Relative pollen productivity estimates (PPE) and relevant source area of pollen (RSAP) for key taxa from vegetation communities in Cathedral Peak, KwaZulu-Natal Drakensburg.
Duthie, Tristan Jane.
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Pollen analysis has proved to be an effective method for elucidating and reconstructing past vegetation patterns, and can be effective in attempting to understand the possible future implications of environmental change. However, ‘true’ reconstructions of past vegetation patterns and distributions based on pollen analysis have proved elusive due to a number of intrinsic limitations in palynological data interpretations. Perhaps the most pronounced deficiency in interpretation of pollen diagrams used for reconstruction is the fact that no explicit spatial context is discernible for where in the wider landscape the pollen originates - consequently, interpretation of pollen diagrams remains innately subjective and predominantly based on intuition. For any given site containing pollen rich sediments, it is important to consider the sources of that pollen, and the means by which it arrived at its preservation site - only by doing this, can one better interpret the pollen assemblage in terms of past vegetation. This research focuses on modern pollen spectra of three vegetation communities (Themeda grassland, Protea savanna, Leucosidea scrubland) in the Cathedral Peak region of the KwaZulu-Natal Drakensberg. The intention is to use models of pollen dispersal and deposition that attach spatial contexts to pollen data extracted from an environment and to link this research to fossil pollen work in the Drakensberg. Fifteen soil surface samples were collected from Cathedral Peak, chemically digested and modern pollen spectra extracted. Vegetation data were collected around each sample point using a 3-tiered ring surveying approach out to a maximum radius of 5 000 m, and distance-weighted using Sutton’s taxon-specific weighting method. Fall speeds of dominant taxa were calculated using Stokes Law for spherical pollen grains and Falck’s assumption for ellipsoidal grains. Pollen and vegetation data were processed through HUMPOL software suite and Extended R-value analysis to calculate Relevant Source Area of Pollen and Pollen Productivity Estimates for each vegetation community. Results showed the source areas of approximately 150 m for Themeda grassland, 100 m for Protea savanna and 100 m for Leucosidea scrubland. Productivity estimates revealed Poaceae (PPE = 1) to be significantly more productive than herbaceous and shrubs taxa analysed (PPE = 0.00057), yet arboreal taxa were significantly higher in productivity (PPE = 6.5) relative to Poaceae. Findings show pollen models have a very relevant place in South African pollen research and can significantly impact future work by strengthening the foundation from which we base our understanding – the interpretation of results.
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