M.W. van Rooyen

Mysterious circles in the Namib Desert: review of hypotheses on their origin

Abstract Circular, slightly concave depressions, devoid of vegetation and often surrounded by a fringe of tall grasses occur in a broken belt in the pro-Namib zone of the west coast of southern Africa. Several hypotheses have been proposed to explain the origin of these so-called fairy circles. The most important of these relate to areas of localized radioactivity; termite activity; or allelopathic compounds released by dead Euphorbia damarana plants. No evidence of increased radioactivity could be detected in soil samples collected from these sites. Although termites occur at these localities no evidence was found to link termite activity directly to the formation of barren patches. Bioassays conducted on soil collected from the centre of the barren patch clearly demonstrated an inhibition of plant growth, while soil collected from the edge of the barren patch had a stimulatory effect on plant growth. No indication of growth inhibition was found in soil collected beneath E. damarana plants. At this stage none of the proposed hypotheses can satisfactorily explain the origin of the fairy circles.

Using diet and plant resources to set wildlife stocking densities in African savannas

Abstract The concept of carrying capacity originally was developed for domestic grazers and does not make provision for the wide variety of diets found in wild African herbivores. In the African savannas, herbivores are classified into 4 basic dietary classes: low-selective grazers, high-selective grazers, mixed feeders, and browsers. Given these conditions, a more appropriate approach was needed than the agricultural method based on livestock units to determine stocking rates for wildlife. Consequently, a new approach was developed that recognizes plant resource variation at the plant community level and differentiates between the grazing and browsing component in the diet of herbivores in the African savannas. The model used to calculate the grazing and browsing capacity on wildlife ranches provides for rainfall variability, quality and quantity of available grazing and browse, dietary requirements of each type of wildlife, and availability of suitable habitat. In this model the conventional conversion of wildlife to a Large Stock Unit has been replaced by a Grazer Unit, which is the equivalent of a 180-kg blue wildebeest (Connochaetes taurinus), and a Browser Unit, which is the equivalent of a 140-kg greater kudu (Tragelaphus strepsiceros). By separating the grazing and browsing components in the diet of wildlife for stocking density calculation, the diversity in the vegetation resources is optimally utilized. This concept is exemplified with an actual case study of a wildlife ranch in a South African savanna. In doing so, quantitative and clearly defined parameters are provided on which to base wildlife management decisions.

Management of the old field vegetation in the Namaqua National Park, South Africa: conflicting demands of conservation and tourism

Springtime mass displays of wild flowers are especially prominent on old fields and other disturbed sites in Namaqualand, an arid region in the north–western part of South Africa. This springtime floral spectacle draws thousands of tourists annually. However, there is a potential conflict between biodiversity conservation and the mass flowering that is a valuable source of income to the region. To develop a management plan for the old field vegetation in the Namaqua National Park, the questions of whether to disturb or not, how often to disturb and what type of disturbance should be applied are of vital importance. The aim of this paper is to report on experimental work to determine the impact of disturbance on mass flowering displays and biodiversity. Results show that although species diversity increased with time since last cultivation, the mass effect of the flowering display diminished. The loss of the mass effect appears to be primarily caused by the increased abundance of a short–lived perennial species (Leysera gnaphalodes) that suppressed the flowering display of the prominent annual species. To maintain mass displays as a tourist attraction, regular disturbance by tilling therefore seems essential. Initially, a four–year rotational tilling programme is proposed to produce a mosaic of fields of different ages to ensure that there will always be some old fields producing a spectacular and uncluttered display. Frequency of disturbance should thereafter be determined by an adaptive management policy. If the management of the old field vegetation is seen in the context of conserving total landscape ecodiversity, this includes conserving cultural bio–landscapes and their intrinsic values. Viewed in this context, human–induced disturbance in the small area set aside for mass displays in the Namaqua National Park (less than 0.05% of the park) becomes justified.

VEGETATION OF THE SOUTH-WESTERN ARID KALAHARI: AN OVERVIEW

SUMMARY The south-western Kalahari, with rainfall of 150–450 mm p.a., can be described as an arid savanna or semiarid desert. This area includes the southern Kalahari dunefields which is considered by most authors to have phytogeographical affinities with the Sudano-Zambezian Region, while others classify the area as part of the Nama-Karoo Region. Extensive vegetation maps are available for the Kalahari areas of Namibia and Botswana. For the dunefield area of South Africa, a detailed syntaxonomical vegetation classification, description and mapping of plant communities has been completed. Rainfall is clearly the main determinant of forage production in this environment. Although the vegetation and animal numbers of the south-western Kalahari conservation areas show definite changes in the short to medium term, mainly in reaction to rainfall, a long-term ecological balance prevails at present and should continue if the present large sizes of these conservation areas are maintained. The introduction of bore...

