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

[摘要] ENGLISH ABSTRACT:Many authors express the value of riparian vegetation in terms of the function and numberof species per unit area. Although riparian vegetation is confined to narrow bands ofplants 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 theJonkershoek Valley, Western Cape Province, South Africa, a checklist was compiled, byreferring to past research and to the PRECIS national database for the South African florafor a list of species recorded from the area. A total of 1 743 taxa and 108 families wereincluded in this list for the Valley.Specific characteristics were attributed to each of the 1 743 species on the basis ofcharacters determined from the literature. Analysis of these data indicates that woodyperennial shrubs with sclerophyll leaves are the representative plant type for the studyarea as a whole. The specialist structural description of a riparian species in theJonkershoek Valley is: an unbranched woody perennial phanerophyte of a height between2.0-8.0 m with microphyllous sclerophyilleaves. This group contributes 63% towards theriparian flora.Riparian habitats occupy only 2.5% of the total study area but contribute 26% of thevascular plants. The riparian communities of the Santa Monica Mountains (USA) cover0.7% of that mountain study area and provide a habitat for 20.5% of the total vascularplants of the area. Both areas, therefore, show a similar level of diversity. Thisremarkable 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 throughthe main stem and it's tributaries. A total number of 139 relevés were recorded whichwere used to identify, characterise and describe the riparian communities. Eightvegetation units, consisting of two groups, three communities, two subcommunities andone form, were described. The one group described the riparian communities while theother described a seepage community. The bigger groups exhibit environmentalproperties over a broader spectrum, while smaller groups exhibit characteristicenvironmental properties.The vegetation is found to represent a continuum rather than discreet entities. Manyindicator species are encountered in the communities. Because of the characteristiccanopy-understorey physiognomy of riparian vegetation, many communities areinterspersed, making it difficult to delineate discreet community boundaries.The vegetation of the riparian zone of the Eerste River in the Jonkershoek Valley, isrelatively pristine. Thirty-six species not native to the Valley were included in the checklistof which only four were recorded during the phytosociological study.

[发布机构] Stellenbosch University