U. LEEDS (UK)—Waves of deforestation like ripples in a pond have advanced 120 kilometers across East Africa in the past 14 years, according to new research.

Forest exploitation started with the removal of the most valuable products first, including timber for export, followed by the extraction of less valuable products such as low-value timber and charcoal in strict sequence.

This “logging down the profit margin” in tropical forests follows the same pattern of removal seen for fish in unmanaged oceans.

The international study, conducted by researchers at the University of Leeds and other organizations in Europe, Africa, and the U.S., tested an economic model that predicts the sequential removal of products from high-to-low value and included visits to forests at varying distances up to 220 kilometers from Tanzania’s largest city, Dar es Salaam, in 1991 and again in 2005, tracking the trees that remained.

Details appear in the Proceedings of the National Academy of Sciences.

Forest degradation moved, on average, 9 kilometers a year out from the city.

For example, charcoal extraction extended 50 kilometers from Dar es Salaam in 1991, but in 2005 it was found up to 170 kilometers from the city.

“The degradation waves have spread rapidly,” says Antje Ahrends of the Royal Botanic Garden Edinburgh and lead author of the paper.

“Urban migration and rising demand for timber, particularly in China, are amongst the major reasons for this. By the end of the study, high value timber logging production took place over 200 kilometers from the city. This is very likely to be unsustainable.”

The ability to predict forest degradation is necessary for new plans to protect forests using payments for ecosystem services, the study says.

Such schemes, like the proposed “Reducing Emissions from Deforestation and forest Degradation” (REDD) being negotiated under the UN Framework Convention on Climate Change, may channel billions of dollars into conservation and poverty alleviation if these instruments can be shown to verifiably reduce carbon dioxide emissions from deforestation and degradation.

“REDD would create incentives for developing countries to conserve tropical forests and to adopt low-emission strategies for sustainable development,” says study coauthor Neil Burgess, professor at the University of Copenhagen.

“REDD could rapidly cut carbon dioxide emissions from deforestation and degradation, which are currently responsible for 15 percent of total emissions from human activity.”

Much logging in Tanzania is illegal resulting in major financial losses. A trade survey by Traffic, the wildlife trade monitoring network, estimated that in 2005 some 96 percent of harvested timber was exported illegally, losing the Tanzanian government an estimated US $58 million of revenue.

Charcoal burning is similarly mostly illegal, but carried out by local people who have no alternative means of income, and is used in towns by poor people to cook their food.

Policy interventions therefore need careful tailoring to the type of degradation activity, and care needs to be taken to provide alternative income sources and prevent increasing levels of poverty in an already poor country.

“This study highlights the value of strong interdisciplinary research coupled with large-scale and long-term datasets,” concludes coauthor Simon Lewis of the University of Leeds.

“Both are needed if scientists are to provide the knowledge to assist managing the natural world sustainably whilst benefiting local people.”

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