The Greening of Sahel: Passive recovery or active adaptation?

The drought years in the Sahel in the early 1970’s that resulted in a large-scale famine gave rise to scientific and policy discussions about land degradation and desertification. A popular belief was that the limited resource base in the Sahel, with vulnerable soils and highly variable and scarce rainfall could not sustain the growing population. The droughts was seen as a stress to a system which was already struggling with a rapidly decreasing resource base (e.g. deforestation of woodlands for agricultural expansion, shortening of fallow times, and soil nutrient depletion) and bad land management practices leading to increased poverty and out-migration.

Sahel Greening.  Overall trends in vegetation greenness throughout the period 1982–2003 based on monthly AVHRR NDVI time series. Percentages express changes in average NDVI between 1982 and 2003. From Hermann et al 2005

New analysis of satellite data, by among others Olsson et al., illustrating a greening trend in the Sahel since 1983 thus comes as a surprise for many people. It has also triggered a scientific discussion of whether this greening is merely a recovery of vegetation due to increasing rainfall, or if this trend at least partially can be explained by widespread changes in land management by farmers in the region. Hutchins et al., in the introduction to a recent special issue of Journal of Arid Environments, suggests that there is increasing evidence that farmers have adapted to the changes during the droughts and made a transition from degrading land use trajectories to more sustainable and productive production systems, suggesting that the recovery in many places actually is an active adaptation by the farmers in the region.

Herrman et al. illustrate in a new paper in Global Environmental Change that although the greening trend at a coarse scale is well correlated with an overall increase in precipitation since the early 1980’s the trend is not uniform, suggesting that other factors have contributed. One of the regions in their analysis where greening is larger than what can be explained by rainfall is the Central Plateau of Burkina Faso. This is a region where large-scale experimentation (and investment) in soil and water conservation techniques (SWC) for small-scale farmers has taken place. Reij et al. shows the multiple impacts these techniques have had on the livelihoods of people in the region (including increased yields, reduced agricultural expansion, and increased tree cover).

Mortimore and Turner reviews the evidence relating to deforestation, woodland and rangeland degradation to show that in certain areas of the Sahel, a transition to intensified land use, although initially involving a loss of woodland, has led to the planting or protection of useful trees on farms (so called farmed parklands) and maintained biomass levels.

Finally, Herrman and Hutchinsson discuss the desertification debate, which to a large part stared as a result of the interest in the Sahel drought in the late 1970’s. They consider four contexts that frame the debate and consider what impact each has had:

  • (1) changes in our understanding of climate variability;
  • (2) changes in our understanding of vegetation responses to perturbation;
  • (3) changes in our understanding of social processes, including house-hold responses to economic perturbation; and
  • (4) changes in our understanding of desertification as a political process or artifact.

They conclude by stressing a need for these broad areas to occur in parallel rather than in series:

Discussion of desertification from the social science perspective still tends to base its understanding of the dryland environment on outdated ecological models; ecologically motivated assessments of desertification, on the other hand, often fail to incorporate new insights from the social sciences; and, finally, because they may be driven by perverse or parochial interests, policies that affect people on the ground may be formulated largely independent of science that is current and thus may serve to degrade rather than enhance the lives of people most affected.

3 thoughts on “The Greening of Sahel: Passive recovery or active adaptation?”

  1. It is also interesting that the Senegal river flow has been increasing. You can read an interview with Dr. Pierre Hubert, Senior researcher at the National School of Mining Engineering in Paris and Secretary-general of the International Association of Hydrological Sciences (AISH) at

    He is comments on how this change is linked to the outbreak of locusts in the region.

  2. LG;
    Glad to see the PNAS has come down with a falsifiable prediction. More of these, so the evidence can be assembled that the deeply compromi$ed PNAS and its models can be shown to not be worth the powder to blow them to smithereenies.

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