Modelling loss of resilience in agroecosystems: Rangelands in Botswana

Economists have recently begun to consider the questions raised by the ecol ogical concept of resilience - a measure of the degree to which a system ca n be perturbed before it switches from one stability domain to another. At a theoretical level, it has been argued that the loss of resilience in an e cological-economic system involves a change in its long-run productive pote ntial, but no consideration has yet been given to the empirical investigati on of this. This paper discusses an econometric approach to the problem, us ing the example of semi-arid rangelands. The long-run productive potential of the system is regarded as an unobserved state variable, change in which is irreversible or at least only slowly reversible. It is estimated by appl ying the extended (nonlinear) Kalman filter. The paper illustrates the appr oach using data from Botswana for the period 1965-1993. The maximum likelih ood estimates of the parameters associated with the loss of resilience mech anism are non-zero. They indicate a small loss of resilience event at the e nd of the long drought in the 1980s. However, these parameters are very imp recisely estimated and are therefore statistically insignificant. We find t hat the sensitivity of the system to exogenous shocks varies with fluctuati ons in both economic and non-economic parameters. Contrary to what is usual ly thought to be the case, the sensitivity of the system to exogenous shock s is only weakly affected by variations in offtake prices, but is very stro ngly affected by variations in the cost of herd maintenance. This suggests that offtake prices may be a weak tool for controlling the size of cattle s tocks and preventing a loss of resilience. On the other hand, taxes on catt le stocks or grazing fees may be very effective.