Scientists show waves of deforestation across region

A new study documents waves of forest degradation advancing like ripples in a pond 120km across East Africa in just 14 years.

Scientists from 12 organisations in Europe, Africa and the US demonstrated that forest exploitation begins with the removal of the most valuable products first, such as 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.

Economic model

The study, published in Proceedings of the National Academy of Sciences recently, tested an economic model that predicts the sequential removal of products from high to low value. Researchers visited forests at varying distances up to 220km from Tanzania’s largest city, Dar es Salaam, in 1991 and again in 2005, tracking the trees that remained.

They found that waves of degradation moved, on average, 10km a year out from the city. For example, charcoal extraction extended 50km from Dar es Salaam in 1991, but in 2005 it was found up to 170km from the city.

"The degradation waves have spread rapidly. Urban migration and rising demand for timber, particularly in China, are amongst the major reasons for this," said lead author Dr Antje Ahrends of the Royal Botanic Garden, Edinburgh. "By the end of the study, high value timber logging production took place over 200km from the city. This is very likely to be unsustainable."

The ability to predict forest degradation is essential if new market-based incentive programmes to protect forests are to be successful.

Reducing emissions

Such plans, 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," said study co-author Professor Neil Burgess of WWF and the University of Copenhagen. "Redd could rapidly cut carbon dioxide emissions from deforestation and degradation, which are currently responsible for 15 per cent of total emissions from human activity".

Most logging in Tanzania is illegal and causes major financial losses. A trade survey by a wildlife trade-monitoring network, estimated that in 2005 some 96 per cent of harvested timber was exported illegally, losing the Tanzanian government an estimated $58 million (Sh4.6 billion) of revenue. Charcoal burning is also mostly illegal, but carried out by local people who have no alternative means of income. Poor people in towns use charcoal to cook their food.

The authors recommend that policy interventions should be carefully tailored to the type of degradation activity.