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Browsing Plant Sciences by Subject "Acacia -- South Africa -- Kathu"
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Item Open Access An investigation into the possible causes of decline in the Acacia Erioloba population of the Kathu area(University of the Free State, 2001) Van der Merwe, Karien; Du Preez, P. J.; Potgieter, G. P.English: Concerned residents have been reporting a decline in the A. erioloba population of the Kathu area to the Northern Cape Nature Conservation Service (NCNCS) since the early 1980's. This is the third study on this subject initiated by the NCNCS, and aims to elucidate the possible causes of decline in the A. erioloba population of the Kathu area. Five investigation sites were identified: the Khai-Apple Nature Reserve (KANR); the farms Lylyveld and Dernaneng, both situated down-wind with regard to the Sishen lscor Iron Ore Mine (SllOM); the Sishen Golf Course; and the farms Swarthaak and Knapdaar, both situated upwind with regard to the SllOM. The Sandveld Nature Reserve on the Free State side of the Bloemhof Dam, served as control site. In order to identify potential problem areas regarding the A. erioloba population of the Kathu area, the A. erioloba population structure of the study and control areas were compared. Irregularities in the structure of the study area indicated that some factor(s) is either a) preventing individuals from reaching middle height classes, or b) kill ing trees in these classes. To eliminate one of these options, another structure study was conducted, comprising dead individuals only. Results indicated that both factors (a+ b) play a role. By means of questionnares that were distributed th roughout the region, three major factors, potentially harmful to the A. eriofoba population, were identified. They are the mining activities of the SllOM, management strategies and natural phenomena. Two aspects of the SllOM were postulated to be potentially harmful to the A. erioloba population: the mine dust formed as a by-product of mining activities; and the lowering of ground water levels. Scanning electron microscopy confirmed that A. erioloba leaves are indeed damaged by mine dust. Through further investigations the effect of mine dust on the transpiration rate, chlorophyll a and b content and protein content of A. erioloba leaves were determined. The results of this study indicated that mine dust has no marked effect on any ofthese variables. The effect of mine dust on the germination of A. erioloba seeds and the growth potential of its embryos were also determined. No inhibitive effect was detected on either of these processes - in fact, mine dust seemed to stimulate both. No trials regarding the effect of the lowering of ground water levels by the SllOM on A. erioloba were conducted, due to its impracticality. Instead, with the aid and insight of geohydrologists it was concluded that the lowering of ground water levels does not affect A. erioloba. The aquifer underneath the mining area is seperated from the other two aquifers in the area (situated under Kathu and the KANR) by a dolorite dyke, which is impermeable to water. This was confirmed in the present study by comparing the water pumping rates of the SllOM to bore hole levels throughout the region. Three management strategies applied in the Kathu area were identified as being potentially harmful to A. erioloba: the overstocking of browsers and mixed feeders in the KANR; pod removal; and the uninformed use of chemicals. The current stocking rate of the KANR compared to its current browsing capacity, revealed that the reserve is grossly overstocked. This results in the suboptimal regeneration of A. erioloba, as seedlings cannot reach the stage where browsing doen not prove to be fatal anymore. Pod removal also inhibits optimal reg eneration, as no A. erioloba soil seed bank was found. This implies that no genetic variation in the A. erioloba pululation is built up over time, which may prove to be fatal in the event of future changes in environmental conditions. The uninformed use of non-specific chemicals in an attempt to eradicate A. mellifera on farms is furthermore also eradicating A. erioloba. One natural phenomenon was hypothesised to be inhibiting to the regeneration of A. erioloba, namely seed predation by Bruchidae. Germination trials revealed that bruchid seed predation inhibits the regeneration of A. erioloba. It is, however, compensated for by producing a relatively large seed yield per tree in an attempt to over-saturate predators. Management recommendations on the effective management of A. erioloba in the Kathu area were made. Recommendations included correct stocking rates, increasing community involvement in conservation, veld monitoring and the correct use of chemicals