that it logged, with the same or similar species.
But two and a half years since the trees were chopped down, there is little sign of recovery.
This coupe was one of more than 3,000 analysed as part of an investigation into the effectiveness of VicForests' attempts at regenerating the forests it had logged.
Researchers trained a machine-learning algorithm to analyse satellite images of logged areas and categorise each pixel into two main categories: successful or failed regeneration.
In this coupe, just 6 per cent of the area was classified as eucalyptus. The remainder, according to the research, was made up of land that was either sparse or completely bare.
The researchers trained the AI model based on observations from ground work at dozens of locations across Victoria. They then tested the model's accuracy by comparing the results to field assessments from other locations. The researchers found it got accurate results nearly every time.
The AI categorisation was then applied to every coupe logged by VicForests since 2004.
Here in the Towong Shire, a local government area in north-east Victoria, the research found more than a third of the area that was logged has failed to regenerate.
That's more than 700 hectares of logged forest that hasn't grown back.
Across Victoria, close to a fifth of all logged land was classified as not regenerated, according to the researchers.
That's almost 13,000 hectares of state forest the analysis found to be standing in a state of ruin.
"The logging industry is basically walking away and handing this forest back in a disgraceful manner," said Trent Patten from Wildlife of the Central Highlands, a conservation group that commissioned and funded the analysis.
Legally, VicForests is required to regrow forests like-for-like. In its marketing material VicForests says it regrows every tree, and those regrowing trees are "closely monitored to ensure future enjoyment of the forest".
"The forest is allocated to VicForests for timber harvesting by the state and under law they are required to return it in a state of recovery," said Simon Ramsey, a PhD student from RMIT University who conducted the analysis.
He and two senior colleagues from RMIT developed the method for training artificial intelligence to categorise the forest into various categories including eucalypts and bare earth.
In a paper submitted for peer-review at a scientific journal, the researchers describe the method and calculate the area of land that has been logged, and doesn't currently have detectable eucalyptus trees growing.
Mr Ramsey then extended the results to look not just at the total area that didn't grow back as eucalyptus, but how that area was distributed across the individual logged areas, or "coupes".
For most forests in Victoria, a coupe can't be considered "regenerated" if there is any continuous single hectare of ground with fewer than 400 eucalypts in it.
But Mr Ramsey's AI analysis found more than 1,100 coupes failed that test.
In fact, dozens of coupes in the analysis had more than 20 hectares – or an area the size of 10 MCGs – that failed to meet that requirement. Some coupes had more than 30 hectares of failed regrowth — leaving nearly the entire coupe unlikely to recover.
The ABC provided VicForests with a list of every coupe categorised as "failed" in the AI analysis.
A spokesman for VicForests told the ABC more than 300 of those were in fact properly regenerated, according to their own on-the-ground surveys. He said 400 of the coupes had been affected by the 2019-20 bushfires and another 100 coupes were still being regenerated, and so couldn't be said to have "failed".
The VicForests spokesman declined to provide the ABC with details of those surveys, or tell the ABC which of the coupes was incorrectly categorised.
"Given the research results have incorrectly identified coupes as being unsuccessfully regenerated when recent on ground surveys have confirmed successful regeneration, no confidence can be placed in the accuracy of the data/research findings," the spokesman said.
Many of the areas found to have failed in the analysis were found to be covered in silver wattle instead of the eucalypts that were there prior to logging.
Sometimes the failed areas were merely covered in bare earth, grass, or weeds like blackberry.
Entering areas like that was confronting for Mr Patten, who lives in Flowerdale on the Foothills of the Great Dividing Range and owns a nearby farm.
"When you go into a forest that has been logged, it's basically dead," he said.
After an area has met the legal requirement for regeneration, it is handed back to the state — and is no longer the responsibility of VicForests to look after.
"Many of these coupes that have failed regeneration have actually been ticked off and handed back to the Victorian government some years back in a failed state," said Mr Patton.
