Vegetation dynamics of urban open spaces subjected to different anthropogenic influences
Putter, Johannes Marthunis
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Urbanisation contributes to the degradation of urban biospheres, and the degeneration of the quality of life for future generations, In the North West Province the urbanisation rate is expected to rise dramatically due to continued drought in rural areas that causes a high poverty rate and low levels of job opportunities. The increasing urbanisation and the need to provide homes for the homeless, place the natural, spontaneous and other vegetation types under extreme pressure. Conservation of open spaces, especially those with natural and semi-natural vegetation, is constantly in competition with urban development. Little research has been done on vegetation in man-made habitats and therefore, planners and national, provincial and local governments in South Africa are unaware of the true biological and ecological value of urban open spaces. Biotope mapping for urban areas based on land-use is one method to determine and map those areas worthy to protect. The map of the urban biotopes forms an important background for planning, management and conservation of urban open spaces. The first urban biotope mapping project in South Africa was completed in 2001 in the city of Potchefstroom. A key for urban biotope mapping was developed, based on German experiences, but adapted to South African conditions. Maps were also drawn up to assist in proposed measures for development and conservation and additional general ideas and proposals to create a better environmental situation for Potchefstroom. Decisions on which plant communities and species must be controlled and which must be conserved could, however, only be based on long-term vegetation dynamics studies. In this thesis, quantitative methods were used to study the vegetation dynamics of certain urban biotopes subjected to different anthropogenic influences. These biotopes include management grasslands, secondary grasslands and a variety of pavements occurring in different land-use areas. Changes in management practices such as the termination of mowing and weeding as well as human impacts such as trampling in areas that haven't iii been disturbed for a while, brought about changes in species composition and/or abundance within one year. Changes in species importance values over time can be attributed to changes in management practices, especially in managed and ruderal grasslands. Experimental studies are, however, needed to verify the results. The time span over which this study took place was probably not long enough, although changes did occur within the first year. Seed-bank analyses were also performed on the different biotopes to investigate the real plant diversity, including plants only present as seeds at the time of the survey. The data collected were analysed using multivariate statistics.