The change in vegetation from open savanna, or mixed grass and woodland, to scrubland. Occurring also in Australia and South Africa, bush encroachment affects the agricultural productivity and biodiversity of 10–20 million ha of South Africa (Ward (2005) Afr. J. Range & Forage Sci. 22, 2). Its probable causes are: increased grazing levels; reduced use of burning to create grassland; changes in rainfall regimes; and the interactions between these factors. However, writing in 2005, Ward (op. cit.) writes, ‘many people believe that we understand the causes of bush encroachment. We do not.’