A remote sensing and GIS scheme for rangeland quality assessment and management in the North-West Province, South Africa

Abstract

South African rangelands contribute 80% of the total area of the country although most of them are believed to be degraded due to anthropogenic activities. In the North-West province of South Africa, degradation of rangeland is of concern mainly because of the long history of environmental and political neglect and over utilization of the land. The North-West province is characterized by three rainfall zones: low, medium and high with three major rangeland management regimes in the form of communal rangelands, protected areas and private ranches. Depending on the amount of rainfall and the type of rangeland management strategies, productivity level differs across the rangelands. However, the differences in the productivity level among these rangelands have not been defined quantitatively in previous studies. The focus of this study was to determine the productivity level of different rangelands and quantitatively identify the underlying differences. Therefore, this study is an attempt to assess the ability of remote sensing SPOT-5 data in extracting and mapping rangeland biophysical information in three rainfall zones in the North West Province, South Africa. Vegetation indices (Normalised Difference Vegetation Index (NDVI), Soil Adjusted Vegetation Index (SAVI) and the Spectral Mixture Analysis (SMA)) were computed and integrated with field based aboveground biomass data using regression technique. A remote sensing and GIS scheme for assessment of rangeland quality and management was established. Results showed that high and medium rainfall areas are more productive than the low rainfall areas. The coefficient of determinations for the impact of rainfall distribution and temperature on above ground biomass (AGB) production was R² = 0.47 and 0.53 respectively. Significant differences (P <̲ 0.05) between different rangeland management regimes across all the rainfall zones were observed. Thus, rainfall distribution, temperature during growing season and rangeland management strategies play major role in determining AGB productivity of rangelands. Evaluation of the performance of the vegetation indices for AGB estimation revealed that the SAVI performed well in the low rainfall areas but the coefficient of determination between the AGB and SAVI was not significant at p≤ 0.05. The SMA also performed better than the NDVI in low rainfall areas but because of its weaknesses in the high and medium rainfall areas this tool is not ideal for quantifying AGB in the North-West province. In spite of its weakness in the low rainfall areas, the NDVI had displayed stronger coefficient of determination with AGB. Hence, the NDVI was found to be the most efficient vegetation index for quantifying AGB in the North-West province. Using GIS, several datasets topographic data, rainfall distribution data, remote sensing data, ground-based data, water resource data and distribution of animal unit data across rangelands were integrated in order to develop a Rangeland Grazing Suitability Scheme. The scheme provides a structure for monitoring grazing capacity of rangelands. This scheme shows the level of grazing that a particular rangeland should be exposed to and it could be very helpful for cattle ranchers and extension personnel in selecting areas for grazing for a given period of time. The scheme has a capacity for balancing forage availability in relation to forage demands by animal units. Results of the scheme showed that private ranches and protected areas in medium and high rainfall zones are highly productive with higher carrying capacity and available foliage to animals than the communal areas and the low rainfall zones. Private ranches and protected areas are under-grazed while the communal areas are exposed to high exploitation and overgrazing in all rainfall zones. In addition, distance to watering points was a limiting factor in accessing forage in the communal lands and Molopo Nature Reserve while slope played a major role in limiting forage accessibility in the Pilanesberg National Park. It is envisaged that adoption of this scheme by stakeholders and rangeland managers would increase the efficiency of rangeland monitoring process thereby increasing their productivity. The scheme has a capacity of balancing forage availability in relation to forage demands by animal units.