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Vegetation change over 40 years in the WeenenIMuden area, KwaZulu-Natal: evidence from photo-panoramas
Abstract
The utility of panoramic photographs for studying the extent and pattern of vegetation change. in particular of bush encroachment, was investigated by revisiting thirteen sites in the Weenen and Muden areas of KwaZulu-Natal that had been photographed in 1955. The
ubiquitous feature of all sites was the marked increase in woody cover, from a mean of 21% woody cover for all topographic units (plains, hill slopes, river bank and river terrace) in 1955, to 59% woody cover in 1998. Although sample sizes were small, the increase in woody cover was greater on hill slopes (45% mean increase in woody cover) than on the plains (26%), and on northfacing slopes (56%) rather than on south-facing slopes (32%). The increase in woody plant COl(erwas accompanied by a change in composition from open or mixed woodland, to one dominated by Acacia species, in particular by A. tortilis at lower altitudes and by A. karroo at higher altitudes. In some cases, scrub Acacia individuals were already evident in the photographs in 1955, and had grown into mature trees by 1998. Recruitment of both Acacia and broad-leafed species was also observed in 1998 and there was a tendency for bush clumps to develop. Broad-leafed species have dominated on moist south-facing slopes and at higher altitudes. Increases of the arborescent leaf succulents. Aloe spectabilis and Opuntia ficus-indica and of the dwarf. stem succulent shrub, Euphorbia pseudocactus have occurred. Fire is no longer a component of this landscape which together with the open condition in 1955, resulting from overgrazing. may account for the vegetation changes that have taken place. Panoramic photographs proved an effective tool for monitoring vegetation change because changes in composition and structure were revealed and because each photograph samples a large area of ground at an adequate resolution.
Keywords: Acacia, bush encroachment, environmental history, savanna
African Journal of Range and Forage Science 16(2&3): 71–88
ubiquitous feature of all sites was the marked increase in woody cover, from a mean of 21% woody cover for all topographic units (plains, hill slopes, river bank and river terrace) in 1955, to 59% woody cover in 1998. Although sample sizes were small, the increase in woody cover was greater on hill slopes (45% mean increase in woody cover) than on the plains (26%), and on northfacing slopes (56%) rather than on south-facing slopes (32%). The increase in woody plant COl(erwas accompanied by a change in composition from open or mixed woodland, to one dominated by Acacia species, in particular by A. tortilis at lower altitudes and by A. karroo at higher altitudes. In some cases, scrub Acacia individuals were already evident in the photographs in 1955, and had grown into mature trees by 1998. Recruitment of both Acacia and broad-leafed species was also observed in 1998 and there was a tendency for bush clumps to develop. Broad-leafed species have dominated on moist south-facing slopes and at higher altitudes. Increases of the arborescent leaf succulents. Aloe spectabilis and Opuntia ficus-indica and of the dwarf. stem succulent shrub, Euphorbia pseudocactus have occurred. Fire is no longer a component of this landscape which together with the open condition in 1955, resulting from overgrazing. may account for the vegetation changes that have taken place. Panoramic photographs proved an effective tool for monitoring vegetation change because changes in composition and structure were revealed and because each photograph samples a large area of ground at an adequate resolution.
Keywords: Acacia, bush encroachment, environmental history, savanna
African Journal of Range and Forage Science 16(2&3): 71–88
