A high resolution Holocene pollen record from Braamhoek, eastern Free State, South Africa

Abstract

A report is given of a palaeoecological study based on the analysis of pollen and a variety of micro- and macrofossils and of the pollen density/influx of a section of peat deposits on marine clay from the Assendelver Polder (The Netherlands). The section, representing the time interval of approximately 4500—800 B.P., was studied at five-cm and one-cm intervals. A detailed reconstruction of the vegetational succession is given. The main phases of which the pertaining syntaxonomy is discussed comprise: (a) a Phragmites—Carex swamp formed under eutrophic conditions on top of marine sediments deposited during the Calais IVa transgression, ca. 4500—4200 B.P.; (b) a Thelypteris dominated swamp that prevailed during somewhat drier conditions; (c) a Phragmites–Carex swamp; (d) a Phragmites swamp accompanied by many herbaceous species during drier and less eutrophic conditions (total duration of phases a—d: from ca. 4200—ca. 2500 B.P.); (e) a Molinia fen developed under mesotrophic conditions (ca. 2500—2300 B.P.); and (f) an Ericaceae—Sphagnum and Eriophorum bog, developed during oligotrophic conditions (ca. 2300—1200 B.P.).Using 14C data, the absolute numbers of pollen grains and the bulk density of the subsamples of the upper meter of the deposit, the pollen influx, the approximate age, the net organic production (NOP) and the rate of peat accumulation was calculated. The mean NOP over the interval 2.68-1.97 m below NAP was 145.8 g m −2 yr −1, the highest NOP was found in Calluna—Myrica peat (311 g m −2 yr −1 and the lowest in Eriophorum peat (41.85 g m−2 yr−1) Peat accumulation was also calculated over the same interval. The calculated peat accumulation rate (CPAR) had a mean value of 0.0767 cm yr−1. The highest CPAR of 0.195 cm yr−1 was found in Calluna—Myrica ppeat and the lowest in Eriophorum peat: 0.017 cm yr−1. The mean duration in years of each subsample over the interval 2.62-1.97 m below NAP was 20.2 yr cm−1.Two layers of local human habitation were present. The one, consisting of a charcoal layer at a depth of 2.25 m below NAP, is of Roman Iron Age (ca. 1800 B.P.) and the other, consisting of a clayey layer on top of the peat deposit, from mediaeval time (ca. 12th century). Although the earliest direct evidence of human habitation at the site itself dates from about 1800 B.P., habitation close to the sampling site probably occured from about 2150 B.P. onward. From then on Man may have influenced the vegetation, mainly by the grazing of domestic animals resulting in a greater supply of nutrients. This could be related with the invasion of Myrica gale into the bog.