Changes in tropical forests are known to be driven by demand in foreign markets. At the United Nations Earth Summit in Rio de Janeiro in 1992, many attendees concluded that Sustainable Forest Management (SFM) was key to achieving the social and economic benefits that can result from forestry, while protecting the forests themselves. Under SFM, logging should take place selectively and rotationally throughout a forest, to prevent the type of deforestation associated with intensive logging.

Jodi Brandt and colleagues at the University of Michigan wanted to find out how different investment sources affect tropical forests. They used two datasets for the Republic of Congo to analyse patterns of deforestation and compliance with SFM during the 10 years since the country passed its SFM forestry law in 2000.

One dataset contained information on sources of investment and forestry management practices for logging companies, while the other showed changes in forest cover from satellite imagery. The researchers first examined whether deforestation rates differed between logging companies based in Asia, Europe and the Republic of Congo, and then assessed how many of those companies had complied with the Republic of Congo's forestry law.

Brandt and colleagues found that European companies were behind more logging than those from Asia or the Republic of Congo. However, they also discovered that European companies were much more compliant with the Republic of Congo's forestry law.

"We were surprized by our finding that there may be an association between the 'sustainable' policy and higher deforestation," said Brandt. "I think an important message here is that human activities often have unintended consequences, and that we need to regularly assess, in an unbiased manner, the impacts of our activities, policies, etc."

These "unintended consequences" might be a growing demand for legal and certified timber. But Brandt said that logging carried out under an SFM policy should not lead to deforestation in the same way that intensive logging would. Instead, she said that it could lead to indirect deforestation – a result of the infrastructure necessary to run a logging site. "For example, networks of logging roads are needed to harvest and transport the timber," she explained. "Logging requires workers, and thus settlements may expand as the logging industry grows." Brandt added that satellite images confirmed the main cause of deforestation to be the construction of logging roads and settlement expansion.

The big question now, believes Brandt, is whether current policies are indeed behind deforestation. But this will require more investigation in the Congo and other nations, using a variety of measures of environmental and social outcome. "Our overarching hope is that this paper stimulates a conversation and more research [about] the sustainability of industrial logging, not just in the Congo but also in other tropical forests around the globe," she said.

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