VicForests denied this, noting the regulations don't say that satellite imagery should be used to check regeneration outcomes.
"Suggestions that coupes removed from the Timber Release Plan were not successfully regenerated has no basis and is in fact, untrue," he said.
VicForests also noted that of the coupes alleged to have failed to regenerate, "almost 100" are "still regenerating" and will be assessed in the future.
"Therefore, these areas cannot be assessed at this time as to successful regeneration or not," the VicForests spokesman said.
"We continue to regenerate coupes until they are successfully regenerated in accordance with our obligations under the Code," he said.
The ABC looked at the more than 1,100 coupes that the AI analysis categorised as having failed to regenerate, and found the majority of them — 690 — had been handed back to the public, and were no longer the legal responsibility of VicForests.
Bushfires burned about 330 of those areas after they were logged, so further work would be needed to determine whether the logging or fires were responsible for the lack of appropriate trees today.
A spokesman for VicForests said that undermines the analysis since some of those coupes were logged up to 19 years ago and burned long after.
The logging itself can increase the risk of fire, said Mr Ramsey, the researcher who conducted the analysis. He said the young plants are very thirsty and dry out the landscape.
They are also a perfect fuel for a spark to burn, he said, describing it as "a well aerated and continuous layer layer of fuel for any fire that comes through".
But the majority of those areas that were found to have failed their regeneration but were handed back to the public — 360 of them — had no recorded fire history after the logging, and Mr Ramsey says in that case it's clear the logging is to blame.
While the researchers say the AI analysis could detect where the regeneration had not been successful, it could not answer the key question of why.
Leading forest ecologist Professor David Lindenmayer has been researching that question, and has found a range of reasons why forests don't grow back after logging.
He said logging could damage soil in two key ways: it can deplete the earth of nutrients, and the machinery can cause severe compaction.
Another reason for the failure is the changing climate.The new trees are trying to germinate in a different world to the one the logged forests established themselves in decades or even a century earlier.
Another cause of failed regrowth is feral deer, which love to eat young trees, said Professor Lindenmayer.
Additionally, native understory plants like wattle, that usually grow between the forest floor and canopy, often quickly dominate after logging, crowding out the eucalypts.
Professor Lindenmayer says it's VicForests' duty and legal obligation to manage all of those issues.
"VicForests is definitely doing a dodgy job, pretty much as they've done for the best part of the last 20 years," he said.
VicForests insists it's doing a diligent job, noting it's placed deer-proof fencing around hundreds of hectares of regenerating forest, put guards around seedlings to protect them from herbivores, and changed its logging practices to retain more trees.
Whatever the causes, experts say the effects of failed or inadequate regeneration are massive.
The forests logged over two decades by VicForests were the most carbon-dense forests in the world, according to research published by Professor Lindenmayer.
VicForests argues logging is good for the climate because young trees suck up more carbon out of the atmosphere than old trees.
"This is because wood products retain carbon and harvested forests are regrown," a VicForests spokesman said.
But if those young trees aren't growing — or burn before they mature — any claimed benefit is lost. And that's a massive cost, said Professor Andrew Macintosh from the Australian National University, who has published dozens of papers on how much carbon is stored in Australia's landscapes.
Professor Macintosh conducted what he called a "conservative first-pass estimate" for the ABC on how much carbon sequestration was lost by the failed regeneration, based on the new analysis.
With nearly 13,000 ha of forest found to not have grown back, Macintosh estimated at least 4 million tonnes of stored CO2 would be lost over 20 years — or 200,000 tonnes per year. That is roughly the equivalent of putting about 100,000 extra cars on the road.
More research would be required to determine how much of that sequestration was lost entirely because of logging, and how much was due to fire or other causes. If areas still being regenerated by VicForests regrow, they will sequester carbon.
"There's a wonderful opportunity to sequester large amounts of carbon quickly in relatively small areas," said Professor Macintosh.
With the forests left unregenerated, the animals that rely on those forests lose essential habitat.
