- A new study indicates that significant networks of informal, unmapped and unregulated roads sprawl into forest-rich regions of Southeast Asia and the Pacific.
- Slipping beneath the purview of environmental governance, construction of these “ghost roads” typically precede sharp spikes in deforestation and represent blind spots in zoning and law enforcement, the study says.
- The authors underscore that the relentless proliferation of ghost roads ranks among the gravest of threats facing the world’s remaining tropical forests.
- The findings bolster a growing momentum toward the development of AI-based road-mapping systems to help conservation biologists and resource managers better keep track of informal and illegal road networks and curb associated deforestation rates.
Roads are being built at an unprecedented rate across the globe. Some 25 million kilometers (15.5 million miles) of paved roads are expected to be built in just the four decades leading up to 2050 — enough to wrap around the equator more than 600 times. But much of this construction is happening under the radar. Networks of unmapped, unregulated and often illegal roads are insidiously spreading into fragile ecosystems. If left unchecked, they threaten to wreak a devastating toll on tropical forests, according to new research.
The new study, published April 10 in Nature, documents 1.37 million km (851,000 mi) of roads sprawling across the islands of New Guinea, Borneo and Sumatra, three hotspots of biodiversity in Southeast Asia and the Pacific that contain the largest combined expanse of tropical rainforest in the world outside the Amazon and the Congo Basin. This total length of roads is between three and 6.6 times more than recorded in officially recognized databases.
The researchers say the discrepancy indicates the presence of a glut of what they term “ghost roads”: informally or illicitly constructed roads carved by loggers, miners, land grabbers or speculators. Typically falling outside of the purview of environmental governance, ghost roads create blind spots in zoning and law enforcement, ultimately posing one of the gravest conservation threats facing the world’s forests.
“Roads are often a death-knell for ecosystems, especially ghost roads, which are often illegal and unregulated,” William Laurance, study co-author and a distinguished research professor at James Cook University in Australia, told Mongabay in an email. “As they proliferate, roads can open up a native forest like a flayed fish.”
Unmapped roads ‘proliferating wildly’
When planned well, roads can connect communities and markets, supporting economic development. But when regulation is lacking, roads have been likened to “arteries of destruction” in tropical forests, paving the way for the extraction of timber, minerals, wildlife and other resources, leaving a hollow and lifeless landscape in their wake.
The sheer number of unmapped roads infiltrating the study region is shocking, the authors say. “In Borneo, none of the existing datasets covered even one-third of the total amount of roads,” Jayden Engert, lead author of the study and a doctoral candidate at James Cook University, told Mongabay. “In some areas, the [official dataset] coverage was less than 5%!”
Ghost roads are “proliferating wildly,” according to Laurance, “especially in developing nations that harbor much of Earth’s biodiversity.” The International Energy Agency estimates that nine-tenths of the world’s burgeoning road construction is slated for countries in the Global South, where governance is often hampered by corruption and a lack of financial and technical resources. Therefore, finding ways to keep track of informal and unregulated roads will be vital to minimizing their environmental harms, Laurance added.
Using high-resolution satellite images, the team of researchers from Indonesia and Australia worked with more than 200 trained research volunteers to manually map roadways in 1.42 million plots of land, each measuring 1 km2 (0.4 mi2). Scrutinizing all the images to pick out each road, often amid dense and remote forest, amounted to 7,000 hours of volunteer effort. They then compared their data set with two globally recognized official databases: the Global Roads Inventory Project, and OpenStreetMap.
Roads precede deforestation
More than one-third of the roads identified as ghost roads were located in oil palm or other plantations across the study region; nearly one-third were in nonplantation agriculture; and up to 39% webbed their way into intact forests. The study cautions that by reducing the costs of transporting forest commodities, such as timber, minerals and poached wildlife, roads — which are typically linked with agriculture in the tropics — rapidly promote deforestation.
To study the deforestation trends associated with roads over time, the team analyzed satellite imagery from between 1985 and 2020 in 12 large landscapes across the study region. They found that deforestation typically peaks soon after a road first penetrates into a landscape. Thereafter, the rate of forest loss slows as road density increases and accessible forests are eroded out of existence. Of 38 environmental, demographic and socioeconomic factors the researchers tested, the presence of roads was found to be the strongest predictor of deforestation.
