​Roads and other infrastructure development projects are expanding globally at the fastest rate in human history, especially in biodiversity-rich developing tropical regions. Infrastructure expansion often promotes forest loss and land-cover conversion, fires, poaching, and other environmental and societal impacts. Understanding where and how these development projects will impact tropical forests is crucial to their survival. My work focuses on modelling the impacts of roads on land use change in tropical forests, in order to identify methods of minimizing the environmental impacts of future development. 

Peer-Reviewed Publications

GHOST ROADS AND THE DESTRUCTION OF ASIA-PACIFIC TROPICAL FORESTS. Engert et al. (2024). Nature.
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Roads are expanding at the fastest pace in human history. This is the case especially in biodiversity-rich tropical nations, where roads can result in forest loss and fragmentation, wildfires, illicit land invasions and negative societal effects. Many roads are being constructed illegally or informally and do not appear on any existing road map; the toll of such ‘ghost roads’ on ecosystems is poorly understood. Here we use around 7,000 h of effort by trained volunteers to map ghost roads across the tropical Asia-Pacific region, sampling 1.42 million plots, each 1 km2 in area. Our intensive sampling revealed a total of 1.37 million km of roads in our plots—from 3.0 to 6.6 times more roads than were found in leading datasets of roads globally. Across our study area, road building almost always preceded local forest loss, and road density was by far the strongest correlate of deforestation out of 38 potential biophysical and socioeconomic covariates. The relationship between road density and forest loss was nonlinear, with deforestation peaking soon after roads penetrate a landscape and then declining as roads multiply and remaining accessible forests largely disappear. Notably, after controlling for lower road density inside protected areas, we found that protected areas had only modest additional effects on preventing forest loss, implying that their most vital conservation function is limiting roads and road-related environmental disruption. Collectively, our findings suggest that burgeoning, poorly studied ghost roads are among the gravest of all direct threats to tropical forests.
MAPPING REMOTE ROADS USING ARTIFICIAL INTELLIGENCE AND SATELLITE IMAGERY. Sloan et al. (2024). Remote Sensing.
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Road building has long been under-mapped globally, arguably more than any other human activity threatening environmental integrity. Millions of kilometers of unmapped roads have challenged environmental governance and conservation in remote frontiers. Prior attempts to map roads at large scales have proven inefficient, incomplete, and unamenable to continuous road monitoring. Recent developments in automated road detection using artificial intelligence have been promising but have neglected the relatively irregular, sparse, rustic roadways characteristic of remote semi-natural areas. In response, we tested the accuracy of automated approaches to large-scale road mapping across remote rural and semi-forested areas of equatorial Asia-Pacific. Three machine learning models based on convolutional neural networks (UNet and two ResNet variants) were trained on road data derived from visual interpretations of freely available high-resolution satellite imagery. The models mapped roads with appreciable accuracies, with F1 scores of 72–81% and intersection over union scores of 43–58%. These results, as well as the purposeful simplicity and availability of our input data, support the possibility of concerted program of exhaustive, automated road mapping and monitoring across large, remote, tropical areas threatened by human encroachment.
MAJOR MINING ROAD COULD BE DEATH KNELL FOR SUMATRA'S LOWLAND RAINFORESTS. Engert et al. (2022). Biological Conservation.
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In October of 2019, the Indonesian Ministry of Environment and Forestry gave approval for construction of an 88 km-long mining road through the Harapan Forest, an area with outstanding biodiversity values on the island of Sumatra, Indonesia (Diana, 2020). The road approval, granted to Indonesian mining firm PT Marga Bara Jaya, immediately prompted protests from scientists and conservation groups in Indonesia and internationally, as well as from indigenous communities residing within the forest (Diana, 2020; Engert et al., 2021). Construction of the road, which is yet to penetrate the Harapan Forest, is likely to cause significant loss of Sumatran lowland rainforest, a critically endangered ecoregion currently represented by only around 3 % of its original extent (Fig. 1) (Laumonier, 1997; Olson et al., 2001).
SPRAWLING CITIES ARE RAPIDLY ENCROACHING ON EARTH'S BIODIVERSITY. Laurance & Engert (2022). PNAS.
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One of the most important demographic events of the past half-century is the dramatic growth of urban areas worldwide. Growing cities, like insatiable amoebas, tend to engulf and devour their surrounding lands, often at the expense of biodiversity (Fig. 1). In PNAS, Simkin et al. (1) project the regional and global impacts of urban expansion on more than 30,000 species of native mammals, birds, reptiles, and amphibians from 2015 to 2050. Their findings reveal that burgeoning cities are a far more serious driver of biodiversity decline than many realize, with environmental impacts comparable with those of planet-altering activities, such as agriculture and forestry.
REROUTING A MAJOR INDONESIAN MINING ROAD TO SPARE NATURE AND REDUCE DEVELOPMENT COSTS. Engert et al. (2021) Conservation Science and Practice.
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Road-infrastructure projects are expanding rapidly worldwide while penetrating into previously undisturbed forests. In Sumatra, Indonesia, a planned 88-km-long mining road for transporting coal would imperil the Harapan Forest, the island's largest surviving tract of lowland rainforest. Such roads often lead to increased forest encroachment and illegal logging, fires, poaching, and mining. To evaluate the potential impact of the proposed road, we first manually mapped all existing roads inside and around the Harapan Forest using remote-sensing imagery. We then calculated the expected increase in forest loss from three proposed mining-road routes using a metric based on travel-time mapping. Finally, we used least-cost path analyses to identify new routes for the road that would minimize forest disruption and road-construction costs. We found that road density inside and nearby the Harapan Forest is already 3–4 times higher than official data sources indicate. Based on our analyses, each of the three proposed mining-road routes would lead to 3,000–4,300 ha of additional forest loss from human encroachment plus another 424 ha lost from road construction itself. We propose new routes for the mining road that would result in up to 3,321 ha less forest loss with markedly lower construction costs than any other planned route. We recommend approaches such as ours, using least-cost-path analysis, to minimize the environmental and financial costs of major development projects.
EMERGING CHALLENGES FOR SUSTAINABLE DEVELOPMENT AND FOREST CONSERVATION IN SARAWAK, BORNEO. Alamgir et al. (2020) PLOS One.
