Soil erosion in the West African Sahel: a review and an application of a “local political ecology” approach in South West Niger

Abstract

A review of soil erosion research in the West African Sahel finds that there are insufficient data on which to base policy. This is largely because of the difficulties of measuring erosion and the other components of “soil life”, and because of the highly spatially and temporarily variable natural and social environment of the Sahel. However, a “local political ecology” of soil erosion and new methodologies offer some hope of overcoming these problems. Nonetheless, a major knowledge gap will remain, about how rates of erosion are accommodated and appraised within very variable social and economic conditions. An example from recent field work in Niger shows that erosion is correlated with factors such as male migration, suggesting, in this case, that households with access to non-farm income adopt a risk-avoidance strategy in which soil erosion is accelerated incidentally. It is concluded that there needs to be more research into the relations between erosion and socio-economic factors, and clearer thinking about the meaning of sustainability as it refers to soil erosion in the Sahel.

Introduction

This paper assesses soil erosion research in the West African Sahel at a number of levels: through an historical review of research and by arguing for a local political ecology of soil erosion, illustrated by a case study from southwestern Niger.

Soil erosion in the Sahel has been studied since the 1930s. The history of intervention to conserve soil is almost as long, if not longer, for the colonial regimes pre-empted research with some large, technocratic conservation programmes. From about the early 1980s these efforts were deemed to have failed, and new programmes emphasised indigenous husbandry, built upon local knowledge, and sought participation by farmers. International policymaking, particularly the Desertification Convention in the 1990s, has institutionalised these tendencies. Yet, many authorities believe that participatory development has not been fully successful in tackling erosion (Scoones et al., 1996; Scoones and Toulmin, 1999).

We begin the paper by a review of research, which is in two parts. The first is of research into biophysical processes. We confine this to soil erosion, or more precisely, to the gross sediment budget and its effects on yield (which act mainly through the loss of available moisture (e.g. Mota et al., 1995)). The review avoids two closely related questions, which would open the debate too far for one paper. The first is soil conservation, which has a very large literature, and some recent reviews (Stocking, 1992; Trench and Batterbury, 1999; Mazzucato and Neimeijer, 2000). The second is the question of soil nutrient flux, which is reviewed by Breman et al. elsewhere in this collection. This section of our review reveals very large uncertainties, as have similar reviews for other parts of the world (e.g. Thompson et al., 1986; Ives and Messerli, 1989).

The second part of the review is of the social and economic associations of erosion. It builds on the work of Tiffen et al. (1994), Mortimore (1998), and Mortimore and Adams in this collection of papers, among others. These writers have found little evidence for the belief that erosion is necessarily linked to high levels of population or to poverty, claims which still make frequent appearances in the literature (e.g. Baidu-Forson and Napier, 1998; Higgins et al., 1982; Mainguet, 1998; Ramaswamy and Sanders, 1992). More important, the critics maintain that because the linkages between these variables are unlikely to be simple, they will not be demonstrated without much more solid evidence than yet exists.

Last, we suggest present priorities for research, based on what we call a “local political ecology” approach. Our suggestions are based on a dictum adapted from Lavigne Delville (1997): “soil degradation [like soil fertility to him] can only be understood in its social context”. The Sahelian social context is so variable, as Raynaut (in this collection) emphasises, both in space and time, that policies to manage erosion must have other kinds of information than mere data on its rates, some gross estimates of economic impact, or generalised notions of natural or social causation. We illustrate this argument from our own research in Niger.