Die gebruik van degradasiegradiënte vir weiveldevaluering in 'n semi-ariede gebied

English: 1. The objectives as determined for this study are; * to classify the main land types in the central and southern Free State into homogenous plant communities; * the quantification of rangeland condition in every homogenous plant community by means of degradation gradients; * to develop easily and quick implementable techniques which can be used by land users te determines rangeland condition (these techniques must be scientificaily acceptable) and * to determine correlations between rangeland condition and grazing capacity. 2. The study was performed in the semi-arid region of the central and southern Free State and includes 35 different land types in the magisterial districts of Zastron, Rouxville, Wepener, Smithfield, Dewetsdorp, Reddersburg, Bloemfontein, Brandfort, Excelsior, Theunissen, Winburg, Thaba Nchu, Senekal, Petrusburg, Boshof, Bultfontein, Edenburg, Trompsburg, Bethulie, Jagersfontein, Fauresmith, Philippolis, Koffiefontein, Jacobsdal, Ventersburg, Virginia, Hennenman and Hoopstad, also includes bordering areas in the magisterial districts of Kimberley and Barkly West in the North Cape province. The study area forms part of a summer rainfall area with a long term average rainfall from approximately 300 mm in the west to 680 mm in the east. 3. With the use of multivariate analysis the study area was classified into 13 different homogenous plant communities which vary from a sour grass- to a mixed sour grass- to sweet grass- to false karoo- to karoo- to a savanna veld type. Degradation gradients were described by means of the ISPD system for every homogenous plant community. This degradation gradients varied from poor denuded rangeland, around water troughs, to well-managed rangeland on the first axis, while degradation on account of selective grazing also occurred on single occasions. 4. The ecological value of species was determined by means of the Gaussian distribution curve. To facilitate the ecological value of species, an index was set up that varied from zero to ten. 5. Indicator species were identified for the study area by looking at the relationship between individual species and the degradation gradients. Dominant indicator species were also identified that made the most important contribution to veld composition at one stage or another on the gradients. 6. Correlations between degradation and effective soil depth, texture and chemical soil characteristics of top soils was determined for each homogenous plant community. At wet and half-wet climate zones it was mainly the P-content that increased during degradation. At the half -dry and dry climate zones degradation leads to a loss in effective soil depth, while texture changes occurred more frequently. 7. As computer equipment can limit the use of the degradation gradient, easier alternative methods were investigated. The main advantage of this technique is that the operators need only to know the key species, that can drastically increase the utilisation value of these techniques. 8. Grazing capacity calculations were done for sheep as well as cattle at every locality. The preference utilisation ratio of species was used to determine the utilisation production for every production plot. Where the grazing capacity's were mostly subjectively determined in the past, a more objective approach was used in this study. 9. With the exception of some homogeneous plant communities, good correlations were determined between rangeland condition and grazing capacity. Exceptions did occur in the Themeda-Cymbopogon mixed sourveld, the Pan-turf Veld and the Broken Parkland where additional data should be collected. 10. Finally the most important characteristics of rangeland condition according to the changing in botanical composition of dominant species, soil changes, and grazing capacity recommendations for both sheep and cattle are tabulated for homogenous plant communities. Land users and operators can use these tables with confidence to estimate the condition and potential of rangelands. If this rangeland evaluating techniques are linked to rangeland management if would ensure sustainable utilisation of the grazing ecosystem.