Geoterra Image (South Africa)

The South African Statistical Association (SASA) turned 70 years old in 2023, having made huge impacts in South Africa and beyond. Through SASA, the statistics community in South Africa has made significant strides in the field, both locally and internationally, ensuring the importance of the discipline is concreted into the academic and industry playing fields. The statistics community continues to grow and remains passionate about growth and development of school learners, undergraduate and postgraduate students, academics and statisticians in industry. The opportunities for statisticians in South Africa are endless, and important to the economic sustainability of South Africa. This paper provides an historical overview of the impacts of the South African Statistical Association and statistics in South Africa.

Rangeland conditions in the Lesotho highland dam catchment areas is important for local livelihoods and regional water supply. We investigated changes in land cover and condition from 1991 (before construction) to 2013, using Landsat imagery. The Normalised Difference Vegetation Index (NDVI) decreased in the catchment areas, while increasing within two protected areas. NDVI decreases were greatest close to the dams and in the high altitude summer grazing areas. Land cover maps were generated for 1993, 2005 and 2013, using structural vegetation classes, as well as categories of grassland based on NDVI. High altitude areas were characterised by grasslands changing to lower NDVI categories, indicating overgrazing in climax sourveld grasslands. Mid-altitude areas were characterised by grasslands changing to higher NDVI categories and increases in woody vegetation, indicating overgrazing in Sweetveld. At lower altitudes, the increase in cultivated areas suggested disproportionately high population growth in the catchment areas. The results suggest that there has been widespread degradation that appears to be more as a result of overgrazing than climate change. The study demonstrates the importance of using a combination of land cover, NDVI and field data in assessing degradation. Natural capital accounting methods provide a useful framework for documenting, monitoring and understanding changes in ecosystem condition.

Increases in woody plant cover in savanna grassland environments have been reported on globally for over 50years and are generally perceived as a threat to rangeland productivity and biodiversity. Despite this, few attempts have been made to estimate the extent of woodland increase at a national scale, principally due to technical constraints such as availability of appropriate remote sensing products. In this study, we aimed to measure the extent to which woodlands have replaced grasslands in South Africa's grassy biomes. We use multiseason Landsat data in conjunction with satellite L-band radar backscatter data to estimate the extent of woodlands and grasslands in 1990 and 2013. The method employed allows for a unique, nationwide measurement of transitions between grassland and woodland classes in recent decades. We estimate that during the 23-year study period, woodlands have replaced grasslands over ~57000km2 and conversely that grasslands have replaced woodlands over ~30000km2 , a net increase in the extent of woodland of ~27000km2 and an annual increase of 0.22%. The changes varied markedly across the country; areas receiving over 500mm mean annual precipitation showed higher rates of woodland expansion than regions receiving <500mm (0.31% yr-1 and 0.11% yr-1 , respectively). Protected areas with elephants showed clear loss of woodlands (-0.43% yr-1 ), while commercial rangelands and traditional rangelands showed increases in woodland extent (>0.19% yr-1 ). The woodland change map presented here provides a unique opportunity to test the numerous models of woody plant encroachment at a national/regional scale.