1. The decline of African livestock systems due to the overgrazing of common range resources has been predicted for over 50 years. Yet instead of collapse, livestock herds in many areas seem to have exhibited sizeable increases through time and to have sustained increasing human populations. We need to consider why, how, and what this implies for the future. What is really the pattern of growth in the aggregate livestock population since arrival of the Europeans (the period for which at least approximate data are available)? What factors have affected the rate of growth and structure of livestock herds? To what extent have expanding livestock populations been confined within fixed areas, or faced expanding boundaries? And what is the evidence for declining resource productivity as a consequence of overstocking? The breadth of these unanswered questions suggests that substantial ignorance still surrounds African livestock development in the modern period. 1
2. This paper looks at African livestock herds in Zimbabwe over the period 1890-1980. The focus is on the livestock system in the tribal areas where, under communal land use, there has been long-term concern with environmental deterioration. Zimbabwe was chosen because it is one of the few African countries for which reasonably accurate historical data are available regarding African (common range) as opposed to European (closed range) herd development.
3. Overgrazing and range degradation, if occurring, should be revealed over time in either a systematic decline in total and per animal livestock output, over time, or in large oscillations in their magnitudes due to a sequence of rising grazing pressure, drought, forage reduction, herd reduction, forage recovery, and herd recovery (Jarvis, 1984). Surprisingly, there is little or no evidence of either in the data analyzed. The Zimbabwe data show quite remarkable, nearly continuous, increases in livestock herds through time. Herd numbers show no sign of encountering a ceiling - their rate of increase has remained high during recent decades. There is also evidence, although limited, that herd productivity has been maintained, and that drought has had relatively little impact on herd numbers.
4. Does this mean that overgrazing is not a problem? That is too strong a conclusion. Changes in the aggregative data are insufficient to provide definitive answers regarding overgrazing and range degradation (Jarvis, 1984); for this, information regarding changes in specific inputs and outputs in tribal livestock systems are required, and such information is not currently available. Nonetheless, the aggregative data - which are the only evidence available - show no overgrazing. This is puzzling.
5. There is much theoretical and empirical evidence to show that an absence of control over a scarce resource will resort in its overutilization, implying economic loss. It appears that, both historically and currently, African livestock in Zimbabwe have been maintained mainly on common range. If then there is no evidence of overgrazing in Zimbabwe, four, not necessarily mutually exclusive, explanations are possible: either 1) specific rules regulating access to common range exist and are reasonably effective, so that the stocking rate is not greatly in excess of the economically optimal; or 2) livestock density was initially far below the optimal level so that even with the growth of herds the critical point has not yet been reached; or 3) the carrying capacity of the Zimbabwe range has been rising rapidly in response to output increasing investments; or 4) the data on livestock output and livestock productivity are deceptive in failing to reflect the declines which have taken place in each of these variables in response to rising herd numbers. These explanations have quite different roots and quite different implications in terms of future livestock sector development and appropriate government policy. A cautionary as well as an encouraging note is therefore merited, given the urgency felt throughout most of sub-Saharan Africa to increase food production.
