Investigation into the plant ecology of the Karstland area in Namibia : with particular reference to the proposed large-scale abstraction of groundwater
Master Thesis
1992
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University of Cape Town
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Abstract
The planned large-scale abstraction of groundwater from the Karst area in northern Namibia prompted concern with respect to possible negative effects on the plant ecology of that area. Although it was thought improbable that the lowering of the groundwater table would result in the deterioration of the vegetation, it was considered necessary to examine the existing vegetation status in order to establish a pre-abstraction baseline datum. It was thus important to establish a broad overview of the current vegetation, any changes in its condition within a two years period, and also the prevailing environmental factors in the Karst area. This was achieved through both manual and photographic monitoring of selected representative transects within the proposed abstraction area during 1986 and 1987. The manual monitoring exercise included the usual measures of density cover and frequency of all species, whereby a full inventory of the transects was established. The environmental conditions were assessed through the collection and evaluation of data on rainfall, groundwater levels and soil conditions, both within the transects and for the area as a whole. Below average rainfall during and prior to the baseline study years, resulting in poor recharge to the groundwater table, was recorded for most of the karst area. Both the vegetation and environmental data were utilized in two ways. Firstly, the 1986 and 1987 vegetation data were analysed, and those aspects indirectly related to the vegetation's vitality status, were then evaluated. A comparison of the parameters such as the quantity of dead material, and the number of standing dead trees, reflected a general decline in vitality over the two year period. In view of the poor rainfall conditions, this decline was interpreted as that which can be expected under natural adverse climatic conditions. Secondly, in order to establish and critically examine the possible relationships between the vegetation data and components of the environmental data, a Canonical Correspondence Analysis was performed. Despite a large amount of "noise" caused by the broad nature of the environmental data, it was possible to identify a number of species which occur within precisely defined environmental conditions. A change in abundance or distribution of these species can in the future first be investigated in terms of their defined vegetation-habitat relationships, and thereafter in terms of any other introduced factors which may be suspected of having an influence. Infra-red aerial photography was another monitoring technique used to obtain a pre-abstraction record of the vitality status of the vegetation. Two surveys were carried out during the baseline period and counts made of stressed and dead trees. A comparison of the counts reflected an increase in stress within the vegetation over this period, thus supporting the findings of the manual surveys. Selected sections of vegetation at various points of interest within the transects, were monitored using fixed point photography on a bi-annual basis. Although these photographic records ret1ected small changes, these were not considered significant. The main purpose of this method is to provide a pre-abstraction record of vegetation at potentially "sensitive" points with which future surveys .could be compared. The usefulness and cost-effectiveness of the three central monitoring methods were evaluated, and an indication provided of how monitoring may continue in the long term as large-scale abstraction goes ahead.
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Chivell, E. 1992. Investigation into the plant ecology of the Karstland area in Namibia : with particular reference to the proposed large-scale abstraction of groundwater. University of Cape Town.