Phytosociological study of the riparian and associated wetland vegetation along the Vet River, Free State Province, South Africa

Abstract

English: The aim of this study was to assess, classify and describe the natural vegetation along the Vet River. The study was restricted to the vegetation of the islands, banks as well as the floodplains. The Vet River is situated in the Free State Province, South Africa. The study area covers approximately 8 928 hectares including the surface area of the Erfenis Dam, which is situated downstream of the confluence of the Groot Vet and Klein Vet Rivers. There are several towns in the catchment of the Vet River which include: Exelcior, Winburg, Theunissen and Hoopstad. The area around the river also has a provincial nature reserves namely: Willem Pretorius Game Reserve along the Sand River, a tributary of the Vet River, the Erfenis Dam Nature Reserve near Theunissen and the Sandveld Nature Reserve downstream of Hoopstad. The area is mostly situated in the Highveld climatic region with cold and dry conditions due to the high elevation and the inland continental aspects of the area. Furthermore the area is characterised by warm summers with strong summer rainfall patterns and mild winters with drought. The rainfall received is mostly in the form of regular showers and thunderstorms during the months of October to March. The geology of the area is dominated by the Karoo Supergroup which was deposited during the period of 310 to 182 million years ago. Only the Ecca, Beaufort and Stormberg Groups occur in the study area. In the area, two biomes are present. These biomes are the Grassland biome (which occur between sea level to 2 850m above sea level) which mainly represent the high central plateau of South Africa and the Savanna biome (occur at altitudes below 1 500m above sea level) which mostly occur in areas with a strongly seasonal rainfall and a distinct dry season which usually occur in winter. The Vet River cuts through seven vegetation types. Various kinds of wetlands occur along the Vet River. All of them falls within the RAMSAR definition of a wetland namely: “wetlands are areas of marsh, fen (peat-accumulating wetland that receives some drainage from surrounding mineral soil and usually supports marshlike vegetation), peatland (generic term of any wetland that accumulates partially decayed plant matter) or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres”. The presence of wetlands in the study area lead to the search for a proper definition for these unique systems as they also perform certain functions and can be seen as valuable ecological laboratories because of their habitat and species diversity. Riparian areas is seen as the interface between aquatic and terrestrial ecosystems, however these areas can also be defined as frequenting, growing on, or living on the banks of streams or rivers. These areas are usually narrow and linear and can be regarded as corridors for migrating species. During the study 240 sample plots were placed within various homogenous vegetation types along the Vet River. The Braun Blanquet cover-abundance scale was applied in this study. The vegetation analysis led to the classification and identification of 14 plant communities, 21 sub-communities and 11 variants which were discussed phytosociologically: The communities can be divided into those communities that occur in the mountains, those communities that occur in the riverine areas on plains and the communities that occur in the floodplains or pans along the Vet River.

Afrikaans: Die doel van die studie was om die natuurlike plant egroei langs die Vetrivier te klassifiseer en te beskryf. Die studie was beperk tot die plantegroei van eilande, oewers en die vloedvlaktes van die rivier. Die Vetrivier is geleë in die Vrystaat Provinsie, S uid-Afrika. Die studie area beslaan ongeveer 8 928 hektaar wat die oppervlak van die Er fenis Dam insluit. Die ErfenisDam is geleë net onder die sameloop van die Groot en Klein Vetriviere. In die opvangs gebied van die Rivier is daar verskeie dorpe wat onder andere Exelcior, Winburg, Theunissen en Hoopstad insluit. In die om gewing van die Rivier is daar ook verskeie provinsiale natuur reservate naamlik: Willem Pretorius natuurreservaat langs die Sandrivier, `n sytak van die Vetrivier, d ie Erfenis Dam natuurreservaat naby Theunissen en die Sandveld natuurreservaat, we s van Hoopstad. Die studie area is geleë in die Hoëveld-klimaatstre ek wat `n koue droë klimaat het as gevolg van die hoë hoogte bo seevlak en die binnela ndse kontinentale invloede van die area. Die area word ook gekenmerk deur warm so mers met sterk somer reënvalpatrone en gematigde winters wat gekenmerk w ord deur droogtes. Die meeste reën val gewoonlik in die somer maande, gedu rende Oktober tot Maart. Die reënvalseisoen word gekenmerk deur donderstorms. G eologies word die gebied onderlê deur die Karoo Supergroep wat tussen 310 en 182 miljoen jaar gelede, gevorm is. Die Ecca, Beaufort en Stormberg-groepe is die enigste wat in die studiegebied voorkom. In die studie gebied kom twee biome voor: Die biom e is die Grasveld bioom wat vanaf seevlak tot ongeveer 2 850m bo seevlakvoorkom en die Savanna bioom wat voorkom in areas met sterk seisoenale reënval en `n kenmerkende droë seisoen wat gewoonlik in die winter voorkom. Die Vetrivier vlo ei deur sewe verskillede plantegroei eenhede. Verskillende soorte vleilande kom langs die Vetrive ir voor. Almal val binne die breë RAMSAR definisie van vleilande naamlik: ‘vleilande is moeras of veenagtige areas 200 wat natuurlike of kunsmatige, permanente of tydelik e water het, wat staties of vloeiend is, vars of brak wat mariene gebiede met ` n diepte van nie meer as ses meter tydens laagwater insluit nie’. Oewer areas w ord as die raakpunt tussen die akwatiese en terrestriele ekosisteme beskou, maar k an ook beskou word as oewer areas waar groei of lewe op die banke van strome en riviere voorkom. Oewergebiede word ook gesien as smal liniêre stroke wat as korridors vir migrerende spesies optree. Tydens die studie is daar 240 persele uitgeplaas in verskillende homogene plantegroeitipes langs die Vetrivier. Die Braun-Bl anquet veelheidsskaal is gebruik tydens die studie. Die plantegroeiklassifikasie he t gelei tot die klassifikadie en identifikasie van 14 plant gemeenskappe, 21 sub gem eenskappe en 11 variante wat fitososiologies beskryf is. Die gemeenskappe kan v erdeel word in die gemeenskappe wat in die berge voorkom, die gemeensk apppe wat langs die rivier op die vlaktes voorkom en die gemeenskappe wat op d ie vloedvlaktes of panne langs die Vetrivier voorkom.