Vegetation dynamics from a coastal peatland: insights from combined plant macrofossil and pollen data

Abstract

This paper reports the results of plant-macrofossil investigations from a peat layer buried within coastal alluvium at the Caburn, a site adjacent to the English chalkland. The data collected are compared against a previously published mid-Holocene pollen sequence with the macrofossil record providing greater taxonomic resolution and establishing a local presence for many taxa. Alnus glutinosa pollen is abundant and Alnus macrofossils are recorded continuously over a c. 3000 cal year period. Fluctuations in the number of Alnus propagules and the presence of seeds of light-demanding herbaceous plants suggest that regeneration occurred at a local-scale, a process which is likely to have been promoted by a rising water-table and sediment consolidation. Taxus baccata macrofossils were also recovered indicating that the high pollen values previously reported may be the result of yew being present within the wetland area. The Tilia macrofossils establish the presence nearby of T. cordata, T. x europaea and T. platyphyllos. High pollen values for Quercus, Tilia and Alnus coincide with the occurrence of their anthers. Deposition within inflorescences is therefore likely to have been an important mode of pollen delivery. The usefulness of both techniques in studies that utilize peats derived from fen carr vegetation are discussed.

Disentangling the pollen signal from fen systems: Modern and Holocene studies from southern and eastern England

“…Ground water conditions remained suitable as a result of rising relative sea-level (e.g. Kiden et al, 2002, Shennan et al, 2006Bradley et al, 2011) with regeneration probably occurring continuously, at a small-scale in a mosaic pattern (Waller and Early, 2015). Areas of swamp and herbaceous fen also appear capable of persisting over long periods.…”

“…Very high values are recorded at some sites (e.g. >50 % TLP at Hope Farm and Redmere), while both modern pollen and plant macrofossil studies (Waller and Early, 2015) have demonstrated that this genus can be present in the local vegetation while producing little or no pollen. Salix is insect pollinated and dioecious, with female biased ratios reported in some populations of Salix cinerea (Faliński, 1980), so in part this inconsistency is likely to reflect poor pollen dispersal and the distribution of male plants.…”

“…Most of the peats are intercalated between marine-brackish sediments and transitional assemblages indicative of brackish conditions (with high Chenopodiaceae pollen values) or marginal aquatic vegetation (with high Sparganium emersum-type), situated at the base and top of these deposits, have been omitted from consideration. Plant macrofossils, which can provide high taxonomic resolution and are generally locally deposited (Birks and Birks, 2000;Waller and Early, 2015), were rarely preserved at these sites; any occurrences have been noted in the following paragraphs.…”

“…Fens like this occupied some coastal lowland sites for several thousand years (e.g. Waller, 1993Waller, , 1994aDeforce, 2011;Branch et al, 2012;Deforce et al, 2014;Waller and Early, 2015) in the middle Holocene, defined as c. 8200-4200 cal. yrs BP (following Walker et al, 2012).…”

Postglacial migration dynamics helps to explain current scattered distribution of Taxus baccata

“…Alternatively, the absence or low pollen abundances of these competitive species in Ireland might be considered as well. Pollen analyses from southern England (South Essex) indicated that after a short period of abundance of T. baccata in the mid-Holocene, the percentage of its pollen declined and that of Tilia and Ulmus increased, suggesting a negative influence of these species on T. baccata (Waller & Hamilton, 2000;Waller & Early 2015).…”