Browsing by Author "Monakisi, Charlotte"

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    Effect of short term rest on riverine systems associated with heavy grazing in Paulshoek, Namaqualand, South Africa
    (2002) Monakisi, Charlotte; Allsopp, Nicky; Hoffmann, Timm
    Arid and semi-arid systems comprise one third of the earth's surfaces. The succulent karoo alone comprises approximately 1660 endemic species and is one of the world's hotspots in terms of diversity. Although these areas are of high ecological value less than 10% of arid systems are conserved. This study was conducted in Paulshoek a remote village in the Leliefontein area of the Namaqualand. Historically Paulshoek has been under continuous selective grazing since the 18th century. A fence line contrast is investigated in an area that was fenced three years ago and in one that has been exposed to heavy, continuous, selective grazing over the past century (both areas were fenced prior to fencing). The objective of this study was to investigate the effect of short-term rest on key vegetation demographic parameters as well as the physical characteristics of communal river systems. No significant differences in plant species richness were observed across the fence line. However, the numbers of plants of each species within the plots were significantly different, depending on presence or absence of grazing. The grazed sites had more species tolerant of grazing such as geophytes, annuals and toxic species such as Galenia africana. Heavy grazing in this ecosystem has resulted in increased proportions of unpalatable species with a slow reduction in the number of palatable species. Species cover was significantly reduced on the grazed sites; however, these reductions were insignificant for Lyceum cinereum species due to large standard deviations. Heavy grazing of palatable sedge species (Scirpus nodosus) resulted in significant reductions in the number of flowers of plants, in the grazed sites. Grazing not only reduced the size of the plants, it also reduced flowering, fruit set and recruitment rate. There was no significant difference in the physical and geomorphologic characteristics of the river across the fence-line. This study indicates that short-term rest has major implications for plant recovery. Educating communal farmers to use a farming system that insures temporary rest on certain areas of the rangelands at certain times of the year will go a long way in improving species richness in Namaqualand.
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    N₂ fixation, plant mineral nutrition and C metabolites in cowpea/maize cropping systems
    (2002) Monakisi, Charlotte; Dakora, Felix D
    The objective of this study was (1) quantify N₂ fixation in sole and mixed cropped cowpea, (2) To access nutrient assimilation by component species in the cropping system, and (3) to determine the effects of cropping system on C metabolites. At harvest the dry mass of both cowpea and maize were highest in sole crops. There was a significant difference in % nitrogen of maize and cowpea plants from the different cropping systems. Total nitrogen content was highest in sole cropped maize and cowpea plants with sole cowpea fixing the most N₂. δ¹⁵N values were lower for the shoots of symbiotic cowpea compared to the maize. Root δ¹⁵N values were also generally lower in cowpea than in maize. The %N derived from fixation (Ndfa) was similar for sole, intra and intercropped cowpea. However the amount of N fixed was significantly greater in sole cowpea compared to intra- and intercropped cowpea. When nutrient uptake and assimilation was assessed in the cropping system, it was found that mineral elements such as Ca, Mg, Cu, Zn and B occurred in significantly greater concentrations in the N₂-fixing legume compared to the cereal partner. However the concentration of soluble sugars and starch remained the same for both shoot and roots of cowpea and maize plants in the cropping system.