That includes endangered animals like the Leadbeater's possum and greater gliders, which are both hurtling towards extinction.
The mature trees also help get water into the landscape for both the environment, and the people of Melbourne.
"Young forests don't provide anything like the amount of water [compared to mature forests]," said Professor Lindenmayer.
To make it worse, he says, the logged areas — particularly those that don't regenerate properly — increase the fire risk to the rest of the forest, multiplying all the other problems.
VicForests denies its logging increases fire risk to the forest.
"So we have a biodiversity problem, we have a carbon problem, we have a water problem, we have a fire risk problem," said Professor Lindenmayer.
Professor Sarah Bekessy researches how to make good decisions when trading off development and the environment. Her work straddles ecology, urban planning and environmental policy.
"These forests clean our water. The tallest, most magnificent forests in the world, in my opinion," said Professor Bekessy.
She said any failed regeneration would mean the public was landed with a major liability rather than an asset.
"We should be able to make money from these forests — from the extraordinary services that they provide to us, the ecosystem services, the tourism opportunities."
And Professor Bekessy suggested a plan.
The first step, she said, is VicForests should be forced to regenerate the forests to the legal requirement.
"It's a very low standard that they've been legally required to meet and if they haven't met it…they should be held to account," she said.
But to repair the forests to a higher standard, she said there's a big opportunity for a new agency — an opportunity VicForests should not be given.
"VicForests is a broken organisation that has lost its way and I don't think they should be rewarded with an opportunity like that," she said.
"What we need is visionary, creative and environmentally focussed organisations to take this challenge on."
Professor Lindenmayer agreed.
"It needs to be a new agency whose job it is to put the forest back together again," he said.
Both said there's a big opportunity in doing that, to involve the First Nations people who cared for the country for millennia.
"VicForests' passionate and professional foresters ensure harvested coupes are regenerated to meet the requirements under the Code of Practice for Timber Production," a spokesman for VicForests said.
"Regardless of the agency undertaking the regeneration program in the future, it is likely the expertise of VicForests staff will be required," he said.
Dr Jack Pascoe, a Yuin man living on Gangubanud Country, west of Naarm (Melbourne), is an expert in how to apply conservation science in the real world.
He said he was disappointed but not surprised to see the extent of failed regeneration found by the AI analysis.
But Dr Pascoe believes fixing the problem presents an opportunity to fix some of the wrongs of the past.
"The act of colonisation largely separated…First Peoples from country. And to this day, First Peoples and the corporations that represent them have very little access to lands," he said.
He said doing that — and bringing a "country first" approach to healing the forest — could have multiple benefits for both the forests and Aboriginal peoples, providing cultural, economic and environmental benefits.
With commercial native logging ending in Victoria by January 1, more than 1.8 million hectares of forest that was open to logging, is now protected from the industry.
About 73,000 hectares of that area was actually logged.
That makes the question of what will be done with all that logged forest a pressing one for the conservationists that have fought for their protection for decades, as well as the government that is responsible for them.
Despite making promises to strengthen the rules around regenerating those forests, there remain questions whether the Victorian government is acting on them
Following reporting of widespread failed regeneration by the ABC in 2021, the Victorian government announced a series of actions to improve the situation.
That included clarifying expected regeneration practices by VicForests, creating new rules to strengthen oversight of those practices, and new rules for confirming whether or not a coupe has been regenerated before it becomes the responsibility of the state.
When asked by the ABC whether the Victorian environment department can point to any progress towards implementing those changes over the past two years, a spokesman for the Victorian government responded with quotes about withdrawing from native forestry.
"We do not take the decision around an early transition out of native timber harvesting lightly. As part of the transition, the Government will deliver a program of land management to manage the 1.8 million hectares of public land and will work closely with Traditional Owners and local communities."
That spokesman did not provide any on-the-record response to a further request to clarify whether there has been any implementation of those promises.
Conservationist Trent Patten is sceptical of the government's commitment to regenerating the forests.
"They're not doing anything at all," he said.