Palaeoecological studies on the development of the world's southernmost palm-swamp peatland ecosystem in Kosi Bay, South Africa

Palm-swamps are known as peat forming environments from several tropical regions. The southernmost peat forming palm-swamps lie in Kosi Bay, at the South African East Coast (27° southern latitude), consisting of scattered homogeneous stands of Raphia australis Oberm. and Strey. It is the only Raphia species endemic to southern Africa and red listed. This study investigates the genesis of a R. australis palm-swamp peatland at Kosi Bay. Environmental reconstruction based on plant macrofossils, pollen, elemental composition and peat qualities, supported by AMS radiocarbon dating unveiled that: i) a shallow peat layer (ca. 55 cm) has accumulated since about 1000 CE under a regionally warm and wet climate, with the first peat forming vegetation community composed of sedges, including Pycreus polystachyos and Cyperus sp. Around 1370 CE a shift to swamp forest occurred. R. australis became established around 1550 CE, following a fire and becoming dominant around 1900 CE; ii) peat accumulation occurred since then at a low rate of 0.038 mm yr⁻¹ (19 g m⁻² yr⁻¹), which is especially low for top soil peat layers, yet indicates rather steady hydrologic conditions on the floodplain with currently low peat accumulation potential. Raphia peat is highly decomposed, with high contents of aromatics, aliphatics, and also of amids. Peat forming parts are the roots, leaves become decomposed in the surface layer; iii) the ecological conditions (eutrophic: C/N 14–20; slightly acid: pH 5–6) resemble rather Amazonian Mauritia flexuosa palm-swamps peatlands than Raphia peatlands of the Congo Basin.