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The ingression of woody plants into savannas, known as bush or shrub encroachment, has become a global concern. Fire has been acknowledged as a key factor in managing woody vegetation in savannas. This study assessed the role of fire in determining the total density, structure and composition of woody vegetation in Ithala Game Reserve, northern KwaZulu-Natal, South Africa. We surveyed woody vegetation in comparable areas with different fire frequencies. In Combretum-dominated woodlands, there was no significant effect of fire frequency on the total density of woody individuals. In old field grasslands, the density of woody plants was greater in areas burnt annually and in areas burnt once every 10 years, compared to areas burnt once every 2–4 years. In these grasslands, areas burnt annually were dominated by woody plants <2 m in height. Herbivore and fire interactions may explain these results. Multivariate analyses also indicated a significant effect of fire frequency on woody vegetation composition. To control dominant encroaching trees such as Dichrostachys cinerea and Acacia karroo (Vachellia karroo), and the development of macrophyllous thickets, an intermediate fire frequency is required (one burn every 2–4 years).