Vegetation change in Northern KwaZulu-Natal since the Anglo-Zulu war of 1879.

Abstract

Historic photographs have been successfully used to compare landscape change over time. I used photographs taken of the grassland biome during and just after the Anglo-Zulu War (1879) in KwaZulu-Natal (South Africa), which are some of the earliest known available landscape photographs. The study area encompassed Fugitives’ Drift, Isandlwana and Rorke’s Drift and included communal and commercial rangelands, as well as conservation areas. These fixed-point photographs showed a dramatic increase in woody cover (< 82.5%) since the Anglo-Zulu War in all three land-use types. Floristic sampling showed that while vegetation structure did not differ significantly, plant species diversity and richness differed significantly for each land-use type. I also used a set of aerial photographs to give a much wider perspective of the landscape changes for the study area from 1944 to 2005. These images indicated that the increase in woody cover was progressive, with most of the woody plant recruitment occurring prior to 1964. Thereafter, the increase in woody plant cover was due to bush-clump thickening rather than recruitment into grasslands. This pattern did not occur, however, in the commercial rangeland, where recruitment into open grassland commenced in the 1980s. Although the theory of patch dynamics is cyclical in nature, this model may fit the patterns observed in the study area. Analysis of rainfall and temperature data showed that there has been a decrease in average annual rainfall since 1902 and an increase in minimum daily temperature since 1973. However, the decrease in mean annual rainfall is not consistent with woody plant encroachment. While the increase in mean annual daily temperature appears consistent with a shift to an environment typical of savannas, woody plant encroachment started before the increase in daily temperature. A survey of long-term residents in the study area with regard to livestock numbers, grazing patterns, fire and wood harvesting was also inconclusive. I, therefore, speculate that increasing levels of atmospheric CO2 is driving bush encroachment, with the other drivers such as rainfall, temperature, absence of intense fires, grazing patterns and land-use, playing a modifying role.