This paper draws attention to some of the problems that arise in understanding the cost and benefit flows in pastoralist systems. These difficulties arise as a result not just of the ecological variability but also as a result of social and political complexities common to the regional contexts of many pastoralist systems. With many such systems, rangelands straddle international borders and are continuous with conservation estate. Livestock management and marketing must be seen in the context of their interplay with conservation values and their involvement with cross-border factors whether economic, political or military. This complicates understanding of the economics of such systems, and forces a different weighting of their costs and benefits. Alongside ways of evaluating potential environmental problems arising from pastoralist use, we need methods to evaluate both the benefits of coexistence of pastoralist land use with highly- rated conservation values, and the economic implications of the access to the free services that use of conservation-estate grazing and water may represent. In addressing the problems of livestock marketing in a fluctuating system, we need to take note of the economic opportunities as well as the constraints. Many if not most pastoralist systems have the possibility of unofficial cross-border trade, whose direction will depend on relative prices. Security issues influence production and marketing and pastoralists' own evaluation of costs and benefits. It is not just the ecological environment that fluctuates in an unpredictable way. The shifting economic and political context creates these less visible opportunities and constraints that make economic analysis problematic and interventions often ill-judged.

The present paper is based on a participatory survey (Homewood 1991) carried out in order to establish baseline information on a little known livestock production system and its role in local ecology and economy. This paper does three things. First it outlines the history of land use in El Kala, the present livestock system and official views on its performance. The paper then sets out a method of successive approximation which works on trade and census figures of dubious validity to derive a better estimate of the real scale and importance of a largely invisible pastoralist economy, with major implications for range and livestock management. This re-evaluation of census and trade figures supports the view that, contrary to official perceptions, pastoralism in El Kala is an economically robust and ecologically sustainable form of land use. Finally, the discussion ties the El Kala case study into a broader network of economic and political complexities. Many pastoralist systems operate within a nexus of constraints that simple technical fixes cannot overcome. In particular, many pastoralist livestock production systems may be barely viable in the broader context of other political interests, despite the fact that they are internally vigorous enterprises continuing successfully to adapt to the opportunities and constraints of present-day African economies while minimising environmental costs. Analyses of ecological and economic sustainability, and technical interventions, may play into the hands of other interests seeking to expropriate the underlying resource.