Abstract
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 effects1,2,3,4,5. Many roads are being constructed illegally or informally and do not appear on any existing road map6,7,8,9,10; 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 correlate11 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.
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Data availability
The datasets used for this study (including comprehensive road maps as a raster of road density at 1-km2 resolution) are available in the Supplementary Information, on request to J.E.E. and W.F.L. or as follows. OpenStreetMap data are available from https://download.geofabrik.de/, and GRIP road data from https://www.globio.info/download-grip-dataset. National and subnational administrative-region data were obtained from GADM (https://gadm.org/). Population-density data were from WorldPop (https://www.worldpop.org/). GDP data were accessed at https://datadryad.org/stash/dataset/doi:10.5061/dryad.dk1j0. Protected-area data were from Protected Planet (https://www.protectedplanet.net/en). Waterways locations were obtained from the Global River Widths from Landsat Database (https://zenodo.org/records/1297434). Elevation data were accessed at http://srtm.csi.cgiar.org, and rainfall data at https://doi.org/10.16904/envidat.211. Data for all soil variables were obtained from Soil Grids (https://soilgrids.org/).
Change history
15 May 2024
A Correction to this paper has been published: https://doi.org/10.1038/s41586-024-07535-5
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Acknowledgements
We thank J. Barlow, R. Chazdon, M. Cochrane, S. Das, M. Goosem, J. Jaeger, P. Negret, C. Souza Jr, R. Talkhani and H. Tao for many helpful comments, and our volunteer road-mappers, including Wild Green Memes for Ecological Fiends, for their efforts. The Australian Research Council, James Cook University and an anonymous philanthropic donor provided support.
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W.F.L., J.E.E., M.J.C., M.A. and S.S. conceived the study; J.E.E., J.E.C. and W.F.L. coordinated data analysis. W.F.L., J.E.E., J.E.C. and M.J.C. wrote the manuscript. J.E.E., Y.I., J.C. and S.S. generated key road datasets. M.J.C., J.E.C., M.A., S.S. and J.S. provided ideas and critical feedback.
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Nature thanks Robin Chazdon, Jochen Jaeger, Pablo Negret and Carlos Souza Jr for their contribution to the peer review of this work.
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Engert, J.E., Campbell, M.J., Cinner, J.E. et al. Ghost roads and the destruction of Asia-Pacific tropical forests. Nature 629, 370–375 (2024). https://doi.org/10.1038/s41586-024-07303-5
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DOI: https://doi.org/10.1038/s41586-024-07303-5
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