A comparative study of seed germination of two Alliumspecies from different habitats in the Negev Desert highlands

Abstract Seed germination of Allium truncatum and Allium rothii from natural populations in the Negev were compared over a range of NaCl concentrations, naturally fluctuating or constant temperatures, light and dark. No germination occurred after the first 7 days of imbibition. The fastest germination was at 10 and 15°C but there was none at 25°C. The higher the NaCl concentration, the lower the germination. Allium truncatum plants inhabit wadis with crowded vegetation and the seeds germinate in the dark better than in the light, in natural and constant temperatures. Allium rothii plants inhabit open areas. There is no difference between germination in light and dark, in constant 5 to 15°C. Germination at 20°C in light is higher than in dark and in naturally fluctuating temperatures the germination in dark is higher.

Vegetation diversity of the Brand-se-Baai coastal dune area, west coast, South Africa: a pre-mining benchmark survey for rehabilitation

Prior to the mining of heavy minerals, the vegetation diversity of the Brand-se-Baai coastal area was investigated to serve as a benchmark for the future rehabilitation of the area. The vegetation was surveyed using the Braun–Blanquet procedure to classify the different plant communities. Six plant communities, some of which include several variants, were identified, described and mapped. A revegetation goal of 30 per cent, rather than 60 per cent, of the number of plant species present prior to mining are recommended. Copyright

Teaching professionalism: a South African perspective

Background: Incorporating the teaching and assessment of professionalism in an undergraduate medical curriculum is a challenging process. There are two components that require attention: the cognitive and the experiential. This article outlines how the School of Medicine at the University of Pretoria (UP), South Africa is addressing the teaching and assessment of professionalism. Aims: To embed teaching and assessment of professionalism in a revised six-year undergraduate medical curriculum. Method: This is a descriptive paper of a curriculum process that has stretched over a number of years. The eight principles regarding teaching professionalism provided by Cruess & Cruess () are used to reflect on the current strengths and weaknesses of teaching and assessing professionalism in the UP undergraduate medical curriculum.  The cognitive component of the curriculum has been addressed by introducing a series of stage appropriate, contextualized assignments in each year of the curriculum. Faculty committee structures supported the development and implementation of this component. Students’ responses to an assignment on the influence of role models provided insight into how the experiential component impacts on their professional development. Results: The teaching and assessment of the cognitive component were relatively easy to put in place. The challenge is to maintain this component. The experiential component appears to be much the same as it was prior to revision. Conclusions: Our way forward is to expand the teaching and assessment of professionalism in the experiential component. We want to facilitate faculty to develop a charter on professionalism. The principles and commitments of the charter will underlie a white coat ceremony for undergraduates. These principles will also provide guidelines for role models in their supervision of experiential learning and can inform criteria for assessment. An assessment strategy to assess professionalism in the experiential component needs to be developed and implemented.

Removal of sodium and chloride from a saline soil by Mesembryanthemum barklyi

Abstract The removal of sodium and chloride from a saline-mined soil by Mesembryanthemum barklyi N.E. Br. was investigated under laboratory conditions. The sodium, magnesium and chloride content of plants increased when grown on a saline soil, while the calcium, potassium, nitrogen and phosphorus content decreased. No significant difference in biomass production occurred between plants grown on saline and non-saline sandy soils.

Salinity-induced changes in anatomy, stomatal counts and photosynthetic rate of Atriplex semibaccata R. Br.

Anatomical changes in the roots and leaves of Atriplex semibaccata R. Br., induced by salinity stress, as well as photosynthetic and stomatal response to salinity, were investigated. As salinity increased, decreases were observed in root diameter and leaf size, as well as in the number of chloroplasts in the chlorenchyma and bundle sheath cells. Development of these two cell types was also inhibited. Net leaf photosynthetic rate and leaf stomatal conductance decreased with increasing salinity. while the intercellular CO 2 concentration increased. Both stomatal closure and inhibition of biochemical processes probably caused the reduced leaf photosynthetic rates. The stomatal indices suggest that the trend towards an increase in number of stomata per unit leaf area with an increase in salinity was not due to decreased epidermal cell size.

The views of Medical Students on professionalism in South Africa

An article on medical professionalism was published in the Annals of Internal Medicine in February 2002 outlining a charter, and the fifth-year medical students of the Medical School of the University of Pretoria were asked to comment on the charter. The question was asked whether the principles and responsibilities as set out in the charter could also be applied to the South African context. The responses of the students could be divided into three groups with overlapping themes: 15, 64% of the students felt that the charter was not at all applicable to our country because of its diverse cultures and languages and the variety of social classes and religions; 24, 02% of the students felt that the charter was a universally acceptable document; and 60, 34% of the students felt that, to a great extent, the charter was the ideal and the goal to strive for, although they only accepted some of the principles and responsibilities while having serious doubts and criticism of others. In conclusion, the majority of the medical students felt that the charter was noteworthy and commendable in principle, but not totally applicable in our country with its unique problems and challenges. Our challenge is to take what resources we have and use it to the benefit of all.