Influence of mountain geomorphology on alpine ecosystems in the Drakensberg Alpine Centre, Southern Africa

摘要

In the Drakensberg Range of eastern Lesotho, periglacial sorted circles, stone-banked and turf-banked lobes, blockfields, block streams and wetland thufur (earth hummocks) are present. These features are of varying ages (likely from Last Glacial Maximum to contemporary) and have been disturbed by soil formation and vegetation growth. This study uses a mixed methodology to investigate relationships between periglacial landforms, slope aspect and their associated ecosystems, and the relative age relationships of these components at Mafadi Peak on the Lesotho-South Africa border. A distinctive alpine flora, belonging to the Drakensberg Alpine Centre of the wider Afromontane phytochorion, is found in association with different periglacial landforms. Vegetation quadrat analysis shows that slope and aspect have no significant effect on vegetation cover, plant species abundance and bare ground cover. The most likely microscale relationships are with surface geomorphic features. The relative surface hardness and thus age of clasts within and outside of the stone/turf-banked lobes show that even within single landforms, variations in weathering exist, likely related to episodic and seasonal alpine cryoturbation. Major soil physical properties (grain size, organic and C/N content) and soil depth were measured. Weathering and soil development, influenced by climate, provide a substrate for a nutrient-deficient, sparse alpine flora and vegetation assemblage. The relationships between periglacial geomorphology and alpine ecosystems are not well understood from southern African high mountain regions, but are important with respect to ecosystem responses to ongoing climate change.