Wild lands void of roads are among the last relatively undisturbed parts of the planet. Although as much as 80 percent of Earth’s land surface is still roadless, that territory has been fragmented into nearly 600,000 pieces, according to new research published today in Science.
These areas are often critical refuges of biodiversity and crucial for regulating the water cycle and the climate, the authors of the study argue. “With the length of roads projected to increase by >60% globally from 2010 to 2050,” they write, “there is an urgent need for the development of a comprehensive global strategy for road development if continued biodiversity loss is to be abated.”
Using OpenStreetMap’s crowdsourced data for more than 36 million kilometers of roads, the international team of researchers—led by Pierre Ibisch of Germany’s Eberswalde University for Sustainable Development—mapped all the roadless areas on Earth (above), excluding Greenland and Antarctica. Because the impact of roads extends well beyond their actual surface area—due to things like pollution, noise, transport of pests and invasive species, soil erosion, and increased human access—they included areas that are at least one kilometer away from a road. They calculated that around 105 million of the 132 million square kilometers of land on Earth remains roadless.
This number almost certainly overestimates the undisturbed territory, the researchers say, because the effects of some roads, particularly major highways, penetrate much farther than five kilometers. And, though OpenStreetMap is the most complete global data set of roads freely available, many tropical countries have not been thoroughly mapped. The rapid pace of road construction in some areas also means many new roads are not yet on the map.
Once the researchers had mapped the roadless areas, they determined an ecological value for the patches based on their size, biodiversity, and importance to the ecosystem (above). Most of the remaining roadless areas are small: Of the 600,000 patches, half are less than 1 square kilometer, 80 percent are less than 5 square kilometers, and just 7 percent of the areas are larger than 100 square kilometers. A quarter of the roadless areas are sparsely inhabited, treeless, and largely barren land. A third are rangelands. Some of the largest remaining patches are in lush, biologically rich areas like the Amazon and the boreal forests of North America.
Unfortunately, the researchers conclude, just 9.3 percent of the remaining roadless areas are currently protected by international conservation efforts. With scientific evidence of the negative impacts of roads piling up, they argue that the most ecologically valuable roadless areas on their map should be prioritized.
“Limiting road expansion into roadless areas,” they write, “may prove to be the most cost effective and straightforward way of achieving strategically important global biodiversity and sustainability goals.”