Timber extraction in vast and remote areas of boreal forest in the Arkhangelsk region, Russia. (Pierre Ibisch)

Scientists Thursday provided a global quantification of one of the most pervasive, but least recognized, 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 kilometer (a little over 3,000 feet) away from any road. “There are some effects that go far beyond 1 km 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 kilometer,” 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 kilometer (. 39 square miles) in area.

Only 7 percent of the fragments were very large — more than 100 square kilometers in area (about 39 square miles). Some of the largest untrammeled areas were in the Amazon rain forest, northern or boreal forests, and in Africa.

Here’s a global map that the authors produced that color-codes different parts of the world based on the size of the roadless areas found in different regions. Note that in red areas, there is basically no roadlessness at all, by the study’s definition, as in these areas, either roads themselves or a 1 kilometer zone on either side of them cover the space:

A global map of roadless areas. The blue color indicates especially large tracks. However, here the map, which is based on the OpenStreetMap data set, in many cases overestimates roadless areas. The reason is that, especially in tropical countries, the roads have not been carefully mapped. The red areas are completely roaded: covered by roads and 1 km buffers alongside either sides of the road. (Credit: P. Ibisch et al., Science (2016))

The map seems to indicate that economic development and the concentration of roads go hand in hand — thus, advanced economies in the United States, Europe and Japan seem to have little roadless area at all.

And it’s important to acknowledge, as the study notes, that the research is probably going on an incomplete data set of the total number of roads in the world. In other words, the picture is likely worse.

The researchers then went on to identify the areas that were both roadless but also had the greatest “ecological value” — for instance, untrammeled rain forest supports much more species biodiversity than roadless desert. These are the areas that, now, are most worth protecting from further incursions.

“The biggest block, most biodiverse roadless areas would be found in the Amazon,” Ibisch said. “We also have valuable roadless areas in the Congo Basin but to a lesser extent, we have more extensive fragmentation there already. And we also would find interesting roadless areas in Southeast Asia, in the tropics. But there are also valuable roadless areas in the boreal zone and even stretching out into the tundra in northern Russia.”

However, the study suggests that conservation goals and roadless areas don’t match — only 9.3 percent of the roadless areas, the researchers found, lie in protected areas. This suggests a major misalignment of priorities.

The consequences of ecosystem fragmentation are myriad, but they include interrupting the natural movement of organisms (and, their genetic material) across habitats, changing temperatures and local climates, and allowing not only human incursions but also the travel of invasive species into new areas, where they can cause a great deal of damage, Ibisch said.

“It is a real issue which‎ gets progressively worse and one that needs to be taken on at scale,” added Tom Lovejoy, an ecologist at George Mason University whose research focuses on the Amazon rain forest.

“Roads reflect development, the model of development that we follow up to now,” Ibisch said. “They also trigger development. It’s both, and here we have to make the point, can we think about an alternative model of development without actually cutting nature into ever more pieces?”