Themeda Triandra Renosterveld in the Heidelberg District

[摘要] ENGLISH ABSTRACT: This study investigated the composition of Themeda triandra Renosterveld in part of theGrootvadersbosch Conservancy and the effects of selected environmental and management variables toprovide guidelines for promoting the presence of Themeda triandra in the veld.The Zürich-Montpellier phytosociological method was used to determine the composition of theRenosterveld communities. The point quadrat method was used to determine the cover of Themedatriandra at three grass dominated sites and compare cover from one site with past cover measurementsat the specific site. Ordination was used to examine the effects of the environmental and managementvariables on the plant communities.Two community groups, five communities and five subcommunities were identified and described.The Themeda triandra – Stoebe phyllostachys Grassland Community Group consists of twocommunities of which one has two subcommunities. The Themeda triandra – Elytropappusrhinocerotis Shrubland Community Group consists of three communities of which one has threesubcommunities.The vegetation units described in this study have not been described previously in the literature. Onecommunity belongs to Silcrete Fynbos while another subcommunity is transitional betweenRenosterveld and thicket and gallery forest. The rest of the plant communities fit the definition forRenosterveld (the local Renosterveld type is Eastern Rûens Shale Renosterveld).Cover of Themeda triandra did not differ significantly either between sites or between years. Thecomparison of Themeda triandra cover between years was done at a site that had been burnt betweenthe last two sampling times yet the cover was not significantly different. This indicates that fire andother management practices did not have a negative impact on Themeda triandra at the site.Unconstrained ordination of the dataset in which cover/abundance values were included, grouped therelevés by moisture and disturbance but the presence/absence dataset indicates that the two communitygroups have a slight transitional overlap. Constrained ordination of both datasets with a) soil variablesand b) management variables, both showed a tendency to separate the relevés into community groups,that did not happen with topographic and vegetation variables. Ordination did not separate thecommunity groups into their subdivisions.The soil variables (both nutrients and texture) influence the vegetation structure and the communitydistribution.Under the existing grazing management regime, fire at three to five year intervals promoted thedominance of Themeda triandra by affecting the structure of the plant communities, the abundance of species other than Themeda triandra, and influencing which plant community is present. The use offire as a management tool was regulated by the importance of the natural veld pastures to the farmers.The natural veld pastures are not suitable for dairy cattle in milk. Thus dairy farmers are less likely toburn the natural veld (no planned burns only chance fires) than those who farm with mutton or beef(planned burns on a three to five year interval).

[发布机构] Stellenbosch University