The contribution of riparian vegetation to the species composition of the Jonkershoek Valley in Stellenbosch, South Africa

Thesis (MSc)--University of Stellenbosch, 2003.

ENGLISH ABSTRACT: Many authors express the value of riparian vegetation in terms of the function and number of species per unit area. Although riparian vegetation is confined to narrow bands of plants along watercourses, kloofs and gullies, it is a specialised habitat for many species. To determine the contribution of riparian vegetation to the species richness of the Jonkershoek Valley, Western Cape Province, South Africa, a checklist was compiled, by referring to past research and to the PRECIS national database for the South African flora for a list of species recorded from the area. A total of 1 743 taxa and 108 families were included in this list for the Valley. Specific characteristics were attributed to each of the 1 743 species on the basis of characters determined from the literature. Analysis of these data indicates that woody perennial shrubs with sclerophyll leaves are the representative plant type for the study area as a whole. The specialist structural description of a riparian species in the Jonkershoek Valley is: an unbranched woody perennial phanerophyte of a height between 2.0-8.0 m with microphyllous sclerophyilleaves. This group contributes 63% towards the riparian flora. Riparian habitats occupy only 2.5% of the total study area but contribute 26% of the vascular plants. The riparian communities of the Santa Monica Mountains (USA) cover 0.7% of that mountain study area and provide a habitat for 20.5% of the total vascular plants of the area. Both areas, therefore, show a similar level of diversity. This remarkable species richness of riparian zones is consistent with that found in other riparian communities i.e. Sweden and France. The study area was sampled by means of relevés arranged along 53 transects through the main stem and it's tributaries. A total number of 139 relevés were recorded which were used to identify, characterise and describe the riparian communities. Eight vegetation units, consisting of two groups, three communities, two subcommunities and one form, were described. The one group described the riparian communities while the other described a seepage community. The bigger groups exhibit environmental properties over a broader spectrum, while smaller groups exhibit characteristic environmental properties. The vegetation is found to represent a continuum rather than discreet entities. Many indicator species are encountered in the communities. Because of the characteristic canopy-understorey physiognomy of riparian vegetation, many communities are interspersed, making it difficult to delineate discreet community boundaries. The vegetation of the riparian zone of the Eerste River in the Jonkershoek Valley, is relatively pristine. Thirty-six species not native to the Valley were included in the checklist of which only four were recorded during the phytosociological study.

AFRIKAANSE OPSOMMING: Verskeie skrywers beklemtoon die kosbaarheid van rivieroewerplantegroei in terme van hul funksie en aantal spesies per oppervlakeenheid. Alhoewel rivieroewerplantegroei beperk is tot 'n noue band van plante langs waterweë, klowe en skeure, is dit 'n gespesialiseerde habitat vir baie spesies. Om die bydrae wat rivieroewerplantegroei tot die spesie-rykheid van die Jonkershoekvallei, Wes-Kaapprovinsie, Suid-Afrika te bereken, is 'n spesieslys saamgestel uit vorige studies en 'n PRECIS nasionale databasis vir die Suid-Afrikaanse flora waaruit 'n lys saamgestel is van spesies wat aangeteken is vir die area. 'n Totaal van 1 746 taxa uit 108 families is ingesluit in die plantelys. Vir elk van die 1 743 spesies, is spesifieke karakters uit die literatuur bepaal. 'n Analise hiervan dui aan dat die verteenwoordigende plant van die Jonkershoekvallei as gehele studie area 'n houtagtige, meerjarige struik met sklerofil blare is. Die spesialis strukturele beskrywing van 'n plant vir die Jonkershoekvallei is as volg: 'n onvertakte houtagtige meerjarige fanerofiet met 'n hoogte van 2.0-8.0 m met mikrofilliese sklerofil blare. Hierdie groep dra tot 63% by tot hierdie flora. Rivieroewer habitatte beslaan slegs 2.5% van die totale studie area, maar het tot 26% tot die vaatplante bygedra. Die Santa Monica Berge (VSA) se rivieroewerplantegroei bedek 0.7% van die bergagtige studie area en voorsien 'n habitat vir 20.5% van die vaatpplante. Beide gebiede toon dieselfde mate van diversiteit. Hierdie uitstaande spesiesrykheid is in lyn met wat gevind is in ander rivieroewergemeenskappe bv. in Swede en Frankryk. Die studie area is gemonster deur relevés wat uitgemerk is langs 53 transekte deur die hoofstroom en die sytakke. 'n Totaal van 139 releves is gemonster wat gebruik is om die gemeenskappe te identifiseer, karaktifiseer, en te beskryf. Agt plantegroei-eenhede, bestaande uit twee groepe, drie gemeenskappe, twee subgemeenskappe en een vorm, is beskryf. Die een groep beskryf rivieroewergemeenskappe terwyl die ander groep "n gemeenskap in die syfersone beskryf. Die groter groepe het wyer omgewingseienskappe getoon, terwyl die kleiner groepe spesifieke eienskappe toon. Dit is vasgestel dat die plantegroei eerder "n kontinuum voorstel as diskrete eenhede. Dit het tot gevolg dat dit moeilik is om die grense van gemeenskappe uit te wys. Vele indikatorspesies is aangetref. Die plantegroei van die rivieroewer van die Eersterivier in die Jonkershoeksvallei, kan beskryf word as relatief onversteurd. Ses-en-dertig spesies wat nie eie aan die Vallei is nie, is ingesluit in die spesieslys waarvan vier tydens die fito-sosiologiese studie aangeteken is.