Fire behaviour a key factor in the fire ecology of African grasslands and savannas.

The effect of fire on natural ecosystems involves the response of living organisms to the release of heat energy through the combustion of plant material. The manner in which and the factors that influence the release of heat energy, involves the study of fire behaviour. In Africa there is a serious deficiency of knowledge concerning the behaviour of fires and this is particularly applicable to the savanna and grassland areas of the continent. Virtually no attempt has been made to quantify the dynamics of the release of heat energy during a fire and the subsequent response of plants to it. The determination of such relationships helps explain many of the apparently inexplicable effects of fire that are often cited in the literature. Research on the effects of fire has been conducted throughout the grassland and savanna areas of Africa, particularly in southern Africa, since the early period of the 20th century. An interesting feature about these early investigations and subsequent research up until 1971, was that it focused on the effects of season and frequency of burning on the forage production potential of the grass sward and the ratio of bush to grass in savanna areas However, in 1971 a conference was convened in the United States of America in Florida, by the Tall Timbers Research Station on the theme of "Fire in Africa". The major benefit that accrued from this conference was the realization that in Africa the study of fire behaviour and its effects on the ecosystem, as described by type and intensity of fire, had been largely ignored in all the fire research that had been conducted up until that time. As a consequence a research program was initiated in South Africa and later extended to East Africa, to characterise the behaviour of fires burning in savanna and grassland vegetation and determine the effect of type and intensity of fire on the vegetation. The overall effect of type of fire is that surface head fires and crown fires have the least effect on grasses and have the potential to have the greatest effect on trees. This is because the heat is released above ground level away from the growing points of the grasses and closest to the growing points of the trees. Conversely, surface back fires have the opposite effect on grass and tree vegetation. This is because the heat is released close to ground level where the growing points of grasses are located and away from the growing points of the trees in the canopy. The overall effect of fire intensity is that grasses are generally not sensitive to increasing fire intensities because their growing points are located close to ground level away from the release of heat energy. Conversely trees are sensitive to increasing fire intensities because their growing points are generally exposed to the release of heat energy in the canopy of the trees. These effects explain why intense fires favour the development of grassland and open savannas and vice versa. The behaviour of surface head and back fires is currently being compared in southern African savannas and tall grass prairies in North America and results indicate that fires burning in grass dominated communities behave similarly and may therefore have similar effects on grass and tree vegetation globally. Forest Fire Research & Wildland Fire Safety, Viegas (ed.) © 2002 Millpress, Rotterdam, ISBN 90-77017-72-0