Minimizing the environmental damage that new roads cause is generally regarded as a good thing. But to do that, it helps to understand just how new roads cause the damage of which they are accused.
Recently, a group of researchers led by Dr. Gonzalez conducted an experiment and proved that immigration is good for the health of animal populations. A road destroys only a small part of the habitat, thus destroying just a few local populations of creatures. So the argument that road-building itself is bad for biodiversity is not self-evidently correct. Those who nevertheless hold this view say that apparently separate local populations of animals are, in fact, parts of much larger populations connected via migration.
According to this theory, when a local population struggles to move about – because of an epidemic, for example – individuals from neighboring communities can fill the gaps.
The implications of the theory are straightforward. Cut local populations off from each other and each is more likely to disappear. And roads are good at doing just that. Testing the theory with experimental roads, however, would be expensive. Dr. Gonzalez's brainwave was to do the whole thing on a much smaller scale.
The team studied moss-covered rocks. On some rocks the researchers left the moss untouched; on others they made "roadways" across to leave the moss isolated. After waiting six months, they found that in the disturbed habitats nearly all the bug population had declined compared with undisturbed moss, and 40% of the species had become extinct.
The real test came in the second part of the experiment. In this, the researchers removed moss much as before, but they left narrow moss paths to bridge the no-bug's-land between islands. The islands with bridges did far better than isolated islands – a result that supports the notion that population exchange is necessary to keep an ecosystem healthy.
Whether these results can be translated to large-scale ecosystems remains uncertain. But if they can, they would cause more, not less, concern about the ecological effects of road-building. On the other hand, they also suggest a way out. In Britain, tunnels are often built under roads for animals of regular habits, such as badgers(獾), to be able to travel their traditional routes without having to fight with traffic. Extending that principle, perhaps special bridges might be a cheap way of letting man and nature rub along a bit better.