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The forests of Borneo—the third largest island on the planet—sustain some of the highest biodiversity and carbon storage in the world. The forests also provide vital ecosystem services and livelihood support for millions of people in the region, including many indigenous communities. The Pan-Borneo Highway and several hydroelectric dams are planned or already under construction in Sarawak, a Malaysian state comprising part of the Borneo. This development seeks to enhance economic growth and regional connectivity, support community access to services, and promote industrial development. However, the implications of the development of highway and dams for forest integrity, biodiversity and ecosystem services remained largely unreported. We assessed these development projects using fine-scale biophysical and environmental data and found several environmental and socioeconomic risks associated with the projects. The highway and hydroelectric dam projects will impact 32 protected areas including numerous key habitats of threatened species such as the proboscis monkey (Nasalis larvatus), Sarawak surili (Presbytis chrysomelas), Bornean orangutans (Pongo pygmaeus) and tufted ground squirrel (Rheithrosciurus macrotis). Under its slated development trajectory, the local and trans-national forest connectivity between Malaysian Borneo and Indonesian Borneo would also be substantially diminished. Nearly ~161 km of the Pan-Borneo Highway in Sarawak will traverse forested landscapes and ~55 km will traverse carbon-rich peatlands. The 13 hydroelectric dam projects will collectively impact ~1.7 million ha of forest in Sarawak. The consequences of planned highway and hydroelectric dams construction will increase the carbon footprint of development in the region. Moreover, many new road segments and hydroelectric dams would be built on steep slopes in high-rainfall zones and forested areas, increasing both construction and ongoing maintenance costs. The projects would also alter livelihood activities of downstream communities, risking their long-term sustainability. Overall, our findings identify major economic, social and environmental risks for several planned road segments in Sarawak—such as those between Telok Melano and Kuching; Sibu and Bintulu; and in the Lambir, Limbang and Lawas regions—and dam projects—such as Tutoh, Limbang, Lawas, Baram, Linau, Ulu Air and Baleh dams. Such projects need to be reviewed to ensure they reflect Borneo’s unique environmental and forest ecosystem values, the aspirations of local communities and long-term sustainability of the projects rather than being assessed solely on their short-term economic returns.
TRANS-NATIONAL CONSERVATION AND INFRASTRUCTURE DEVELOPMENT IN THE HEART OF BORNEO. Sloan et al. (2019) PLOS One.
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The Heart of Borneo initiative has promoted the integration of protected areas and sustainably-managed forests across Malaysia, Indonesia, and Brunei. Recently, however, member states of the Heart of Borneo have begun pursuing ambitious unilateral infrastructure-development schemes to accelerate economic growth, jeopardizing the underlying goal of trans-boundary integrated conservation. Focusing on Sabah, Malaysia, we highlight conflicts between its Pan-Borneo Highway scheme and the regional integration of protected areas, unprotected intact forests, and conservation-priority forests. Road developments in southern Sabah in particular would drastically reduce protected-area integration across the northern Heart of Borneo region. Such developments would separate two major clusters of protected areas that account for one-quarter of all protected areas within the Heart of Borneo complex. Sabah has proposed forest corridors and highway underpasses as means of retaining ecological connectivity in this context. Connectivity modelling identified numerous overlooked areas for connectivity rehabilitation among intact forest patches following planned road development. While such ‘linear-conservation planning’ might theoretically retain up to 85% of intact-forest connectivity and integrate half of the conservation-priority forests across Sabah, in reality it is very unlikely to achieve meaningful ecological integration. Moreover, such measure would be exceedingly costly if properly implemented–apparently beyond the operating budget of relevant Malaysian authorities. Unless critical road segments are cancelled, planned infrastructure will fragment important conservation landscapes with little recourse for mitigation. This likelihood reinforces earlier calls for the legal recognition of the Heart of Borneo region for conservation planning as well as for enhanced tri-lateral coordination of both conservation and development.
INFRASTRUCTURE EXPANSION CHALLENGES SUSTAINABLE DEVELOPMENT IN PAPUA NEW GUINEA. Alamgir et al. (2019) PLOS One.
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The island of New Guinea hosts the third largest expanse of tropical rainforest on the planet. Papua New Guinea—comprising the eastern half of the island—plans to nearly double its national road network (from 8,700 to 15,000 km) over the next three years, to spur economic growth. We assessed these plans using fine-scale biophysical and environmental data. We identified numerous environmental and socioeconomic risks associated with these projects, including the dissection of 54 critical biodiversity habitats and diminished forest connectivity across large expanses of the island. Key habitats of globally endangered species including Goodfellow’s tree-kangaroo (Dendrolagus goodfellowi), Matchie’s tree kangaroo (D. matschiei), and several birds of paradise would also be bisected by roads and opened up to logging, hunting, and habitat conversion. Many planned roads would traverse rainforests and carbon-rich peatlands, contradicting Papua New Guinea’s international commitments to promote low-carbon development and forest conservation for climate-change mitigation. Planned roads would also create new deforestation hotspots via rapid expansion of logging, mining, and oil-palm plantations. Our study suggests that several planned road segments in steep and high-rainfall terrain would be extremely expensive in terms of construction and maintenance costs. This would create unanticipated economic challenges and public debt. The net environmental, social, and economic risks of several planned projects—such as the Epo-Kikori link, Madang-Baiyer link, Wau-Malalaua link, and some other planned projects in the Western and East Sepik Provinces—could easily outstrip their overall benefits. Such projects should be reconsidered under broader environmental, economic, and social grounds, rather than short-term economic considerations.
HIDDEN CHALLENGES FOR CONSERVATION AND DEVELOPMENT ALONG THE TRANSPAPUAN ECONOMIC CORRIDOR. Sloan et al. (2019) Environmental Science and Policy.
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​The island of New Guinea harbours one of the world’s largest tracts of intact tropical forest, with 41% of its land area in Indonesian Papua (Papua and Papua Barat Provinces). Within Papua, the advent of a 4000-km ‘development corridor’ reflects a national agenda promoting primary-resource extraction and economic integration. Papua, a resource frontier containing vast forest and mineral resources, increasingly exhibits new conservation and development dynamics suggestive of the earlier frontier development phases of other Indonesian regions. Local environmental and social considerations have been discounted in the headlong rush to establish the corridor and secure access to natural resources. Peatland and forest conversion are increasingly extensive within the epicentres of economic development. Deforestation frontiers are emerging along parts of the expanding development corridor, including within the Lorentz World Heritage Site. Customary land rights for Papua’s indigenous people remain an afterthought to resource development, fomenting conditions contrary to conservation and sustainable development. A centralised development agenda within Indonesia underlies virtually all of these changes. We recommend specific actions to address the environmental, economic, and socio-political challenges of frontier development along the Papuan corridor.

