From the perspective of adaptive response, desertification differs from drought not only in its time perspective (a long-run process as opposed to a short-run event), but also in the extent to which it can be considered as exogenous to the human system. The question of adaptation becomes subsumed in the larger one of causation. To what extent are the communities that inhabit areas prone to desertification themselves responsible for the degradation that threatens their livelihood?

It was argued in chapter 1 that a simplified definition of desertification as ‘the degradation of ecosystems in arid or semi-arid regions’ has theoretical and practical advantages. The standpoint of the present chapter is therefore ecological. Its objective is to review field evidence for ecological degradation, in relation to land use, in four of the subsystems proposed in table 1.1: the woodland, grassland, soil and morphodynamic subsystems (the hydrological subsystem was discussed in chapter 6). The evidence is ambiguous if not, in places, contradictory. Such an outcome should be expected in a complex, multivariate problem involving most aspects of the relationship between a society and its environment. Nevertheless it is only by accumulating judgements based on empirical studies that environmentalist slogans can be replaced by more balanced evaluations. This case study gives ground for questioning conventional wisdom that emphasises the role of ‘over-exploitation’ at the expense of that of meteorological drought.