While the role of fire and of other herbivores such as the giraffe in the woodland-savanna transition have been described by several observers, Herbert Prins and his associates emphasized the role of many other herbivores, including impala and buffalo, in this process. The seedlings of trees such as Acacia establish only infrequently; these rare windows of opportunity arise when populations of browsers such as impala are reduced through disease epidemics. Competition for grass from superior grazing ungulates such as buffalo may force elephants to overexploit woody vegetation. A complex interaction of the competition-facilitation process within the browser-grazer community, with fire playing the role of a "superherbivore," determines the transitions between woodland and grassland in semiarid Africa.
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