Popular Publications

Roads of destruction: we found vast numbers of illegal ‘ghost roads’ used to crack open pristine rainforest.
​Bill Laurance, The Conversation, 11/4/24.
In relation to: Ghost roads and the destruction of Asia-Pacific tropical forests (Engert et al., 2024)
Unseen and unregulated: ‘Ghost’ roads carve up Asia-Pacific tropical forests.
​Carolyn Cowan, Mongabay, 11/4/24.
In relation to: Ghost roads and the destruction of Asia-Pacific tropical forests (Engert et al., 2024)
Build around the forest, not through it, study says of Sumatra trucking road.
​Hans Nicholas Jong, Mongabay, 28/9/21.
In relation to: Rerouting a major Indonesian mining road to spare nature and reduce development costs (Engert et al., 2021)

Media

Ghost Roads and the survival of tropical forests

Centre for Tropical Environmental and Sustainability Science Seminar Series, James Cook University
Over half of the roads in the tropical Asia-Pacific region are not included in existing road maps. These unmapped roads have serious implications for environmental conservation and management.

Centre for Biodiversity and Conservation Science Seminar Series, University of Queensland 
Watch Video (recommended version)

Centre for Tropical Environmental and Sustainability Science Seminar Series, James Cook University
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Re-routing a major road to spare nature and money

Construction of a major mining road threatens the Harapan Forest of Sumatra, an important tract of lowland rainforest hosting elephants and tigers. We provide alternative road routes that would limit the destruction and reduce costs.

International Conference on Ecology and Transportation (ICOET 2021)
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Data

A comprehensive roadmap of the Asia-Pacific region.
In development, to contribute visit Global Roadmap or email [email protected]
Time-series maps of road network expansion.
​In development, to collaborate email [email protected]

About me

I am an ecologist with a focus on conservation science and spatial ecology.

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[email protected]