Gradient analysis of bottomland vegetation in three land types of the Highveld region

MSc, North-West University, Potchefstroom CampusThe need for improved management and a better ecological understanding of the veld in South Africa cannot be over emphasised. The influence of grazing on the veld species composition and veld condition in general is especially important and the contract research undertaken by the Potchefstroom University for C.H.E. deals with this aspect for the Highveld region of South Africa. The study forms part of this research. The study area is the bottomlands (terrain unit 5) of three landtypes in the Highveld region namely, Bb25, Ca6 and Bc25. A total of 95 sites (30 x 30m each) were evaluated. Special attention was given to sites with varying environmental characteristics and differ enc es due to grazing. A nearest plant survey (200 points) using a wheel- point apparatus was carried out. At each point observation, the nearest plant was identified, the distance to the nearest plant was measured and the diameter of tufted grass species was measured. A soil sample ( 0-30cm) was also collected in the middle of each site and analised for calcium, magnesium, sodium, organic matter, phosphate and pH. Direct and indirect gradient analysis procedures · were used to identify species responses to grazing and soil related gradients. Multiple regression and Principle Components Analysis were used to model these responses and to identify the important soil factors. The results of these approaches are discussed separately and also summarised in the form of habitats with the associated community organisation and change due to grazing. The results showed that two important gradients influence species composition in the bottomlands, namely drainage and grazing. Drainage is essentially a function of the soil, slope and the position of the site in the landscape. It was also evident that grazing interacted with the habitat, and/or caused changes to the habitat. This observation suggests that the grazing gradient can be named a grazing/habitat interaction gradient. Soil base status and soil sodium level were linked to this interaction and this in turn was linked to the parent material. Overgrazing increased the aridity of the site and this was attributed to the increased run off and donga formation in overgrazed areas. The point to tuft and tuft diameter measurements indicate that basal cover changes from large widely spaced tufts in undergrazed sites to small closely spaced tufts in overgrazed sites. The species modeling procedure did show some success with those species that had linear rather than strong curvilinear responses, and with those species that were abundant. The habitat and associated community organisation and change described by the model were closely related to field observations. The fact that certain species differ in their reaction to grazing with changing habitat was emphasised in this part of the study. The conclusions drawn from this study emphasise the influence of habitat on both management objectives, and the response of species to grazing. The possibility of using multidimensional response surf aces to understand a species response to multiple factors is suggested.Master

The impact of fertilization veld in terms of species composition and basal cover of grazed veld in the Potchefstroom area.

The impact of fertilization on veld in the Potchefstroom area was investigated. Nitrogen and phosphorus were applied annually from 1972/73 until 1981/82. The control plots and the fertilized plots were grazed with year-old steers. Species composition and basal cover were recorded using the wheelpoint technique. The results clearly indicated the formation of a soil fertility gradient as a result of the fertilization. Although there was a decrease in the ecological status of the fertilized plots, the production and palatability of the sward increased and thus also animal performance.Keywords: animal performance; basal cover; botany; composition; cover; ecological status; fertility; fertilization; nitrogen; palatability; performance; phosphorus; potchefstroom; production; retrogression; soil; soil fertility; south africa; species composition; succession; technique; vel