Plantsosiologie van die Bloemfontein-Wes-Distrik

[摘要] English: The aim of this study was to identify, characterize and interpret, ecologically, by using hahitat properties, the major vegetation units and their variations.The study area covers approximately 350 000 hectares. Most of the area is intensively utilized for farming practice.The western parts of Bloemfontein are, geologically underlied by the Ecca group. The hilly appearance of this area is caused mainly by dolerite intrusions.Bloemfontein is situated in a semiarid region, having dry, cold winters with frost and warm summers accompanied by a low, irregular rainfall. The mean annual rainfall is 564 mm,but it varies greatly.As far as the biotic environmental factors are concerned, man, especially, plays a great part by affecting the composition of the vegetation and the condition of the habitat.A total of 254 sample plots were used to survey the area. A combination of classification techniques was used to interpret the vegetation, ecologically, and to identify and classify plant communities.The study area was stratified according to land types. The number of sample plots was chosen subjectively and pro rataaccording to the size of each land type within each landtype.Five separate plant sociological tables were compiled, and the results of each of these are discussed separately. Because the Bloemfontein area was previously studied bydifferent authors no survey was made in the Ea-land type.Thirty five plant communities were identified and described.These communities are summarized in a synoptic table for the entire study area. In the synoptic table four vegetation units could be identified. These units are:(1) Communities of the other Rhoetalia ciliato-erosae(2) Communities of the lowland areas(3) and (4) Disturbed communities of the lowland areasThe most important tree species are Acacia karroo, Buddleja saligna, Celtis africana, Cussonia paniculata, Ehretia rigida, Grewia occidentalis, Heteromorpha trifoliata, Oleaeuropaea subsp. africana, Rhus lancea and Ziziphus mucronata.The dominant shrubs include: Euclea crispa, Euphorbia mauri tanica, Rhigozum obovatum, Rhus burchellii, R. ciliata en R. erosa.The dominant grass species are Aristida congesta, A. diffusa, Chloris virgata, Digitaria eriantha, Eragrostis curvula, E. lehmanniana, E. obtusa, E. superba, Heteropogon contortus, Themeda triandra and Triraphis andropogonoides. Among the dwarf shrubs and herbs Asclepias fruticosa, Berkheya onopordifolia, B. pinnatifida, Chenopodium album,Felicia filifolia, Lactuca dregeana, Chrysocoma ciliata, Cirsium vulgare, Hermannia bryoniifolia, Hertia pallens, Lantana rugosa, Melolobium candicans, Nenax microphylla, Nidorella resedifolia, Protasparagus laricinus, P. striatus, P. suaveolens, Rumex crispus, R.lanceolatus, Salsola kali, Salvia stenophylla, S. verbenaca, Solanum coccineum, S. incanum, Stachys rugosa, Tagetes minuta en Walafrida saxatilis are the most important.The stratification of the study area into land types and the compilation of a separate plant sociological table for each land type resulted in the successful identification of ecologically sound plant communities.

[发布机构] University of the Free State