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Within South Africa, grassland and savanna biomes constitute 61% of the total area. These ecosystems form the foundation of two economically important industries, wildlife conservation and livestock production, which in 1989 were valued at one billion US dollars. The sustainable use of rangelands relies on the utilization of areas without degradation due to either over-grazing or bush encroachment. Models can aid both wildlife managers and livestock owners in establishing a range of carrying capacities under the variable climate of southern Africa. Two different versions of the ACRU-Veld model were designed and constructed as an add-on module to the ACRU agro-hydrological model to simulate southern African rangeland processes. The ACRU-Veld module simulates grass, tree, herbivore and fire processes in grassland and savanna ecosystems. An original FORTRAN version was developed and tested with the ACRU 300 series model in savanna areas in the Kruger National Park, South Africa. The module was tested against recorded grass biomass and wildlife data (1989-1995) from the Northern Plains Region of the Kruger National Park (KNP), South Africa. This testing period was important to model performance as included the 1991-1992 drought, the worst drought ever recorded in the Kruger Park. From the model testing phase, several important points were noted for model improvement. Subsequently, an updated, object-oriented version of ACRU-Veld was designed in the Unified Modeling Language (UML) and implemented in the Java programming language as an extension to the ACRU2000 modeling system. Many of the problems encountered with the original version were re-formulated utilizing the new spatial structure of the ACRU2000 model. At this point the new ACRU-Veld model is working and is being re-tested with the KNP environmental data.