Nadine Laporte, WHRC

THE world's forests are disappearing and Africa's are vanishing faster than those of any other continent. A report by the UN Food and Agriculture Organisation published in March reckoned that between 2000 and 2005 the continent with about 16% of the world's forests accounted for 55% of the total losses. But reliable numbers are hard to come by. That is why a set of data pieced together by Nadine Laporte and her colleagues, of Woods Hole Research Centre, in Falmouth, Massachusetts, is so applauded by conservationists and local governments alike.

Dr Laporte and her colleagues have put together information from more than 300 satellite images. The conclusions they draw were published in Science on Friday June 8th. These data track the progression of logging roads in a region covering 4m square kilometres of central Africa between 1976 and 2003. No one has attempted anything so ambitious before in Africa. And those who have applied similar techniques to Latin America's forests have tended to use complicated algorithms to measure vegetation changes. These run in sophisticated computers. Dr Laporte wanted something simple, robust and cheap that anyone could use.

On mapping the results an awkward patchwork of polygons emerges. The logging roads branch within the forest, in places just 1km apart. They are most dense in the Cameroon and Equatorial Guinea, where selective loggers have moved through most of the countries' forest at least once, creaming off the most valuable species. It is Congo-Brazzaville, though, that has suffered the most rapid road construction of late. The rate of road-building has roughly quadrupled over 30 years.

Most forestry experts, however, are watching the Democratic Republic of Congo. Although still troubled by sporadic outburst of violence after a long civil war the country is now as peaceful as it has been for some time. The civil war was widely portrayed as having been financed by rampant timber harvest. In fact annual timber production fell to about a sixth of its level in 1960. Two-thirds of the forest that still remains in the region is in Congo. Now that the protective cover of war has lifted it is here that loggers are likely to seek new bounty and other foes of the forest will move in. Dr Laporte's methods can help to track their progress

In central Africa selective logging—the removal of a few choice specimens—rather than complete deforestation is the usual method of earning cash from the trees. But Dr Laporte fears that Congo has a high enough population density to drive deforestation in the name of bagging more land for agriculture. As logging roads grant better access to the forest she expects people to move in, and eventually to do so in droves.

At least the opportunity to exploit Congo's forests is handed out fairly, on paper anyway. In 2002, the World Bank pushed through reforms that threw out speculative concessions. These were generally gifted to a privileged and corrupt few that had enough influence or cash to get them. These days companies are supposed to implement management plans and half of tax revenues are supposed to find their way to local communities. In reality, few can be bothered with the former, nor do companies pay the proper rent on the land. And almost all of what is paid remains in the central government's coffers.

Still, the policies in place today are a great improvement on the World Bank's ideas of old. During structural adjustments of the early 1990s, it halved the value of the CFA franc, the currency used in much of the region. That halved the costs for foreign logging companies operating in central Africa, promoting wanton degradation by operators who promptly left at the first sign of regulation. Dr Laporte has yet to look for this pattern in the new data, but she has found it in less comprehensive pools of numbers. The study usefully illuminates the effects of both illegal and legal logging over time. Depressing reports of how quickly the world's forests are disappearing are commonplace. Ones that may give a clue to better policy are rarer, and welcome.