What’s more, the team found that roads cause just as much deforestation within protected areas as they do outside of such safeguarded lands. Once the team controlled for road density, they found that protected areas had only a modest additional effect on preventing forest loss. “This suggests [that] protected areas can only actually reduce deforestation if they prevent road building,” Engert said.
But roads continue to scythe their way into protected areas the world over, according to Laurance. A major worry, he said, is the trend of road and other infrastructure construction within protected areas for mining and fossil fuel extraction — an insidious phenomenon often leading to what is known as “PADDD,” or protected area downgrading, downsizing and degazettement. “Our study helps to illustrate just how damaging PADDD can be for protected areas,” Laurance said.
Megaprojects afoot
State-led plans to transform forested regions in many parts of the study area into economic and industrial powerhouses feature efforts to improve road infrastructure. Megaprojects such as the Pan Borneo Highway and the Trans Sumatra Toll Road risk opening up a plethora of threats to once-inaccessible forested land through illegal offshoots.
To curb the proliferation of ghost roads branching off from new major highways, Laurance said it will be vital to ensure the surrounding land is legally protected. “Otherwise, it’s far too easy for land invaders to clear forests and engage in land speculation — or for poachers, illegal gold miners, loggers or drug producers to invade the forests,” he said.
The findings from Sumatra, Borneo and New Guinea reflect patterns uncovered in previous studies in other parts of the world. Studies in the Brazilian Amazon, Cameroon and the Solomon Islands, for instance, have documented between 2.8 and 9.9 times more road length than reported in official databases.
Carlos Souza Jr., an associate researcher at Brazilian conservation nonprofit Imazon, who wasn’t involved in the study, said it’s a good example of how citizen science can be leveraged to make labor-intensive and challenging tasks more achievable. “Mapping roads with visual interpretation is labor intensive,” he said. “The study demonstrates well how crowdsourcing can be used to solve scientific problems.”
Road-tracking tech needed
Souza said he’s hopeful that artificial intelligence technologies can accelerate road mapping at scale, a feat he said will ultimately help to guide policymakers and conservationists in their efforts to protect forests and people from illicit land incursions and deforestation. He was part of a team that in 2022 combined satellite monitoring with artificial intelligence algorithms to reveal that 41% of the Brazilian Amazon is already bisected by roads or located within 10 km (6 mi) of one.
Large data sets, like that of the new study, will be vital to train such AI-based road-mapping systems, Souza added. “The next step is to apply AI to all tropical forests,” he said. “The AI must be combined with Human Intelligence (HI) to use the information effectively to avoid future deforestation and forest degradation associated with roads, which is still mostly undetectable.”
Echoing Souza’s confidence in new technologies, the study authors underscore the need for a globally applicable automated road-detection system. They estimate it would take roughly 640,000 human-hours to conduct a global-scale analysis of road networks using satellite images alone — far too long a process to keep pace with the rate at which ghost roads are expanding.
In a separate study published in early 2024, several of the same researchers detailed how they used their volunteer data from satellite maps to train an AI model that can pick out the roads within them with an accuracy of up to 81%.
“In practical terms, such an automated system is one of the most urgent conservation needs for tropical forests today,” the study says. “Nothing else will keep pace with the contemporary avalanche of proliferating roads.”
Carolyn Cowan is a staff writer for Mongabay. Follow her on 𝕏, @CarolynCowan11.
Banner image: A logging road slices through tropical forest in Sabah, Malaysian Borneo. Image by Rhett A. Butler/Mongabay.
Citations:
Engert, J., Campbell, M. J., Cinner, J. E., Ishida, Y., Sloan, S., Supriatna, J., … Laurance, W. F. (2024). Ghost roads and the destruction of Asia-Pacific tropical forests. Nature. doi:10.1038/s41586-024-07303-5
Botelho, J., Costa, S. C., Ribeiro, J. G., & Souza, C. M. (2022). Mapping roads in the Brazilian Amazon with artificial intelligence and Sentinel-2. Remote Sensing, 14(15), 3625. doi:10.3390/rs14153625
Sloan, S., Talkhani, R. R., Huang, T., Engert, J., & Laurance, W. F. (2024). Mapping remote roads using artificial intelligence and satellite imagery. Remote Sensing, 16(5), 839. doi:10.3390/rs16050839
See related story:
In Borneo, dwindling forests face further fragmentation as roads spread
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