An ecological economic simulation model of a non-selective grazing system in the Nama Karoo, South Africa

The Nama Karoo region of South Africa is characterized by low (similar to 200 mm) and variable annual rainfall, which results in grass and shrub biomass production, which is low and highly variable in space and time. These characteristics of Nama Karoo rangelands challenge the ability of the region's livestock farmers to make a sustainable living. In this paper we model a farming system, which attempts to create an environmental buffer of forage reserves by restricting access of livestock within numerous small camps. This is achieved by using a multi-camp infrastructure, which forces the livestock to remove non-selectively most of the available forage within a camp. Non-selective grazing in small camps allows for long rest periods of each camp, and these rest periods build up forage reserves for the dry years, A computer model of a 7000 ha farm was used to simulate rainfall and above-ground plant biomass accumulation, and to test the economic merits of investing large sums of money in multi-camp infrastructure. The model shows that 60 camps or more allows time for forage reserves to build up, but that more than 150 camps becomes too costly. Our simulations suggest that given 250 mm yr(-1) rainfall and the agriculturally recommended stocking rate, camp numbers of 60-80 provide higher profits than other camp numbers investigated. However, with higher rainfall and more animals, increasing camp numbers up to 150 is economically viable and more ecologically desirable. At low rainfall (< 200 mm yr(-1)) production is too low to warrant investment in multi-camp infrastructure. (C) 2002 Elsevier Science B.V. All rights reserved.