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

Groenewald, Johannes Philippus (2014-12)

Thesis (MScConsEcol)--Stellenbosch University, 2014.

Thesis

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.

AFRIKAANSE OPSOMMING: Rûens Silkreet Renosterveld (RSR) is ʼn Kritiek Bedreigde veld soort,in die Overbergstreek van die Wes-Kaap Provinsie van Suid-Afrika. Omtrent 80% van RSR is uitgeroei deur landbouprakteike van die afgelopetwee eeue. RSR bevat baie unieke en skaars plant spesies en het dus ʼn baie hoë bewaringswaarde. Dit word aanbeveel dat alle gebiede wat die tipe plantegroei bevat, bewaar behoort te word. Baie min van die oorblywende RSR word formeel beskerm en die grootste gedeeltes wat nog oor is, kom voor op plase waar dit vir weiding ingespan word. Die veld soort is skynbaarbaie sensitief vir oorbeweiding, asook vir beweiding in die verkeerde seisoen. Hierdie studie het na die uitwerking van verskillende weidingsmetodes op natuurlike veld op aangrensende plase in Buffeljagsrivier, ʼn klein plaasgemeenskap in die Oostlike Overberg, gekyk. Verskillende metodes was gebruik om die plantegroei se samestelling en struktuur van ʼn lae, middelmatige en oorbeweide gebiede met mekaar te vergelyk. Inligting oor die biodiversiteit van RSR, veral oor invertebrate, was moeilik om in die hande te kry. Spesies lyste so volledig as moontlik was in die studie vir al die vertebrate en plante opgestel. Lyste is ook opgestel vir alle insek ordes en families, wat in die studiegebied versamel is. Daar is ook aparte lyste opgestel vir alle Lepidoptera en Orthoptera, in die studiegebied. Verskillende metodes was gebruik om insekte te versamel en te monitor. Die interaksies tussen plante en diere, wat voorkom in die studie gebied, is ook bestudeer Twee plantsoorte, Acacia karroo en Searsia glauca, is uitgesonder en so veel moontlik biologiese interaksies is opgeteken. Ander interaksies was ook aangeteken soos hulle in die veld aangetref is. Die studiegebied het meer as 400 plant spesiesbevat. Van die was meer as dertig van bewaringsbelang. Sewe-en-dertig persent van die plante wat aangeteken is, is endemies tot die Kaapse Plant Koningryk. Daar is altesaam 127 bolplant spesies gevind wat net meer as die helfte van alle bolplant species wat vir die Langeberg Kern aangeteken is. Haworthia groenewaldii is ʼn nuwe plant spesies wat in die studie gebied ontdek is. In die studie area is 214 insek families in 23 insek ordes opgeteken. Van die is 103 Lepidoptera species (waarvan vyf moontlike nuwe spesies is) aangeteken in die studiegebied. Negentien insek spesies van 14 insek families in vier ordes het interaksies met A. karroo getoon. Interaksies tussen vier-en-dertig insek spesies van 25 insek families in sesordes het met S. glauca getoon Een-en-sestig voël spesies was geassosieerd met A. karroo en 42 met S. glauca. Ander interaksies watgewaar is, sluit ruspes op voedselplante in. Twaalf verskillende paddas, 22 soorte reptiele, 30 soorte soögdiere en 122 soorte voëls was ook in die studie gebied aangeteken. Uit die huidige studie is dit duidelik dat die gebied ʼn baie hoë biodiversiteit besit wat beskerm moet word. Daar is ook bevind dat weiding die samestelling en struktuur van RSR kan beïnvloed. Verdere studies oor die plant/dier interaksies in RSR behoort gedoen te word en hopelik dien die huidige studie as ʼnbegin vir verdere navorsing oor hoe ons die unieke veld soort vir die nageslag kan bewaar.

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