No abstract

Summary Vegetation on islands in the perennial swamps of the Okavango Delta exhibits a marked zonation pattern. Island fringes are generally characterized by a broadleaf evergreen riparian community of Syzigium cordatum, Ficus verruculosa, F. natalensis, F. sycamorus, Phoenix reclinata, Garcinia livingstonei and Diospyros mespiliformis. This gives way towards island interiors to a community dominated by Acacia nigrescens, Croton megalobotrys and Hyphaene ventricosa. The central regions are characterized either by short, sparse grassland dominated by Sporobolus spicatus or are completely devoid of vegetation with sodium carbonate (trona)‐encrusted soil surrounding a central pan of extremely high conductivity. An indirect gradient analysis indicated the important determinants of vegetation distribution as being not only elevation, depth to groundwater and distance from the water source, but also as groundwater chemistry (conductivity and pH) and soil chemistry (sodium concentration). These studies were supported by a direct gradient analysis approach with species tolerances to depth to groundwater, groundwater conductivity and soil‐surface sodium concentrations having been established. Feedback interactions of vegetation and groundwater elevation and chemistry, as well as soil chemistry, are evident and appear to be responsible for the vegetation dynamics in the study area. Résumé La végétation des îles dans les marais permanents du delta de l'Okavango présente un schéma de zonation marqué. Le bord des îles se caractérise généralement par une communauté riveraine à larges feuilles toujours vertes de Sizigium cordatum, Ficus verruculosa, F. natalensis, F. sycamorus, Phoenix reclinata, Garcinia livingstonei et Diospyros mespiliformis. Celle‐ci cède le pas vers l'intérieur à une communauté dominée par Acacia nigrescens, Croton megalobotrys et Hyphaene ventricosa. Les zones centrales, soit se caractérisent par une prairie courte et clairsemée où domine Sporobolus spicatus, soit sont complètement dénuées de toute végétation, avec un sol encroûté de carbonate de soude entourant un centre où la conductivité est très élevée. Une analyse indirecte du gradient indiquait que les facteurs déterminants pour la distribution de la végétation ne sont pas seulement la hauteur, la profondeur de la nappe aquifère ou la distance par rapport à une source, mais aussi la composition chimique de l'eau (sa conductivité et son pH) et celle du sol (concentration en sodium). Ces recherches ont été confirmées par une approche directe de l'analyse du gradient, de la tolérance des espèces face à la profondeur de l'eau, sa conductivité et les concentrations en sodium de la surface du sol ayant étéétablies au préalable. Les interactions entre la végétation d'une part et le niveau et la composition chimique de la nappe aquifère d'autre part, ainsi que celle du sol sont évidentes et semblent être responsables de la dynamique de la végétation dans la zone étudiée.

No abstract

No abstract

Strategic and well-planned use of feedback in the assessment process is key to promoting learning. This paper evaluates the role a two-stage test process played in guiding and assisting student learning in a second-year module at the University of KwaZulu-Natal, South Africa. Having been provided with verbal and written feedback without grades from the first test, students were given the opportunity to write a different, second test, and each was required to choose which one was graded. Students were generally very positive about the assessment process, most participated willingly and fully, many learned differently for the second test, and there was evidence of meta-cognitive awareness and understanding. Despite this, a number of students experienced difficulty and frustration in judging the quality of their work. The discussion focuses on process and learning issues, on the utility of feedback and on formative test assessment procedures. Approaches to assessmentBased on behaviorist educational theories which assume learning and behavior can be accurately determined and brought about in a rational way, assessment in institutions of higher learning has traditionally been geared towards testing whether students have achieved a set of pre-determined goals. The focus therefore tended to be content and product oriented, giving rise to summative, examinations-driven and norm-referenced assessment approaches. Since it is well recognized that assessment is one of the major factors that influences students' approach to learning in formal educational settings