Scientists yesterday provided a global quantification of one of the most pervasive, but least recognised, ways that humans are marring the coherence of the natural world - by building endless numbers of roads.
Roads fragment natural habitats, and the more of them there are, the smaller and more compromised those habitats become. At the same time, roads give humans access to remote, once pristine regions, where they can begin logging, mining, accidentally (or intentionally) starting fires and much else.
In the Amazon rain forest, for instance, the fragmentation of the landscape that occurs because of deforestation - to which roads also contribute - upends the entire nature of the ecosystem. Once sunlight can penetrate into the rain forest from a cleared area to its side, rather than being mostly blocked out by the lush canopy from above, the forest floor dries out, the forest itself heats up, trees collapse more easily, there isn't enough range for many key species, and on and on.
The new study, published in the journal Science by a team of 10 conservation scientists at institutions in Germany, Greece, Poland, the United Kingdom, Brazil and the United States, used an open-source, citizen science database of global roads. The researchers then combined this with an assessment from the research literature of the size of areas alongside roads that are compromised ecologically by them. This allowed them to count up the world's remaining truly untrammeled areas and assess their number and size.
They defined these areas as starting 1 kilometre away from any road. "There are some effects that go far beyond 1km actually. It's a gradient of course, of impacts fading out, but the majority of problems is occurring in this belt or buffer of 1 kilometre," said Pierre Ibisch, the study's first author and a researcher at the Eberswalde University for Sustainable Development in Germany.
Using this metric, the study found that the Earth's land areas (excluding Antarctica and Greenland) were 80 percent roadless, which may sound like a good thing - but peering in closer, the researchers found that roads had divided that land area into some 600,000 pieces. More than half of these were less than a square kilometre in area.
Only 7 per cent of the fragments were very large - more than 100 square kilometres in area. Some of the largest untrammeled areas were in the Amazon rain forest, northern or boreal forests, and in Africa.