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Truck laden with logs drives along forest road
Rhett Butler, Author provided

Roads of destruction: we found vast numbers of illegal ‘ghost roads’ used to crack open pristine rainforest

One of Brazil’s top scientists, Eneas Salati, once said, “The best thing you could do for the Amazon rainforest is to blow up all the roads.” He wasn’t joking. And he had a point.

In an article published today in Nature, my colleagues and I show that illicit, often out-of-control road building is imperilling forests in Indonesia, Malaysia and Papua New Guinea. The roads we’re studying do not appear on legitimate maps. We call them “ghost roads”.

What’s so bad about a road? A road means access. Once roads are bulldozed into rainforests, illegal loggers, miners, poachers and landgrabbers arrive. Once they get access, they can destroy forests, harm native ecosystems and even drive out or kill indigenous peoples. This looting of the natural world robs cash-strapped nations of valuable natural resources. Indonesia, for instance, loses around A$1.5 billion each year solely to timber theft.

All nations have some unmapped or unofficial roads, but the situation is especially bad in biodiversity-rich developing nations, where roads are proliferating at the fastest pace in human history.

rare species of orangutan
The Tapanuli orangutan is the rarest species of great ape in the world. It lives only in northern Sumatra, where it is imperilled by roads and dam building. Maxime Aliaga, Author provided (no reuse)

Mapping ghost roads

For this study, my PhD student Jayden Engert and I worked with Australian and Indonesian colleagues to recruit and train more than 200 volunteers.

This workforce then spent some 7,000 hours hand-mapping roads, using fine-scale satellite images from Google Earth. Our team of volunteers mapped roads across more than 1.4 million square kilometres of the Asia-Pacific region.

As the results rolled in, we realised we had found something remarkable. For starters, unmapped ghost roads seemed to be nearly everywhere. In fact, when comparing our findings to two leading road databases, OpenStreetMap and the Global Roads Inventory Project, we found ghost roads in these regions to be 3 to 6.6 times longer than all mapped roads put together.

maps of northeast borneo, one using openstreetmap database and the other with many more ghost roads added
Mapped roads in northeastern Borneo using a leading road database, OpenStreetMap (left), and with the ghost roads identified in this study added (right). Author provided, CC BY-NC-ND

When ghost roads appear, local deforestation soars – usually immediately after the roads are built. We found the density of roads was by far the most important predictor of forest loss, outstripping 38 other variables. No matter how one assesses them, roads are forest killers.

What makes this situation uniquely dangerous for conservation is that the roads are growing fast while remaining hidden and outside government control.


Read more: Indigenous defenders stand between illegal roads and survival of the Amazon rainforest – Brazil's election could be a turning point


Roads and protected areas

Not even parks and protected areas in the Asia-Pacific are fully safe from illegal roads.

But safeguarding parks does have an effect. In protected areas, we found only one-third as many roads compared with nearby unprotected lands.

The bad news is that when people do build roads inside protected areas, it leads to about the same level of forest destruction compared to roads outside them.

Our findings suggest it is essential to limit roads and associated destruction inside protected areas. If we can find these roads using satellite images, authorities can too. Once an illegal road is found, it can be destroyed or at least mapped and managed as a proper legal road.

Keeping existing protected areas intact is especially urgent, given more than 3,000 protected areas have already been downsized or degraded globally for new roads, mines and local land-use pressures.

photos of burning Amazon forest, illegal roads in Africa, and poaching of a forest elephant
Illicit roads cause destruction worldwide, from carbon emissions from the burning of Amazonian forest for cattle pasture (A), to road building and forest destruction in central Africa (B), to poaching of rare animals such as this forest elephant killed by poachers near a Congo Basin road (C). M. Andreae (A) and W. Laurance (B,C), CC BY-NC-ND

Hidden roads and the human footprint

The impact we have on the planet differs from place to place. To gauge how much impact we’re having, researchers use the human footprint index, which brings together data on human activities such as roads and other infrastructure, land-uses, illumination at night from electrified settlements and so on. You can use the index to make heat-maps showing where human impacts are most or least pronounced.

We fed our ghost road discoveries into the index and compared two versions for eastern Borneo, one without ghost road information and one with it. The differences are striking.

When ghost roads are included in mapping the human impact on eastern Borneo, areas with “very high” human disturbance double in size, while the areas of “low” disturbance are halved.

das
This is what the human footprint heatmap for east-central Borneo looks like, first without ghost roads (A) and second with ghost roads included (B). Author provided, CC BY-NC-ND

Artificial intelligence

Researchers investigating other biodiversity-rich developing regions such as Amazonia and the Congo Basin have found many illegal unmapped roads in those locales too.

Ghost roads, it seems, are an epidemic. Worse, these roads can be actively encouraged by aggressive infrastructure-expansion schemes — most notably China’s Belt and Road Initiative, now active in more than 150 nations.

For now, mapping ghost roads is very labour-intensive. You might think AI could do this better, but that’s not yet true – human eyes can still outperform image-recognition AI software for mapping roads.

A golden dove in a Southeast Asian rainforest. William Laurance

At our current rate of work, visually mapping all roads – legal and illicit – across Earth’s land surface just once would require around 640,000 person-hours (or 73 person-years) to complete.

Given these challenges, our group and other researchers are now testing AI methods, hoping to provide accurate, global-scale mapping of ghost roads in close to real time. Nothing else can keep pace with the contemporary avalanche of proliferating roads.

We urgently need to be able to map the world’s roads accurately and often. Once we have this information, we can make it public so that authorities, NGOs and researchers involved in forest protection can see what’s happening.

Without this vital information, we’re flying blind. Knowing what’s happening in the rainforest is the first step to stopping the destruction.


Read more: The global road-building explosion is shattering nature


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