Biodiversity and ecology of critically endangered, Ruens Silcrete renosterveld in the Buffeljagsrivier area, Swellendam

[摘要] ENGLISH ABSTRACT: Rûens Silcrete Renosterveld (RSR) is a critically endangered vegetation type in the Overberg region of the Western Cape Province of South Africa. In the last few centuries about 80% of it has been severely transformed by agriculture. The RSR contains many unique and rare plants species, and has very high conservation value. It is recommended that all remaining areas of this vegetation type should be conserved. However, very few of these areas are formally conserved and most are on farms where they are used for grazing of domestic livestock. The RSR appears to be sensitive to overgrazing and to grazing at a time of the year when it is sensitive to major change. This study examined the effects different grazing regimes had on the RSR vegetation on farms in Buffeljagsrivier, a small farming community in the Eastern Overberg. Different methods were used to compare vegetation structure and composition, of heavily-, medium- and under-grazed areas.Information on the biodiversity in RSR areas was found to be scarce, with almost nothing known of the invertebrates. In this study a comprehensive checklist of plants and vertebrates in the study area was compiled. An insect order/family list and separate species lists of Lepidoptera and Orthoptera were also compiled. The insects were recorded by using different collecting and observation methods. A study was also made of the major plant/animal interactions occurring in the area. For this study, the focus was mainly on interactions with two dominant woody plants, Acacia karroo and Searsia glauca. Other interactions were also noted.Different grazing regimes affected both structure and plant composition in the different grazing camps. Some plant species were found to be more dominant in heavily-grazed areas and some more in under-grazed areas. Heterogeneity in grazing pressure of the camps contributes to make the whole area more diverse and may have enabled the high biodiversity to persist in the area.More than 400 indigenous plant species were recorded in the study area of which more than 30 plant species were found to be of conservation concern. 37 % of the overall species are endemic to the Cape Floristic Region. The study area contained 127 geophyte species. This is 51 % of all the known geophyte species that occur in the Langeberg Centre. A new plant species, Haworthia groenewaldii, was discovered in the study area. Overall, 214 insect families in 23 insect orders were also found in the study area. A total of 103 Lepidoptera species was recorded. About five moth species are possibly new to science and still need to be scientifically described. Some plants and insects were recorded beyond their known geographical ranges. Twelve different frog, 22 reptile, 30 mammal and 122 bird species were found to occur in the study area.Nineteen insect species from 14 insect families in four orders associated with Acacia karroo trees were found in the study area. Thirty-four insect species from 25 families, in six orders, were found to be interacting with Searsia glauca trees. Sixty one bird species were associated with A. karroo and 42 with S. glauca. Other interactions that were observed included caterpillars feeding on host plants. For the Lepidoptera list, the possible plant species on which the juveniles feed was also investigated.This study unequivocally showed that this geographical area has a very high overall biodiversity that needs to be conserved. It also found that grazing can affect the composition distribution and combination of this biodiversity. Much research is still to be done on plant/invertebrate interactions in the RSR. This study provides a baseline for further research on future actions to conserve this unusual and special area in terms of invertebrate biodiversity especially for generations to come.

[发布机构] Stellenbosch University