Namaqualand is a semi-desert area situated in the winter rainfall region of South Africa hosting the world’s richest succulent flora, and is one of only two arid areas to classify as a global hotspot of biodiversity. The Goegap Nature Reserve, east of Springbok, lies in the Upland Succulent Karoo. After all the livestock were removed and the reserve fenced in 1969, a long-term monitoring project was initiated to record possible vegetation changes under the reduced grazing pressure. The first monitoring was done in 1974 when two line transects, of 1 km each, were surveyed. These surveys have been repeated annually covering a period of more than 30 years. When the reserve was enlarged in 1990, five additional line transects were set out in highly degraded areas. The main aim of this study was therefore to determine whether any changes in the vegetation in terms of species composition, species richness and life form richness in the monitored line transects could be detected. Rainfall as possible force driving these changes was also examined. It was found that changes did indeed take place in the vegetation. The species composition revealed notable changes over the entire monitored period, specifically in the two longest established line transects, whereas in the case of the species richness changes were also detected, but to a lesser extent and not notable in terms of an overall increase or decrease in the number of species. These changes are referred to as fluctuations. Rainfall can be regarded as a definite environmental driving force, with the time, intensity and duration of importance, specifically to the annual species composition. Overall, the veld condition improved and continuous monitoring of the line transects on a regular basis should take place to improve our understanding of the complex dynamics of this ecosystem. Because the changes in species composition are reflected in changes in grazing capacity the results are of direct importance to the management of the wildlife on the reserve. / Dissertation (MSc)--University of Pretoria, 2010. / Plant Science / unrestricted

Le palmier-dattier constitue une des rares cultures à vocation alimentaire adaptées aux conditions climatiques extrêmes (sécheresse, salinité), telles que rencontrées à Djibouti. Dans un contexte de ressources en eau fortement limitées, la connaissance des modalités de l’alimentation hydrique du palmier dattier est essentielle. L’objectif de ce travail de recherche est d’acquérir cette connaissance, dans le contexte pédoclimatique de Djibouti, par la réalisation d’un suivi in situ du fonctionnement hydrique du système sol-palmier, à l’échelle d’un individu, et la quantification du puits racinaire du palmier-dattier. Un palmier-dattier, pleinement développé, a été instrumenté à l’échelle de la cuvette d’irrigation, à l’aide de plusieurs tubes d’accès de sonde à neutrons, pour le suivi de la teneur en eau volumique du sol, et de plusieurs tensiomètres, répartis de 10 à 160 cm de profondeur. Trois expériences d’infiltration/redistribution a été réalisées successivement, la première sans altérer le fonctionnement du système sol-palmier, la seconde après avoir coupé le palmier, tout en permettant l’évaporation de la surface du sol, la dernière après avoir couvert la surface du sol afin d’empêcher l’évaporation. Les résultats mettent en évidence une forte hétérogénéité des propriétés hydriques du sol, avec une stratification liée au contexte sédimentaire littoral. L’impact du puits racinaire sur la dynamique hydrique du sol est observé jusqu’à 80 cm de profondeur. Pour la période fraîche, les besoins en eau du palmier dattier sont estimés à 130 L par jour, avec une fréquence d’irrigation d’une fois toutes les 2 semaines. Pour la première fois, le coefficient cultural du palmier dattier (kc = 1,39) a été établi dans les conditions climatiques de Djibouti. Les résultats obtenus contribueront à une meilleure gestion de l’irrigation et à une meilleure maîtrise du risque de salinisation du sol dans le contexte pédoclimatique de la République de Djibouti. / Date palm is one of the few food crops adapted to the extreme weather conditions (drought, salinity), such as encountered in Djibouti. In the context of highly limited water resources, knowledge of the date palm water requirements is essential. The objective of this research was to determine the date palm water requirements, in the Djibouti pedoclimatic context, using in situ monitoring of water transport in the soil-plantatmosphere system, at the scale of a single date palm tree, and to quantify the date palm root water uptake. A fully developed date palm tree was instrumented at the irrigation basin scale, using several access tubes for neutron probe for monitoring the soil volumetric water content, and several tensiometers, installed from 10 to 160 cm depth. Three infiltration/redistribution experiments have been performed successively, the first without alteration of the soil-plant system, the second after cutting off a date palm tree while allowing the surface evaporation, the last with covering the soil surface to avoid evaporation. The results show large heterogeneity in soil hydraulic properties, with stratification linked to the coastline sedimentary context. The root water uptake is observed up to 80 cm depth. The date palm water requirements in the fresh period are estimated at 130 liters per day with a frequency of irrigation of one time every two weeks. For the first time, the date palm cultural coefficient has been established in the Djibouti climatic conditions (kc = 1.39). The obtained results will contribute to better management of irrigation and to improve the control of soil salinization in the pedoclimatic context of the Republic of Djibouti.