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Global map of roadless areas reveals roads fragmenting majority of land

December 15, 2016

Roads now fragment land to such an extent that, worldwide, only 7% of patches created by roads are greater than 100 square kilometers (38 square miles), a new study reports. The results dramatically highlight the footprint of humans on Earth. There are numerous direct and indirect environmental impacts associated with the presence of roads, including deforestation and fragmentation, chemical pollution, noise disturbance, and increased wildlife mortality, among others. To gain a better understanding of the extent and impact of current road systems, Pierre L. Ibisch et al. analyzed two global datasets, OpenStreetMap and gROADS. They also reviewed 282 publications that assess the spatial influence of roads, finding that the effects of these manmade structures most often extend about one kilometer (km) from the road itself; thus, in their effort to build a global map of roadless areas, the researchers included a one km buffer along each road evaluated, as these areas have high road impacts despite being roadless. Their results show that, although roadless areas make up about 80% of Earth's terrestrial surface, these areas are dissected into about 600,000 patches. More than half of the patches are less than 1 square kilometer; 80% are less than 5 square kilometers; and only 7% are greater than 100 square kilometers. The authors note discrepancies in the type of biome affected by fragmentation, where tundra-, rock- and ice-covered biomes are nearly entirely roadless, while temperate broadleaf and mixed forests are the most fragmented. In total, about one third of the world's roadless areas are in regions with low biodiversity, low ecological functions, and low ecosystem resilience values. Lastly, Ibisch et al. look at the portion of roadless areas that fall under protection, finding significant deficiencies. They suggest that further degradation of the world's remaining roadless areas will occur without rapid shifts towards greater protection.
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American Association for the Advancement of Science

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