In the Republic of the Congo, the total length of logging roads is two times that of the national roads, LaPorte said.
The highest logging-road densities were found in the coastal nations of Cameroon, Equatorial Guinea, and Gabon.
Historically most of the logging in Africa is for export, LaPorte said, so the practice is often done close to the coastline and the ports.
Logging in Cameroon has extended inland in recent decades after the earlier harvesting of coastal forest, she added.
Most of the logging in central Africa focuses on high-value trees like mahogany that are exported for use in furniture in Europe and Asia.
In contrast, most of the wood in Brazil's Amazon forest is used domestically.
A New Frontier
Documenting the growth of logging roads enables scientists to understand the extent to which the environment is being changed.
The study found that the area undergoing the most rapid change was in northern Republic of the Congo, where the rate of road construction has grown about four times over the three decades.
But LaPorte warns that a "new frontier" of logging expansion may also be opened in the Democratic Republic of the Congo, known as the DRC, as that country achieves greater political stability and attracts interest from foreign logging companies.
(See related: "Endangered Gorillas 'Held Hostage' by Rebels in Africa Park" [May 23, 2007].)
The DRC, which is about the size of western Europe, contains almost two-thirds of the region's remaining forests.
The study, which will appear tomorrow in the journal Science, shows that the DRC has the lowest logging-road density—at least that has been measured thus far. But the country's population density is three times greater than that of its Republic of the Congo neighbor.
"We should be very concerned about logging in areas where we have high population density," LaPorte said.
"If you have lots of people and you do logging at the same time, what happens is you're going to have deforestation," she said, "and you will go from a forest ecosystem to an agricultural system."
Robert Nasi of the Center for International Forestry Research in Montpellier, France, said the paper is a "useful resume" about the expansion of roads in Central Africa. But, he said, it also seems "short of many approximations or [has] missing information."
Nasi added that roads drive development in places like central Africa.
"With roads come all the blessings—access to medication, access to markets for your products—and all the curses of development ... [such as] increased harvesting of natural resources and agricultural encroachment."
The shrinking of Africa's tropical forests could also have global climate change implications, researchers warn.
Forests store up to half of the Earth's terrestrial carbon stock, or 45 times the amount of carbon emitted every year through the burning of fossil fuels and the production of cement.
The DRC is estimated to hold 8 percent of the Earth's carbon, which is stored in living forests, according to a recent report by the environmental group Greenpeace.
The DRC's intact rain forests "act as a break on further acceleration of climate change by serving as a vast carbon reserve," said Phil Aikman, international forest campaigner for Greenpeace in London.
When forests are cleared for agriculture or other use, up to half of the carbon they held may be emitted into the atmosphere, the report said.
The Greenpeace report authors write: "Given the pivotal role of the forest in terms of climate change, it is deeply worrying that to date no concrete steps have been taken to stop degradation of the DRC's forests."
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