From: Andy Soos, ENN
Published December 12, 2011 11:46 AM

Dead Trees in the Sahel

The Sahel is the ecoclimatic and biogeographic zone of transition between the Sahara desert in the North and the Sudanian Savannas in the south. It stretches from west to east across the North African continent between the Atlantic Ocean and the Red Sea. It is a sort of coast line for the arid Sahara desert to the north. There is an on-going long term drought in this region. A new study, which is scheduled for publication Friday, Dec. 16, in the Journal of Arid Environments, was based upon climate change records, aerial photos dating back to 1954, recent satellite images and old-fashioned footwork that included counting and measuring over 1,500 trees in the field. The researchers focused on six countries in the Sahel, from Senegal in West Africa to Chad in Central Africa, at sites where the average temperature warmed up by 0.8 degrees Celsius and rainfall fell as much as 48 percent. They found that one in six trees died between 1954 and 2002. In addition, one in five tree species disappeared locally, and indigenous fruit and timber trees that require more moisture took the biggest hit. Hotter, drier conditions dominated population and soil factors in explaining tree mortality, the authors found. Their results indicate that climate change is shifting vegetation zones south toward moister areas.


"In the western U.S., climate change is leading to tree mortality by increasing the vulnerability of trees to bark beetles," said Gonzalez, who is now the climate change scientist for the National Park Service. "In the Sahel, drying out of the soil directly kills trees. Tree dieback is occurring at the biome level. It's not just one species that is dying; whole groups of species are dying out."

The new findings put solid numbers behind the anecdotal observation of the decline of tree species in the Sahel.

"People in the Sahel depend upon trees for their survival," said Gonzalez. "Trees provide people with food, firewood, building materials and medicine. We in the U.S. and other industrialized nations have it in our power, with current technologies and practices, to avert more drastic impacts around the world by reducing our greenhouse gas emissions. Our local actions can have global consequences."

It was once theorized that the drought in the Sahel primarily was caused by humans over-using natural resources in the region through overgrazing, deforestation and poor land management. In the late 1990s, climate model studies suggested that large-scale climate changes were also triggers for the drought.

The Sahel’s farmers are largely cleared of blame for the 20th century’s Sahel droughts. The Sahel region’s droughts in the 1970s and 1980s were more caused by the recent warming of the Indian Ocean, and not by over farming causing environmental degradation as previously assumed, according to a new joint Scidev/UN study. With both a 3.5 C. rise in the Niger's temperature over the last decade and with irrigated land accounting for only 0.1% of the Niger's inhabitable land, made a regular famine crisis inevitable in most years.

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Photo:  Patrick Gonzalez

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