Vegetation ecology of the putative Palaeo-Kimberley and Palaeo-Modder rivers and their catchments, Free State, South Africa

English: The Free State is often seen as a flat and boring landscape with no prominent features in the region. However, when looking at the western Free State an intriguing landscape with numerous pans is revealed. Several researchers have investigated this area and the reason for the existence of these pans is still unclear. Suggestions are that these pans might be the remnants of two putative palaeo-rivers (Palaeo-Kimberley and Palaeo-Modder). This study investigated the present-day vegetation found in the catchment and investigate data from Baden-Baden that can contribute towards the understanding of the vegetation during the past and specifically the Quaternary. This will contribute towards the understanding and predicting the vegetation and climatic changes in the future. This study was conducted in the western parts of the Free State between the Vet- and Modder Rivers. Southern Africa’s geology and topography was influenced by the break-up of Gondwana; some of these imprints are still present today. Geologically the Free State is mostly dominated by the Karoo Super Group with the Beaufort and Ecca Groups as well as dolerite outcrops prominent in the western Free State. The topography is relatively flat with some depressions bordered by the presence of lunette dunes on the south-eastern sides. Dolerite outcrops provide some small hills in the undulating landscape. Climatically the area falls within the Highveld climatic region with cold and dry conditions due to the high elevation. Rainfall is confined to the warm summer months (October to March), while the winters are mostly cold and dry (summer-rainfall). Thunder storms in the afternoon and early evenings are the main source of precipitation. The rainfall in the Free State decrease towards the western parts, while the evaporation increase. The high evaporation of the western Free State is much more important in terms of the semi-arid climate than the low rainfall of the area. Summer rainfall is highly variable as the past two years experienced below average rainfall in the area. Life on land depends on complex interactions between geology, climate, landscapes, organisms and community structures that are shaped by the features, but which themselves also contribute to the evolution of the ecosystem structure. Thus, a strong association exists between habitat shifts and species diversification. The geology, topography, soils and climate of the study area have changed over time. Landscapes are characterised by the three elements of structure, process and change. The landscape makes an imprint on the vegetation and changes in the landscape cause changes in the vegetation. Today’s vegetation in the western Free State is thus, the product of the present environment but also of the past. The region’s vegetation falls in two biomes. The Grassland biome (between sea level and an altitude of 2 850 m above sea level) occurs mostly on the central plateau of South Africa and the Savanna biome (present below 1 500 m above sea level) in areas with a strong seasonal rainfall and a dry season mostly in winter. Patches of Inland Azonal Vegetation (present at 1 000 m to 1 600 m above sea level) are also present in the western Free State. Eleven different vegetation types occur in the study area. During this study 410 sample plots were placed in homogenous vegetation types in the western Free State. The Braun-Blanquet method has been applied to study the present-day vegetation. Analysis of the present day vegetation led to the identification of 24 different plant communities, 43 sub-communities and 29 variants. The communities were grouped into community-groups that occur in the wetland and water related areas, the grassland and karroid communities occurring on the plains and the woody communities limited to the dolerite outcrops and some deep sandy areas on the plains. Reconstructing the changes in vegetation during the past is done by using fossil pollen from peat deposits around springs. These pollen deposits are limited to organic sediments which are rare in the semi-arid and arid areas of South Africa and thus the western Free State. Sites such as Florisbad, Deelpan etc. have been investigated in previous studies and revealed an alteration between wet and dry periods from these data sources gaps in the chronological timescale has been revealed. These gaps are partially filled by the data from Baden-Baden, a thermal spring near Annaspan. In this study pollen from the Baden-Baden sediments was extracted, mounted on slides, counted and identified under a microscope. The results revealed the first presence of pollen during isotope stage 2 in the central parts of South Africa. Future research can provide further insights into the development of the Grassland biome and the changes in climate. This will contribute towards understanding and predicting the vegetation and climatic changes in the future.