Veldtipes, verspreiding van die groter soogdiere, en enkele aspekte van die ekologie van Kaokoland

Abstract

Initiated in 1975, the purpose of this study was to obtain basic ecological information needed for the conservation, management and utilization of the fauna and flora of Kaokoland, S.W.A. Accordingly the vegetation of the area was classified into veldtypes and the status, distribution and movements of the bigger mammals were determined. To assist in the description of veld types, quantitative classification of the vegetation was based on the variable quadrant plqt method for trees and shrubs and the steppoint method for herbs. Information thus gathered was used to determine species composition and to estimate density per hectare, mean height, mean crown diameter, mean stem diameter, mean number of stems and canopy cover for the different plant species. In conjunction with bioclimatic and geographical divisions the above mentioned quantitative information of the vegetation resulted in the description of homogeneous vegetation units. In this way the vegetation was separated into fourteen veld types. The location, boundaries, topography, geology, soil, treestratum, shrubstratum, herbstratum for each veldtype and the major plant communities within each are described. In addition the vegetation of the drainage lines and the plants associated with springs are described. A synopsis of previous descriptions and classifications is also presented. It was found that the vegetation of Kaokoland ranges from a subtropical savanna with a maximum density of 2 085 trees and shrubs per hectare in the east to a nearly vegetationless desert with less than one shrub per hectare in the west. This gradient from east to west coincides with the gradient for rainfall. Some of the plant species occurring in each of the bioclimatic regions are specific for that region and ecologically adapted to it. Information on the bigger mammals was obtained through ground and aerial surveys conducted on a seasonal basis. Information collected included locality, numbers, habitat, distance from open water, group size and when possible also group structure, feeding and behaviour. This information was used to quantify the distribution and status of 36 species of bigger mammals. Social structure, habitat preference, movement and seasonal changes of the separate parameters were determined for the more common and easily observed mammals. Group structure, sex ratios, reproduction and feeding of some species are briefly discussed. Of the 36 mammal types studied, 21 are regarded as common, 6 as rare but in no immediate danger of extinction, the status of 3 as unknown, and 6 are regarded as highly endangered. The endangered types are Diceros bicornis, Aepyceros melampus petersi, Sylvicapra grimmia, Hippopotamus amphibius, Panthera leo and Lycaon pictus. Of these, two seem to be already extinct, i.e. Hippopotamus amphibius and Lycaon pictus. Because the different aerial surveys differ in time and space it was impossible to determine trends in game numbers. The results of the aerial surveys range from 2 256 bigger m~mals in the dry season to 8 006 in the rainy season. Therefore information on the past and present distribution of the various ma;nmals are used as indicators of trends. With the exception of single smaller antelope and predators, all bigger mammals show a decline in their range of distribution since 1970.

Die doel van hierdie studie was om basiese inligting vir die daarstelling van 'n meestersplan vir die bewaring, bestuur en benutting van die fauna en flora in Kaokoland, S.W.A., te versamel. Hiervolge.:1s is die plantegroei kwalitatief en kwantitatief volgens veldtipes geklassifiseer en die status, verspreiding en bewegings van die grater soogdiersoorte bepaal. Om die plantegr<Jei te kon klassifiseer, is daar vir die borne en struike van die varieerbare kwadrant oerseelmetode, en vir die kruide van die stappuntmetode gcbruik gemaak. Die 374 data sodoende verkry is tot digtheid per hektaar, gemiddelde hoogte, gemiddelde kruindeursnee, gemiddelde stamdeursnee, gemiddelde aantal stamme en kroonbedekking van die verskillende plantsoorte en spesiesamestelling verwerk. Bogenoemde kwantitatiewe gegewens is verder aan die hand van bioklimatiese en geografiese gebiede as kriterium gebruik om die plantegroei van Kaokoland in homogene eenhede te verdeel. Sodoende is die plantegroei van Kaokoland in 14 veldtipes verdeel. Die veldtipes, tesame met die plantgemeenskappe wat in 'n spesifieke veldtipe herken kon word, is as volg beskryf: ligging, grense, topografie, geologie, grond, boomstratum,struikstratum, kruldstratum, en 'n oorsig van vorige werkers se plantegroei beskrywing en indeling. Verder is ook die plantegroei van die dreineringsisteme en die plante wat met fonteine geassosieerd is, beskryf. Daar is gevind dat die plantegroei van Kaokoland van 'n subtropiese savanne in die ooste, met 'n maksimum digtheid van 2 085 borne en struike per hektaar, tot 'n feitlik plantlose woestyn met minder as een struik per hektaar in die weste, wissel. Hierdie oos-wes gradient hou met die reenval verband. In elke bio-klimatiese gebied word plantsoorte wat spesifiek en ekologies by die gebied aangepas is, aangetref. Die grater soogdiersoorte is deur middel van grond- en lugsensusse, op 'n seisoenale basis bestudeer. Inligting soos lokaliteit, aantal, habitat, afstand vanaf oop water, tropgroottes en waar moontlik ook tropsamestelling, voeding en gedrag is versamel. Deur middel van die inligting is die verspreiding en status van 36 van die grater soogdiersoorte in Kaokoland bepaal. Van daardie diersoorte wat algemeen in Kaokoland voorkom en maklik waargeneem kon word, is ook die sosiale struktuur, habitatvoorkeur, bewegings en die seisoenale variasie daarvan, bepaal. Waar moontlik is die tropsamestelling, geslagsverhouding, voortplanting en voeding bespreek. Daar is gevind dat van die 36 soogdiersoorte wat bespreek word, 21 volop in Kaokoland voorkom, 6 skaars is, maar nie in onmiddellikc gevaar van uitsterwing nie, 3 diersoorte se status onbekend is en 6 met onmiddcllike uitsterwing bedrcig word of onlangs uit KaokoIand verdwyn het. Die bedreigde soorte is: Diceros bicomis, Aepyceros melampus petersi, Sylvicapra grimmia, Hippopotamus amphibius, Pantlzera leo en Lycaon pictus. Dit wil voorkom asof twee van hierdie ses bedreigde soorte, naamlik Hippopotamus amphibius en Lycao;z pictus, plaaslik reeds uitgesterf is. Aangesien die onderskeie lugsensusse in tyd en ruimte verskil, was dit onmoontlik om die tendense in die wildgetalle te bepaal. Die getalle verkry met die lugsensusse wissel van 2 256 in die warm droe seisoen tot 8 006 in die reenseisoen. Daar is dus klem gele op die huidige en vroeere verspreidingsgebiede van die wildsoorte. Afgesien van enkele kleiner antiloopsoorte en roofdiere is daar gevind dat alle ander grater soogdiersoorte se verspreidingsgebiede sedert 1970 gekrimp het of besig is om te krimp.