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Rainforest: the problem with roads

Posted by Lindy on January 19, 2012


http://e360.yale.edu/feature/as_roads_spread_in_tropical_rain_forests_environmental_toll_grows/2485/

Taken from an article by William Laurance

Brazil is currently building 7,500 kilometers of new paved highways that crisscross the Amazon basin. Three major new highways are cutting across the towering Andes mountains, providing a direct link for timber and agricultural exports from the Amazon to resource-hungry Pacific Rim nations, such as China.

Despite their environmental costs, the economic incentives to drive roads into tropical wilderness are strong. They are:

  • a cost-effective means to promote economic development
  • give access natural resources
  • local communities in remote areas often demand new roads to improve access to markets and medical services
  • new roads can be used to help secure frontier regions

Roads that cut through rainforests can also create barriers for sensitive wildlife, many of which are ecological specialists. Studies have shown that even narrow (30 meter-wide), unpaved roads drastically reduce or halt local movements for scores of forest bird species. Many of these species prefer deep, dark forest interiors; they have large, light-sensitive eyes and avoid the vicinity of road verges, where conditions are much brighter, hotter, and drier. A variety of other tropical species — including certain insects, amphibians, reptiles, bats, and small and large mammals — have been shown to be similarly leery of roads and other clearings. And by bringing naïve rainforest wildlife into close proximity with fast-moving vehicles, roads can also promote heavy animal mortality. For some creatures, especially those with low reproductive rates, roads could potentially become death zones that help propel the species toward local extinction.

Although the direct effects of roads are serious, they pale in comparison to the indirect impacts. In tropical frontier regions, new roads often open up a Pandora’s box of unplanned environmental maladies, including:

  •  illegal land colonization
  • fires
  • hunting
  • gold mining
  • forest clearing.

“The best thing you could do for the Amazon,” said the respected Brazilian scientist Eneas Salati, “is to bomb all the roads.”

In Brazilian Amazonia, my colleagues and I have done studies showing that around 95 percent of all deforestation occurs within 50 kilometers of highways or roads. Human-lit fires increase dramatically near Amazonian roads, even within many protected areas. In Suriname, most illegal gold mining occurs near roads.

Paved highways are especially dangerous to forests. They provide year-round access to forest resources and reduce transportation costs, causing larger-scale impacts on forests and wildlife than do unpaved roads, which tend to become impassable in the wet season. The proposed routes of new highways often attract swarms of land speculators who rush in to buy up cheap forest land, which they then sell to the highest bidder.
Perhaps the most damaging aspect of paved highways is that they spawn networks of secondary roads, which spread further environmental destruction. For instance, the 2,000-kilometer-long Belem-Brasília highway, completed in the early 1970s, has today evolved into a spider web of secondary roads and a 400-kilometer-wide swath of forest destruction across the eastern Brazilian Amazon.

Can the environmental impacts of tropical roads be minimized? In theory, the answer is “Yes, partially.”

  • Frequent culverts can reduce the effects on streams and hydrology.
  • Impacts on animal movements can be reduced by keeping road clearings narrow enough so that canopy cover is maintained overhead, providing a way for arboreal species to cross.
  • In high-priority areas rope-bridges are being used to facilitate road crossings of monkeys and possums.
  • For small ground-dwelling species, culverts beneath roads can allow road-crossing movements
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