Long-term changes in the woody vegetation of the Kruger National Park, with special reference to the effects of elephants and fire

Abstract

As part of the investigation reviewing the South African National Parks policy on the management of elephants in the Kruger National Park in South Africa it was decided to assess the current density and structural diversity of the woody vegetation in the park as it is affected by elephants and fire. The management policy used till recently, limited the population to approximately 7000 elephants, based on a conclusion that 6000 elephants (1 per 1.94 km2) was the highest number of elephants that could be carried in the Kruger National Park. The inclusion of the effects and interaction of fire in the investigation arises from the general recognition that elephants and fire can have a highly significant impact on the species and structural diversity of tree and shrub vegetation in African savannas. In the absence of quantitative data describing the condition of the woody vegetation in the Kruger National Park, subjective comparisons of changes in the density of large trees were made for the periods 1940 vs 1960 and 1960 vs 1986/89 using aerial photographs based on four of the major vegetation landscape units in the park. The results indicate that in the vegetation landscapes in areas with granitic soils there were no significant changes in the density of large trees between 1940 vs 1960 whereas a moderate decline occurred in the vegetation in the areas with basaltic soils. Conversely during the period 1960 to 1986/89 there was a dramatic decline in the density of large trees in all four major vegetation landscape units. On-site inspections and botanical surveys suggest that the decline in the density of large trees is the result of the effects of the interaction of elephants and fire. This had arisen because during the period 1960 to 1986/89 systematic burning programs had been introduced at the same time as elephant numbers had risen sharply. The results presented suggest that the changes in the woody vegetation do not involve a decrease in species diversity but rather a change in structural diversity where the woody vegetation is being transformed into a short woodland community interspersed with a low density of large trees. It is concluded that if it is desirable to prevent further structural changes to the woody vegetation then the current density of elephants should not be allowed to increase, the frequency of burning should be significantly reduced and the ignition procedure altered to allow or simulate point ignitions of fires.