Deforestation spreading out from Dar es Salaam

The study, by an international team of scientists, supports an economic model that predicted the sequential removal of products from high to low value radiating out from major demand centres. 

The authors conclude that tropical forest degradation can be modeled and predicted, an important finding in shaping policies such as the Reducing Emissions from Deforestation and forest Degradation (REDD) negotiations taking place within the United Nations Framework Convention on Climate Change. 

Researchers visited forests at varying distances up to 210 km 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 each year out from the city. For example, charcoal extraction extended 50 km from Dar es Salaam in 1991, but in 2005 it was found up to 170 km from the city. 

Similarly, the areas where mid-value timber was logged ranged from 50–170 km out in 1991, but had moved a further 110 km by 2005 and the high value timber logging area had moved out beyond 220 km, at a rate of around 9 km per year. 

This is despite most logging and charcoal production in Tanzania being illegal and the cause of major financial losses. 

Forestry, governance and national development: Lessons learned from a logging boom in southern Tanzania, a TRAFFIC study published in 2007, estimated that in 2005 some 96 percent of harvested timber was exported illegally, losing the Tanzanian government an estimated USD58 million in revenue. 

“Government regulations do not currently prevent forest degradation, but they can successfully prevent complete deforestation,” said Jumapili Chenga, a TRAFFIC Programme Officer based in Tanzania. 

Kisiju, the only forest in the study area without any legal reserve status, was the only one completely cleared by 2005. 

Urban migration and rising demand for timber, particularly in China, are amongst the major reasons for the rapid spread of degradation waves.

“Such studies provide valuable information for bilateral dialogue between Tanzania and China as one of the main consumers of timber from the region,” said Chen Hin Keong, Global Forest Trade Programme Leader of TRAFFIC.

The paper’s authors recommend that policy interventions should be carefully tailored to the type of degradation activity, and care should be taken to provide alternative income sources and prevent increasing levels of poverty in Tanzania.

Further research is also needed to understand the impact of international and domestic demands on timber from Tanzania and the region due to rising populations and affluence.

“This study highlights the value of strong interdisciplinary research coupled with large-scale and long-term datasets,” said Dr Simon Lewis of Leeds University, a co-author of the paper. 

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

The full study Predictable waves of sequential forest degradation and biodiversity loss spreading from an African city by Antje Ahrendsa, Neil D. Burgess, Simon A. H. Milledge, Mark T. Bullingg, Brendan Fisherh, James C. R. Smarti, G. Philip Clarkej, Boniface E. Mhorok and Simon L. Lewis is published in the Proceedings of the National Academy of Sciences.