December 18, 2016 7.01pm GMT
If you asked a friend to name the worst human threat to nature, what would they say? Global warming? Overhunting? Habitat fragmentation?
A new study suggests it is in fact road-building.
“Road-building” might sound innocuous, like “house maintenance” – or even positive, conjuring images of promoting economic growth. Many of us have been trained to think so.
But an unprecedented spate of road building is happening now, with around 25 million kilometres of new paved roads expected by 2050. And that’s causing many environmental researchers to perceive roads about as positively as a butterfly might see a spider web that’s just fatally trapped it.
The new study, led by Pierre Ibisch at Eberswalde University for Sustainable Development, Germany, ambitiously attempted to map all of the roads and remaining ecosystems across Earth’s entire land surface.
Its headline conclusion is that roads have already sliced and diced Earth’s ecosystems into some 600,000 pieces. More than half of these are less than 1 square kilometre in size. Only 7% of the fragments are more than 100 square km.
That’s not good news. Roads often open a Pandora’s box of ills for wilderness areas, promoting illegal deforestation, fires, mining and hunting.
In the Brazilian Amazon, for instance, our existing research shows that 95% of all forest destruction occurs within 5.5km of roads. The razing of the Amazon and other tropical forests produces more greenhouse gases than all motorised vehicles on Earth.
Animals are being imperilled too, by vehicle roadkill, habitat loss and hunting. In just the past decade, poachers invading the Congo Basin along the expanding network of logging roads have snared or gunned down two-thirds of all forest elephants for their valuable ivory tusks.
Worse than it looks
As alarming as the study by Ibisch and colleagues sounds, it still probably underestimates the problem, because it is likely that the researchers missed half or more of all the roads on the planet.
That might sound incompetent on their part, but in fact keeping track of roads is a nightmarishly difficult task. Particularly in developing nations, illegal roads can appear overnight, and many countries lack the capacity to govern, much less map, their unruly frontier regions.
One might think that satellites and computers can keep track of roads, and that’s partly right. Most roads can be detected from space, if it’s not too cloudy, but it turns out that the maddening variety of road types, habitats, topographies, sun angles and linear features such as canals can fool even the smartest computers, none of which can map roads consistently.
The only solution is to use human eyes to map roads. That’s what Ibisch and his colleagues relied upon – a global crowdsourcing platform known as OpenStreetMap, which uses thousands of volunteers to map Earth’s roads.